The AM Forum

I was wondering if class E rigs tend to be wider than typical AM rigs due to the way they work, or is it likely to be that they pass high frequency modulation so well?

I know there are different ways of modulating rigs, not just class E, using pdm and other methods, which require a low pass filter I think.

Is there any limit in the high frequency that a class E rig can transmit?
In normal AM gear, you have mod transformers, or sometimes just screen bypass and plate bypass caps that will limit the extreme high frequencies, at least somewhat.

Do most people who run equipment that passes very high frequency stuff usualy limit the transmitted audio in some way, or do they let it all through?

As a side question, what happens when someone runs lots of positive modulation, say 150% positive and does not limit the high end, does the extreme high frequency stuff pass through at really high mod levels?

The reason for asking is I was listening on 80 last nite, and was getting quite loud 'splatter' from a station 10 Kc away, and looking at the signal, it basicly looked like a triangle more than 20 Kc wide, which is nothing like AM modulation normaly looks like, even if its wide.

The audio sounded good, and loud, and it was a class E rig I think, and I am just trying to figure out why it would be so wide.

If someone wanted to limit the high frequency stuff, what would be a good cutoff point?

I am a bad person to ask as I can not hear much above someplace around 3500 Hz.
I imagine many AM operators are old codgers who also cant hear much high frequency stuff, but what is a good cutoff point?
I think I have my cutoff set at 3500 hz which would be a 7 Khz wide AM signal.

Brett

 

Brett,

    last night on 3885 there was a guy from Kansas running a class E rig. His audio was very distorted to me, and then I turned on the BFO; his carrier was very raspy and was FM'ing along with his AM. He said he was having VFO issues. I was just listening, and I don't think he knew he was as broad as a barn door.

    I'm sure his rig was sick, and this is in no way a whack against Class E..

   Maybe that guy is the same one your were commenting about?

Regards,
Jim
WD5JKO

I was looking at the signal of an AM'er last night (NE station) with the SDR waterfall display around 3885 and he was very wide-easily 30KHZ on peaks. It was past "wide"...
Carl
WA1KPD

No, that was the group I was trying to listen to.
One person in that group looked like they had one sideband, but sounded ok, the other station was the guy who sounded poor, and might have been wide, someone did come on and tell him it was real wide.

I was getting all the splatter from lower down.

Brett

  So wide you didn't even need an SDR to have a clue !
But the class of operation was not the determing factor.

Class E has little to do with it, assuming the operator has it tuned correctly. The width you were seeing was most likely due to high frequency audio response. Most of the Class E guys are using a PDM modulator, so the limitation on the high frequency response is determined by the cutoff of the lowpass filter at the output of the PDM modulator.

Since very few receivers allow for more than about 16 kHz of bandwidth, and then only when band conditions permit, running any audio above 7-8 kHz is completely useless. Cutting it off at 4 or 5 kHz would most often not even be noticed, other than for those off frequency.  ;)

The tranmitter I use will modulate out to over 100 kHz. I usually limit it to about 5 kHz. Just because you can doesn't mean you should.  ;D

I had the PRO II on last night between roughly 9 and 11 PM and also heard the same thing and the station I heard was running Class E stuff. And it wasn't the first time I heard this station with that type of signal.

Getting back to the questions, if you build a class E rig and dont get it right, can it be real wide?
Will the typical class E rig pass 30 Khz and beyond if you dont limit it? What are the limits?

Where do the pdm modulator filters come in?

If you was to limit your TX bandwidth, what would the maximum frequency be?

I can see running wider signals during the daytime when the band is mostly empty, and tighter at nite when there may be a qso 5 Kc away, maybe on each side, sometimes I hear people on 3872, 3880 and 3885.

Brett

I guess you are not using a pdm modulator then, since it would be limited below 100 KHz, no?

What is the typical pdm modulator filter frequency? How do you figure that when building one?


So if someone is running a class E rig and is over 20 KHz wide, its likely just the audio?
Where does all that 10 plus Khz stuff come from? Is it really in the typical male voice?

Brett

I believe I engaged the fella in a QSO.  Come to think of it,  I was answering him back on 3.885 and he never would come back to me.  I could hear him perfectly there.  Then I kicked on the bfo and realized he was "testing" down on 3.880, so I went down and engaged him in a QSO.  What I didn't know was there was a ssb qso going on underneath him.  They became a little peeved and moved off to 3.885.  (I later apologized to them saying I had not realized they were there.)

But yeah, he was running a class E rig and I asked him if it was a K7DDY kit.  I think he responded that it was his own homebrew roughly based on Steve, WA1QIX information.  It's amazing the Sidebanders didn't move even farther away come to think about it since I was hearing him so well at 5khz away that I thought he was there.  He was a nice enough fella, I doubt he realized he was so wide.

That was not the guy I was thinking about, he was on 3872.
I was trying to hear the guys on 3885 or there abouts. Since they were out west I think, they were not as strong as the 3872 group.

Looking through the class E stuff here, it looks to me like the filter on a high power pdm rig can not be too good, and I wonder if anyone ever did any tests on the output of these rigs?

Looking at the info, I guess its common to pass to 12.5 Khz (which seems real wide) and to use a 100KHz sample rate to get plenty of samples at 12.5 KHz, then filter it 40 or 60 db in the output.

If you were running 500 watts carrier out, would 60 db be enough?
If you ran 500 watts carrier and modulated it to 2000 watts plus pep, would 60 db be enough?

I have not compaired a lot of class E rigs to other types, you dont always know what a guy is running.
Some signals on the bands seem quite narrow but great sounding, some seem great sounding and very wide, some are very narrow and sound it, etc.....

I am trying to figure some stuff out (slow work day) on how someones signal could look like a flattened triangle (VERY unusual).
I have also seem some other really odd stuff that I am trying to figure out, like a good sounding signal of a limited bandwidth, but when they STOP speaking, they get a lot of modulation at high frequencies that then fades away, like parasitics or a filter ringing???

Brett

 

The LP filter corner is largely determined by the PDM switching frequency. I'm guessing switching frequency is above 50 kHz, so the LP filter could easily be greater than 10 kHz.

Take a look at the spectrum of someone saying S, H or similar sounds. The spectral components extend beyond 10 kHz. And if the operator was boosting the highs, the levels will be much greater.

I'm not using a PDM modulator. I'm using a low-level balanced modulator.

Most PDM's run at a switching frequency of between 70kHz and 200 kHz. This sampling frequency essentially samples or takes snapshots of the audio at predetermined intervals and varies the pulse width or duty cycle of a PWM circuit. The output filter then produces the original audio voltages for the RF final stage.

The audio bandwidth is limited by filters in the audio chain. Steve's designs include filters for limiting the audio bandwidth.

Most of the terrible audio and wide bandwidths I hear are from SSBer's.

By clicking on the ClassE Forum button above, there is a wealth of information on how class E works.

Phil - AC0OB

I have a H mode linear design flat out to almost 30 kHz. A low level modulator is as flat as you want it. I set the corner on my PDM rig at about 8 KHz and the 80 KHz switching is down over 75 dB. You can't hear my sidebands 10 miles away. A negative peak limiter is a must on a class e rig so the carrier is never switched off this will generate a lot of broadband crud. I hear some class e signals very wide and set that way on purpose.

I have looked at the class e info, but dont know what the typical builder ends up with.
What if you skimp on the filter, what happens?
What if its only 50 db down and someone builds a high power rig, what would it do/sound like?

I cant say I see many real wide ssb signals, some are quite dirty, but even the worst has only been maybe 5kc wide.  Audio is audio, some guys sound very good, some sound not so good, just like on AM.

I have never seen an ssb signal 20 plus KHz wide, not to say it does not happen, I have just never seen it.
90% seem to be under 3khz, but they do tend to get very close to each other and AM signals, I think because they can without it bothering them.

