The AM Forum

I've been tweaking my home-brew linear/transmitter combo with audio and power drive to get the perfect combo.  I think I'm at a point where I've found the perfect match.  I'm using 200 watts carrier and my PEP-hold feature on my Daiwa wattmeter is showing that I'm at 1200 watts peak.  My math tells me that I'm at 150% positive peak.

I was talking with WV5G last night in NM who told me that my audio sounded great.  We ran a test and I increased audio to 1400 watts, but he started to notice distortion at that level.  In our discussion, he mentioned that he'd never heard a class E rig on the air, and that the audio level between my rig and an E rig would be equivalent.

I thanked him for the compliment, but that I had heard many E rigs on the air back east and the audio quality is unmatched.  

I would like to say thanks to all who have helped me get my station to where it is today, from parts to technical support.  As I gather parts for my 40 meter E rig, hopefully I can put super-efficient and quality sounding RF on the air from Phoenix as well.

Jon
KA1TDQ

Yup!

That's what my math shows.  Too bad we weren't closer.  Hope your new QTH is working out.  Congrats on your project

Al

Keep in mind Jon that when you run extensive asymmetrical modulation percentages, you will sound distorted on many receivers due to the conventional envelope detector.  So if you want to sound good on most people receivers turn it down a notch or two and run some voice processing to keep the average percentage up. 

Joe GMS

This is true, although not because of the conventional (non-sync) detector, it's because the receivers are improperly designed (including in the detector!!).  If the envelope detector is properly designed, it can (in theory) demodulate unlimited positive peaks.  Of course this is not technically practical, but you get the idea.

Its great that you CAN do it, but it might not be best to run it that way.
Just what transmitter is it?

How do you limit the negative modulation?
I do not think 150% to 95% is normal for most voices.
I also hear lots of great sounding class E rigs but they are all very wide, and many have so much modulation that they sound distorted on many receivers.
What is the point of that?
SSB has a very high peak to average ratio, lots of audio, does not make me want to run it.

The transmitter is my single FET, class C rig.  I have a 2.5db attenuator in line to the linear which gives me 20 watts carrier to drive the linear.  The carrier output of the linear is 200 watts. 

I'm using a 3-diode keep alive circuit as a negative peak limiter. 

And, maybe >100% isn't for all voices, but I spoke with that station in NM and a guy in CA last night and both said my audio was awesome.  Listening with my headphones on and my ricebox receiver RF gain turned down, it sounds good to me too.

Before, I was running a big carrier and less audio and didn't get many hoorah remarks.  This change seems to be for the better.

Jon

This is true, although not because of the conventional (non-sync) detector, it's because the receivers are improperly designed (including in the detector!!).  If the envelope detector is properly designed, it can (in theory) demodulate unlimited positive peaks.  Of course this is not technically practical, but you get the idea.
[/quote]

Yep I agree, but probably most of the stations I talk to are using envelope detectors that are poorly designed.  I believe they are generally happy with their receivers so its very unlikely they will change.  So, based on the larger population that I want to sound good to, I have chosen to not run extended peak modulation.  It seems like on most receivers going up to 120% is ok, but much past that and you get the nasty peak distortion in the detected audio.     

I want to evaluate the Kahn symmetrical audio circuit and give that a try.  For those not familiar with Kahn's circuit here is a link.

https://www.google.com/patents/US3060389

Also, here is some older dialog from this site on this dialog:

http://amfone.net/Amforum/index.php?topic=25597.0;wap2

Saying that, whatever you choose to operate is as good as it gets.   The subject of good audio will never die.

Joe - GMS
   

I was very wide when I tried the 3 diode peak limiter.
Have you had someone look at your signal?

I think it had something to do with the diodes not being fast enough on the high frequency stuff.

Nobody has taken a look at my signal as far as I know. 

If I were wide, then I could replace the diodes with IXYS fast recovery epitaxial diodes.  That might help. 

But, 'round these pah-ts, there's a group of sidebanders that get on 7.288 but clear out around 9am for the 7.293 AM crowd.  It works out really well.  I haven't come across swishing VFO's yet.  Being wide wouldn't be too much of a problem.  Nighttime turns into a power contest with radio China.

I had a funny QSO one time... I called CQ and this guy from CA came back to me on LSB, not knowing that I was on AM.  In fact, I don't think he knew what AM was.  Anyway, he'd give me quick one or two sentence replies and I'd old buzzard back on mine.  After about three exchanges, he had to go.

