which is more important: high power carrier, or high modulation level??

[WBear2GCR]

Regarding "negative 99%" and not much positive modulation. On occasion ops with normally great
AM audio bring up a new rig or configuration with just this condition. Happened last week in fact.
At least on a "normal" detector (R-390A) it sounds ok to the ear, but lacks "punch" somehow compared
to the same rig making positive modulation properly.

Also, as far as audibility, no doubt in my mind that in terms of overall performance regardless of conditions
I'd prefer to have >100% peak positive modulation over a carrier and >100% positive peak modulation. Now
IF the bands changed and propagation went back to 40+ years ago conditions, that equation might come
out differently. Uncertain.

Seems like the magic "D-104" presence rise curve is nearly ideal for AM. (assume that AM ops are
using the JFET follower or a 10meg input Z, so there is proper bass). Just apply the curve.

Unclear to me what that HB rig configuration is where you have to choose between carrier power and
modulation power? Seems like one ought to be able to balance the two for some optimized set up??

[K1JJ]

But, with a regular AM diode detector, SSB-with-carrier has around 30 per cent distortion at 100 per cent modulation.

73,
Kevin, WB4AIO.

Hi Kevin,

I'm curious... why is this so?    If we tune to one side of a clean AM ssb signal that has one only sideband, how does the diode detector even know that there is only one sideband? IE, where does the 30% distortion come from compared to a normal AM signal with two sidebands?

A friend just sent me an email saying:  "A simple diode detector - consider the response curve of a diode. As voltage increases the diode starts to conduct. This is not linear below .7 volts for a silicon diode. This can be improved with bias on the diode so it never gets below the junction thresholds. An active rectifier with a diode and op amp compensates for this K2US Rob has a nice detector design."      …. Maybe this is what you are referring to?


BTW, good explanation you did earlier on higher audio frequency differences. My ears hear similar threshold preferences, though my upper limit is about 9 KHz these days.

T

[WB4AIO]

But, with a regular AM diode detector, SSB-with-carrier has around 30 per cent distortion at 100 per cent modulation.

73,
Kevin, WB4AIO.

Hi Kevin,

I'm curious... why is this so?    If we tune to one side of a clean AM ssb signal that has one only sideband, how does the diode detector even know that there is only one sideband? IE, where does the 30% distortion come from compared to a normal AM signal with two sidebands?

A friend just sent me an email saying:  "A simple diode detector - consider the response curve of a diode. As voltage increases the diode starts to conduct. This is not linear below .7 volts for a silicon diode. This can be improved with bias on the diode so it never gets below the junction thresholds. An active rectifier with a diode and op amp compensates for this K2US Rob has a nice detector design."      …. Maybe this is what you are referring to?


BTW, good explanation you did earlier on higher audio frequency differences. My ears hear similar threshold preferences, though my upper limit is about 9 KHz these days.

T

I am no mathematician, but if you visualize the rotating vectors, two sideband vectors rotating in opposite directions around the carrier vector at the modulating frequency creates a sine wave envelope. A single sine wave vector the same size as the carrier rotating around the carrier creates the same envelope as a two-tone test -- and is, in fact, identical to a two-tone test.

The envelope of a two-tone test is overly broad at the modulation crest and very narrow near 100% negative, compared to a true AM waveform. So, on a diode detector, it sounds distorted. I got the 30% figure from an article by Costas, but can't remember which one.

73,

Kevin, WB4AIO.

[WD5JKO]

  Interesting discussion.

I attached a few scope plots. These are from a 20A on AM with with and without "wavelets" at the same carrier level and peak power. The difference is I introduce negative cycle loading, and make it progressive. I called it PNCL, "Progressive Negative Cycle Loading". I have trapezoid plots as well, but I would exceed the max 3 images per post.

The interesting thing is that with PNCL 'ON', the audio is really loud and punchy with a diode detector receiver. The distortion is not really bad at all for communication purposes.

Jim
Wd5JKO

[WB4AIO]

  Interesting discussion.

I attached a few scope plots. These are from a 20A on AM with with and without "wavelets" at the same carrier level and peak power. The difference is I introduce negative cycle loading, and make it progressive. I called it PNCL, "Progressive Negative Cycle Loading". I have trapezoid plots as well, but I would exceed the max 3 images per post.

The interesting thing is that with PNCL 'ON', the audio is really loud and punchy with a diode detector receiver. The distortion is not really bad at all for communication purposes.

Jim
Wd5JKO

Very clever design. I like to run without clippers, but when conditions (or QRMers) demand it, it's nice to have that in your bag of tricks.

73,

Kevin, WB4AIO.

[K1JJ]

Jim,

Yes, that is an interesting progressive NPL design.  It does exactly what is needed for rigs with wavelets or even a conventionally modulated  AM rig.  It works especially well when going for 200% AM modulation or any modulation level for that matter..

I could never understand why clipping the negative peaks like that could sound so clean until I realized that there is very little power involved at the negative peaks compared to the free-running positive peaks.

