Oh, how do you convert from WPEP to WRMS? Does it have to be converted to
voltage and multiplied by .707?

Chris
"Chris" wrote in message
k.net...
| 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
|
|

Chris wrote:

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

Zero. As universally used, SSB means "single sideband suppressed
carrier". There is no transmitted carrier in this mode.

And, modulation percentage has no meaning when talking about SSB, since
it refers to the relationship between the modulation and the carrier.

Roy Lewallen, W7EL

Chris wrote:

Oh, how do you convert from WPEP to WRMS? Does it have to be converted to
voltage and multiplied by .707?

Chris

While the conversion from PEP to RMS is simple for a sine wave or other
simple waveform, it's not simple when dealing with a real voice
waveform. It depends heavily on the characteristics of the voice, and
any audio processing (such as compression or RF clipping) that might be
taking place. Typically, the PEP value of an unprocessed voice waveform
is many times the RMS value.

Roy Lewallen, W7EL

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.

You're dead right of course Peter.

i believe you're AM broadcasters are limited to 125% positive while here
in the UK we have 100% positive peak limit.

FYI the late model Nautel PDM broadcast transmitters are capable of
around 200% positive peak and up to 50KHz in frequency response!

Broadcast transmitters are limited for obvious reasons.
--
Philip de Cadenet G4ZOW
Transmitters 'R' Us
http://www.transmittersrus.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

"Chris" wrote in message
k.net...
I think I've got it figured out. For AM, the carrier should be 1/8 of the
PEP maximum or 1/4 of the max carrier. So an amp rated 100W AM/FM/CW, 200
WPEP SSB should run with a 25 W carrier on AM. Does that sound right to
everyone?



The peak power on AM is 4 times the carrier power. But, don't forget, AM
has TWO sidebands, not one.

Pete

"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

CBers are very susceptible to urban myth and legend. Not understanding the
"normal" nature of an AM carrier, often they won't see the needle move very
much (assuming some cowboy jockey hasn't been in the rig snippin' and
clippin'), they get kind of excited. "HEY! I ain't got no "swang", so
therefore, they think they
aren't "gittin'" out. Voodoo techs have been able to take advantage of this
by monkeying around with the sets and/or using funky, cheap meters to show
the unknowing how much their radio is "swangin'". "LOOK! Ya got 8
watts o' carrier and 40 watts of 'swang'"! The CB guys eat it up! AND
willingly part with $$$ to get this "Swang". Swing is fully embedded in CB
psyche and, like the "coax length" (18 FEET! 18 FEET! Ya gots to have 18
feet of coax!!!!!!) bullsh--, it is part of the "holy" grail of CB radio!
LMAO!


J

Such as believing that an M3/CB Fools' Licence makes
then into a Radio Ham overnight.

"Jerry" wrote in message
. ..
CBers are very susceptible to urban myth and legend.

Jerry, you can trust me when I say that hams have their full share of
beliefs in voodoo physics and misunderstandings about how even the
simplest phenomena take place. A quick scan of the
rec.radio.amateur.antenna archives provides ample evidence in itself,
but there's plenty of other evidence scattered about.

So let's not be too hasty at calling the kettle black.

Roy Lewallen, W7EL

Jerry wrote:

CBers are very susceptible to urban myth and legend. Not understanding the
"normal" nature of an AM carrier, often they won't see the needle move very
much (assuming some cowboy jockey hasn't been in the rig snippin' and
clippin'), they get kind of excited. "HEY! I ain't got no "swang", so
therefore, they think they
aren't "gittin'" out. Voodoo techs have been able to take advantage of this
by monkeying around with the sets and/or using funky, cheap meters to show
the unknowing how much their radio is "swangin'". "LOOK! Ya got 8
watts o' carrier and 40 watts of 'swang'"! The CB guys eat it up! AND
willingly part with $$$ to get this "Swang". Swing is fully embedded in CB
psyche and, like the "coax length" (18 FEET! 18 FEET! Ya gots to have 18
feet of coax!!!!!!) bullsh--, it is part of the "holy" grail of CB radio!
LMAO!


J

In article ,
Gary Schafer writes:
Well Chris, you got a lot of good advice and some completely wrong
advice. Funny thing is nobody really answered your question!

[lots of useful information snipped...]

This is how you convert average power to PEP. I say average power
because RMS power is really a misnomer. There is no such thing as RMS
power as so many commonly refer to. It is really AVERAGE power. It is
derived from RMS current and RMS voltage but what you get when you
multiply RMS voltage by RMS current or resistance is an AVERAGE value,
not an RMS value.

I completely agree about RMS 'power'. RMS applies to a voltage or
current waveform.

Caveat: you cannot simply multiply RMS voltage by RMS current unless
you have a purely resistive load. Oddly enough, if the load is a
fixed resistance (measured as a conductance G) in parallel with a
reactance then the E_rms^2 * G (E_rms^2/R when purely resistive)
value continues to apply. When it is a fixed resistance in series
with a reactance, I_rms^2 * R continues to apply. And these extend
to the nonsinusoidal case as well, again under the restrictions
given above (fixed G in the first case, fixed R in the second).

This may seem trivial but it becomes important when trying to convert
from one form to another. Using the wrong notation can give you wrong
answers.

As to the above, the average voltage or current of a sine wave is 50%
of the peak.

Actually, it is .6366 times the peak. The averaging is done continuously
over the positive half cycle of the sine wave, and is essentially the area
under the sine curve divided by the length of the half-cycle (2/3.14159,
or, if you calculated in degrees, 114.592/180).

The true average value of a sine curve is to average over a full cycle,
but is not very interesting: it's zero. The .6366 number is useful
because it is what a VOM typically measures - average DC voltage
after passing through a full-wave rectifier and before applying a scale
factor of .7071/.6366 to produce E_rms - all based on the assumption of
a sinewave input.

Average value of voltage or current waveform is of limited use; but
RMS value is directly related to the ability to deliver power to a
resistive load.

The rms value of a sine wave is .707 of the peak voltage or current.
If you multiply .707 (rms voltage) by .707 (rms current) you get .5 or
50%. This is AVERAGE. It is no longer an rms value.

By the way, the definition of peak envelope power (PEP) is: "The
average power contained in one RF cycle at the crest of the
modulation envelope". (note that the definition says "AVERAGE power"
not RMS power)

The average power is in fact all that is of interest in AC circuits,
and is the average over time of "instantaneous power" E*I.

If you do not use average power you have to deal with the fact that
reactances accept power during half of the cycle and then feed it
back during the other half; and for nonsinusoidal waveforms do the
same but in not so regular a pattern.

PEP is just averaging over the shortest reasonable interval (one
cycle of the carrier frequency), then keeping only the largest
such value seen. Useful to regulators because it is a measure
of your maximum capacity to interfere with other signals.

[...]

73
Gary K4FMX