Jon

The design goal for conventional diode detectors most certainly isn't 150% upward modulation, so I'm not sure it's accurate to say they are improperly designed - rather, they are a design compromise.  Where most diode detectors fall down is excessive capacitance downstream; ie to filter the carrier to provide DC, generally for AVC.  If a receiver has a separate AGC detector, an AM diode detector can often be improved by reducing the filter capacitance.

Hallicrafters SX-101s in particular can be vastly improved by removing the .01 uF capacitor (as I recall) in the ANL circuit.  Of course this renders the ANL inoperative but the peak clipping is improved considerably.

Bottom line, there's no really justifiable reason to run such large positive modulation, since you don't know what the other guys will be running for receivers.

I backed off the audio last night and I don't think anyone really noticed.  I'm running 1000 watts peak now.  It gives me more room now anyway for hard "P's" or a laugh.

Jon

Speaking of wide someone was on this week I think Wed on 40m and even on my digital rx I could copy them about anywhere between 7290 and 7282. And strong too. That is a bit much I think. I thought my RX was broke at first.
I didn't try going above 7290 to see how high it was but wish I had now. As someone running 7 watts and getting out I don't get it. However to each his own.
don

Some of the class E guys are 25 KHz wide, most run at least 20 KHz.
Some run processing that makes the signal dense out to 10 KHz each side.
When I run my screen mod setups, I likely am wide because the rig will pass high frequencies just fine and I have nothing to limit the high frequency stuff enough.
I have an EQ but that only cuts the audio 6 or 12 db (range switch).
Old rigs had lots of crappy transformers, lots of screen and plate bypass capacitance to reduce highs, even after mods to the audio.

Class E, broadcast transmitters, some flex radios, and screen modulation can have no limits below 20 KHz.

So you can have someone 20 KHz wide, running very high power, taking out 3860 to 3885.
There is no reason for that, no one is listening with a 20KHz passband, but some people would like to be even wider. After all, its all about them.

Its VERY good you can hit such good positive peaks, because at 130% positive you will be very clean.
Clean sounds good, and tends to not be real wide.

I guess you are doing the 3 diode limiter in the low power part, I did it at the high power part, with brick diodes rated at 14kv and 1 amp, maybe that was part of the problem, lots of slow diodes in series...

John is spot on.  Receivers were designed based upon accepted standards and there was no reason for the detector to be set up for a modulation level beyond what they were expected to receive. 

Many listeners will experience considerable distortion at those high levels and although it is fine for groups interested in experimentation,  operating with that level of modulation is rather rude when checking into general AM nets and large round tables.

   Seems to me that a high average percentage of modulation is desirable, whether it be from raising the density (processing), or high peaks (to no more than 140'ish %) increasing the average. Either method will enhance copy-ability at the receiver end, especially if the frequency response is Taylored to make the best out of 100 - 4K audio response.  The effect to a round table of hams where most are averaging 30% modulation is huge....but is that rude?

   Sure, some receiver detectors will tilt as they distort a high peak. The hint of fuzziness at that peak and a bit thereafter is usually not bad unless the transmitting station is broadcasting a highly distorted modulation to begin with.

   What really sounds terrible to me are those that run low level AM from a balanced modulator, or SDR exciter that is driven to the point of producing "wavelets" (> 100% downward modulation).

   I routinely run peaks at ~ 140% with my Gonset G-76 station. I always get good reports, and folks copy me under adverse conditions. Is it high fidelity, NO, but it works, is received fine, and with good reports.

   I contend those that run high peaks that end up sounding terrible are usually broadcasting more distortion than what the receiver will produce from an over capacitively loaded diode detector. The exception would be the "wavelet" guys that are not transmitting a distorted signal, but instead are transmitting a signal not compatible to be received with a mere diode detector.

   Jon, I'd like to hook up with you sometime, 7290 +/- ?

Jim
Wd5JKO

   

Be careful about calling a station wide unless you provide full data. I've measured stations some call wide as having 5kHz products at -40 dBc. But they were 30 over S9!! That puts the 5kHz products at about S7. Yes, you are gonna hear them even in a 3.5kHz passband given the skirts on most BA receiver I.F.s.

These stations that are supposedly 20 khz wide, how are you determining this? Using a spectrum analyzer or waterfall display on an SDR, or just guessing by tuning up and down with your receiver? The perceived bandwidth of a signal on a receiver is the sum of the transmitter's bandwidth and the receiver's bandwidth, so if you have a wide receiver, that's gonna make the signal seem wide.

Thank you!  The voice of reason  ;)

I'm not sure why there is a discussion of class E rigs here with respect to bandwidth.  I suppose I am more than familiar with the design of most of the class E rigs on the air.  They *ALL* have a whole lot of filtering before and as part of the modulator.  How many DB down at the edges?  LOTS!  This is born out all the time when observing spectrum displays (which are now quite common) and you can see how many DB down the signals are at the filter's edges.  

