New Class E transmitter status

[steve_qix]

It's probably related to the way the AM signal is generated.  The "fold back" affect isn't present with modulated RF amplifiers, and that probably accounts for the major difference in sound.  As long as the transmitter is never modulated too heavily, in theory,   if   the Flex is a low distortion system (can't speak to this - just don't know)  it _should_ sound as good as the best stuff on the air.

Case in point - Ken W2DTC runs a low level transmitter into a linear.  He used to use a true modulated RF amplifier to generate his low power signal, but changed to a Flex at some point.  To my ears, the other system sounded better, at least at high levels of modulation.

[n1ps]

Maybe what you should do Al is use a 12AX7 as a pilot lamp 

Wayne's world is a neat one!!  Beautiful work.  Look forward to hearing your new rig.

p

[K1JJ]

An AM signal generated by a low level precision balanced modulator chip should normally create a signal that is cleaner than a class E rig. After all, the class E rig is dealing with high level modulation that is harder to control with extreme precision.

Once the low level balanced modulator AM signal is amplified up to a KW level using (properly adjusted) clean linear amplifiers with -30dB or better IMD, the resulting AM signal is nearly flawless.

I think the common illusion that a class E transmitter is better sounding than a clean balanced modulator linear system is simply because most linears struggle to put out a few hundred watts and the signal to noise on the band makes them appear not as clear. Whereas, with my own 24 pill class E PDM rig, I can put out a very "healthy" signal that just quiets the background.  It takes a lot of heat to do the same with my linear system so I don't bother. There are a few guys running big linears, like Ken, who sound tremendous and quiet the frequency.

I think a good part of a hi-fi signal is an absolutely quiet room as well as the band noise being covered up. The result is all you hear is me me ME!!  :-)

However, just to be having this discussion certainly is a testimonial to how good the class E rigs are, considering the efficiency, etc.

T

[Steve - K4HX]

Yep. The venerable NE602 circuit used by a few of us was capable 2nd order IMD on the order of -60 dBc, THD below a tenth of a percent and a bandwidth of at least 500 kHz. Never gonna get that with Class E or any other high level modulation scheme. Nope... never did.

[WD5JKO]

Yep. The venerable NE602 circuit used by a few of us was capable 2nd order IMD on the order of -60 dBc, THD below a tenth of a percent and a bandwidth of at least 500 kHz. Never gonna get that with Class E or any other high level modulation scheme. Nope... never did.

   A balanced modulator rig on AM, and pushing the modulation such that the occasional voice peak exceeds 100% downward modulation will create those little "wavelets" seen on a scope as the phase swaps 180 degrees. We now move into DSB with reduced carrier, and when received on a receiver with a diode detector, the audio is dreadful....Still the THD transmitted is low..Just the receiver can't handle it unless a sync AM detector is used or a zero beat product detector.

   I hear lots of Flex guys doing this and they don't know what I'm talking about. This guy (a W5) was doing about 150% upward modulation, but the downward made it sound dreadful until I switched to SSB receive. I was running my CE 20A on AM, so I upped the audio and cut the carrier a bit until I was making two opposed trapezoids on the scope. He said I sounded great, but on his Flex receive he had the sync AM button enabled. The others in the round table could not copy at all with their AM diode detectors.

  Back to point, Steve QIX said, "Case in point - Ken W2DTC runs a low level transmitter into a linear.  He used to use a true modulated RF amplifier to generate his low power signal, but changed to a Flex at some point.  To my ears, the other system sounded better, at least at high levels of modulation."

  My bet is that a diode detector was being used here, and at the "high levels of modulation" there were wavelets which are very apparent, and don't sound good at all...even on the occasional voice peak.

Jim
WD5JKO

[K1JJ]

Jim,

Yes, the wavelets can really tear up a diode detector.

Back in the late 80's I built up an upside-down tube transmitter. It was a pair of class C 4-1000A's in upside down.. or better called, a high level balanced modulator.  What a bear that was to build and get working.

The bottom line is it sounded FB until I went over 100% negative and the wavelets appeared. I then got reports of grunge in the audio from the diode detector guys. Those few with sync detectors (Willie W3DUQ) said it sounded FB at even 200% audio and big wavelets..

I finally converted it back to a conventional pair in parallel, plate modulated and used negative peak  limiting to increase the audio. It worked FB then.

The bottom line is when running a balanced modulator, it might be best to run the audio up until the wavelets begin to appear and then back it off.  Let the normal voice assymetry dictate the positive peaks.

