[AMRadio] coupling cap on the moduation transformer secondary


Donald Chester k4kyv at hotmail.com
Tue Aug 16 21:41:34 EDT 2005



>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.

Don k4kyv





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