The AM Forum

It's amazing what you can find while browsing YouTube on a rainy day. Tom K1JJ made reference to a post on YouTube by "MotorMouth" who apparently is legendary on 11 meters. I viewed a couple of his related posts and found two that caught my attention. In the last three minutes of the video below, the guy shows some scope patterns that look pretty impressive. He does seem to be able to reach 300% positive peaks without smacking the baseline.

http://www.youtube.com/watch?v=26cB7BeLmbE

Another related video, with fairly poor focus at times, shows more of the same kind of asymmetry in the audio. At about 2 minutes into the video, the camera shows the device they are using, called "The Mauldulator".

http://www.youtube.com/watch?v=C2oe7q59SwQ

Anyone care to guess what is inside "The Mauldulator"? Perhaps a version of the HUZ zener diode limiter? Or a version of the QIX keep alive circuit? At any rate, to their credit, looks like they are having a good time with the toys they play with.

Whatever they're trying to do, anything much over 80-90% positive is gonna create copious distortion in yer typical diode detector.

Yea, but just think of the "SWANG".

Check the reflection in the meter windows.
Motormouth's buddy hissself.  Really proud to work the "Maul."
A little photoshopping and we'd get a visual.
http://www.youtube.com/watch?v=AHSSC9eyfRI&NR=1 (http://www.youtube.com/watch?v=AHSSC9eyfRI&NR=1)

I agree 100%.

73

Jack

Also;

Looks like he massages a low level signal by reducing the carrier and keeping the original peaks. (if the pix and description are representative of the real mauldulator.  In one of the tube vids, he makes the statement that oscilloscope vertical gain has to be turned up because the carrier is now less. Then her runs it through an 811.  So much for his SS lecture on ancient tubes.  ;D

http://www.motormouthmaul.com/mmm2_003.htm (http://www.motormouthmaul.com/mmm2_003.htm)

That sounds precisely the same as "ultramodulation" to me.

Hi Rick,

 I think he needs more presence...lol 8)


73

Jack

Another possible approach is by using a low level audio circuit that will artificially create more gain in the positive direction than the negative direction, About 10 years ago the Huzman designed one up and I built it. It was actually two op amps with audio split between them. One op amp had a gain adjustment. They were combined at their outputs to produce an asymetrical waveform. I was able to re-make my voice with 300% positive peaks. The waveform looked great. However, in that day of diode detectors, all I heard were complaints of distortion when I ran it up. I concluded that the natural voice asymetricity is all that's needed - 130% positive is all I run these days, maximum.

It was a cool circuit, though.

T

Yep,

Very interesting find Rick. His website has very succinct advice regarding how to use a scope and the importance of using one when operating AM or at the very least when setting up an AM transmitter. He seems to have a very good technical background. Apparently, he is also a licensed ham on the west coast AM scene. Looks like he knows what he's doing.

I wonder if he designed and developed the board himself? From the picture on his site it looks like a professional layout.

Tom, I have definitely found that a few of my receivers get very unhappy when tuned to stations with excessive asymmetry in the audio. The worst of all is my portable Grundig (G5) which has difficulty with a few stations on the AM broadcast band that run very heavy audio. They sound a little gritty while other stations that peak right at around 100% sound very clean. I would agree with W1JN that going overboard might look great on the scope, but it can be nasty on the other end depending on what receiver the other guy is using. I think your 130% target is a good one to aim for. It should sound loud, but shouldn't rip through the detectors of most receivers. Be careful with that HUZman technology, you might get strapped and find your life taking a different turn...

Ah well, so much to learn, so little time. Think I'll take a nap!

:O)  

since when do cb'ers care about distortion?

Derb,

 Around my parts there's a couple of CB operators with Behringer Mics and Processors and Yaesus
and Ikems on 11 meters man...they sound like Broadcasters...lol....smooth audio...

And we have a VHF'er FM on 2 that sounds like Tom Brokaw  :) Audio is out of control brother..LOL

73

Jack.

Capt jack
I bet dollars on donuts some of those 11m sharks swim these very waters.. arrghh arrgh.

LOL.. ;D

73

Jack.

oh yeah they hang here big time. AM Fone is whirl wide, and there's no doubt , U no it is.  8)

I think it's Great man... :)

73

Jack.

I don't recall running into him in the W. Coast AM scene.


Ah, that's why. His tech license limits his HF AM stylings to, well, realistically, 11 meters.