The class E rig I have works very well with a low level negative peak limiter. However, the sync detector will solve all of these problems.  Maybe eventually we all will run sync detectors and the wavelet problem will go away.

T

[steve_qix]

The thing is, it's not necessarily relevant that a particular balanced modulator or other low level non-modulated scheme is capable of near-perfect audio - the reality is that the standard AM detector can't handle any "fold back" (wavelets, or whatever one wants to name it) at any level.

This was and is my point.  It is *very* hard to control this.  The only real way to do it is to put a dc coupled negative peak limiter (clipper) just ahead of the balanced modulator (and dc coupled to it) to prevent the audio from ever reaching the point of "fold back".  As far as I know, no one is doing this.

At the receive end, I'm using a very low distortion, precision rectifier detector, and it sounds fantastic when demodulating fantastic sounding AM signals. But, the slightest amount of fold back from a balanced modulator, and the demodulated received signal will quickly degrade.

Does the FT-101 use a "real" modulator for generating AM?  Those rigs tend to stand above all other multimode transceivers with respect to audio quality (when modified, of course).

[Steve - K4HX]

Many years (at least 5) of on-air tests running 120-130 percent modulation with the 602 circuit showed that no one ever noticed the difference between that and 100 percent modulation, diode detector, sync detector or otherwise. I would randomly switch between the two settings from QSO to QSO and within QSOs. Once I pushed beyond that amount of modulation, the complaints began. The same was true when running the FT-101, which doesn't use a balanced modulator. Most receivers do not do well with high levels of positive peak modulation, no matter how it is created.

Controlling fold-over or wavelet creation via low level processing is no more difficult than preventing baselining or over modulation of standard AM methods. It's all based on the input audio levels.

If you don't tell people what you are running, they usually don't "hear" things. Once you specify (be it a mic, a type of modulation, model of transmitter, level of processing, lowpass filtering, etc), all of a sudden, the ears on the receiving end become golden.   The power of suggestion combined with prejudices and biases are a powerful thing. Add in poor receivers, AGC distortion products, less than pristine audio amps, headphones or speakers and the downward trend continues.

In other words, I find most over the air audio reports to be less than helpful and often quite amusing. The only guy I've ever trusted with over the air audio reports was K3ZRF. He forgot more about audio than most of us will ever know and he had good ears and an excellent receiving/audio system.

[Pete, WA2CWA]

If you don't tell people what you are running, they usually don't "hear" things. Once you specify (be it a mic, a type of modulation, model of transmitter, level of processing, lowpass filtering, etc), all of a sudden, the ears on the receiving end become golden.   The power of suggestion combined with prejudices and biases are a powerful thing. Add in poor receivers, AGC distortion products, less than pristine audio amps, headphones or speakers and the downward trend continues.

Back in the 90's when many were still running plate modulated transmitters and solid-state rigs were somewhat frowned upon, I would occasionally run my Kenwood Twins (tube finals/driver but every else was solid-state) with the SB-200 linear. They used low level audio driving a balanced modulator. When I mentioned the transmitter, the audio reports were never great with many contacts. There always seemed to be some issue. Weeks later I made some contacts and rather then mentioning Kenwood Twins, I opted for low level AM exciter driving a SB-200 linear. Audio reports were great, sounds like a great plate modulated rig, etc. As Steve says, prejudices and biases can be a powerful thing when it comes to an audio report. If I'm working someone, and I can understand what they're saying without straining my ears, their audio is fine. I don't care how many boxes of "stuff" they have, or don't have, between the mike and the rig. If I wanted to listen to Hi-Fi audio, I'll go turn on the stereo.

[K1JJ]

Yep, we hear what we wanna hear sometimes.  In hypnotism it's called positive or negative hallucinations.


Steve/ QIX,

OK, I see that when you mentioned "foldback" you were referring to the wavelet problem. I thought you meant ALC foldback.

Yes,  I think if someone ran a negative peak limiter before the BM, it would solve the wavelet problem. The BM system would generate the cleanest audio out there, suitable for diode detectors.  And as Steve/HX said, it is easy to limit the audio, even with a conventional ricebox (modified correctly)  using low level audio processing. I do it now with my FT-1000D.

This wavelet problem is not well known and should probably be talked about more. After all, it is easy to see it occur on a standard o'scope and can be prevented.

I may look into that negative peak limiter idea for the 1000D.