I think a lot of the AM/ssb stuff goes on because the AM guys are running wide and maybe not so great receivers, while the ssb guys can dial it down to 2.8 Khz with very sharp filters. The ssb guys then wipe out the AM qso and dont really hear the AM guys.

On the other hand, the wide AM signal last nite was taking out 2 seperate ssb qso's and 2 other AM qso's....

No wonder tempers flare and heated words are exchanged....

Brett

When I'm operating SSB on a crowded band, during contests, VHF band openings, etc. I can dial down the receive and transmit bandwidth to around 1.8 kHz. Nearby adjacent crud disappears.

BTW: Class-E isn't a modulation method.... it's a class of amplifier operation.

One thing that would be helpfull, if if everyone used the same definition of "wide".
Seems like some are talking about audio pass-band width (one sideband), and others, the total occupied width.. (both sidebands)... Gets kinda confusing when were talking different standards...  :)

Steve's PWM design uses approx 190khz switching freq. With a filter cut-off of 13khz. But as most of you know, that's where the audio would START to roll off.. it isn't a brick-wall filter.

The main reason for the filter, is as an integrater.... to make a DC from a square-wave pulse-train.


The "triangle" mentioned is probably just how the rig is EQ'ed.


I would also suggest that if the AMer in question is a member of this board, you may as well say who it was.
And give them the chance to answer for themselves.

  I think the original K7DYY "Junior" may have been class E. The Senior however is class D and is a very clean TX that rolls of at about 3.5 KC.

Both the SR and JR are Class-D.
Bruce did have some class-E stuff at least posted on his site a few years ago......

Some random thoughts about bandwidth:  (I think most of us know this already, but just to be sure)

Any amplifier used for AM (which includes class e, linear, class C plate modulated, screen modulated, etc) is simply a platform to either amplify an existing modulated signal or mix audio and RF to create a modulated signal.   ALL of these systems can be built inherently clean as a whistle with -30db (or better 3rd order product figures)  In theory, this equates  to about 0.1% distortion. Very clean indeed.

I've built a 24 pill class E PDM FET rig in the past and found it to be as clean as any linear or class C plate modulated rig. It's all about how the particular rig is set up and implemented. The designs are fine. But some particular rigs are just plain dirty and splatter because of other real-world problems. Some is simply operator error.

Splatter is severe distortion.  This is totally different than when someone runs a clean rig but decides to feed through + - 15kc wide audio. The signal may be "clean" but is wide because the highs are not rolled off at say, +- 5kc.

The challenge of any AMer is to sweep his rig from 40hz -7kc and make sure it passes these frequencies cleanly. Also do an IMD test to see if there is any potential splatter problems.  Computer software will let you do IMD tests easily these days.  There's guys on the air with spectrum analyzers built into their rigs who can look at your rig too.


One quick test to try is if you are running a linear for AM -  to talk on LSB and have someone listen to you on USB. Your signal should drop at least 30db or more when listening to the other side. I hear several ssb stations on 75M who are almost as loud on the opposite sideband due to severe IMD problems. Tune up the band and you will hear the crackling more than 4kc away. If the linear amplifier passes these tests on ssb, it is probably OK on AM too.  

Another point is that on ssb, we can quickly tell if someone has a bandwidth problem cuz most are 3 kc wide or so. But on AM, we don't know if the guy is running 3kc audio or 15kc audio.  Tuning across a dirty AM signal will show nasty products to have a spitting/crackling sound as you tune away. Clean highs will have a wispy sound with little low frequencies mixed in as you tune away.

So, bottom line:  ALL conventional amplifier systems can be made to be clean. (including class E)  A wide signal may be clean – it’s just that the operator chooses to run wide audio frequencies. It doesn’t mean the signal is splattering.   Splatter is caused by amplifier distortion. We can run 3kc wide audio through a dirty transmitter and be 30kc wide as a result. However, if we run 15kc audio through a CLEAN transmitter, it will also be 30kc wide, but still clean. (+ - 15kc)

BTW, it doesn't matter how narrow you run your receiver bandwidth - if you're listening in a 2kc bandwidth and someone is 15 kc away and splattering severely, you will still hear him on your frequency - assuming his products extend that far.

Hope this helps.

73,

Tom, K1JJ

Moreover, the problem may very well have nothing to do with the audio bandpass at all.  There could be a parasitic in the modulator.  There could be a parasitic in the final, causing intermodulation.  The RF could be getting into the VFO and causing feedback/FMing.  Could be any number of things.

Last, it's easy to blame someone for being "wide" without also recognizing the limitations of your own receiver.

  You are correct.  I had a Senior for about a year and it was not putting out much beyond 3.5 > 4.0 KC. None of that 7KC + crap from the K7DYY.

I agree on the receiver limitations, on a poor receiver, there is really no way to tell if the signal is really wide.
But a spectrum analyzer does not have those problems, nor does the flex 5000.

Brett

I really get a charge out of guys 20 KHz wide complaining about SSB signals 5 KHz away.

   Generally, with a decent , selective reciever that is operating properly..if you hear a fellow who is S9 when his carrier centered in your pass band and you are still hearing  him spitting and sputtering 10 KC up the band, while stronger stations (S-9+30)in his round table are not being heard.. It may be reasonable to suspect he is a bit wider than the stronger stations  (?)

And that is exactly what goes on with this fellow, who sometimes then turns things up to drive them away, ranting and raving about those damm ssb guys....

I dont have a problem if a guy wants to run a real wide signal, in the daytime, if he can find an open 25 KHz or so, but to do it at prime time, and cause problems for 2 other AM qso's and 2 other ssb qso's....

I just wonder if something is wrong with the radio, or its being over modulated, or its just no cut of the high frequency audio.

If you run a 32V3 at 100 watts, I dont think you need to worry about excessive bandwidth, as the signal wont be very strong. But running a high power rig takes some responsibility I think, limiting the negitive modulation and the high frequency stuff.
Most people seem to do that quite well.
If you are going to spend thousands of dollars on audio processing equipment, maybe get something to check the transmitted signal?

Brett

A while back there was another thread pertaining to bandwidth and I think Don, KYV, wrote an great description as how to correctly measure the same. As in any industry, there are accepted standards, with specific details as how the measurement is performed. Radio, not being my ball of wax, leaves me to believe some of us don't have that standard tatooed inside our eyelids, nor have the proper equipment for the measurement.

73's
wd8kdg
Craig

YES!!  (Especially if everyone is runnning similar transmitted AUDIO bandwidths and the stronger signal is NOT splattering)

Comparing many signals with the offender is a great way to get a feel for what is happening. But in general, you will need to use a front end attenuator to standardize all signals so that they are the same strength when compared.

Before giving out bandwidth reports to anyone on AM, it pays to spend some time listening in the AM broadcash band and seeing just how your receiver handles these stations, weak and strong. Since most AM BC stations are generally clean at +- 5KC, this is a good standard to train yourself.

Also listen to many ssb stations to get a good idea how they should spread out. I find the cleanest ssb stations are usually above 3900 and in groups of low key type conversations. These guys seem to tune up their amps correctly. The widest ssb signals are found (lately) in the DX window 3786-3800 as many try to squeeze the last watt out... ;D  The extended ssb guys are usually clean, but there are exceptions. You can hear the clean wispy sound as their signals tail off when tuned across - not grungy splatter. Since most ssb QSO's are spaced/channelized  3kc apart, the ones that are operating and not complaining are usually clean. Most ssb rigs use 2.4kc filters (or less) so they have a built-in standard which AM does not have.

If a spectrum analyzer is not available, I sometimes will simply listen to my own signal in another receiver. Put a 18" clip lead off the back of the receiver and adjust it's length (rolled up) until your signal is S9 +40. Then as you talk, tune up and down the band to see what the crud sounds like and looks like on the S-meter.  If the receiver is not leaking in RF and is not being overloaded, it will tell you the story.  I consider the point when your side crud is down at least 40db to be the point of "reasonable" roll-off.