What's the General License Limits.. 8)

73

Jack

Well, a General gets you onto the 75 meter AM Ghetto, which on the W. Coast tends to be very genteel anyhows.  ;D 

The 'Scope patterns are beautiful!!!! I see the trace blanking, would that be from the video syncing? I cannot get a nice trace like that. The display is always moving about, apparently he is using some sort of triggering to get such a nice trace.
Pinching the carrier was impressive WOW!!! Endless modulation.

Don, would that be characteristic of Ultra Mod???

That's it!!!! They like to see the power meter schwang up when they talk and the guy on the receiving end wants to see his meter pegged if possible.
I ALMOST swear this youtube was our Don in there, but listening closer it almost sounds like the DERB!!
http://www.youtube.com/watch?v=hXfod6pgymc&feature=related
Phred

MAULDULATOR.  Awesome!

using a maverick 250 to drive an 811A ? huh.

Wawasee made a classical "modulator" with a 6BQ5 running some 750V on the plate, grounded grid. It worked well giving only a few watts carrier and high peaks.

What is he doing with DB-9 connectors? interesting anyway if it is all analog.

Phred,

What type of scope are you using?  Any of the Tektronix, HP, or similar "lab grade" scopes have no trouble providing this type of display.  You do need a scope with a real triggered timebase, the Heathkit monitor scopes and TV service type scopes with recurrent sweep cannot do this properly. 

You can easily find high quality scopes for little money at hamfests and it will find a lot of use on your repair bench.  I use a couple of Tektronix 7854 mainframes with an assortment of vertical and horizontal plug-ins on the bench and some older Tektronix scopes (Types 545A, 555, and 556) are stationed at various points for monitoring.

The mauldulator is possibly a differential compander. "It runs on +/- 15 Volts and 24 Volts DC." - and in one page of developmental images there it shows an audio power stage/DC supply breadboard (bread-sink?) hooked to the breadboard of the IC's, and this hooked to the test CB, more of an audio frequency power supply with DC offset to replace the modulator in the CB?

maybe in the CB, which most often today uses an iron-less dc coupled modulator, has a 12V supply and runs the final at 6V for carrier. That is normal Cobra 146GTL stuff.
If this modulated DC voltage is intercepted and the negative half compressed and the positive half expanded (to as much as 24V), then there is 4x carrier voltage possible. The fact that he is going to 3X would account for the added headroom to preserve fidelity, plus avoidance of the real possibility of blowing up the CB final by over-voltage stress.

(The same nonlinearity-type effect to some degree can be had by varying the screen voltage in a voltage amplifier pentode such as a 6GH8 section as I learned designing an APH-1050  tube amp mod some time ago. The sound is quite good, but referenced to the DC plate voltage, the (large signal) negative signals are compressed compared to the positive ones when my "linearity" pot is improperly adjusted. Corrolary: what is good for hi-fi music <> what is good for CB Mauldulation.)

The +/- 15VDC is for the op-amps on the board etc.

It seems like it would compress the negative half of the modulating wave and expand the positive half, or have essentially the same effect. the "symmetry" control varies this action's depth.

This also explains why a DB-9 is a good choice -the several wires necesary. Where does he get the +/-15V and +24V for the production project? a package supply maybe. A mobile version might be of interest but clumsy due to the 24V@6A peak?

Good guess on the secrets of the Mauldulator?

BTW there are 4 diodes on the production PCB along with the several ICs. Not that that's what they are for, but it is funny.

What are the better boatanchor receivers to receive high positive peaks?

Carl
KM1H

Anything with a separate AVC detector channel (ie most nationals, super-pros, SX-28, and R-390s).

Worst are Hallicrafters with ANLs ie SX-101, SX-100, etc - they start distorting at 60% modulation.

You all sound good on my receivers, especially the SDR, 'ceptin' fer Steve.  ;D

He always overMauldulates.

I have a pair of Homey Tennis shoes but that don't make me a Mud Duck...lol.. :-X

I found an on-air demo of his "Mauldulator" in action.

http://www.youtube.com/watch?v=TmvDVn8xnMk&feature=related (http://www.youtube.com/watch?v=TmvDVn8xnMk&feature=related)

At best, it produces fair "contest" audio.  :-\ But the guy has a flair for working "maul" into his product names. Check out:


http://www.11meteroutlaws.com/viewtopic.php?f=41&t=160 (http://www.11meteroutlaws.com/viewtopic.php?f=41&t=160)

I had an exchange of PMs from Mauldulator "motormouth". Seems like a knowledgeable person on fire about his hobby of high power CB as we are about A.M. Amateur radio. At least his CB modulation is sine waves and not overmodulated square waves. We have created a good thing with either West Coast Sound  or East Coast Sound on A.M.
Apparently extreme high power CB is very popular on the Left Coast. 5KW or more is not unheard of.
He mentioned that some of the secrets are from using computer audio recording software to "pump up" the TX audio.