6 poles at the modulator input with the 3dB point a little above 5kHz is, in my estimation, a pretty reasonable filter.  Then you put a 6 pole filter AFTER the modulator with its corner at around 9kHz, and you have a lot of filtering.  The 2nd filter is always higher than the first to avoid unwanted effects in the pulse width modulator itself.

It is really obvious when a transmitters has filtering and when it does not.  The ones with filtering (such as most class E rigs) drop off pretty quickly at the filter edge.  The others?  Well, not so much.

The bottom line?  Absolutely none of this matters that much in the long run.  Frankly, it is VERY rare that a station's excessive bandwidth (translated: high frequency response or unmitigated excessive distortion) causes a problem.  

What is more likely to cause problems is a large disparity in the signal strength of the station you want to hear, and the station 10 or 12kHz away that you don't want to hear, but is 40 dB stronger than the one you're desperately trying to copy.  Been in that position many times.  The most useful answer?  Use a better receiver.  That's what works for me.

I've been on ham radio for more than 40 years.  I can only think of a handful of times in 40 years that someone being "wide" actually caused a problem with copyability.  Real strong station nearby?  Yup, that can be a problem, but not due to excessive bandwidth.  Sidebands? Maybe.  If it were just a carrier maybe I could copy the other guy.  Excessive sideband energy?  Very Rarely.  Annoying? Only if you let it.

<End Soliloquy>  ;D

Regards,  Steve

Only once every 40 years?
This guy might have caught your interest. ;D

Almost had to be a fellow AM'er to know what he was doing.

Class E:

http://n2dts.smugmug.com/Ham-radio/i-ZxTSnCR/X2
3865 to 3885.

Normal AM guys:
http://n2dts.smugmug.com/Ham-radio/i-JZp3kbg/X2

I can produce lots of examples too.  There is no point to it.

This finger pointing is not productive.  If someone doesn't like class E that's ok - everyone's entitled to their likes and dislikes.

The widest AM station I've ever heard, and the widest ones I hear now are not running class E rigs, but WHO CARES???  This is not relevant to anything practical or useful.

All of this talk about AM bandwidth is HIGHLY counterproductive and we should stop it, else we (as a mode) will get what the bandwidth police appear, by their constant talk about it, to be advocating.  An FCC regulation about bandwidth which we absolutely do not need and certainly do not want.

So you will support me running my new 5000 watt rig that is 100 KHz wide?
Surely that will not attract any unwanted attention by anyone, at least as long as we do not TALK about it on line.

And I never pointed anyone out (maybe you can tell by his signal?) and did not single out class E, I said like some other methods, it CAN be wide.
I think your wonderful dx60 modulator goes as wide as a class E rig...

Boy! this thread turned unpleasant in a hurry.  Please let's not start up a class "E" vs a class "Y" ( as in "classy" or class C) dialog.  A properly adjusted PDM AM transmitter that operates in class E has very low distortion hence very low distortion products that show up in the sidebands.

Brett, I looked at your first example and I cannot derive the carrier level so I cannot tell what the sideband levels are with respect to the carrier although I admit this might be a poster child for a poorly adjusted AM transmitter.

And please let's not get into a bandwidth confrontation.  In my view any type of AM modulation needs to be properly adjusted with proper gain distribution across all processing stages.  Properly designed and adjusted AM transmitters will not occupy an inordinate bandwidth but will be determined by the band pass of the audio that excites the modulator.  Improperly designed or inadequately monitored AM transmitters have the potential of occupying greater bandwidth than is necessary due to the distortion products of the modulating signal and the inability of the station operator to detect these distortion products.

We have the opportunity for these different modes of AM design and operation to make us good experimenters using good engineering practice..

Al

The thing about that first picture is if that signal was only S9 and not S9+30 and higher, then that excessive sideband stuff might not actually be noticeable. Same with the second picture, add 10 dB to that signal and you might end up with something close to the first picture.

Much wider actually.  The class E rigs and the SDR radios and most rice boxes have ACTIVE and purposeful bandwidth limits in their designs.

My dx60 modification has no such limitations, and therefore can be and probably will be much wider than any class E rig (well, at least any that I designed).

This thread has been derailed by a red herring, and I would like to bring it back to the discussion as it began:  Highly asymmetrical modulation and what that means at the receive end.

Thank you  8)

I did a spreadsheet on the carrier level vs sideband products.  Here's the JPG plus the worksheet.  I used 5 and 12 KHz delta frequency as sideband products.

