I will probably get some flames from this but here it goes. I have been into
CB radio for a number of years but don't agree with most of what I hear.
That's just one of the reasons I'm looking to amateur radio. One of the
things I often hear in CB circles is that one should turn a 4 watt AM radio
down to 1 1/2 watts and let it "SWING". How is this possible? What really
happens when you do this? I think I know. So, how much carrier should you
have for an amp or final stage with a known max output. In other words, if
it can produce 8 watts max unmodulated carrier, is a 4 watt carrier ideal?
If it produces 100 watts, is 50 watts ideal? How much "space"does it need
for proper modulation? Is there a website that explains this well? I'm an
electronics tech thirsting for knowledge.

Chris

There is no limit to AM modulation, it is not limited to 100 percent
in the positive direction. It is limited to 100 percent in the negative
direction, to prevent cutoff. Positive limits are set by the mdoulation
linearity of the output stage with increasing positive voltage.
Most AM BC broadcasters in this country use assemtrical modulation
for this reason.

Peter

It sounds like a technique I remember calling "controlled carrier". The
carrier power was reduced when you weren't talking, then was increased
with the audio in an AGC-like manner. Sounded a little weird, but not
badly distorted. The objective was to reduce the average dissipation of
the final stage, so smaller tubes and a lighter duty power supply could
be used.

But I don't see why you'd use a method like this with a low power
transmitter, since it's trivial to make one that easily handles the
power requirements of standard AM. So I don't really think that's what
is meant by "swing". I'd bet good money that whatever "swing" is, it
doesn't improve quality or signal strength, and very likely introduces
distortion that causes splatter. If the transmitter was designed for
100% modulation of a 4 watt carrier, and you reduce the carrier without
a proportional reduction of the audio, you'll be overmodulating and
consequently distorting and splattering.

What are the supposed benefits of this "swing"?

Roy Lewallen, W7EL

"Roy Lewallen" wrote in message
...
| It sounds like a technique I remember calling "controlled carrier". The
| carrier power was reduced when you weren't talking, then was increased
| with the audio in an AGC-like manner. Sounded a little weird, but not
| badly distorted. The objective was to reduce the average dissipation of
| the final stage, so smaller tubes and a lighter duty power supply could
| be used.
|
| But I don't see why you'd use a method like this with a low power
| transmitter, since it's trivial to make one that easily handles the
| power requirements of standard AM. So I don't really think that's what
| is meant by "swing". I'd bet good money that whatever "swing" is, it
| doesn't improve quality or signal strength, and very likely introduces
| distortion that causes splatter. If the transmitter was designed for
| 100% modulation of a 4 watt carrier, and you reduce the carrier without
| a proportional reduction of the audio, you'll be overmodulating and
| consequently distorting and splattering.
|
| What are the supposed benefits of this "swing"?
|
| Roy Lewallen, W7EL


To reduce the drive power to an amplifier and make the modulation louder.

Chris

Chris wrote:


To reduce the drive power to an amplifier and make the modulation louder.

Chris

I see. But reducing the carrier won't make the modulation louder, only
more distorted.

Well, let me back up a little. What I said is true if the modulation is
100%.

But let's suppose that the transmitter is capable of only 50%
modulation. In that case, you *can* make the modulation louder by
increasing the amount of audio applied to the carrier. If the
transmitter is fundamentally designed to handle 100% modulation, this
would require only more audio gain or a "hotter" microphone. That would
be the best way to make your modulation louder.

But let's say that instead, you reduce the carrier from 4 watts to 1.
Then the 1 watt carrier would be 100% modulated. (100% modulation of a 4
watt carrier takes 2 watts. 50% modulation takes only 1/2 watt, which
will modulate a 1 watt carrier 100%.) Now you have 100% modulation of
the 1 watt carrier. There's the same amount of transmitted audio power
as before -- 1/2 watt --, so you're really not making the audio any
stronger, and no one will be able to copy you any better than before.
(In fact, your weaker signal will have more trouble getting through in
the presence of noise or interference.) But if you're the only signal
being heard, the receiver's AGC (automatic gain control) will react to
your weaker carrier by turning up the receiver's gain, making the audio
sound louder. The person receiving your signal can make your audio just
as loud with a 4 watt carrier by manually turning up the volume.

So I'll relent and say that reducing the carrier might make your audio
sound louder -- but only if your transmitter is undermodulated in the
first place, there's no stronger signal to control the receiver AGC, and
if you don't reduce the carrier so much that it makes the modulation
exceed 100%. But your ability to get through interference and noise will
probably be reduced.

Roy Lewallen, W7EL

So let's use a typical amp rated at 100 watts AM/CW/FM and 200 watts PEP on
SSB. Assuming that the transmitter is modulated at 100%, how many watts
should the carrier be?