Fred

I have found these evaluations useful:  http://www.w1vd.com/BAreceivertest.html

Distortion spec's relative to modulation level also bandwidth frequency response.

Rob

The guy seems pretty cool to me. I dont care if he is on CB or not.  I thought his audio was nice and clear. Its a welcome change to the flat topping distortion most Cbers run. Maybe he will ed U cate some of them into running cleaner stations.

I still dont understand how this board works. The web page is unclear.

C

Ive been satisfied with the HRO-60, SX-28, and NC-240D so far but havent had some of the others on line when known hi level 150% positive peak stations are on. Most anything sounds OK on the BCB which I guess is limited to 125%.

Are there any SWBC stations using the high level?

Carl

I don't know, Carl.
Most SW stations run low modulation to reduce the distortion of selective fading. I listen to a Russian station on 9660 and it has this low modulation and very bassy audio. Those Russian ballads sound really nice. You can see the carrier making some movement on the bass, but that's about it. They're probably running 250KW too.
Seems like the power houses run lower modulation and go with the huge RF into your radio.

The other side of the spectrum is WBCQ AFTER Tron adjusts the mod and EQ for the muddy bass sound, Allan Weiner RE-adjusts for the accentuated screetchy high end and baselining the carrier.

Fred

I was thinking that some of the US located bible thumpers may be pushing it much harder as they do seem to stand out with others of comparable signals.

The only problem is that I can only take listening to them maybe 30 seconds every hour ;D

Carl

Here is that Wawasee modulator. It's not the same design as discussed, and I was wrong about the drive method (forgot after too many years)  but it is a classical modulation-increaser. It's kept cut off so that 4W in makes 2-3W out, but 12W in makes about 30W peak. It's amazing that 670V was put to a 6BQ5 and was reliable.

Those local religious and political stations - ugh. never was there more a collection of nuts with access to big radios. You are going to hell unless you pay! Get on the phones! (to send me, the preacher, money, even though I have been dead for years and these are just tapes). The government is using mind control! God spoke to me... The apocalypse is coming! Buy gold now! Flying Saucers! buy MREs now! {insert further alarmist current events rumors and legends here} The government is secretly doing research on the citizens! (Free tinfoil hat with every order!)

That has been my observation too Fred. I noted one exception though while having a QSO on 7.290 MHz last Wednesday morning. There was an incredible trashy noise that sounded like splatter covering the top 50 kc of the 40 meter band. While tuning through the noise, I could hear the remnants of a female voice. When I ventured up to 7.405 MHz I came across Radio Marti and found them to be running in full guitar-amp distortion mode. I guess the engineer took the day off and someone must have cranked the audio up. Or, they might have been experiencing hardware failure of some type.

At any rate, I took a look at Radio Marti's signal with the much maligned 756 Pro III bandscope and could see artifacts exploding up and down the band, right to the limits of the bandscope (+ and - 100 kc). Quite a sight to see (and hear). At any rate, I haven't had any radios on for a couple of days so I have no clue if they corrected it. Maybe they should install a Mauldulator?

There has been contact with the Gummint about their splatter and they claim their ancient GE 250kw transmitters are within spec. The proccessors are within guidlines for shortwave b'cast. I really hate tone-deaf engineers and someone who just goes by the book and doesn't have a clue to troubleshoot a "SYSTEM". Probably doesn't even use a 'scope
The FECES will never question their own.
Write a letter to Radio Marti. An engineer will definitly write back

Fred

In case anyone was wondering what's going on with the "mauldulator" circuit, here it is.

John give you permission to give that out?

If not,  that's kind of wrong.

I sat on that schematic for over a year,  because he did NOT want it public domain.   He has taken measures to hide the part numbers,  etc.

I'm. all for reverse engineering for personal reasons,  use,  etc.   But taking someone's design who specifically has asked it NOT be shared,  is shitty.

--Shane
KD6VXI

No, but I stumbled upon it publicly posted on another forum, so I thought I would share it here.  It was already out there.  Knock off copys on ebay and all.