Jim, WD5JKO... My on-air schedule is really sporadic. Infant,new baby on the way, job, etc.  It would be better if we could email or text each other maybe a half hour before hand. My phone has email capability. My email address is navy.gov@gmail.com. Let me know the best way to contact you for a sched.

By the way, I went barefoot this morning talking to Tucson. My carrier was 28 watts with peaks hitting 140 watts. That's 156%. Everything sounded fine to me as well as the guy I was talking to who was using an SX-111 receiver. 

So, full speed ahead!

And Jim, I'll leave the linear on for ya.

Jon
KA1TDQ

Those running high power should be more aware of what they are doing whether its class E or plate modulation. These stations tend to be heard out farther away.

I hear this all the time from guys in the Midwest and I hear this all the time. Example: existing AM QSO in Michigan on 3880 running 100 watt class txs, the band is open at 7pm, and the EC group on 3873 fires up 10 mins later running 500-1000w, and has at it. The usual..oh I can hear a weak QSO in there on 3880 is put out there, and it continues almost daily. Who cares about the guys on 3880 or other adjacent QSOs. Their QSO is now being trashed. Sure, get a better receiver...really...??  A red herring? No...its reality...but lets not talk about it..

Someone's operating practices need to be overhauled and re-examined.

Al VE3AJM

Yeah, the 3880 thing has been problematic since I've been around.  I'd be up on 3885 talking with the east coast guys, and a QSO would fire up on 3880 from out in Ohio.  The 5kHz hetrodyne is deafening, and of course the sidebands were right there overlapping!  Nothing can be done about this except to not do that (use frequencies that are too close together).

As a rule, I avoid using 3880 if I can because it will cause interference (or be subject to interference) from/to 3875 3885 and 3875, which are well used frequencies.  Yeah, yeah, we can go anywhere, yeah, yeah yeah.... I know that.

This is not a bandwidth problem, this is a "too close for comfort" problem.  The group currently on 3873 moved down from 3875 to get further from 3880.  They would have gone to 3870, but there is a regular group of sidebanders who use 3868, and well you know the scene..

But, I would make a prediction that IF the 3873 group moved to 3870, SOMEONE would try to have a QSO on 3875, and then problem proceed to complain about the "wide" stations on 3870.

If you have a good signal, you can't win sometimes.

IMHO, 3880 is not a good choice because in theory, a 3880 QSO pretty much precludes anyone else using the so-called "AM window" (3885 or 387x) without causing interference or being subject to interference.

It's an OLD OLD problem - goes back as far as I do in this hobby which is over 40 years.

"Doc, it hurts when I do this"  Doc:  "Don't do that!"   ;D

I would say that with the example that I gave, it was a transmit bandwidth problem, whether the cause was overmodulation and/or the 25+ kc audio frequency response from the 73 people. At that time, even 3885 was being trashed. So the entire "AM Window" was unusable. The 3880 QSO was pre-existing. But then, we really shouldn't be using 3880?? and the 3873 group had already done the right thing and moved from 3875 just to help out? Aw..ain't that nice  ???

What is the purpose of having a transmitter with a 25 or 30 kc audio bandwidth and having the Ss and Ps, and frictive sibilance being heard out so far? We aren't transmitting music. Why do you want music response? Most guys will use the typical vintage receiver with a 6-8kc receive bandwidth, some a little more some a little less. Seems like a lot of wasted energy and power used unnecessarily, that's only going to tick off a whole lot of folks.

I moved down the band years ago to get away from all that. I see that the attitudes haven't changed much.

Al VE3AJM

Shelby, Budley

I particularly like your comments about being careful about our measurements.  We need to realize that it's the rx bw and the tx bw that needs to be factored in while determining one's transmitted bandwidth.  The other thing to note is that if an AM station is very strong and we try to QSO 5 KHz away, we are going to hear the sideband products that may be >-30 dBc.  If we are trying to listen to a station with only a few dB signal level above those sideband products from the strong station, we are going to have an interference problem (interference as defined where two signals are detected at the same time).

If we look at that spreadsheet I created and assuming a correlation between the 32 dB / S9 and the screen, and then factor in the receiver bandwidth there will be interference with the weaker station between at 5, 10 KHz carrier spacing.

Steve

AM carrier spacing:  5 KHz is just too close.  Looking at the numbers in the spreadsheet one would have to have a greater than the -70 dBm (3 dB / S9) and then tune off to one side away from the strong station in order to hear reasonably well the station that is being listened to.

Jon

150% positive modulation level?  Yes!  It is very possible with the human voice to achieve these levels with the negative modulation levels of <95%.  That is especially so today with common knowledge of modulation asymmetry coming from the human voice.  