T

Too many generalities here. What does wide mean - exactly. Give me some real numbers or a mask. Just because you can hear (whatever that means) a station up the band does not necessarily mean they are wide.

I've heard a lot of complaining from some who purposely chose to operate only 5 kHz from another strong AM signal/QSO and then complain about splatter. Such an approach is hardly being reasonable.

That said, there are some who are very wide, either on purpose of out of ignorance (neither is acceptable) and they think they are doing AM a favor by "cleaning out the Window."  There is no window and they are cleaning nothing but are making a ton of enemies (on which they seem to thrive).

Uh.... a qualified NO to both.  As Steve said, "what's too wide?"- that's the first question.  Next, if you don't understand the limitations and functions of either piece of gear, you're not gonna get meaningful measurements.

I could use a spectrum analyzer to "prove" your signal is a megahertz wide.

Neither one is a panacea.

Yes, the "Us and Them" mentality does lots of damage to AM.  A modern ssb receiver can operate very close below an AM station on 75M and barely know the AMer is there cuz of the opposite side suppression of his ssb receiver. However, the AMer complains cuz he is hearing both sidebands in a wider bandwidth. Losing battle. Beating up on the ssb guys only makes it worse.

Commercial AM broadcash stations use 10kc spacing between stations.  7-8 kc is a reasonable spacing between ham AM stations, though the ssb crowd will come in MUCH closer and not even know they are interfering with the AM QSO.  Tough problem, indeed.

T

I had a problem years ago, with reports that my signal was splattering on voice peaks.  A quick glance at the scope showed a normal looking pattern, but upon closer investigation, I could see "hair" growing on the positive voice peaks.  Apparently something in the modulator was ringing or going into parasitic oscillation.  I tried several things at low level and with the driver stage, with no effect.  Then, while browsing in some old Radio handbooks, I noticed a circuit showing a class B modulator that had a 100Ω resistor in each plate lead.

I looked in my junk box and found a couple of what looked to be about 20-watt, composition resistors at somewhere between 50 and 100 ohms (I'll have to measure them with the ohmmeter next time I think about it).  I connected them between the plate leads and the plate caps of the modulator tubes, and sure enough, the "hair" was gone and I didn't get any more splatter reports.

I have seen suggestions that tube type modulators be cross neutralised just like a push-pull rf stage.  Never tried it, but it might be a worthwhile experiment.

A class D or E rig, tube type rig and a pulse duration modulator all have one thing in common: garbage in, garbage out.  The splatter and distortion could be occurring somewhere early in the audio chain at frequencies that transformers in the later stages of a tube type rig would filter out due to their limited frequency response, but that a perfectly linear modulated stage with near zero distortion and response from DC to daylight would pass unimpeded.

Something that many hammy hambone types are apparently not aware of is that the apparent bandwidth on the dial of the receiver as you tune across as signal is the sum of the bandwidth of the transmitted signal and the passband of the receiver.  An unmodulated carrier with zero bandwidth will be audible across 3 kHz of dial display when receiving with a 3 kHz SSB filter in the receiver.  A SSB signal will be audible across about 6 kHz.  A 7 kHz wide AM  signal will be audible across 10 kHz of dial space.  Add the slope at the edges of the i.f. bandpass filter and the signals will appear even wider.

I once got a chuckle when a slopbucketeer with a terribly crappy, raspy, distorted sounding signal called me to complain that there was something wrong with my transmitter; I had a "wide" carrier.  He  could hear the heterodyne squeal almost 3 kHz away from my frequency!

Also, if your spurious distortion products are reduced to 40 dB down outside the normal passband, that is considered a clean signal according to good engineering practice, meets FCC specifications and exceeds the specs of many commercially manufactured rigs, especially older ones.  But if you are coming in at 60 dB over S9, that means your distortion products are still coming in at 20 dB over S9.  If the noise floor happens to be very quiet, even at S9 signal strength the -40 dB products may be audible outside the normal passband.

Maybe what we really need is some regulation by bandwidth. I think there was some talk about this in the past.

Or not. Most of this discussion has centered around not knowing how to measure bandwidth. Having a rule that cannot be enforced is useless.

It may also be good practice to put a 1000 ohm resistor in series with each modulator tube grid. This is commonly done with class A or AB1 push-pull audio power amplifiers to reduce the possibility of parasitic oscillations in the output stage.

I don't think you would want to do this in a class AB2 or class B modulator stage, however. You want to keep the impedance between the audio driver stage and the modulator grids as low as possible, to keep the driver regulation high as the modulator tube grids are driven positive.

73,

Bruce

Brett:

There are some very good comments and technical information here. I'll offer my thoughts...

As one who is experienced with both tube transmitters and Class E, I feel when operated correctly the class E transmitters are naturally capable of passing wider and cleaner audio than a typical tube rig (say an un-modified Valiant which passes audio only to about 3-4kc for a total occupied bandwidth of up to 8kc). Tube rigs often have limited power bandwidth that creates a drooping occupied bandwidth as the measured frequency is increased from the carrier.

The PDM modulators on Class E rigs tend to be flat with full power bandwidth and have a high frequency limit as based by the PDM filter. Most of these are set at 8-12kc and drop fast (12-24db/octave) and thus have an occupied bandwidth of up to 24kc. Mine starts diving at 8kc, and I also have a low level 36db/octave brick wall filter set at 6kc at the end of my air chain. In result and also due to previous audio processing, I have a good amount of RMS audio power occupying a 12kc RF bandwidth, but nothing outside of that as it is generally better than 40db down.

A few Class E folks use a linear modulator that has no inherent bandwidth limitation. Thus the vocal sibilance is the frequency limiting component.

As usual, when examining a signal one has to keep a keen eye out for receiver overload or the noise blanker adding it's own artifacts.

Hope this helps.

73,
Dan
W1DAN

Hi John

Just a quick question from my own curiosity and lack of knowledge. Hey this is a part time hobby and I have no formal radio education other then that needed to get an Advanced in 68!

The station I was observing on the SDR-IQ was in QSO with several other AMers on 3885. With the waterfall display I could see horizontal voice peaks out about 25 KHZ either side. I could tune down using a narrow filter setting and hear splatter from those peaks way down the band.

I am very impressed with the filtering on the SDR so "I presumed" what I heard was true. I should also note that when the other stations were on they occupied a very small piece of the spectrum.

There was an AM QSO on 3890 that was able to continue and I could filter out the 3885 QSO until the wide signal came on

So the question is; Am I truly seeing a wide splattering signal or to your point, am I "proving" something that is not correct?

To another posters point, if I remembered the stations call I would PM him and let him know. But I do not. I do hear him a lot on 75. Hopefully it was inadvertent.

73

Carl
WA1KPD

Carl,

Where were the off freq. signals relative to the noise floor on your SDR?
I can see horizontal, freq. spikes even as far out as 50 kc from the carriers of  typical AM operators in a quiet part of the band on my QS1R, say the 3733 crowd.

Also how much contrast are you using on your waterfall display? At high 'beta' everything shows up.  normal 'beta' not much except the signals down 40dbv or so from the carrier.

But I will say that some very strong ham signals (-40dbv carriers at my location) show freq. spikes many kHz's farther out and  harder than much stonger, clean BC signals (-10dbv) down.  For whatever reason, some ham signals are far dirtier or simply don't have high pass filtering.  

Hard limiting without filtering, of course, generates approximate square waves with sidebands tapering off into the aether  ;D
I think a lot of guys overprocess signals and try to put  'smilie' roll-off characteristics on the air.  (Hi bass, low mid's, hi treble)

What's a "horizontal frequency spike"?

