Should I say you bet I can do that?

[OldTech03]

I will admit to playing the devil's advocate here to some degree it was my clear intent to have this conversation and I am quite happy with the results and the response. I proudly held a GR2nd and admittedly it was many years ago and has long since expired but Andy I do know what you were trying to say as well as others.
With respect to the, what good does modulation %age in excess of 100 accomplish and at what point does the amount that exceeds 100% become unusable? like fodder that falls to the ground when harvesting corn? It just so happens I still remember the good ole days like CaptainK was referring to broadcast stations, at least the I worked for my boss at the time was also broadcast engineer he wanted to run at a 115% and since the FCC allowed 125% with 98% neg peaks "I think I got that right" it may have been 100 but I think we always tried to keep the negs just below 100 we would often incorporate a jump to 125% in our advertising audio if you doubt the difference that can make ask the Captain if a sudden 10% increase can get a listeners attention especially on some of the older tube type and solid state receivers that had poor AVC circuits after adverts we went back to normal sailing 115 or less depending on the content and time of day that was the way we did it at a small 10K station way back when they still had hitching posts. But good conversation keeps my mind busy while I'm stuck in a bad place. And Thanks Captain for awakening past memories almost like being a young man again.

 

[Handy Andy]

if a sudden 10% increase can get a listeners attention especially on some of the older tube type and solid state receivers that had poor AVC circuits after adverts we went back to normal sailing 115 or less depending on the content and time of day that was the way we did it at a small 10K station way back when they still had hitching posts.

They may have done away with hitching posts, but this thing they call Automobile is really something. They park anywhere - and sometimes they move - else they just sit there. Like a dog waiting for it's owner to arrive form home - to take it for a walk or "run". Some are very quiet and some can be very loud, and some just produce so much gas that they call "Exhaust" makes me wish for the earlier days of what they used hitching posts for...

But anyhoo, your comment is still in force today - VISIO and others simply call it Volume Averaging - yeah right - blasts ya' right out of the chair...

 

[Tallman]

I don't know about that. I would prefer the scent of a filtered diesel exhaust over Horse Flatulence and road apples in the street..

 

[StrangeBrew]

Tell them this...

Show me a radio that can actually hear 300% modulation - and I'll tune yours to it.

....

The above pretty much sums up the problem as I understand it.

Not a tech and never claimed to be so I can't address the more technical discussion here, but I can share a bit of "CB wisdom" that was handed down to me a long time ago.

From what I was told if done right you can get boatloads of modulation from a CB radio with very little distortion, the problem is that most receivers would create their own distortion when trying to decode it. The number recommended as an upper limit to me was about a 5:1 Peak to Dead key ratio for a good loud but still clean sound in the receiving stations speaker. Note that some receivers could decode higher ratios but we're aiming for lowest common denominator here.

So it went like this:

Cleanest possible signal go with 4:1 ratio

Loud audio but still quite clean 5:1 ratio

Larger swing to dead key ratios than that would only be used to compensate for a lack of linearity in an amp, the output of the radio would be adjusted with the goal of attaining the above 4:1 or 5:1 ratios on the amps output.


Of course this is for 11 meters so if you're on the ham bands YMMV.

 

[Mustang 131]

I received a call last night just before turning in for the night it was a customer of mine that had me fix up one of his cobra 29LTD's the short story is he wanted to send the radio back to me he said the radio was working fine but wondered if he would benefit from me making it produce 250 or 300 Percent Modulation as he had seen on YouTube video. I'm not going to answer that I'm going to do as I would have 49 years ago when I was standing in front of 28 wanna-be technicians. So Classroom can any of you tell me "Honestly" why this is a "Good" or "Bad" idea? This has to do with Honesty so I'm told! so please you will not hurt my feelings tell me what you would tell one of your customers if you work on radios asked to do this.

Been down that road. If you simply want to be loud, by all means go ahead. Just don't pinch that carrier too much. And forget about any wideband audio. Generally speaking...those mods sound like crap above around 160--200% on a typical CB receiver. But many exceptions to that exist.
With all that out of the way.....I run about 170% peaks positive...99% negative.

 

[TheRealPorkchop]

Ain’t I a stinker?

 

[Rwb]

View attachment 27476

Ain’t I a stinker?

yep you are

 

[Tallman]

Should have cleaned out your chamber pot/helmet before you put it on.

 

[357magnum]

I agree with Tall , burned Diesel fuel Yes ! Digested Alfalfa ? After owning horses over 40 years .. I'll take a Corn binder !

 

[jon666]

when my shop was open, had a sign on the door if you want garbage mods go elsewhere. we don't do that no flashy lights no echo boards no beeps will be done in my shop.thank you

 

[rabbiporkchop]

Why would it be useless?