Correct modulation phasing: Decades ago using the correct phase in one's modulation chain was not a common experience - So I think we need to address this reality by using correct measurement methods.  We can probably look for the "pearls" on the negative side of our modulation levels but accurately determining the positive modulation levels is another matter.  One needs to have a good means of measuring both the positive and the negative modulation levels in order to guard against flat topping on the positive peaks. It is very easy to be aware that something is wrong when either asymmetry is the wrong way or there is none.

Finally, we need to measure the distortion products of our AM transmitters as part of our AM experience - that should be our goal of applying good engineering practice of our amateur radio station.  
Yes, with today's advance in technology, we need to know that our stations are putting out reasonably low distortion products and have control over our transmitted bandwidth.

One more thing: Audio bandwidth: We need to have control over our transmitted audio bandwidth - we need to know what it is and have means to control it. I am not affixing a value to this - I think we need to know what it is and be able to control it.  Another goal in good engineering practice.

Another good thread might be the proper demodulation of the modern amateur radio AM station.  We have the technology, we should work towards using it.
Al

Anyone remember the mid 70s when there were equally high power tube rigs running around everywhere (pre dates the class E rigs).  Pretty wide stuff back then - a WHOLE lot wider than the modern rigs.  And, a LOT of people had these big tube rigs at that time.

What did we do?  We dealt with it.  Maybe something's been lost over the decades.  Maybe we were tougher (or perhaps more realistic and/or more live and let live)?  Don't know, but I do know we didn't yammer about it all the time.  In fact, I really don't remember hearing about "wide" sigs at all (except from the slop buckets) - and those rigs were PLENTY wide - wider than what's out there today because there was no filtering whatsoever.  I used to run such a rig - pair of 304TLs modulated by 833As.  Not a filter in sight.

But, back to "wide" sigs from 3873 for a moment.  There may be a few old-style transmitters on 3873, but all of the modern ones have 5.-something kHz 6 pole audio filters, and an approximate 10kHz 6 pole output filter.  So, it must be an old transmitter you're hearing with 25+kHz audio frequency response.  None of the ones I designed can do that, and I don't think the Flex radios can either.  Hmm... maybe a modified FT101 or something like that?

Again, no one at least on 3873 can do that - well, ok, there is one person, but he's using vintage AM equipment that's been modified..  The modern rigs are not able to do that sort of high frequency response.  Too many filters.  It's just a fact.  If a modern rig is "wide", it's operator error which can happen with ANY transmitter - AM, SSB, etc. etc. and we've all heard it.

Well, I was down there in the low end of the badn within the past 6 months or so and my QSO got pretty heavily interfered with because someone fired up about 6kHz from where I was.  We moved down the band a bit and carried on.  That's life on ham radio.  It was a WHOLE lot worse 40 years ago than it is now, that's for sure.  The bands are so much less crowded now.  And, we don't have the slop-bucket wars we had back then.  I'm sure glad THAT isn't happening too much - at least not around 3885.

Something just occurred to me.  I operate on 3885 all the time when the group 3873 is on and I never hear any interference from them at all.  And sometimes I'm even n 3880 and I don't get it.

Not my experience and not what the spectrum analyzer shows.

Reality check needed.

Having built a Class E rig and several tube rigs, I don't see how the Class E design results in any more bandwidth issues than the more traditional designs. Any one of these transmitters can be made to sound great or terrible depending on how the modulation is controlled.

Since this thread began as a discussion of asymmetry, I also feel that there's far too much of a fascination with positive peaks given their negligible contribution to perceived volume, which comes from average modulation, not peaks which contain very little energy. Additionally, there's a point where voice asymmetry maxes out and anything beyond that is artificially generated by clipping the negative peaks. That's where its very easy to get into trouble.

Yet another argument against excessive positive peaks is the much greater risk of punching a hole in the insulation in expensive mod iron or damaging other components. For those who care, a 375 watt carrier exceeds 1500 watts PEP above +100% mod. It's more effective to maximize the carrier, reign in the peaks, and properly process the audio.

Broadcast engineering has been driven for almost a century to develop transmissions that were both clean and loud because big dollars depended on it. There's an easy lesson in that.

Anyway, back to the original topic.  It would be interesting to know what sort of receiver the other fellow was using.

I went over to another ham's place a few years ago and Brent W1IA (who sounds really good) was on the air.  Well, he sounded quite poor on this guy's R390 (might have been an A variant -  can't remember).  Point being, the detector in that particular R390 was clipping QUITE BADLY all modulation above about 80%.  That was one of the worst detectors I had ever encountered until in one of my own receivers, an RME45 (an RME forty-something - I don't remember right now) was a REALLY bad detector.  I ripped that one out and put in a precision rectifier type of detector and cleaned it up pronto.