Ans.: -that which shows up perpendicular to the time axis on the waterfall display.
..."What, don't you respect Wilsiz'ms?  ;D

See all the little squiggles ?  right and left of the CW sig's.

..uh, er, in this case most are from lightning strikes somewhere outta the picture, but dirty AM looks similar , they just disappear right and left of the carrier.  I'll have to snap a better AM example.

Ah... should have guessed...

I never use a waterfall display....   :)

Much more usefull info in the normal spectrum display.

What I was seeing was there, and not any fault of the receiver.
Other signals were just as strong and were narrow.

Using the flex 5000 which is the 3rd receiver on the sherwood list:

http://www.sherweng.com/table.html

The top receivers are all very close in specs.

I had an sdr-iq in the past, its good if a bit clunky to use, and yes, at any reasonable signal level, what you see is what you have, not something the receiver is generating.

If the signal is weak and/or far away, you might not see much, but if its 20 over, you see it quite clearly on most sdr receivers, and hear it in other receivers.

Brett

A few randomized thoughts...

Anyone can run almost any rig and make a mess on the band.

The filters in a given PDM modulator are usually analog filters. IF said filter is say a second order filter at 5kHz. (-3dB point) and the signal is 40dB over S9, then there is an audio component at 10kHz away that is only 24dB down from 40dB over, or 16dB over S9! If someone is listening at 10kHz away to an S9 QSO, I would expect that they would think they're hearing major splatter. Obviously, in the case of the use of an even higher order filter, there would be less energy out there... A 4th order filter would get you 48dB at 10kHz...

Let's all not forget that AM is + and - the audio bandwidth.

Also, I have a really slick little +/-4.5kHz Murata ceramic filter in the IF of my 440S, and it really does let me listen to an AM QSO that is only 5kHz  separated with relative ease.  It sounds pretty good. Also in the SSB mode I usually have very little difficulty copying an SSB QSO that is within about 2-3KHz of the carrier of a strong AM QSO... it's not quite so easy using my R-388 (yet... until I mod the filter scheme)

               _-_-bear

It used to be very common to have a big roundtable on 40 meters on 7285, 7290, and 7295, without problems.
That was before the days of broadcast rigs and class E rigs.
I was just listening to 3 seperate qso's on 3874, 3880 and 3885, and they were not causing me any problems with a 5.2 or 6 KHz filter.
Modern sdr stuff is brick wall filters, sort of like the old mechanical filters were, only much better.
Most of the other (non sdr) modern gear is not as good, but good enough for close ssb.

Brett

I have a friend with a SDR rx who has told me that some of the grungy signals he sees come from hams operating ssb with exciters driving solid state amps.  IIRC they are frequently Icom exciters driving either Ameritron s.s. amps or the PW1, and there has been a problem with the fancy Yaesu 9000 rig but that may have been a single case or something Yaesu fixed.  

There are spectrum analyzers and spectrum analyzers.  Rigs like the Icoms with "fish finders" are not spectrum analyzers.  Ditto for the older CRT panadaptor station accessories--these are intended to find signals--that's about it.  

My impression is that the participants here work hard to insure our modulation is below 100% negative, audio is ~ 5 Kc or less, and are properly loaded and linear and you all set a good example for me.  I also think that "clean" should apply to everyone regardless of carrier power.    

Brett, in going back through the posts I am trying to figure out what you want--you generated an interesting discussion but it seems that since you started using your SDR receiver you have found some station that bothers you.   Until you can identify this station I don't think anyone can help you.   The best course of action is to probably send the operator a very diplomatic and tactful message about his signal if you hear him again.  If it is or were me putting out the garbage that is something I would appreciate and seriously investigate.  Whomever it is, he may blow you off.  Then you can either accept grunge signals as a fact of ham life, or do something?  ...not sure what but whatever you do, make sure you have your act together  ;)  Personally, I always want to hear from competent hams with accurate measuring devices.  Some yahoo with a fish finder is another matter. :D    

<<<It used to be very common to have a big roundtable on 40 meters on 7285, 7290, and 7295, without problems.
That was before the days of broadcast rigs and class E rigs.>>>

I have a hunch that on this, you are probably going to have to live with the status quo if you want to be a happy ham  ;D 


All the best and 73

Rob
K5UJ

It used to be common that those QSO interfered with each other greatly and reduced the ability to enjoy good AM audio, in my experience. Five kilohertz is way too close. Even if all the participants in both QSOs had rigs that produced ZERO energy a mere 3 kHz from their carriers, there would still be 1 kHz of overlap.



How so? If you are 4.5 kHz from your center frequency, you are only 500 Hz from carrier the other AM signal 5 kHz away. This would be well into the audio/sideband. Or it is the filter only 4.5 kHz wide total (+/- 2.25 kHz).

The measurement of occupied bandwidth is standardized by the ITU under SM.328 and actually two methods are acceptable:

x dB and the 99% Power methods

For the x dB method the total signal power is used as a reference and the and the high and low spectral sides are found where the envelope is x dB down. x is typically 26 dB for common modulations like AM. The occupied bandwidth is the difference between the high and low - 26 dB points.

For the 99% Power method, typically a digital method is used to divide the signal envelope in to bins. Starting outside the sidebands, bins are subtracted one by one from the upper and lower sides of the envelope until only 99% of the power remains. Essentially 0.5% of each sideband power is removed. The occupied BW is the difference between the last two bins that were removed to reach 99%.

A fancy Agilent spectrum analyzer would be able to do both of these automatically. 

Well, the reason I brought it up was to try to figure out if it was something in the typical class E rig, the way it was being run, if you did not get the filters right what would happen, etc.
I have heard you can get parasitics in them that wipe out fets...

As the weather cools off, there is less motorcycle and yard stuff, and my ham radio activity picks up.
The flex, being very interesting, also has me listening and actualy operating much more than I normaly would be.

Plus, it does not hurt for people to think about what they are doing, and how they might do better.

As far as getting close, with a good receiver, I really dont have a problem with 5kc spacings with 90% of the AM signals on the band, I guess the high end stuff rolls off some, to a low enough level where it is not noticable.
Right now there is an ssb group on 3890 that is 2.7 Khz wide, and an AM signal on 3885.407 and in 5.2 KHz passband set, I dont hear the ssb guys at all. There is also a strong AM signal on 3880 and I get some low artifacts that dont bother the signal on 3885.407 much at all.
If all I had was a 6 or 8 kc filter, it might be more of a problem, but I dont remember it being much of a problem on 40 in the old days....
Now some people back then used to take out half the band, Irb comes to mind...I could always tell when he was on...

Brett


 

Here is an example of what I was referring to. It is an AM broadcast signal on 840 KHZ. Note the voice peaks either side of the carrier (red line) extending out about 5 KHZ.

The station the other night had the same peaks, at about the same strength extending about 25 KHZ either side of the carrier

Also interesting in this pic to see the data stream on WCBS 880

Carl
WA1KPD

Here is timtron (2 min ago).

Icom DSP based radios have a grunginess sound you can pick out of a pileup, almost.

If it's a clear night on 75 meters, you can hear the Icom's on 80... :)

On a serious note, Icom's with DSP generate a sound that is ALL their own.  They do make decent AM, though.


--Shane

I had a pro 3, cant say I was impressed on rx or tx, but it was simple to use, the band scope was better than anything else besides sdr stuff.
The auto notch gizmo worked fantastic.

Brett

Pretty interesting.  That's probably WHAS Louisville on 840.  Guess they're analog at night.  The CBS owned stations are all doing digital day/night.  I think the mask is analog out 10 khz then 5 khz for the IBOC digital on each side of carrier.  So WCBS would go down to 865.  The CBS stations here on 670 and 780 do the same thing.   I'm only 10 miles from the 670 tx site so it wrecks my reception of WSM on 650.   WGN on 720 quit IBOC (the rumour is they didn't want to pay the Ibiquity fee) and are now supremely all beautiful sounding analog.  A great receiver audio evaluation tool.  Tuning across them reminds one of the way AM used to be (and ought to be).  