Heaven forbid you publish the schematics of an illegal manufacturer and operator!  LOL

That mic input can't possible work! Running the TLO-84 op-amp open loop at DC. That schematic is missing a lot of wires.

Several things keep coming to mind each time the "positive peak" topic surfaces...

1) You only get 1500 watts PEP max. That's 375 carrier watts modulated up to but not over 100% positive. Do you really want to lower your carrier just to be wowed by what you see on a peak meter?

2) Average mod, not peaks, determine perceived volume. It's in the math, it's proven, it's inarguable. Short time peaks (nS) carry very little energy compared to increasing average modulation over longer periods.

3) +200% is a very impressive claim but it sounds like hell on the majority of receivers. It's this simple: Clip your positive peaks or it will be done for you in a distorted mess by most receivers.

4) Mod iron and bypass caps need to be rated for the dramatically higher voltages caused by cranking up the positive peaks. There's no way I'd take that chance, particularly with the mod iron.

Conclusion: What's more important? Do you like saying "200% positive peaks" on the air or do you want to sound loud *and* clean to others in the QSO? The broadcast world figured this out decades ago. Why reinvent the wheel over and over and over and over... ?

Well, it seems that it was slightly misrepresented in one of it's writeups. The author (the guy supposedly authorized to do the installs and setups) had explained that it was "essentially a transmitter", which isn't correct. It's an audio chain / modulator circuit. I suppose it would be fun to work through the schematic to calculate the parameters and possibly breadboard up to do some testing, but just not interesting enough to devote any spare time to at the moment. If the circuit is viable, maybe it could be used on lower power SS rigs like the HR-2600 for better AM response... properly adjusted of course. 

The circuit, as shown, won't work - as someone has already pointed out.  However, allowing for the reverse-engineering anomalies, or drawing errors, etc...

...what is shown in the schematic is a clipper.  D1 through D4 form a bi-directional clipper. D5, D6 and the related components form a circuit that will cause some amount of asymmetry.  The capacitor values are all missing, so trying to figure any frequency response adjustments is not possible.

Many people here on AMFone could design this or something which performs the same function, perhaps by different means, if they so desired.  Not rocket science, but definitely interesting that someone productized this and were/are successful with it!

Lineair series modulator with sufficient headroom and run the audio first through a simple multiplier, squaring the signal. That gives something like a mauldulator signal. .
At the receiver side you can do it reverse by square rooting the signal and you are back to normal. Is there a gain like in compression technics to reduce noise?
Interesting...

'prime minista' has a 20-30KW water cooled PA. It's OK but just looks like a bunch of more or less featureless black metal boxes in the pics I saw. OK if no one gets to see it.  Nice high power stuff but some control panel stuff would be nice.

This sounds similar to what I’ve been doing with my Flex 6500. On AM, I adjust the output of the 6500 to produce 200W out of my Acom 1000. This gives me ~ 800-900W out on peaks (1:4 ratio). Next, I adjust the AM Carrier on the Flex to reduce the 200W to 100W. The peak output is still at 800-900W. My reason for doing it was to reduce the operating temperature of the ACOM, which it does by 8-10 degrees C.

Hello All

I am the designer of the circuit you fellas are talking about in here. I see a few snarky comments that I think make the authors feel better, but for the most part, I think you have been fair. An unscrupulous person has chosen to take my design and call it his own. He claims that he "designed and developed" it and claims to be applying for a patent. I decided to do a thorough search and found this thread.

First off, QIX is correct, that circuit won't work the way it is drawn, but the asymmetry part of it is correct. His analysis is also correct. The D1-D4 section was added to add a "tube sound" and the harder you hit it, the more it emulates that sound. It has no business being in this circuit. All of the audio processing and effects should be done in the rack gear or audio processing software. This was the first generation circuit, more of a proof of concept. That stage is removed from the second generation and that design also runs off a single voltage instead of three and has other enhancements that were learned from using this one.

As for the comment of this being "an illegal manufacturer and an illegal operator", this is an audio device, not an RF device. That statement would be analogous to calling a gun an illegal device. If I use it for target shooting it is perfectly legal. If somebody uses it for a murder, it is still a legal device being used in an illegal manner. This thing can be and has been attached to several amateur radios and that is the only way I use it. I have it on a Retro 75 modulating the final MOSFET output, and I am also building a power supply/modulator to provide the HV on ARC-5 T-19 tube transmitter. John himself has used it to modulate a lower stage of a yaesu FT-7 and a Kenwood TS-440. We have both been on 3870 here on the California Central Coast talking to each other on those.

