[AMRadio] When talking about AM power


John Coleman jc at pctechref.com
Fri Oct 9 11:12:32 EDT 2015


I'll make a statement on PEP vs Carrier: 

Sine wave audio modution at 100% --- PEP = 4 X Carrier
 But if the audio is not sine wave, then the polarity of the modulation,
with respect to the power supply that it is modulating, will determine the
ratio of the PEP to CARRIER.

making the assumption that 100% modulationis defined as = carrier pinch off,
then it is quite posible to have a 1000 watt carrier and 1500 watt PEP
output.

Reversing the non sine wave modulation polarity might send the PEP to as
high as 4000 Watts.  To get legal, with this senario one might need to
reduce the carrier to 200 Watts

The interesting thing about this is, that with the 1000 watt carrier or the
200 watt carrier, the side band energy might be the same as long as the Peak
to Peak audio voltage is not changed.

So if your not using an osiliscope to monitor your signal then you really
have no idea.

the following two links may clear up what I am trying to say.

note the fianal and the modulator have separate supplies and the final
supply is on a variac.

Same audio voltage from the modulator in either case. Same audio output
level. 

Less plate voltage on the final in image008

Audio modulation 180 deg phase change.  (mod XFMR plate caps reversed)
 
http://www.qsl.net/wa5bxo/asyam/image006.JPG


http://www.qsl.net/wa5bxo/asyam/image008.JPG

The fig image008  Produces much less RF current to the dummy load or
antenna. but has the exact same PEP and sideband energy.

Thanks for reading
John, WA5BXO





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