T

[steve_qix]

It may be that we are not talking about the same thing here - many people, in an attempt to generate a lot of asymmetry using balanced modulators, *do* push things to the point of generating "wavelets" (folding back, etc.), and this effect does not take place with a conventional modulator.   It's a case of practice (reality) verses theory.  In reality, this is common.  In theory it doesn't have to happen, but it does and that's the way it is.

And, yes, sadly, many receivers out there, and in daily use start to fall apart with high levels of positive (or even negative!) modulation.

[WD5JKO]

I may look into that negative peak limiter idea for the 1000D.

   Keep in mind that the limiter threshold must change with different carrier levels out of the BM. Maybe there is a way to make the threshold track the carrier level such that you don't need to add another knob. Also if you do build a negative peak limiter for the 1000D, I think you want to bypass it when running SSB. It would be a real trick to make the threshold auto track carrier level, and to have the limiter go away on SSB, and to do so without an extra switch and pot.

Jim
WD5JKO

[WA3VJB]

Steve,

Where you say...

And, yes, sadly, many receivers out there, and in daily use start to fall apart with high levels of positive (or even negative!) modulation.

... you are taking an interesting perspective.

As you've acknowledged previously, when you run reduced carrier DSB you will eventually reach the design limitations of many diode detection circuits among receivers.

Consequently, the transmitter has the shortcoming of failing to provide adequate carrier, effectively "falling apart" in its ability to deliver a good sounding signal to the typical station you're trying to talk with.

[Steve - K4HX]

It all comes down to KYE - know your equipment. Any modulation system can be made to sound crappy when run improperly. And just about any system can be made to sound good, when run properly. The reality, in practice, is that the balanced modulator has been used for decades where low distortion, wideband modulation is needed. It is the corner stone of modern telecommunications. If it were as horrible as claimed here, such would not be so.

I'm sure Al will be able to run all his different modulation systems properly.  He already sounds better than most with his plate modulated rig and also the one with the dreaded  balanced modulator.

[W3GMS]

Well put Steve and lets not forget the original post that Al has made 

Al is a well seasoned op and regardless of what rig he has been on, he always sounds very good to me.  That includes his Flex and Collins gear. I am sure when he receives his Class E, PDM  modulated rig, he will sound very good as well.  In addition, I am sure that Al will maintain his bandwidth to adhere to consider those signals 15 KHz each side of center frequency.  Excessive bandwidth need not occur if one tailors the audio properly.  Unfortunately with an audio system that is so flat over a wide frequency range some op's use that in not a good way and enjoy causing interference.

For me, I enjoy listening to the different technologies because as you know each one produces a different kind of sound.  When properly set up and when working within the limitations all can present a very good radio sound.  One simply has to know the limitations and not push it beyond what its capable of.     

Joe, GMS   

[K1JJ]

On a different note about balanced modulators...

I was on recently with Chuck/ K1KW as he demonstrated VELY EEEESSB hi-fi SSB using his Flex. I was listening on my HPSDR using a 100 w audio amplifier into four wall mounted speakers.   He ran the audio at DC to 10 KHz bandwidth and I also listened in 10 Khz.   Let me tell you, Charlie, the audio sounded tremendous! I could not tell the difference between this and regular full carrier AM.  And it took up the space of a +- 5KHz  AM signal.

Then we switched to DSB "reduced carrier" AM and he ran the audio up past 200%++ generating big wavelets and foldback.  Using my sync detector, the audio was fabulaous and sounded like full carrier hi-fi AM. (of course)
The peak audio power was outstanding.

This required SDR's or equivalent precision on both ends - and unfortunately would exclude a lot of AMers due to equipment.  But there's many ways to skin a cat to get high fidelity.

Once PDM generated high efficiency linear amplifiers become mainstream, the cycle will be complete.

Lest we forget the romance of old school AM techniques...      (I hope to always own a plate modulated xmitter)

T

[w1vtp]

Tom

Comments to your post:

"...I was on recently with Chuck/ K1KW as he demonstrated VELY EEEESSB hi-fi SSB using his Flex. I was listening on my HPSDR using a 100 w audio amplifier into four wall mounted speakers.   He ran the audio at DC to 10 KHz bandwidth and I also listened in 10 Khz.   Let me tell you, Charlie, the audio sounded tremendous! I could not tell the difference between this and regular full carrier AM.  And it took up the space of a +- 5KHz  AM signal...."

Yes, a much overlooked feature of Flex by many.  My early experiments with HIFI SSB have proved very good with the exception of the AVC being generated on the audio which makes for an annoying increase in background noise between modulation.  This can be helped by programming very slow recovery on the AVC.