The operation of the circuit is actually quite simple. It takes an audio signal and leaves everything below a set point the same level as the input (gain of 1, R13/R11), and the signal above the set point is amplified by a factor of one or greater depending on the value of R1. The diodes D5 and D6 gate the directional nature, and the high speed op amp makes up for the diode voltage drop. This approach is similar to the one in the K1JJ speculation early in this thread. In fact, the method he described is similar to one of the earlier circuits that was the foundation of this design. The problem was that we got some crossover distortion or switching noise with that approach when we tried to combine the separate halves.

We had another intermediate approach between that one and this final design that had two pots to adjust levels but it was clumsy because one of the pots affected both levels. I finally came up with the design in the D5-D6 area. It works slick. You just adjust your audio level input to the stage so that the negative peak is around 95% or so modulation on the carrier, and then adjust the asymmetry pot R1 for whatever positive peak value you desire. The output of this stage is DC shifted to adjust the DC resting voltage on the collector or drain of the RF output stage to adjust carrier level. The output impedance of the asymmetry stage is not the same in both directions because of the separate paths. It is imperative that the high impedance buffer stage be used or performance will be severely degraded. Also, 300% peaks are mentioned in this thread, which is more than possible if R1 was 20k, but that would be silly. In my own implementation of this on 80M I have a max allowable of 150% and routinely set it at 130%.

During this past week I released a drawing in Facebook of this circuit for everybody to see because I was annoyed with the person taking it for his own. I am actually grateful for somebody posting it here because that establishes at least that date that it was in the public domain. Thank you Shane for your valiant effort and concern about whether John and I would approve.

N1BCG, I have no argument against your math. Your logic and math is impeccable. You're argument might be more with all of the AM Broadcasters that continue to use it. Check out this link of a nice amateur conversation with asymmetry https://www.youtube.com/watch?v=9m1bo08YmoE&feature=share

In closing, one person in this thread remarked "since when do cb'ers care about distortion"  There are a great deal that do. John cares about his sound both there and on the amateur spectrum. I am not apologizing for anybody doing anything illegal, but I won't look down my nose at them so that I can feel superior. Some of those people are doing things at a level and caliber that is impressive no matter what frequency they are on. Of course there are many loud mouth idiots that put more signal where they don't want it with their improperly biased dirty splatter boxes that have no low pass filters on the output, but that is not everybody. For the record, I have complained about those folks too. See this link https://www.youtube.com/watch?v=q-DWG0voti0

73 Dave  KA6BFB

I was following this a while back and was wondering if it could be used with today's SDR radios, like Flex or Anan? You mentioned that you released the circuit on FaceBook - would it be possible to post a link to it? If you prefer, perhaps to <my call> @ gmail.com ?
Definitely interesting ...

Regarding the CB comments, so many people here probably got their start on 27 mhz, as I did from the late 1960's. We all needed to start somewhere!
Thanks

U.S. broadcasters are limited to 125% positive peak modulation. None in my area approach this limit.

I have enough asymmetry in my voice that no processing is needed to get 130-140 percent positive peak modulation. For most ops and most transmitters, this sort of circuit is probably not needed or appropriate.

Hello WA2SQQ

I have a Flex 1500 and I looked at the output circuitry of that years ago, and if memory serves the amplifier stage was linear and this won't work well at all for this circuit. I seem to recall that there was the ability to DC couple the audio in to the radio, and if that's true you could use the asymmetry circuit as it is in this thread. Steve, K4HX brings up a good point about the natural asymmetry in most men's voices. You want to be able to have the ability to invert the audio going into the asymmetry circuit if you want to in order to pick what you want to do in reference to that natural asymmetry. The third generation of this circuit does that. Or you can just reverse both of the diodes and that will do it.

Dave  KA6BFB

The point of this board,  the one I made (using a THAT processor chip)  and others is to be able to compress and then increase talk power.

Processing should reduce the peaks so as to increase your avg modulation.   Then run through an assymetry board to increase loudness.

In cars,  we call it 'torque under the curve'.   

I've built this one as well.   Mine does 420 pct pos peaks.   This does 500.

Dave,   you and I spoke about this board before, heartedly.   No matter,  people should choose to public domain something.   Not have it chosen for them. 

IOW,  you're welcome :-)

Tell John I said hi.