Here is wgn in south jersey 10 over s 9.
it looks like something is off to the side of the main signal...

Look at this crap!

It's "9kHz" - ok, sometimes I have to tune slightly off to one side, but the filter works nicely... the rest of the IF selectivity of the 440S is still in play as well... a +/-2.25 filter is too narrow to listen comfortably imho. I got a few filters from Murata and test listened to them for the best balance between wide and narrow, this one won. I can probably scare up the model # and you can check my math and the filter, send me a PM?

 ;D

610 is a class B channel IIRC i.e. used by regional 5 kw stations like WMT over in Iowa--the one you are seeing is probably over near you in the East.   yeah that's the IBOC response, you have your analog out 10 khz then the digital for 5 more khz.

if you listen on a wide enough analog rx you'll here the digital coming though like bacon sizzling.  makes my superadio unuseable in wide setting. 

re the 720 plot I note that there are one or two other stations there exhibiting assymetric sidebands--notice WLW on 700 has a lot below carrier not much above for example.  I don't know how to operate a flex receiver so can't say what's happening there.

On some signals, there is not much modulation, and there is some sort of digital stuff off to one side, on some signals its on the upper sideband, on others its on the lower sideband.
The big 610 signal has a much wider audio, and those two big digital things, not all the signals look like that, some still look like normal AM signals...

If I tune in the signals off to the side and narrow down the passband, say of the 720 signal, it does sound like bacon fry.

Do some signals transmit AM stereo? In digital?
Where does the station id info ride? Some car radios came up with info when you tuned them in...

Brett

Interesting Talk here.. 

Alot of people want HiFi AM.  Thats what we strive for and I think I alot of people get carriered away.  One of my AM friends wants MAX bandwidth with the best tone.  His radio is 25KC wide on AM.  I have measured him. He sounds wonderfull but I keep telling him that its pointless because most of the people that are listening to him are on RXers that cant go that wide. I listen about 10KC wide most of the time but when its rough out, I go down to 5KC.  Sure, some fidelity goes away but thats the price you pay when the band is rough.

So.. what is optimal for transmit?  5kc? 6? 8?   What in your opinion is the least amount of bandwidth you can run to have HiFi AM?

My new Transmitter has to be limited in the audio rack.  It will pass 20 to 15K. 

My opinion is that it is technically pointless to allow an amateur radio AM transmitter to pass high frequencies in excess of 5 to 8 Khz.; this would of course represent a channel bandwidth of 10 to 16 Khz.  The human voice has very little energy much above 4 Khz, and we cannot legally transmit music, which would require the audio frequency response be out to at least 10 Khz for decent reproduction.

The more important point is, I believe, the shaping of the transmitted audio response to make the audio as high-fidelity (or "bright" sounding, to use a somewhat overworked adjective with regard to the high frequencies) as possible, while minimizing the total occupied bandwidth. The AM broadcast community began doing this in the late 1980s with their adoption of the NRSC preemphasis curve, to compensate in large part for the very poor IF characteristics of AM car radios and the like.  Personally, I think the NRSC boost  vs. frequency curve is too benign for my tastes and for the IF passband characteristics of most AM receivers, but it does represent a good starting point. An excellent treatise on this very subject was written by the truly great audio engineer Bob Orban; you can access it by going to the Orban website and look for the tab for Bob's technical white papers.

This whole thing with high-fidelity transmission of AM is an imperfect science, due to issues of poor SNR and dynamic range because of atmospheric noise, receivers with non-standard IF passband characteristics, non-standard frequency equalization and frequency tailoring at the transmitter end of the link, etc. Don't get me wrong; I enjoy transmitting the best sounding signal I can with the equipment I have available, but I really do realize the limitations of what I am trying to attempt, much to my dismay!

Just my 2 cents worth!

73,

Bruce

Brett, you absolutely cannot assume this.  While it may very well be the station splattering, there are other possibilities here as well.

"Horizontal spikes" were mentioned above.  In my experience using high-end Agilent analyzers, this is a classic case of ADC overload, DSP windowing limitations, and/or mixer non-linearities.  In the former case, a strong signal is overloading the ADC and causing low-level artifacts that spread across the sampling bin.  The culprit could very well be a signal or signals well out of the frequency span you're looking at.  

Even if the ADC isn't overloading, the method of windowing used in the software affects how faithfully an input signal(s) is/are displayed.  The "window" is the function applied to the Fourier transform of the signal (i.e. the time domain component of the sample) to attenuate the edges of the time record.  This is done because the FFT of complex signals will end up with leakage across the time record bins (blocks of time-domain sample points) - consider this to be analogous to smearing of the frequency spectrum you're looking at (does this look familiar in the context of the horizontal lines you're seeing?).  

Various window functions provide better frequency resolution at the expense of dynamic range, and vice versa.  A rectangular window has the worst performance in this respect, providing perhaps -40 dB of signal leakage between bins.  What this means is a signal (that perhaps you're not even seeing on the pan display) is leaking thru all the bins and this shows up as a horizontal line.  Windowing is explained in the SDR-5000 manual, but it does not explain succinctly how this manifests itself on the display.

I cut my teeth on the HP 89441A vector signal analyzer which is not all that different, fundamentally, from the SDR-5000.  Its manual contains the best explanation I've seen of all the factors affecting signal analysis using DSP methods.  Chapters 18 and 19, although having some 89400-specific discussions, provide an outstanding tutorial on this subject.  The manual (about 4 MB) can be found here:  http://cp.literature.agilent.com/litweb/pdf/89400-90038.pdf

Next, consider that the SDR-5000 hardware has no narrow-band filtering.  The bandpass filter and low pass filter after the mixer all have relatively wideband responses and, as they are L/C filters, will roll off gradually as opposed to the relative "brick wall" nature of a crystal filter or DSP filter.  You then must consider that when you hook the radio to an effective antenna, the *total* power contained within the response of the filter can be considerable.  The mixer in the SDR-5000 essentially is an array of high-speed flip-flops, providing the necessary I/Q outputs for the DSPs (as I recall this mixer was the subject of a QEX article some time back).  While its performance is certainly impressive like any mixer it's not perfect, and we cannot discount that a strong out-of-band signal (or a whole lot of medium-strength signals) can cause low-level artifacts.

The bottom line here is this:  while the SDR-5000 certainly exhibits good performance in a number of areas, it -like any receiver - isn't perfect.   Because spectrogram displays like the SDR-5000 allow you to see very low level stuff very clearly (those horizontal lines would never be noticed if you didn't have the spectrogram display) - which one cannot see on a swept spectrum analyzer - it lends itself to providing evidence (true or not) that someone is too wide.

They may or may not be; the fellows under discussion could well have issues with their transmitters and be splattering horribly.  Indeed spectrograms can be the best tool out there to quickly identify the source of a dirty signal.  But you can *never*, in the presence of other signals, state with certainty that what you're seeing isn't being generated in the receiver.  

All of this reinforces the fact that regulation-by-bandwidth is even *less* than worthless because of all the misunderstandings about bandwidth measurement.   Just because something is seen on a spectrogram display doesn't mean the station is "too wide" - stuff 40 dB down from the carrier (although easily seen on a spectrogram) is NOT necessarily proof of a "too wide" signal.

Cool. I have a 9 kc filter in my 51J-4 and found it to be a rather good compromise between fidelity and selectivity. If a strong AM station is only 5 kHz away, I'm usually switching to the 6 kHz filter or QSYing.  :D

Post the part numbers when you get a chance. Those 455k units are probably useful in many receivers.

The Flex has an IF of 10 KHz or 11KHz if I remember. You will get responses every multiple of the IF.
This problem was eliminated when the mixer was deleted in the Perseus, QSR1 and HPSDR Receivers.