Less power makes it more difficult to make a contact in DX especially when conditions are weak.

I thought being heard was the objective on radio.

That's the whole point. Why would you want to reduce your power to make yourself sound louder at close range but unable to make the trip in DX?

Useless?? How so? It is louder than a radio of similar carrier power but only 100% modulation.

Louder is completely useless in dx. Reducing your carrier only hurts your performance. It might sound impressive in the parking lot to other people but a reduction in power always equates to a reduction in performance. Keep in mind we're not talking about commercial broadcast stations that can afford to waste power because they have paid advertisers. Stretching out the positive Peaks and reducing the carrier does absolutely nothing for long distance communication it only hurts it. You really do need that carrier. If anything, speech compression would be a step in the right direction to increase your mean power. Dropping the carrier simply reduces your mean power.

 

[TheRealPorkchop]

Dude, you sound more like a radio repairman than a truck driver...

And yet you care to argue with a man that’s been in commercial radio most of his life? Really... you wanna go there?

Sit down on the front row, I believe the man is about to school your ass.

 

[Tallman]

Less power makes it more difficult to make a contact in DX especially when conditions are weak.


That's the whole point. Why would you want to reduce your power to make yourself sound louder at close range but unable to make the trip in DX?

Louder is completely useless in dx. Reducing your carrier only hurts your performance. It might sound impressive in the parking lot to other people but a reduction in power always equates to a reduction in performance. Keep in mind we're not talking about commercial broadcast stations that can afford to waste power because they have paid advertisers. Stretching out the positive Peaks and reducing the carrier does absolutely nothing for long distance communication it only hurts it. You really do need that carrier.

I'm sorry but I don't think you really know how this works. The carrier is not that important once it has been modulated. In AM all of the information is in the side bands and not the carrier. That's why the single side band is so effective. The transmission is 100% information.
AM is comprised of carrier, and the modulation which results in Carrier Plus the upper side band, and the lower side band.
Carrier plus and carrier minus the modulation gives you the upper side band and the lower side bands. If carrier is so important in DX why does every go to power mikes?

 

[kopcicle]

Okay , for the members that are not interested in re-hashing this because they have better things to do than rehash this ....

PEP of an AM signal is four times the carrier power IF fully modulated.

100% steady modulated 100 w carrier = 400 watts PEP or 150 watts average or "heating" power. Of this 150 watts average or "heating" power, 100 watts is in the carrier, and 25 watts average power is in each of the two AM signal's sidebands.

Carrier average power = 2/3 of the total 100% modulated average power

Total of both sidebands, average power = 1/3 of total average power under 100% modulation

Average power one sideband = 1/6th average power with 100% modulation

Peak Envelope Power 100% symmetrical modulation = Four times carrier power.

https://www.bucek.name/pdf/ta7222.pdf

So lets take a quick look at the specs
@ 13.2 volts and 10% THD 5.8W typ .
@ 13.2 volts and .5 % THD 1W typ.
The "knee" in the THD/Pout curve is at about 3W. THD rises near vertically from there. THD loosely equates to IMD.

5 x 4 = 20 or 7.5 average 5 watts is in the carrier, and 1.25 watts average power is in each of the two AM signal's sidebands. 2.5W is easily within .5% THD @ 13.2 volts into 2 ohms.

Then consider the very common 2SC1969 swap into a '29 or a B+ mod (supply voltage to collector instead of regulated 8v from the mb3756 et al) for 10w carrier.

10 x 4 = 40 or 15W average 10 watts is in the carrier, and 2.5 watts average power is in each of the two AM signal's sidebands. 5W is easily 10% THD @ 13.2 volts into 2 ohms. Hummm.

Now keep in mind that this ONLY holds true for 100% steady modulated carrier.

Without going into a discussion about voice processing (the new-speak word is "pre-distortion") It is near impossible to continuously 100% modulate an AM signal and maintain legibility. Nominal duty cycle alone (1 in 4 or 25%) has to allow for pauses. Before anyone mentions EQ's and my Kenwood radio frequency based voice processing I'll allow that some come close to 100% and do an accurate reproduction of the voice input. Still, no voice processing will or can completely fill the sidebands with out leaving artifacts of the processing. Just add that on top of the THD% and IMD.

Any audio phools here? What would you rather listen to ? Less than .5% THD or 10% THD at 3db louder?

In the above example I'd rather have 5W of .5% THD fed into ...
http://www.communication-concepts.com/an762/
Than 10W of garbage fed into a dipole.
I'd gladly halve my power for intelligibility.
The essential caveat here is the limitations of the TA7222AP , TA7205P, etc.
Direct audio injection of a harmonically clean audio signal makes all the above a wasted discussion. Then the only limitation is the dissipation of the PA.

Skool's out ...

 

[TheRealPorkchop]