Poll: Over-Mod Myth

[LeapFrog]

True story:
Two local operators - several decades ago - rented a single engine airplane and flew over the Santa Clara Valley in CA ('Silicon Valley'). They brought with them a 5 watt walkie-talkie. Walked the dog on everyone. Everyones - and I do mean everyones - S-meters were all pegged completerly to the right of the meter. Loud and clear and wall to wall. No one else could talk when they keyed up . . .

Did modulation % have anything to do with it?
No.
Did power have anything to do with it?
No.

Soooo; what does that tell you?

A clean signal can walk the dog!
EDIT: But it begs serious questions about radiation patterns & antenna placement, should I be in the clouds?

 

[Robb]

A clean signal can walk the dog!

Yes; but that is only half an answer.
The other part was the superior position of the ANTENNA.

 

[LeapFrog]

You beat me to it lol, I just finished typing my edit!

 

[Robb]

Mt Hamilton/Lick Observatory overlooks Silicon Valley and the CA Central Valley; guys would also go up there and 'walk the dog' on everyone as well. Same principle; different method.

 

[LeapFrog]

A little pinch ain't a bad thing (too a point). Most of the splatter associated with over modulation comes high frequency, especially above 10k.

That being said the more positive the the modulation, the louder you are period. You may not be understood. But a 400% peak contains more energy then a 200% peak.

When you say above 10Khz are you referring to adjacent channel splatter?

One of my major concerns is that, while 400% is greater than 200%, the periods of time when the carrier is pinched equals 0 output, In my mind the transmitter should never shut off for any period of time. If the transmitter is shutting off, the signal will lose "integrity" & create distortion ( and audio fading in and out @ the receive station, maybe that's just atmospheric conditions the cause that though)

I'm trying to grasp in my mind what is happening when these guys run big class c linears behind an over-modulated (resistor and capacitor modified) swinging Cobra 29 LTD. While the carrier is pinched off and the relay is still engaged for the amplifier, what is coming out of the back of it, harmonics, nothing? Or is the shut off period so miniscule in the grand scheme that it's not going to be noticed at all minus the distortion created by the neg. peaks going over 100%.

Sidenote: It took me a little while to realize a simple "npc mod" does not exist for AM only transformer modulated radios (Cobra 25/29) without re-working much of the radios audio and pa sections to include an AN-612 and an "AM regulator transistor" but then it would become a Cobra 29/148 hybrid (Minus sideband modes) lol.

 

[sp5it]

You want big AM audio, run big carrier modulated in last stage.
Mike

 

[LeapFrog]

You want big AM audio, run big carrier modulated in last stage.
Mike

I really only care about the audio fidelity, I can "get loud" with asymmetrical modulation and amplify the output if need be.

(I want the PA stage to be truly linear, so I need to low level modulate the rig... One day.)

Project: a Cobra 29 LTD, no mmm, no asymod etc. Low level, asymmetrical amplitude modulation with an external (optional) audio input or "direct inject". An exciter it will become, meaning at that point you wouldn't be "getting out" far without a linear power amplifier.

But I'm a fool with a dream of turning the Cobra 29 into a ten meter rig, complete with a vfo and FM mode.
Just as a learning exercise.

sp5it, yes this thread is all about transformer modulated AM only rigs, with "big" audio.
The poll is asking about people over modulating these radios for an increase in audio "loudness" and "shooting skip", I'm just very curious about what is happening in those radios when they over modulate, as they are commonly configured "around these parts" to do just that.

 

[543_Dallas]

Once you get to the point your audio starts to sound distorted you're not making progress. If they can't understand you you're just a nuisance.

Same goes for the guys that like to crank up a d104 and talk into it at arms length. When I'm near them they are loud and obnoxious but out to the distance where their carrier is an s unit or 2 above the noise floor you can barely make out what they are saying.

All that distortion plus the fan noise, television and other crap in the background makes it hard to copy them at a distance. A clean signal can be intelligible just above the noise floor.

 

[Tallman]

True story:
Two local operators - several decades ago - rented a single engine airplane and flew over the Santa Clara Valley in CA ('Silicon Valley'). They brought with them a 5 watt walkie-talkie. Walked the dog on everyone. Everyones - and I do mean everyones - S-meters were all pegged completerly to the right of the meter. Loud and clear and wall to wall. No one else could talk when they keyed up . . .