I'm currently using a Class A series modulator in a 25 watt AM TX here.  Passes audio BEAUTIFULLY to 100K and beyond.  I've sent a 50khz tone FM modulated (I injected it via the audio processing software in the PC) and was able to actually send two seperate audio channels out.

Of course, 50 kc away, people wouldn't be too happy :)  So all of my testing was dummy load only.  After playing with this test, I learned to put am audio low pass filter in line, and as one of the last things in the chain.

I've also found that NB settings can wreak HAVOC with AM and Hi Fi.  I'd get people telling me how horrible the radio sounded, I'd talk them into disabling or otherwise getting rid of the noise blanker, and WOW, YOU SOUND BEAUTIFUL!


--Shane

There used to be a a stereo AM analog method called C-QUAM which transmitted AM Stereo, which in my opinion sounded better than DRM or the current digital IBOC (Inband-Buzz-On-Channel) krap.

The main problem for analog AM stereo was the limited bandwidth of the IF and RF stages of current receivers, and nightime propagation.

Starting about 1981, companies such as Sprague and Sony started developing wide-band receivers that had wide and narrow band capabilities. The wide band bandpass was over 19kHz at -3dB down.

I contracted with a number of stations in the Midwest in which we installed AM exciters (mostly BE exciters) in currrent transmitters at the time, and the AM stereo was superb on the right receiver.

If interested in AM Stereo, there is a site that discusses the history of AM Stereo:

http://www.amstereoradio.com/

Phil - AC0OB

hello All,
I wanted to quote Bruce, but this website is optimized for firefox and a long reply or a long quote makes the entire display in a reply jump up and down while typing. Gary's explanation....anyway

The bandwidth issue for A.M. has soley been from the manufacture of inferior equipment to the general listening public for A.M. broadcast. Poor/cheap engineering of auto and home radios the last few years, and now the implementation of IBOC that forces narrow I.F. bandwidth to filter out the digital garbage.
I don't understand why we are trying to to force 20-20kc of audio through any transmitter for the transmission of the human voice. Very nice high end and a natural sound of the letter H or S is perfectly audible with a bandwidth of 7kc. To obtain that F.M. sound is not very neighborily, especially if the transmitter/exciter/linear cannot handle the extra audio without distortion.  


Fred

Current AM Broadcast audio sounds like doogiepoopie to me with the 5kc bandwidth limitation.

I have no idea if that is due to the way that the stations have their processing set up ior if (as I suspect) the 5kc bandwidth limitation just doesn't sound very good for broadcast audio - even for "talk" programs.

Good example is that the local (multiple translators across New England and NY) WAMC simulcasts on 1400 AM (daytimer, down to nil watts during the nite) and flipping from AM to FM in the car is so very night and day... the audio on the AMer sounds pretty similar to most of the other AM (like WGY) stations in this market...  who put the wool sweater  and socks over the mics??

But that has little to do with the way AM amateur radio stations ought to be set up.

Maybe I will have to come out with a box that has switchable high slope 5, 7.5 & 10kHz LP filters that can go inline with the mic, or inline at line level? Anyone think this is of interest??

                       _-_-bear


PS. did I mention I am always right?  ::)

station ID is encoded in the IBOC part of the signal (In Band on Channel, a protocol developed by Ibiquity)

The 30 khz plot is  spreading out from carrier, 10 KHz audio then 5 KHz digital.  
sort of like this:
                           |
                 _    __ |__    _
                | |__ /--|--\__| |


You don't always get that but I have seen other flex displays where it is consistent so I suspect you are doing something with yours that you are not aware of because I can pretty much guarantee you, these commercial stations are not transmitting drastically asymmetric side bands.   Yes, not all AMs are running IBOC so you will find many that are analog only.   Some switch it off at night and run it in the daytime when co channel QRM via skywave is not an issue.  I don't think any AM stereo is going on anymore but don't hold me to that.  

re bandwidth--at night I try to limit myself to 4 KHz with a baseband filter that has a 96 dB cut; in the day I open thing up a bit more but sometimes at night I forget to switch in the filter.  The other night a W2 I was working said he could not understand me because of the lack of highs in my audio due to storm QRN and asked me to boost them so I obliged by bypassing the filter for him.

Last time I swept my rig it was flat from around 20 Hz up to 10 KHz which is what you want but that doesn't mean you tx that wide; you just have a flat response and faithful reproduction of the frequencies you do transmit.  This is not to difficult with modern s.s. rigs like my 1000MP -- the challenge is gg to be when I start running the HT20 and try to get that flat from (I hope) 40 or 50 Hz up to 5 KHz.  DeYellifiying it right?   :D  Or just running it stock with a Hi Z xtal mic and getting that nice crisp punch.

Consumer AM receivers have been rolling off audio lower and lower over the years--car radios now start rolling off at 2 to 3 KHz.  This is an attempt to compensate for the higher noise levels found on AM these days coming from the usual suspects.  A couple years ago Clear Channel announced they were going to start cutting analog audio at 5 KHz--don't know if they did it or not but A.  so much AM is "talk" radio now and B. consumer recievers mostly don't hear above 4 KHz so if they had done that it would have probably been mostly unnoticed.

We have a local station that programs music of your life in full 10 KHz nrsc mask audio and if you have a decent rx, like a modded prod. detector feed to a hi fi audio tube amp driving big speaker it sounds very good.   most listeners don't have this. 


73

Rob
K5UJ  

YES! DEMOD,
I remember hearing that beautiful stereo in a GM Diesel the company owned. The stereo separation was unbelievable and the overall sound was great. It was a station skipping into the Washington DC area, while I was working one night.

FRED

Another thought:

  If you taylor your audio to sound Great at 15KC wide on AM, Then a guy listens to you at 5KC, You tend to sound horrible.  Alot of AMers dont get this.  If you taylor your Audio to sound great in a smaller bandwidth such as 6 or 7KC, You tend to sound good at those lower bandwidths.  The next time you hear someone that is real HiFi and wide on the band, Narrow down and you will see the effect.  It changes the guy on the valiant or DX100 little.



Clark

A friend in the Broadcash Engineering industry was actually bringing up a country station in Bakersfield a couple years ago.  I was interested in using some C-Quam stuff, and he has the test equipment to get a station set up CORRECTLY.

Last I heard, it was all still sitting on the bench at that project.  The owners of the station decided Bakersfield, Ca didn't need ANOTHER AM station.  Supposedly it's all sitting ready to go, towers and all.

So, I think their just might still be a demand for SOME C-Quam.  It could ALSO be that this station HAD all the stuff, and was bringing it (back) online when they had an ownership change.

--Shane

Clark,

I've noticed that effect also but it is not produced only by txing wide bandwidth.  It is due to the op's inability to eq his audio correctly.   If you tx a flat audio plot i.e. a roll up to around 150 hz then a flat line across and roll off at about 4 KHz or 5 or 6 whatever, a ham's audio will sound FB in a 6, 8, 10 or 12 KHz passband.  

What causes the lousy audio from a wide sig in a narrow p/b rx is when the op gets the idea that the way to eq his audio is to boost the lows and highs and attenuate the midrange.  I started out doing that because I was told that was the thing to do.  Where this came from I don't know but somehow the notion that eq sliders should look like a big smile got started.   But if an op eqs watching a time delay spectral audio display and tests by monitoring himself on narrow and wide passbands he can have it both ways.  

73

rob

I agree.  I run 20 to 20K through the TX, Then I plot it on a recievers output to the laptop.  You can really see your audio this way.  I have attempted to get mine nice and flat.

CLark

Bear,

You could design your own or start with Steve's anti-aliasing filter as a template:

http://www.classeradio.com/easy_e_pwm_alternate_filters.pdf


We have one here as well, KMRY, and the audio on the SuperRadio in Wide Band mode sounds great.