Point being, some receivers are just plain BAD.  Too fast AGC is another big cause of distortion in receivers.  I gave up about 20 years ago and finally built a receiver (build a solid state receiver using a BC-1004 as a platform) and that one has very good fidelity.  The absolute best I've used is a sync detector - a Sherwood - hooked to a receiver with a well filtered AGC line.  Great sound!

No kidding. None are so blind that will not see (hear).

That's a good point.  Unless we're using a receiver that has been engineered for high fidelity audio, there's no good judge out there.  99% of hams (me included) are using a rice box receiver or something out of the 50's that's only getting older (and possibly not working properly on top of that).

Having said that, with all my operating down here, I've only had good to great comments about my audio.  Twice people have said, "Wow, there's no distortion in your audio."  And I've received no complaints about anything (too loud, too wide, etc).  

And, I'm just a ham.  I've made a real effort to put together a good sounding home-brew station.  Not corporate standard... just within the FCC parameters and a desire to sound "good".  And, people say I sound "good".  

Mission Accomplished

Jon

Same here.  Its impossible for me to operate on 85 .  Most of the guys on 73 are not the problem but one in particular completely wipes things out.  Before you assume I am using a poor receiver that is not the case. 

So for me, the solution is just go to some other part of the band.   Its something that is likely not to change. 

On another note, some folks like to be extreamly wide to keep the SSB ops from getting to close to them.  The SSB - AM wars are not dead if you listen to 73 at all. 

Joe - GMS   

   

We all want to be clean and loud, and the b'cast industry figured it out decades ago. Unfortunately, two circuits in every commercial processor sold that contribute a lot to clean and loud are also the most misunderstood: Phase rotators and clippers. Let me explain...

Phase rotators increase audio density (loudness) by reducing asymmetry. Since compressors reduce gain based on the peak to peak voltage of an audio signal, asymmetric waveforms are *reduced* in level more than symmetric waveforms. Average volume ends up being higher for waveforms that require less gain reduction. Phase rotators are available online for under $20, completely built, and can easily be added to your audio chain before your processing.

Peak clippers have gotten a very bad rap because of circuits that utilize just two diodes, and when driven hard, generate loads of harmonics and distortion. What makes clippers invaluable for clean loudness is the careful regulation of the driving audio and proper low-pass filtering that follows. Some form of peak audio limiting is needed prior to the clipper circuit to maintain a reasonable clipping level. Since any clipping creates harmonic energy, a Low Pass Filter should be used after the clipper. Also suffering from a bad rap, these circuits are usually the first to get torn out of boatanchors, and understandably so since they aggressively strangle high frequency response (clippers in Johnson Viking Valiants are driven with unprocessed audio...yikes...thus the need for radical filtering). The LPF should only filter out everything above the highest audio frequency you want to transmit. Multi-pole filters with steep slopes will give you the best highs and neighbor-friendliness.

It's easy to borrow these proven concepts from broadcast processor manufacturers, and by employing both circuits with a consumer audio processor in between, you will achieve a very clean and loud signal.

Maybe someone running a Flex or other good receiver can make a recording and we can hear it!!  Unfortunately, propagation to your part of the world from my part of the world is a bit unreliable, at least on 75 meters.

Nice work !!!!!

Regards,  Steve

Apparently I'm missing all the "fun" in the AM Window.  I only hear about the Texas traffic net and they're more of a minor annoyance.  Haven't had a run in with a disgruntled SSBer is ages.... and don't get any interference when I'm up on 3885 from any one on 3873.

But, I'm not on every night anymore since I've been back in the workforce, and when I am on, it's usually late at night.  Only on sporadically in the early evening when all the action is apparently taking place.  Hmmmmmmmm  maybe that's a good thing?  Of course there's the 160 meter portion of the 75 meter band if one wants some solace.

Regards,  Steve

I didn't know about this. Is this something new??? Where do I set my dial?

Ah !  Joe GMS can tell you better about this than can I

All:

I thought I should redo the spreadsheet that I did earlier.  I'm calling the first line in Brett's first line "Example 1" and the second line "Example 2"   Remember this is an extrapolation between the S meter readings as the carrier level and the display in dBm.  I picked peaks at (very) approximately 5 KHz and 12 KHz on the left hand side of the display.

