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are class e rigs wide?




 
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N2DTS
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« on: November 09, 2009, 02:27:28 PM »

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

 




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« Reply #1 on: November 09, 2009, 02:41:37 PM »


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
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Carl WA1KPD
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« Reply #2 on: November 09, 2009, 02:49:46 PM »

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
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« Reply #3 on: November 09, 2009, 02:55:09 PM »

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
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kg8lb
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« Reply #4 on: November 09, 2009, 03:10:16 PM »

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
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  So wide you didn't even need an SDR to have a clue !
But the class of operation was not the determing factor.
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Steve - WB3HUZ
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« Reply #5 on: November 09, 2009, 03:18:48 PM »

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.  Wink

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.  Grin
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« Reply #6 on: November 09, 2009, 03:22:16 PM »

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

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.
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« Reply #7 on: November 09, 2009, 03:29:23 PM »

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





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N2DTS
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« Reply #8 on: November 09, 2009, 03:39:02 PM »

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.  Wink

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.  Grin

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


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« Reply #9 on: November 09, 2009, 03:44:52 PM »

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.
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« Reply #10 on: November 09, 2009, 04:05:36 PM »

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

 

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Steve - WB3HUZ
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« Reply #11 on: November 09, 2009, 04:09:09 PM »

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.



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.  Wink

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.  Grin

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



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« Reply #12 on: November 09, 2009, 04:12:39 PM »

Quote
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?


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
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« Reply #13 on: November 09, 2009, 04:33:04 PM »

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.
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« Reply #14 on: November 09, 2009, 04:37:15 PM »

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




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Pete, WA2CWA
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« Reply #15 on: November 09, 2009, 05:29:53 PM »


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.




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« Reply #16 on: November 09, 2009, 05:35:56 PM »

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...  Smiley

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.
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« Reply #17 on: November 09, 2009, 06:44:54 PM »



But yeah, he was running a class E rig and I asked him if it was a K7DDY kit. 

  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.
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« Reply #18 on: November 09, 2009, 06:49:00 PM »



But yeah, he was running a class E rig and I asked him if it was a K7DDY kit. 

  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......
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« Reply #19 on: November 09, 2009, 06:53:14 PM »

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 Ė itís just that the operator chooses to run wide audio frequencies. It doesnít 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
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« Reply #20 on: November 10, 2009, 04:06:25 AM »

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.

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« Reply #21 on: November 10, 2009, 08:05:23 AM »



But yeah, he was running a class E rig and I asked him if it was a K7DDY kit. 

  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......

  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.
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« Reply #22 on: November 10, 2009, 08:38:07 AM »

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



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.


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« Reply #23 on: November 10, 2009, 09:04:11 AM »

I really get a charge out of guys 20 KHz wide complaining about SSB signals 5 KHz away.
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« Reply #24 on: November 10, 2009, 09:49:47 AM »

   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  (?)
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