Phil - AC0OB

Here are some more shots of the AM band, I am not 'doing' anything with the flex, it just shows you the spectrum, you cant do anything but change the amaount of freq you look at.

There are plenty of signals that have something off one sideband, others that look normal, etc.

Brett

another one

What I'm doing now, is running a behringer 1124 parametric eq as a bandpass filter.  it has a cut of -48 dB on each of left and right channel.  I cascade them.  

there are a few problems with this though.  1.  It's a behringer, i.e. hard to figure instructions and user interface.  2.  I think it adds a bit of A to D-D to A distortion.  3.  As a parametric eq. to work it you have to be versed in the audio world lingo of octaves and all that which I admit I do not really understand.   I had to get an initial setup from a friend to get started, from which I made a few alterations.  

But once it is setup, you can have cutoff presets in different memories and simply dial in your rolloff.  

There's probably a better solution in a nice sounding gentle roll off  passive filter however, that can be switched in and out.

Rob
K5UJ

I used a 20 band analog graphic equalizer in the past, the vx2000 ($100.00) does it now.
You can pick up eq's used for about $50.00, small rack mont units...


Brett

Rob,

The modern Behringer stuff is big  bang for the buck, and if it does 48db/oct is FB.
Cascading standard analog filters can lead to wierdness in the passband, but that's another story for another day...


The octave thing is merely a doubling of frequency. Or halving of frequency.

1000Hz center freq, one octave up = 2.0kHz one octave down = 500Hz. simple enough...

                  _-_-bear

  My neighbor has 2 class E rigs . The 100 watt rig is 20 inches wide, the 400 watt rig is only 19 inches wide. Go figger ?

Time to interject a bit of technical reality  ;)

First, class E transmitters are not wider than any other transmitter type.  I have run transformerless modulators constructed from tubes, and the audio performance is identical to my class E rigs.  The absolute widest signal that I have heard on 75 meters within the past couple of years is, in fact, coming from a valient.  This can be backed up by Bruce, who has observed the same station.  No names - the guy is a good guy, and once made aware of the issue, is now actively correcting the problem.

Second, the bandwidth of any pulse width modulator is generally NOT limited in the output filter, but rather is limited in the INPUT filter (anti-aliasing).  You CAN limit it in both places, but is HAS to be limited in the input filter first otherwise there is a good possibility of high frequency distortion.

Third, unless we know how many DB down from the carrier the sidebands are, we don't "really" know the bandwidth of any given signal.  I've heard "wide" sidebands, but when I moved the receiver up to the carrier, I find the sidebands were 70dB or more down where I was listening (about 10kHz away).  I'm not sure that qualifies as wide.  And, I have to add the width of my IF in there, which means I was really listening to more like 5kHz away and not 10....

4th, the flattened triangle of the power bandwidth curve can be created with any good transmitter.  It simply means the station in question has a very high power bandwidth capability, and does not imply wide, simply flat.  The fact that the sides were triangle shaped indicates some type of roll off was in use.  Easily created by a good audio processor, and I have heard lots of them.

All that being said, this is not a class E thing.  Old Irb was PLENTY wide with his DX100  8)

Regards,

Steve

Steve,
Thank you..........a little common sense.
Bill 

After that fresh air I'd like to suggest we all stop using terms like wide and narrow.

We should also stop throwing bandwidth numbers around as if they were absolute. The AM community is better than this.

Ok, so how would you have me put that someone is taking out 2 qso's on each side of his 20+ KHz (wide) signal?
If three people are in a round table, at roughly the same signal strength, and two look to be about 6 Khz wide, and not interfering with other qso's, and the other guy is as above, how would YOU put it?

The question I started with was basicly could something be wrong with a class e rig (or rather the pdm modulator) or is it the operator?

I am suspecting because it can pass 15KHz audio, it is passing 15 KHz audio and at high levels...

Brett

Now broadcast rigs are also suspect.  Where will it end?

Well shaooot, my little ole K7DYY Sr is 300 watts and only 6 inches wide.

:P

Rich

Bear,  yeah I think perhaps cascading analog filts does some phase shifting problem--the behringers are DSP but just using one channel to get 48 dB cut is probably plenty.  My pal nearby calls me Overkill -- well deserved label.  

Steve -- great to have you weigh in -- tnx

Brett, I did some thinking about your observation of some bc stations having asymmetric sidebands and I stupidly didn't think of this earlier--if you are taking instant snap shots of spectrum of course you will see this.   When you look at say, 80 kHz chunk of the AM bc band, or enough to get a plot of 7 or 8 stations, you have to sample for several seconds.  Are you doing that?  If you are getting an instantaneous look, you are going to see good plots for locals coming in on ground wave but due to uneven arrival, lack of rx diversity reception and selective fading, the skywave stations will show that unevenness between upper and lower sidebands.   It's just normal skywave--nothing wrong or amiss.   Your flex radio panadapter is like other pieces of analytical equipment--takes time to get the hang of it.  I suggest you spend a few months fooling around with it.

73

Rob
K5UJ

With over 30 years in network broadcast and audio I can only refer to a VERY wise man who once said (regarding bandwidth):


"I don't understand why some people like to limit other peoples activity, or
choices.
It seems to me like there is very little important communication going on in
ham radio, so why stress the narrow bandwidth? Would it block some critical
or important communication?

Ham radio just seems like a bunch of people who enjoy fooling with radio
equipment, so why not just let them fool with it?


What about operating on an empty band, the operator still must (by law)
sound like a cheap cell phone?


There are other modes much narrower than ssb, why not not ban ssb as wasting
spectrum?


People should try to get along, I dislike contests, they can take over and
ruin a band, I am not fond of RTTY, or slow scan TV, or ssb, or many other
things other hams do, but the last thing I would want to do is restrict
something that others find enjoyable. "

Hmmmm..

73 to all the FINE sounding signals just "fooling" with Ham radio..

First thing would be to contact the person, tell him what you observe and how you observe it. I've had some bloopers on the air like an arcing grid tank. A report from a concerned fellow ham was welcome.

The point of my post is bandwidth numbers are thrown around by hams as if they were finite values like counting bricks.

This ISN'T QRZ.

This group used to collectively teach much better than the average amateur radio clusters I've encountered. There are lots of people digesting every post on this site. We are still doing well but some things need attention.

Reducing bandwidth to absolutes isn't accurate. This group collectively knows better than to ignore roll-off.

You posted "look at this crap" with a garden variety common IBOC AM broadcast signal which has been commonplace for several years. FCC says it is perfectly fine. I'm with you. It ruins AM BC DX. Who is right? The broadcaster who's signal you are looking at is broadcasting within CFR. They are in the right.

The whole reason AM users hang out in the ghetto is they are aware of friction with other fone modes. Otherwise they could set their bandwidth to sound like a warmed over ricebox on AM and live with lesser quality than a good current ssb system.

A constructive continuation of this thread would be how to view an acceptable AM signal verses a defective one on your equipment. This would include measurement errors found with experience and measures to mitigate them.  

Apologies to grammar police et al.

It is not a classE thing, so don't single out classE equipment.

Most likely the operator, just as in SSBer's who don't know how to properly equalize, errr, adjust an equalizer for a SSB signal, or who "over equalize" thinking boost is always better than cut. People who fail to educate themselves in audio chains and RF really should not touch anything but the VFO, IMHO.

Phil - AC0OB

First off I don't have a dog in the fight about class E. If it makes nice sounding AM I am all fer it.

My problem is what I heard and saw the other night. I am just trying to understand it.
Here is a shot tonight of a CBer that had a wide signal. He was not particularity strong but you could hear him up and down  about 50KHZ from his center freq. he is only S4 so it is not a strong signal.

So this is what I meant by a horizontal frequency spike. As he yells into the mike you can see the horizontal effect. You can also see the sig rise up on a fair amount of the spectrum.