Recap: I do not know what levels of modulation the example stations used so cannot characterize which signal is "friendlier" for co-channel operation.  So I redid the spreadsheet to include what I could read off the screen.  It is very hard to pick a screen shot that represents accurately what was going on but I went with what I had.  While I was at it, I did some more work on my S meter vs dBm table.  The PDF will not show the math behind the table but I'll include the XLS file so I can be checked on my math.  Some of you SDR guys might find the S meter vs dBm table helpful.

If I had to pick a "neighbor,"  I'd pick the station as represented in Example 2.  I offer no further characterization other than that.  I stand by my previous comments.  Let's all be good stewards of the frequency spectrum that has been given to us

Later on, I'll probably strip the signal display pages and upload the S meter info as a stand alone file for future use in the "Hints and Kinks" section

Al

No guarantee in that portion of the band. Several years ago I was trying to work some European AM stations on 3705 kHz. This was just past midnight local time and when the band would usually be pretty quiet. I kept getting strong splatter. I tuned up the band and eventually came across the source - a Class E station on 3725 kHz.

Pete, I think Joe makes a reference to 3.705 that it can resemble the gentleman's band, on 160M at times.
I'm starting to study for the Extra class to get below 3.700 and enjoy some AM there.

And Jon,,,is there another one in the oven?? b-a-b-y??
Fred

Fred - Sounds like it  :)  Congrats Jon and to your wife.  Nice family

Al

Yup. It's one is 13 months old and #2 is 3 months in the oven.

Jon

Although, the area around 3.705 is far from resembling the "gentleman's band". Got to remember this is 75 meters.


With the active discussion and proposals about cutting 50 KHz of the Extra phone band portion for data modes since there seems to be a notion of lack of activity ( http://amfone.net/Amforum/index.php?topic=37939.0 ), more Extras should operate down there to make some noise on a regular basis.

Congratulations!  When I finally had 2 kids, I was pretty much off ham radio for quite a while.  Got back into it once they got older.  Now we're empty nesters. Time flies!!!!!

When she was pregnant with the first one, I was in a mad dash to get everything built before he was born.  I figured I wouldn't have much time after that.  I completed the linear before he was born, but then started the single FET rig after his birth.  I managed to get that one done with the mother-in-law living with us and helping out. 

Next project is simple... building a power supply for an Elmac A54 that I got from eBay.  And I'm slowly gathering parts for the 8 FET E rig.  I've started drilling holes on the heat sink for the RF FETs.  Not a big start, but it's a start.

Jon

My reference is that many of the same op's and style are the same on 1.885 and 3.705.   So much so that I seldom get on 1.885 much anymore.   We all have preferences of where we enjoy operating and I find 3.705 very enjoyable.  This conclusion for me has been derived from over 45 years on 160 and comparing it to whatever time the 80M sub-band has been available to us for phone operation.  Other than some of the AWA AM events along with the AM TX rally, I just don't enjoy operating within the "Getto" on 75.  Some people like the adrenalin rush of the happenings on 3.873 but I just don't enjoy the level of confrontation.  As I said, to each their own and be glad we can pick and choose what floats our boat and operate in the part of town we enjoy.

This difference of opinion between our operating styles and what various people enjoy is just something that we all need to respect and move on.     

Joe GMS       

Your wrong again Pete, this is the 80M band and not the 75 meter band and I suggest you spend more time listening and joining in on the many great AM QSO's on 3.705!   :)

Joe

75 meters and/or 80 meters; I'm sure the readers get the point. When I do operate 75/80 meters, I actually spend most of my 75/80 meter operating somewhere between 3705 and 3725. But, I'm also one who generally enjoys one on one type QSO's, so very very rarely will I join into a roundtable. Some AM roundtable-type QSO's, unless they're break in-type, are a perfect remedy for insomniacs. You'll also very rarely find me on 75/80 meters during the late afternoon or early evening hours unless maybe on a weekend. I generally hit the 75/80 meter band during the late evening hours after 10 or 11 PM.

One egregious example of excessive bandwidth turned out to be a 20kHz subcarrier. The operator was running some kind of brokered programming.

 ???

I enjoy all of you as company.  We all have different personalities interests..  I cannot remember anyone I have met in the AM community - who is in conversation with me that I did not appreciate.  The only blight I can see on 75 or whatever band are those who jam QSOs or throw their carrier on without IDs  or generally go out of their way to be obnoxious.

It's sort of like going to a party - there are some I would naturally be attracted to and some who after getting to know I sort of just wander off somewhere else.  Pete (CWA) I would like to hear you on more often.  I can't remember the last time I've heard you.