--Shane
KD6VXI

Shane, thanks for posting an explanation about its workings, and clearing up the origins of the board original design/intellectual property for all to see. This issue of someone claiming your work as theirs is also being discussed on a certain unique CB forum - in fact its topic there had a link to this topic. Some people can be dastardly and I hope you can prevail in asserting your rights if that is your intent.

Ahhhhh. Interesting subject. The fact of the matter is the traditional AM system has it's limits. The ability of the transmitter to modulate to a level that is wanted and the ability of the RX detector to recover the modulation. As said many times a conventional diode detector will only handle so much modulation before it does an ax murder job on the signal. We have to look at why we do AM. AM is by no means an energy efficient mode compared to SSB but has many positive aspects of its' use. the big draw for me is the beauty in simplicity. The ease of achieving a natural "High Fidelity" type of sound. Yes the average human voice does have a certain amount of asymmetrical characteristics. A true high fidelity communications system requires that both ends of the circuit are up to the job. As we all know it is a compromise between loudness and overall naturalness of the signal. Most of us know the limits of what our transmitters will do for modulation. Those of us who use older diode detector receivers accept a certain amount of distortion. Forcing positive peak modulation is creating harmonic distortion of the operators voice. It is tolerable to a point. After a while it begins to be grating .The other factor is the system of modulation used and how badly does it fall apart when making"Phatt" modulation. I would rather run more carrier power instead. It's all about signal to noise ratio in the end. Good broadcash style audio processing to keep the average  modulation up as well as tailoring the audio response curve of your microphonium pre amp circuitry. IE: upper mid range pre-emphasis /reduction in the mud frequencies /having a real deep low end but not overemphasized. Obviously we all have our unique voices . Each individual operator requires a different set of curves to make it right. There is no"one size fits all" in the AM audio game. AM is what it is . If you have the ability to modulate 300% just turn up the carrier wick and strap.
Tim WA1HnyLR

A lot also depends on what you're trying to accomplish. If achieving massive peaks is your thing and you don't care how it sounds, go for it, but you're still limited to 1500 watts PEP in most cases. That means you're going to have to drop your carrier level (for those who actually care).

Then there's the issue of what is seen vs what is heard. Peaks, by nature of their short duration, contain very little energy so they look impressive yet accomplish very little. If the objective is to be loud and clean on anyone's receiver while maximizing the S/N ratio then the focus should be on getting as much average modulation power into the 1500 watt envelope as possible. -100% is one limit and anything over +100% will cost you in carrier power. 375 Watts modulated at +100% IS legal limit as is 200 Watts at +167%.

There's a formula for this:  Max Carrier W = ((3873 / (MOD% + 100))^2

Some more examples of what creates 1500W PEP:

%Mod    Watts

100         375

125         296

150         240

200         167

300         94  (Yep. Full legal limit with just 94W @ +300%)
            
Loud and clean on all radios has been the goal of broadcasters for decades and broadcast processing manufacturers have thoroughly documented how it's done. That's a wheel that doesn't need to be reinvented.

As you can tell, this is the topic I can be baited into most easily.  Argh!!

I can't not mention three critically important factors of asymmetry which are almost never discussed.

1) Natural asymmetry

Most voices, particularly male, create asymmetrical electrical waveforms where one polarity has a higher magnitude than the other when measured at the output of a transducer (microphone). After amplification and being added to a carrier, that waveform will appear as asymmetrical modulation on a scope or modulation monitor.

Caveat: Asymmetry is -not- always uniform over the total vocal range. This is a BIG deal because lower frequencies often have the -opposite- asymmetry to higher (presence) frequencies. Hold that thought...

2) Artificial asymmetry

The need to prevent negative peaks from cutting off the carrier at -100% is well documented and clippers are often used to accomplish this. Slowly increasing modulation to the point where negative clipping *just* begins will show you exactly how asymmetric your voice is naturally. This is the point where your signal is at its cleanest.

Caveat: Going beyond this point increases perceived volume, BUT, it also increases distortion on *all* receivers, even SDR, because the negative waveform is getting increasingly cut off. This can look amazing on a mod monitor but it comes at a cost, particularly if you don't have a low-pass filter to reduce the harmonics generated by the clipping action.

Oh yes, then there are those other frequencies mentioned earlier that have an opposite "polarity". Those are now generating even more distortion since they present even greater energy to the negative clipper.

3) Controlled asymmetry

It's possible to be both loud and clean on the majority of receivers whether boat anchors or SDRs, and taking a page from broadcasters will yield decades of refinement in this pursuit.