Many of the class E rigs run 150%++ positive peaks with negative peak clipping and sound good, while doing  -25 to -30 DB 3rd order IMD from what I have personally measured on my own E-rigs in the past.   In contrast, when running a balanced modulator rig (low or high level) the wavelets cause distortion on the diode detectors and most guys end up limiting them to ~100%-120% positive - and never really knowing why this is required.


Kevin - OK on the explanation for the 30% diode distortion.

T

[KQ6F]

My ANAN will transmit AM normally (carrier + both sidebands) or (carrier + LSB) or (carrier + USB).  I fed a 1 kHz sine wave into it and listened through a RF sampler on a SDR.  The attached scope shots show the demodulated audio using conventional AM detection and using SAM detector.

When using conventional demodulaion the one-sideband only audio looks significantly distorted but oddly when modulated with voice doesn't sound that bad.  There's no difference between (carrier + LSB) and (carrier + USB).

Using the SAM detector cleans everything up to perfection.

Rod KQ6F

[W4DNR]

Back in the mid seventies, I help install a Harris MW-50A  transmitter ... pulse width modulation 50KW carrier.

At 50KW carrier the pulse width was 50% duty cycle. 

100% pulse width was 200kw ( instantanious )

At 50KW carrier 200KW peak equaled 100% positive modulation.   

The transmitter wouldn't make more than 100% modulation at the selected HV that the C.E. wanted to  run.
( taping the voltage up a couple of thousand volts resulted in positive peaks above 120% )

So, since the transmitter was "peak limited" by the 100% pulse width, the C.E. backed the carrier down to 40KW or so.

Now, the transmitter could achieve 125% positive modulation with asymetric audio processing.

I lost the argument, but the C.E. wanted to make the modulation monitor look good for the owner who liked seeing that modulation monitor meter pegged.

I couldn't tell a difference one way or the other , but I never had the opportuniy to listen from a couple hundred miles.

As far as the FCC was concerned, running the transmitter at 40KW wasn't within the +5% / -10% rule.

Maybe we got longer tube life. . .  Heaven knows those 4CX35,000 tubes weren't cheap.

Don W4DNR

 

[KD1SH]

Awesome thread; learning cool stuff here. But sometimes a great thread needs a dumb-as-a-turnip question from the peanut gallery. What the heck is a "presence rise"?  More specifically, what makes a rise, or "bump" in someone's audio spectrum, a "presence" rise, and not just a plain old old rise?

Seems like the magic "D-104" presence rise curve is nearly ideal for AM.

[KK4YY]

Awesome thread; learning cool stuff here. But sometimes a great thread needs a dumb-as-a-turnip question from the peanut gallery. What the heck is a "presence rise"?  More specifically, what makes a rise, or "bump" in someone's audio spectrum, a "presence" rise, and not just a plain old old rise?

Seems like the magic "D-104" presence rise curve is nearly ideal for AM.

Sub-bass > Bass > Low midrange > Midrange > Upper midrange > Presence > Brilliance
https://www.teachmeaudio.com/mixing/techniques/audio-spectrum/

[KD1SH]

Thanks - I've Googled "presence rise" in the past and come up with nothing.  I have - ignorantly, apparently - used the terms "presence" and "brilliance" in a very subjective sense, without realizing that both terms were actually identified with ranges in the audio spectrum.

Sub-bass > Bass > Low midrange > Midrange > Upper midrange > Presence > Brilliance
https://www.teachmeaudio.com/mixing/techniques/audio-spectrum/

[K1JJ]

When using conventional demodulaion the one-sideband only audio looks significantly distorted ….
Using the SAM detector cleans everything up to perfection.
Rod KQ6F

This matches what Kevin said earlier about the ssb-with-carrier distortion in the diode detector.

Could you try another test?  Put through a heavily modulated AM DSB-with-carrier signal... with wavelets (balanced modulator) and see if it also produces diode distortion.

T

[WD5JKO]

Thanks - I've Googled "presence rise" in the past and come up with nothing.  I have - ignorantly, apparently - used the terms "presence" and "brilliance" in a very subjective sense, without realizing that both terms were actually identified with ranges in the audio spectrum.

Bob Heil does a good job describing this phenomenon:
https://youtu.be/DvJhCKyFwVc

Quick story. Most of us who work 75m are aware of how the band goes long a little after sunset. When this happens the local signals drop 20DB or more and the audio sidebands commingle with the noise. Since the noise is bad, the guy receiving is inclined to reduce the Rx bandwidth. One night in the AM Window (ghetto?) there were two "tall ship" AM stations with "woofer audio" (sounded like Howard Stern on satellite radio). As the band went long, the copy of these guys became impossible. There was still plenty of carrier present, but just unintelligible audio. Then when I was about to give up, here comes Charlie W5TOP (sk now) calling CQ. He was weak, but perfectly readable. Charlie was running a stock Ranger (no amplifier) along with a D-104 Mic.  