He was bragging about running an old Yeasu into a HB amp putting out 500 Bird Watts on peaks.

I saw the same type of sig that night on 75 and just wonder did I really see a sig that was that wide or is my equipment fooling me?

Thanks

Carl
/KPD

Carl,
That's splatter....

As you can see, I use mostly the panadapter...

Hard to tell how significant a signal is, just by a change in background color....

Better to say "The transmitter seems to be putting out a lot of energy at 25khz away from the carrier...."  than to say it's "wide"...     ;D

Check out WBCQ from just a few minutes ago.........

If we just look at the waterfall display, some would say that  it's over 50kc wide....
In reality, it's about 8kc.

What design was involved?  At least with my designs, they all have filters that start rolling the audio off above 5kHz or so.

Hmm - SDR panadapters are not calibrated Spectrum Analyzers maybe?

OK-FINE................ I guess it's about time I chime in on this one.

A "wide signal", music, art, beauty, and sexual perversion all have one thing in common.
It is only in the eyes of the beholder.

When you refer to a "WIDE" signal are you referring to a clean high fidelity signal, or a dirty transmitter spewing "artifacts" all over the band. Any one of us out there pretty much knows what an AM signal should sound like, and how much bandwwidth it SHOULD take up. this is pretty much common sense and good operating practice.

Like Dave and others have said: "I dont want to sound like a cheap cell phone!" But, by the same token, if I'm putting out an unusually wide signal, I would expect someone in the AM community to let me know so I can check it out. Also I also had a problem tossing "artifacts" all over the band one night. I was kind of sleepy and not watching the scope, come to find out I had a porcelain insulator supporting the tank coil arced through and with carbon tracks that was causing the problem on mod peaks. thanks to someone telling me I had "artifacts" I headed a possibly larger problem off at the pass.

The issue of AM bandwidth has always been the subject of heated discussions and lots of pissing and moaning. It always gets some people's feathers ruffeled. Any wide bandwidth caused by dirty, defective or improperly adjusted transmitters should not be tollerated. However, the bandwidth required to put out a CLEAN, good sounding signal should be a non issue. I will always accept constructive criticism from someone that I consider to know what they are talking about. As far as the SSB crowd goes, they would piss and moan about our bandwidth if it was 100Hz! ! !

                                                                    The Slab Bacon

Yep, I had one of those too. I bought it after seeing how WIDE my neighbor's Class E rigs were .

   Some people seem think wider is better. Not sure I agree .

Fun thread and gettin' wider, oops, er ah "longer."

I believe I was the first to define 'horizontal frequency spikes,'  ;D

-Great technical (or lack thereof) of measurement discussions.

'Excessive' or 'dirty' bandwidth kind of reminds me of  one of the US Supreme Court judge's opinion in relating to porn,
"I know it when I see it."

Well, "I know it when I hear it" too.

Check out these two local BC stations.
Which one is using the old plate modulated BTA?
Which is complying with the restricted modern standard?
Which sounds like crap?  Well, believe it or not, you actually have to listen to the audio.

That was what I was asking about, if the pdm modulator could have a problem, or if it was just the case of passing 15 KHz audio.

I think its kind of rude to run that bandwidth at nite on a crowded band and take out 4 other qso's, I dont have a problem if someone wants to go 30 KHz wide in the daytime or when there is lots of room.

It makes no difference to me, as I cant hear anything above about 3500 hz anyway.


But I have no idea if it was the audio, or something wrong with the rig.

I would like to look at signals and see what happens when you overmodulate a class E rig, and what the signal looks like when it passes a lot of 10 KHz and above stuff.

I would GUESS just passing a lot of high end would not look like a squashed triangle, but more like normal modulation with less in the sidebands, but also dont know what 150% positive modulation with lots of highs looks like. Can you do that on a class E rig?

Brett

This sounds like the old, "What's My Line" TV program.

I would guess the Country station is using plate modulation while the "local" station is using an IBOC mask.

Phil - AC0OB

  Wouldn't the actual program material make a difference as well ?  IE :Processed snare drums and cymbals VS a James Earl Jones voice over ...

  Apples to apples ?

Brett:

Any AM transmitter, regardless of type will splatter up and down the band in the same way if driven over 100% negative (and thus reach carrier cutoff). This creates complex products (spikes, square waves that also mix with themselves) that can be as wide as the tank circuit. The math is the same regardless of type.

AM modulation is the multiplication of the RF carrier by an audio signal.

For a mathematical discussion of good AM, look here:

http://en.wikipedia.org/wiki/User:WillWare/Radio_theory

It seems you are closing in on the idea of someone overmodulating as compared to cleanly modulating high frequency audio.

It'd probably be good to carefully look at strong AM broadcast stations (non IBOC) that are not overmodulating and compare this to someone obviously splattering on the CB band. Listening, tuning and looking at your spectrum display will reveal the clues over time.

As usual, you must be sure that your receiver and display are not creating their own artifacts. I have fooled myself doing this.

When you get a chance, let us know if it is overmodulation you suspect or just clean wide audio. By all means have a discussion with the operator.

Hope this helps!

73,
Dan
W1DAN

None of this has anything whatsoever to do with class E.

The EXACT SAME components are generated using a tube rig if it is operated under the same conditions.  The very same thing happens if there is overmodulation of either a class E RF amp or a class C tube RF amp.  The pulse width modulators behave identically in either case as well.

THIS IS NOT A CLASS E THING.  This is an individual transmitter thing.  Tube, solid state, DYY design, QIX design... it is NOT a class E thing.

You can pretty much make any technology (tube or solid state) do pretty much the same thing.  Having built quite a few PWM transmitters from tubes and MOSFETs, I can tell you with absolute certainty they do exactly the same thing.

As far as my designs are concerned, I could "dumb them down" to match some of the other offerings out there, but I have been leaving those decisions up to the operator.  I do offer much tighter filters, and the designs are published, and the parts are available as part of a PWM class E kit, if desired.  All of my designs are capable of reduced frequency response, but again, that is up to the operator.  I only say all of this because the majority of the class E transmitters out there are of my design, and that design provides a robust, high capability platform.  What the operator does with it is an individual thing.  Kind of like buying a high performance car.  The operation of that car is up to the driver.

Regards,

Steve

"Thrown around" yes, and handed to them by those who want to substitute quantity instead of quality as a measurement standard.

Dave said -

man, 5 pages of beating a dead horse.

To a bloody, quivery, gelatinous mass.

Not a uncommon occurrence. We can probably do 20 pages on how to cook a steak on a grille.

Yea, quit bad-mouthing Class E. Move on to Class F already.

Cooking steaks.. Hmm.  Going to Grill up some tonight.


Clark

yeah!
What's for dinner net.

Beating right along,  ...(hmm, steaks sound good.)
Check out this bad boy.

Sure.  The changeover to cymbals and rock from voice programming shows up half way down the waterfall.

the subject of AM bandwidth always seems to get most AMers bowels into an uproar! Especially the thought of legislated bandwidth limits.

All I got to say is one of the reasons I'm on Am and not on SSB is simple"

And speaking of steak and the "Whatz fah dinnah net" I'll have to call the war dept and see Whatz fah dinnah  ;D  ;D

                                                   The Slab Bacon

better yet, let's fire up on 3733.

last one in's a rotten egg.

Later-
fired up the 813's rig, made a couple of calls and then just realized that the entire east coast is socked in from Ida, lightning and all.   AHE's probably unhooked all his antennae, etc.
....oh well

Ride this horse!

The 10 kHz spacing on the BCB guarantees adjacent channel interference. That is why they skip a few channels in local coverage areas. 10 kHz is not enough even with legal AM if you are talking HiFi.

Ride this horse!(http://www.google.com/images?q=tbn:uvRxMSeuOfPUmM::www.archvis.biz/webstorage)