All broadcast processors sold in the past 30 years incorporate "phase rotation" circuitry to greatly reduce asymmetry at all frequencies.

"Great Zorks! What does that do to my manliness!?!"

Nothing. Hear me out... a phase rotator is also known as an all-pass filter that slowly changes the phase with a change in frequency. For example, at 50Hz the phase change may be 0 degrees, but it slowly increases with frequency so that by 3-4kHz the phase is shifted 180 degrees and so forth. By the way, complete phase rotator circuits are available for less than $20 on the net.

"I just lost my monster positive peaks. Now what?"

Simple. You now present that mostly symmetric and consistent waveform to your negative peak limiter and decide how much clipping/asymmetry you want. Keep in mind that peaks by nature of their short duration contain very little energy no matter how impressive they appear. Your "loudness" will come from an increase in average, not peak, modulation which is what compressors do.

Put all this together and you have a clean and loud station as heard by everyone.

Every time I see the use of diodes to clip the negative I think that there ought to be a better way.

Seems to me that it would be more expensive, but one could pretty accurately split the audio signal, much like a class B
amplifier does, or even an AB, and then take each half wave stream/side and process it separately. One could apply a soft knee limiter to the negative going half and use whatever gain one wished for the positive. You'd need to take into account the "zero crossing" area to prevent "crossover distortion" but that would not be terribly difficult to accomplish electronically.

I'm guessing the reason this sort of method is not used much is the cost and complexity of that negative going soft knee limiter.

Anyone think of a reason that my proposed method would not work as described?

That is what this circuit does, except it uses one circuit to do it. The diodes don't clip the audio, they provide different paths for the positive and negative halves in the same amplifier stage. One direction has a gain of one, and the other direction has a gain set by a pot. The op amp gain makes up for the diode drop and there is no distortion. See the attached video for the audio signal with the asymmetry. The positive peaks are changed with a pot. After that, see it applied to a carrier. See the video at https://www.youtube.com/watch?v=x3ZnCy9TQxQ&feature=youtu.be

This circuit has no clipper.

A LOT of the distortion heard,  past 125 pct,  is caused by negative cycle loafing,  negative peak limiting,  whatever you want to call it.

This circuit,  as well as the one I came up with,  does NOTHING to the negative peaks.   You set your audio input level to give you the amount of negative going modulation you want,  90 to 100 pct.

Then,  dial your positive peaks to whatever percentage you want.

It stretches the positive peaks.

In all actuality,  it's a precision peak rectumfrier.  Not much different than  what makes the needle swing in a bird.

Years ago a pro audio board discussed this method of creating assymetry without negative peak distortion.

--Shane
KD6VXI

gotcha... so as long as you don't set the "reference" level (the negative) to high, ur good to go... assuming you have
the available power on the positive going side, and you have the requisite absolute polarity correct... VG!

simple enough.

                           _-_-

Yes.

I have a video of mine in action, on a sinewave.

This is the rf modulated signal.  I had the baseline audio a little hot  and am over mod in the negative region by a couple pct.

https://youtu.be/cajJYlqSv6Q

Somewhere I have baseline audio as well.

https://youtu.be/HsJ1KK8HFgA

Since a pic is worth a thousand words,  maybe a video is worth more?   Lol

--Shane
KD6VXI

Shane, do you have a schematic available on this pro audio board? I would like to see how they did it.
Also, send me an email some time. I would like to chat.

Dave  KA6BFB

...but in the end, it's average, not peak, modulation that affects perceived loudness.

Amplitude x Time = Energy

Shane

Your second video looks like it has a little crossover distortion

Dave KA6BFB

Lol.   Wanna see distortion.   This is my revision one.

https://youtu.be/Br8WNE7hp5g

BCG:  I run phase rotation (from 2 to 8 poles),  multiband compression and a peak limiter.   My avg mod is way up there.   Once it has run through all processing,  I run it into an assymetry module,  allowing me to set avg mod where I want it,  since my peak to avg ratio is very low.

Dave,  the schematic was never presented,  a gentlemen proposed a precision peak rectifier for assy creation.

Your method was actually patent in 2011 I believe....  

http://www.patentsencyclopedia.com/app/20110255701

And here's the pro audio board (web board,  not pc board)  post.   About half way down.


https://www.gearslutz.com/board/geekslutz-forum/670584-modifying-peak-limiter-produce-asymmetrical-waveforms.html


Dave,  John has my number.   I don't always answer,  but I do call back.