Al

The most recent time I heard you Al was on 40 meters. I think the last time we worked on 75 it was after 12 midnight. I think you said you couldn't sleep or had to pee or something and decided to play some radio since you were up. I'm on almost every day but generally roam the 10 and 15 meter bands with an occasional pop up to 6 meters.

Occasionally, like today, you can find me on 20 meters generally using some vintage SSB transmitter or transceiver.

I went the other way today.
I hooked up the four 4-125 rf deck to the push pull parallel 100TH mod deck and ran 500 watts carrier and 1500 watts pep.
That is what the rig wanted to do at 90% negative so that was what it did.
No color on the plates of the 4-125's.
Had a very nice long qso with W8LXJ (Bob) for hours.

Couldn't sleep.   Don't have that other problem  ;D

Give me a call some time if you hear me.  I don't think 20 meters would work for us

Al

Off topic, but quick question...

Steve:  The output coil for your 8 FET class E rig for 75 meters has a value of 5uH.  That give is an Xl value of 122 ohms.  Do I just calculate the new coil value for 7.293 MHz using the 122 ohm value?  If so, it comes out to 2.66uH.

The reason why I ask is because I found a nice commercially made coil that I just need to cut for the specific value.

Jon

That's pretty much right.  Cut the tank capacitor and the coil if half from whatever values you use on 75 meters and it should work.

Regards,  Steve

Interestingly, the ideal carrier/sideband ratio topic came up in a 40M discussion with K1KW on Saturday. There are infinite combinations of carrier level and sideband level that result in a 1500 Watt PEP, but where is it optimal?

For example, you can get 1500PEP with 375W@100%, 200W@174%, and at the extremes, 1500PEP DSB with no carrier and 1500W CW with no mod.

Here's something else to consider. Back in the 80s, Leonard Kahn developed his "Powerside" system for AM b'cast stations. It emphasized one of the sidebands and suppressed the other so that the total carrier + sideband energy remained the same. This was to help stations that experienced interference from other stations on first adjacent frequencies by concentrating the modulated energy in the sideband furthest from the other station. Cool, eh? And the FCC approved it.

We had this system at my 1490 station since we got slammed by then WTOP 1500 in DC. It was effective for analog receivers, but unfortunately, it came at a time when digital tuning became the norm, so there was no practical way to tune slightly to the stronger sideband.

Makes me wonder about an amateur radio application since sideband cancelation due to propagation would be reduced.

Well, I often do that on the receive side with the sdr.
sdr-radio has buttons that allow you to select upper or lower sideband only AM reception, which works well if something is on one side causing interference.
You can also slide the passband over and it seems to work about the same way.

There ARE guys running single sideband with a carrier, I used to have a KWS-1 which did that, sounded nasty.

Its not like the carrier does not do anything, it quiets the frequency, and a big strong carrier is nice.
You just need to put enough audio on it to be heard.
Are we working DX? Or are we having pleasant round tables or break in?
There is no need to sound like a commercial on TV with super loud audio, and any distortion (in the rig or in the detector) just makes copy harder.

Get the peaks going the right way, control the negative modulation, use some mild compression to keep the audio level up, do a little EQ if needed and call it good.

 

You experienced this on a broadcast band or amateur radio band?

I think that's a common problem with the KWS-1.  I know of two operators of KSW-1 and they both have that problem.  Problem is with the carrier and the drifting problem the KSW-1s have nowadays it's very challenging listening to them on SSB.  I still don't get why Collins didn't simply add a separate AM board instead of that "Oh, by the way, here's AM" approach.  My FT-301 has a separate  AM board as, I am sure, do other rice boxes.  The KSW-1s need a lot of maintenance to bring them up to the original standards.  Not sure if the drifting problem has a fix.

I was bored, so I made a YouTube video showing 180 watts carrier and my highest voice peak was 1200 watts.

After reviewing the video, I really appreciate the need for class E stuff.  I'm belching out so much blower noise for PW power.

Anyway, here's the link:

https://www.youtube.com/watch?v=wCbCmiNE2rY (https://www.youtube.com/watch?v=wCbCmiNE2rY)

...not a lot of activity on 40 meters tonight.

Jon

I can do that with tubes and no blowers, just a muffin fan on 1/2 speed.
More like 200 watts carrier and 1000 watts pep without any negative peak clipping.
A pair of 4-400's with screen modulation would do 300 watts, 1500 pep and not need any fans or blowers, 10 Hz to 20KHz if you want.

With the dx60B/qix modulator and the pair of 4x150's I could do 25 to 200 watts carrier and 600 watts pep.

Things tend to sound better with normal 4 times carrier mod levels though.

The amount of electricity I used for radio does not matter to me, my wife uses more to dry her hair...