Jim
Wd5JKO

[KQ6F]

Could you try another test?  Put through a heavily modulated AM DSB with carrier signal with wavelets (balanced modulator) and see if it also produces diode distortion.

Sorry, I don't have an AM transmitter with a balanced modulator nor any other means for generating a wavelet signal.

Rod KQ6F

[WD5JKO]

Could you try another test?  Put through a heavily modulated AM DSB with carrier signal with wavelets (balanced modulator) and see if it also produces diode distortion.

Sorry, I don't have an AM transmitter with a balanced modulator nor any other means for generating a wavelet signal.

Rod KQ6F

The Flex 5000 SDR makes wavelets. The ANAN should be the same. Just lower the carrier on AM, and raise the audio level....Just like my 20a!

Jim

[KQ6F]

The Flex 5000 SDR makes wavelets. The ANAN should be the same. Just lower the carrier on AM, and raise the audio level....Just like my 20a!

Jim

ANAN runs software called OpenHPSDR that is completely different than the older PowerSDR that the Flex 5K runs.  This newer software contains an amazing library called WDSP, developed by Dr. Warren Pratt.  Among other things it prevents AM over-modulation.  It's impossible to produce wavelets.

Rod KQ6F

[AG5CK]

The Flex 5000 SDR makes wavelets. The ANAN should be the same. Just lower the carrier on AM, and raise the audio level....Just like my 20a!

Jim

ANAN runs software called OpenHPSDR that is completely different than the older PowerSDR that the Flex 5K runs.  This newer software contains an amazing library called WDSP, developed by Dr. Warren Pratt.  Among other things it prevents AM over-modulation.  It's impossible to produce wavelets.

Rod KQ6F

Hi Rod,

 If you go into the setup menu under the transmit tab you will find AM carrier level. If it is at 100% there will be no wavelets no matter where the drive level on the main screen is set. Lower the carrier level to 50% and give it a try.

[Steve - K4HX]

There's a crappy animation I made many years ago illustrating what what Kevin is saying. The red vector is the carrier (is is rotating too, but present we are using a strobe light, so it's motion is stopped). The yellow and green vectors are the two sidebands. If we tune of to one side, one of those two vectors will be reduced or even eliminated. The resulting or corresponding envelope will not look the same (distortion).

http://www.amwindow.org/misc/av/phwenvanim.mp4

You can use the slider to move through the animation slowly.

But, with a regular AM diode detector, SSB-with-carrier has around 30 per cent distortion at 100 per cent modulation.

73,
Kevin, WB4AIO.

Hi Kevin,

I'm curious... why is this so?    If we tune to one side of a clean AM ssb signal that has one only sideband, how does the diode detector even know that there is only one sideband? IE, where does the 30% distortion come from compared to a normal AM signal with two sidebands?

A friend just sent me an email saying:  "A simple diode detector - consider the response curve of a diode. As voltage increases the diode starts to conduct. This is not linear below .7 volts for a silicon diode. This can be improved with bias on the diode so it never gets below the junction thresholds. An active rectifier with a diode and op amp compensates for this K2US Rob has a nice detector design."      …. Maybe this is what you are referring to?


BTW, good explanation you did earlier on higher audio frequency differences. My ears hear similar threshold preferences, though my upper limit is about 9 KHz these days.

T

I am no mathematician, but if you visualize the rotating vectors, two sideband vectors rotating in opposite directions around the carrier vector at the modulating frequency creates a sine wave envelope. A single sine wave vector the same size as the carrier rotating around the carrier creates the same envelope as a two-tone test -- and is, in fact, identical to a two-tone test.

The envelope of a two-tone test is overly broad at the modulation crest and very narrow near 100% negative, compared to a true AM waveform. So, on a diode detector, it sounds distorted. I got the 30% figure from an article by Costas, but can't remember which one.

73,

Kevin, WB4AIO.

[kb2vxa]

Hopefully the confusion has cleared up, but for Justin Case... When talking microphone, presence refers to mid voice range, brilliance refers to upper voice range, and presence rise is raising mid audio frequencies typically by 6dB or so. Now for the D-104 magic, now is the time for Astatic's published frequency response curves if anybody still has them. Basically a 47K load as in Charlie's stock Ranger produces a good presence rise for punch while an 11M load flattens it out for AM Gangsta audio. Here's a kinky hint (Hints And Kinks parody) for the hi-fi audio set that makes fiddling with EQ and filters old hat. Use a D-104 with a fixed 11M load in the transmitter and a switch somewhere in the mic input to place a 47K resistor across it. For those who want an FCC legal transmitter, (;->) putting this M derived Pi section LP filter in the speech amp chain I cropped from the Heathkit Apache clipper/filter will do the trick. I measured it dead nuts brick wall at 3KHz, if your neighbor on the band complains he's too close!

[kb2vxa]

Due to a slight mishap that lost the page, this post contains the schematic.

[KD6VXI]

D104 measured vs astatic supplied graph.

--Shane
KD6VXI