--Shane

Shane

You got my hopes up. I was hoping that the patent you referenced was my circuit so that the Florida Counterfeiter would be thwarted in his alleged patent application. Unfortunately, it is not my circuit. Figure 18 on the patent is the closest. This circuit actually might have a slight advantage even though it is more complex. Since part of this circuit is always conducting, a slower op amp can be used because there is not a need to overcome the diode drop quickly. It would have been interesting if it was my circuit, since my circuit was sold a full two years before that patent was issued.

Dave  KA6BFB

I hadn't looked at the patent doc,  other than a abstract available on my phone.   It came up looking for the second page I posted (and had seen a few years before).

--Shane
KD6VXI

If you don't want distortion just use "controlled carrier" !!
Keep the right amount of residual carrier to satisfy the receiver AGC, maybe use a linear amplifier designed for SSB, it will be just fine. (R. Drake said, I suppose.)

I do that.

Well put Clark.  Most Boatanchor transmitters would fill well with this application.  An exception, perhaps, would be my 32V1 that HLR modified.  Dunno what "magic" he did but I easily hit 125% positive peaks with it so I probably would not be interested in putting a phase rotator in it. 

However, the Viking II    I have in the back room might do well with that circuit you refer to

Al

Regarding 300% positive modulation:

You need to consider just what objective that 300% positive modulation is going to do for you.  This is only going to consider what occurs in attempting to transmit extreme asymmetrical, and not mention receiving it right now.

*If you are aiming for loudness, the greatest point to consider is the peak to average ratio of the audio you intend to modulate the transmitter with.
*You need to have a transmitter capable of supplying that peak power without distortion to whatever audio waveform you intend to create.

If, for example, you are intending to use a transmitter capable of supplying a 100 watt carrier, for 300% positive modulation, (I haven't worked out the math here, so please accept the generalizations), that transmitter will need to provide nearly a kilowatt of undistorted output power at the desired % of modulation.  If you are trying to achieve extremely asymmetrical AM modulation in the transmitter circuitry, you will wind up with a severely distorted audio modulation envelope and most likely generate significant splatter. The place for creating asymmetrical audio is in the audio processor, external to the transmitter.  The place to create the capability to supply that peak power is in the transmitter.

In my over half century of high power AM broadcast experience, and with designing commercial AM and FM audio broadcast processors, here is a tip I offer to anyone wanting to try out 300% positive modulation.....

*Design your transmitter to handle any waveform of modulating audio with which you wish to send it, so that it can handle every form of asymmetry you throw at it.  It must handle that audio WITHOUT DISTORTION. Of course, the negative peaks will clip at -100%.  The positive peaks must be passed through undistorted up to 300% (or whatever limit you wish to set). You can generate a very asymmetrical sine, triangle, or sawtooth wave with many audio generator devices.  Once you have a transmitter that can handle those waveforms without distortion, then you buy/build an audio processor which will develop a very asymmetrical wave.

In broadcast, we first use a phase rotator/all pass filter to REMOVE any asymmetry (so we have a consistent waveform on which to process), then we use equalization, compression, limiting, clipping and filtering to achieve our desired peak to average ratio.  THEN we use special circuitry to create how much CONTROLLED asymmetry we want as our final product. 

Theoretically and/or just for fun, you can insert varying amounts of carrier into a DSB transmitter to find out for yourself just how much of a difference you can hear (and the resultant artifacts) as you vary the ratio of carrier to sideband power.

Read about what some broadcasters are doing with a technique called MDCL.  If properly applied, you can actually appear to run more power without exceeding the FCC's peak power output limitation.  https://en.wikipedia.org/wiki/Dynamic_carrier_control (https://en.wikipedia.org/wiki/Dynamic_carrier_control)

Have fun!

73
Ted  W8IXY

Hi Ted

I designed the circuit this whole thread is revolving around. I had no intention at the time for that kind of operation and I think it is ridiculous. The circuit is flexible enough that it can easily do it but it is not very practical. I use around 120% for my transmitter on 80M if I use that at all. When listening on my Icom 706 with the noise blanker on, anything above that sounds awful. I think the 300% claim started out as a way to brag what it could do, not what it should do. I could be wrong on that though. I clicked on the original Youtube thread and it is no longer available.

73  Dave KA6BFB

Dave,

John sent me your phone number.   Been pulling 60 to 80 hr weeks since at work.   Haven't forgotten about ya.

--Shane
KD6VXI