Chris
"Roy Lewallen" wrote in message
...
| Chris wrote:
|
|
| To reduce the drive power to an amplifier and make the modulation
louder.
|
| Chris
|
| I see. But reducing the carrier won't make the modulation louder, only
| more distorted.
|
| Well, let me back up a little. What I said is true if the modulation is
| 100%.
|
| But let's suppose that the transmitter is capable of only 50%
| modulation. In that case, you *can* make the modulation louder by
| increasing the amount of audio applied to the carrier. If the
| transmitter is fundamentally designed to handle 100% modulation, this
| would require only more audio gain or a "hotter" microphone. That would
| be the best way to make your modulation louder.
|
| But let's say that instead, you reduce the carrier from 4 watts to 1.
| Then the 1 watt carrier would be 100% modulated. (100% modulation of a 4
| watt carrier takes 2 watts. 50% modulation takes only 1/2 watt, which
| will modulate a 1 watt carrier 100%.) Now you have 100% modulation of
| the 1 watt carrier. There's the same amount of transmitted audio power
| as before -- 1/2 watt --, so you're really not making the audio any
| stronger, and no one will be able to copy you any better than before.
| (In fact, your weaker signal will have more trouble getting through in
| the presence of noise or interference.) But if you're the only signal
| being heard, the receiver's AGC (automatic gain control) will react to
| your weaker carrier by turning up the receiver's gain, making the audio
| sound louder. The person receiving your signal can make your audio just
| as loud with a 4 watt carrier by manually turning up the volume.
|
| So I'll relent and say that reducing the carrier might make your audio
| sound louder -- but only if your transmitter is undermodulated in the
| first place, there's no stronger signal to control the receiver AGC, and
| if you don't reduce the carrier so much that it makes the modulation
| exceed 100%. But your ability to get through interference and noise will
| probably be reduced.
|
| Roy Lewallen, W7EL

Roy Lewallen wrote:
It sounds like a technique I remember calling "controlled carrier". The
carrier power was reduced when you weren't talking, then was increased
with the audio in an AGC-like manner. Sounded a little weird, but not
badly distorted. The objective was to reduce the average dissipation of
the final stage, so smaller tubes and a lighter duty power supply could
be used.

No, "controlled carrier" was something else.

In 100% positive modulation, the carrier amplitude is constant
regardless of program material. You (somehow!) maintain proper absolute
phase through the chain so that you know a positive-going audio signal
at the transmitter audio input terminals will result in increasing power
in the modulated carrier. You then allow the positive-going signal
peaks to exceed 100% while limiting negative-going peaks to less than
100%. Broadcast modulation monitors are able to display negative-going
and positive-going modulation peaks independently.

(at a broadcast station, the FCC requires that carrier power be between
-- IIRC, my copy of Part 73 is missing -- 80 and 110% of the authorized
figure. DX-60B-style controlled carrier wouldn't comply, though I
suppose you could develop a system that didn't swing the carrier quite
as far.)
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

Doug Smith W9WI wrote:
Roy Lewallen wrote:

It sounds like a technique I remember calling "controlled carrier".
The carrier power was reduced when you weren't talking, then was
increased with the audio in an AGC-like manner. Sounded a little
weird, but not badly distorted. The objective was to reduce the
average dissipation of the final stage, so smaller tubes and a lighter
duty power supply could be used.


No, "controlled carrier" was something else.

A quick web search shows that what I described is properly called
"dynamic carrier control". My mistake. I only recall having seen one
such amateur transmitter, and it was over 40 years ago. . .

Roy Lewallen, W7EL

Roy Lewallen wrote:
A quick web search shows that what I described is properly called
"dynamic carrier control". My mistake. I only recall having seen one
such amateur transmitter, and it was over 40 years ago. . .

I owned one, a Heath DX-60B. Got my General in 1974, DSB-carrier AM
phone was already essentially obsolete. When I got a 33 signal report
from a 40-meter station four miles away, I decided to stick to CWgrin...

Seems to me there was a circuit for homebrewing dynamic carrier control
in the ARRL Handbook for awhile.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

"Roy Lewallen" wrote in message
...
Doug Smith W9WI wrote:
Roy Lewallen wrote:

It sounds like a technique I remember calling "controlled carrier".
The carrier power was reduced when you weren't talking, then was
increased with the audio in an AGC-like manner. Sounded a little
weird, but not badly distorted. The objective was to reduce the
average dissipation of the final stage, so smaller tubes and a lighter
duty power supply could be used.


No, "controlled carrier" was something else.

A quick web search shows that what I described is properly called
"dynamic carrier control". My mistake. I only recall having seen one
such amateur transmitter, and it was over 40 years ago. . .

Roy Lewallen, W7EL

The Heath DX-60 used "controlled carrier" modulation. It was a
form of screen modulation.

Pete