[AMRadio] coupling cap on the moduation transformer secondary

Geoff w5omr at satx.rr.com
Tue Aug 16 22:38:02 EDT 2005

Donald Chester wrote:
 >You don't need 10 Hz low end response, thats wasted power since most 
receiver/speakers won't
 >reproduce that. Also, the capacitor is just another source of stored 
energy in your radio, to deal
 >with from a safety standpoint. More is not always better.

But to avoid excessive phase shift distortion, the uniform frequency 
response should extend at least one octave above and one octave below 
the intended range of frequencies of the modulation.

Therefore if, for example, your target is to actually transmit audio 
ranging from 100~ to 5000~, the speech amplifier/modulator should be 
essentially flat from 50 to 10,000~.   Even "communications quality 
audio" response of 300~ to 3000 would require at minimum a uniform 
response in the audio section of the transmitter of  150~ to 6000~.

UTC ran this recommendation in their LS- series transformer catalogue, 
and I seem to recall seeing it in Thordarson's Tru-Fidelity catalogue also.

yeah, I'm thinking the same thing.  So, if I don't have enough C in the 
output of the power supply, I could always add another, which would make 
them in parallel, which would ADD to the total capacitance in the power 
supply, and whatever coupling capacitance was used would effectivly be 
(as I understand it) in series with that power supply output capacitance. 

Which means if there's 10uF in the supply, and 10uF to be used as 
coupling, then a total of 5uF would be seen, as far as coupling is 
concerned and if BC stations are using 1 and 2uF and you're using 4uF, 
Don, then I should be in no danger of hurting anything here.  ;-)

Neat discussion - I like it.

73 = Best Regards,

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