[AMRadio] Power Levels

[Gary Schafer]

Wt8r at aol.com wrote:

>
>        I'm new to the list and would like to know more about how you arrive
> at your numbers.
>
>        75% of 500W is 375 Watts output of carrier power alright, but where
> did the "X4" come from to get the PEP figure?
>
>        I also wonder what the relationship is between RMS power and PEP
> power?  that is, if I tune my rig up to 1500 W PEP output and without
> changing anything, switch to CW, what is the reading on my wattmeter?
>
> 73 de
> Dave in Dayton, WT8R
>

Hi Dave,

There is sometimes some confusion as to what PEP really is. If you tune your SSB
amp up to 1500 watts output as seen on your watt meter that is 1500 watts average
power or as some call it "RMS". If the peaks of your SSB signal reach that 1500
watt level that is 1500 watts PEP. If you go to CW you have 1500 watts average and
1500 watts PEP. They are the same in that case.

If you put the SSB rig in the AM position you must reduce the carrier output so
that you have 375 watts showing on the watt meter. Do this without changing any
tuning of anything. When you modulate the 375 watt carrier to 100% modulation the
peaks will be hitting 1500 watts just like they did on SSB. The only problem is you
may not see it on your peak reading watt meter like you do on SSB because the AM
carrier fools the watt meter a little. If you do a long oooo you will see it hit
the 1500 watts.  The best way to see it is with a scope connected to the output.
Get a level reference on the scope with the 1500 watts of carrier. Now when you
switch to AM you will see that the carrier level of 1/4th the power shows exactly
1/2 the voltage level on the scope. When you modulate, the peaks on the scope will
hit that same reference level on the scope that you set up which will be equal to 2
times the carrier voltage level which is 4 times the power even though the watt
meter may not quite get there.

Exactly the same relationship exist with a plate modulated transmitter.

Remember power = voltage squared divided resistance. With the scope you are
measuring the voltage on the 50 ohm load or antenna.

73
Gary  K4FMX