Did modulation % have anything to do with it?
No.
Did power have anything to do with it?
No.

Soooo; what does that tell you?

Uhhhh, That when it comes to antennas height makes might?

Wait for it!:
:
:
:

:
:The Ground Plane

 

[LeapFrog]

When I'm near them they are loud and obnoxious but out to the distance where their carrier is an s unit or 2 above the noise floor you can barely make out what they are saying.

A clean signal can be intelligible just above the noise floor.

This is my major concern, although the radio sounds louder it will become a less effective means for communications further than a "local area".

(barefoot for sure, but with power added I have no clue how well the over modulating radio would perform in DX attempts, I have no desire to find out first hand, but I am interested.)

 

[TM86]

Mt Hamilton/Lick Observatory overlooks Silicon Valley and the CA Central Valley; guys would also go up there and 'walk the dog' on everyone as well. Same principle; different method.

Last time I was up there (in the 80's) they had posted signs indicating radio transmitters of any kind were banned from use around the observatory. Guess they got tired of having RFI messing up their measurements.

I heard Mount Umunhum is going to be opened to the public soon, so that could prove interesting.

 

[Robb]

Last time I was up there (in the 80's) they had posted signs indicating radio transmitters of any kind were banned from use around the observatory. Guess they got tired of having RFI messing up their measurements.

I heard Mount Umunhum is going to be opened to the public soon, so that could prove interesting.

Yep.
Also, Mt Diablo was a popular spot - too.

 

[binrat]

Once you get to the point your audio starts to sound distorted you're not making progress. If they can't understand you you're just a nuisance.

Same goes for the guys that like to crank up a d104 and talk into it at arms length. When I'm near them they are loud and obnoxious but out to the distance where their carrier is an s unit or 2 above the noise floor you can barely make out what they are saying.

All that distortion plus the fan noise, television and other crap in the background makes it hard to copy them at a distance. A clean signal can be intelligible just above the noise floor.

And don't forget the airplane flying over head.
I had a D-104 on an Icom 707. Worked great once you turned everything down on it.

 

[Tallman]

This is my major concern, although the radio sounds louder it will become a less effective means for communications further than a "local area".

(barefoot for sure, but with power added I have no clue how well the over modulating radio would perform in DX attempts, I have no desire to find out first hand, but I am interested.)

The asymmetrical modulation does not sound distorted if done correctly. As long as you do not pinch the carrier off or flat top the positive peaks you will be sounding loud and proud. I had many people try to buy my S45HP because it sounded so good and I always turned them down. And yes I still have it and still not for sale.

 

[LeapFrog]

The asymmetrical modulation does not sound distorted if done correctly. As long as you do not pinch the carrier off or flat top the positive peaks you will be sounding loud and proud. I had many people try to buy my S45HP because it sounded so good and I always turned them down.

Absolutely, this can be accomplished with a single diode and a variable resistor on the radios using an EPT3600 circuit board. On my dummy load and with a nearby receiver the test results were excellent!
Loud, and clear!

A relevant quote from a fellow forum member who shall remain anonymous:
"You have to wonder sometimes if the engineers left some extra bits in the circuit for modders to discover."

Most of the time in the CB world, the price point (and regulations) would be a huge limiting factor for something like this to happen, but I almost feel like the export radios were created with asymmetrical modulation in mind. It is almost too simple to accomplish on the older exports.

I have to try this on my Grant XL, perhaps it was an engineer who worked for Uniden that really made this happen, as the superstar 360 FM and 148 GTL-DX are copies of the Uniden design. ( thank you Robb for the history on these two exports ) In my opinion somebody had this information for a long time (npc mod) and then went public with it at some point.

But that's all just speculation, perhaps it's a fluke and somebody truly discovered it on their own by working it out with a schematic and a test radio.

It would be nice to get some information about the origin and discovery of this circuit modification (npc) directly from Bill Eitner, seeing as how Billy Dean Ward is now deceased. Somebody has to know where it came from, I doubt both of these individuals came about this discovery on their own at different times.

-Leap