"...Then we switched to DSB "reduced carrier" AM and he ran the audio up past 200%++ generating big wavelets and foldback.  Using my sync detector, the audio was fabulaous and sounded like full carrier hi-fi AM. (of course) The peak audio power was outstanding..."

I have had too many negative comments from the diode detector users, so have had to restore more carrier into my 5000 AM.  It just isn't worth producung the comments inferring that there is something wrong with my audio and that I need to turn it down.   Maybe in time as more add exalted carrier reception or sync AM detection to their receivers.  I just got tired of getting bad audio reports

Al

[KB2WIG]

" I just got tired of getting bad audio reports. "

Now you know how I feel .... ..


klc

[WA3VJB]

The most reliable approach to transmitted loudness is a combination of good mic technique, equalization, and compression.

When set up effectively, the result works with most of the receivers out there. The loudness also is apparent to stations receiving with synchronous detection.

I don't grasp why some people are seduced by a reduced-carrier method, if the goal is to be heard well on receivers designed for a full carrier signal.

[kb3ouk]

The most reliable approach to transmitted loudness is a combination of good mic technique, equalization, and compression.

When set up effectively, the result works with most of the receivers out there. The loudness also is apparent to stations receiving with synchronous detection.

I don't grasp why some people are seduced by a reduced-carrier method, if the goal is to be heard well on receivers designed for a full carrier signal.

I've wondered the same thing. Some of the most readable stations I've heard that were not running big power were not running over 125% modulation either. I usually run just a little over 100% at 200 watts carrier, and I've found that the biggest difference I can make to change whether someone can hear me or not is in the microphone. When you're putting out a signal that is lacking in carrier to begin with, the last thing you want to do is modulate it so much that it makes it appear to the receiver like there's even less carrier.

[WA3VJB]

When you're putting out a signal that is lacking in carrier to begin with, the last thing you want to do is modulate it so much that it makes it appear to the receiver like there's even less carrier.

Amen.

Supports what Tom said too about how the carrier, when there's enough of it, helps create a quieting effect.  Ken DTC is indeed a prime example. So was Gary, W2INR, who never used much compression but gave us plenty of carrier for the wider dynamic range he achieved.

There's a lot of information in the carrier, contrary to traditional theory.  It provides not only a pilot for the typical receiver's AGC, but it also provides guidance to listeners for the spacing of words and thoughts during a transmission, minimizing the chance for doubles and removing the VOX syndrome^* entirely.




^*Say this aloud:  EIN business, OOZing OX here, OW copy, Ver ?

[Jim KF2SY]

But doesn't loudness = power?

http://www.youtube.com/watch?v=IiZeOgxpCmI

[kb3ouk]

But you can be loud without having to run a huge amount of modulation. When we are limited to 1500 watts PEP, I think it would be wiser to sacrifice high postive peaks and run a large carrier, than sacrifice carrier to run large peaks. Listen to the foreign broadcasters on 40 meters, those guys are loud naturally because they are running an insane amount of power, but also because they are probably running no more than 125% modulation, probably more like something between 90% and 110%. And they are definitely not running negative peak limiters either.

[Steve - K4HX]

Under rag chew conditions (signals are not near or at the noise floor), AM received on a system with a diode detector and conventional AGC, the signal-to-noise ratio is determined by the carrier level. So, big carrier means big SNR. With a big SNR, the level of modulation is much less important.

High percentages (well beyond 100%) of positive peak modulation also make the effects of selective fading more severe.

[K1JJ]

A point to consider is that a sync detector will allow us to hear audio cleanly  that is chock full of 200%  wavelets OR fading in the QSB   OR  running conventional "diode detector" levels.  It handles everything.

But, possibly 80% of AMers run diode detectors, so it makes running big audio (or BM foldback wavelets) not a good idea.

Too bad a diode detector wasn't like using a black and white TV.  Color transmissions are still received in black and white.    If a diode detector ignored big audio, we'd be OK, but it doesn't... :-)

I'm glad the wavelet subject was brought up. When running the FT-1000D, I used to employ the wavelets as a "safety net," just like a negative peak limiter, and probably too aggressively. I plan to set my low level audio limiter to avoid ANY wavelets from this point on.  

This means -98% negative is the limit and positive peaks will be what my natural voice allows.  A balanced modulator will then do a flawless job at it, as heard by a diode detector.

T