[AMRadio] T3 Mod iron specs - Audio limitations, harmonics, etc.


John Coleman jc at pctechref.com
Wed Feb 20 19:01:10 EST 2008


	Brian, you can extend the frequency range with external equalization
to some extent.  This is some what dependent on the overall slope and depths
of the roll off in the original circuitry.  
	
	It always results in phase shifts of the audio where a normal
harmonic in a persons voice get shifted so as to change the shape of the
output wave form.  This shape change can make a difference in the
requirement of peak power from the transmitter that it may not be able to do
with out reducing overall power.  On the other hand it could change the
shape in such a way as to reduce the peak demand on the XMTR giving the XMTR
more head room so you might be able to put out a little more average power
than before.  But be assured that there will be a phase shift in the lower
frequencies fundamentals with respect to the harmonics in the male voice
causing the peak demand to change one way or the other. 

	If the extending of the frequency is too great in the low frequency
end and not enough in the high frequency end then intelligibility will be
lost on weak signals during demanding circumstances.

	One must of course watch out for over drive of a pre amp stage while
trying to extend its roll off.

John, WA5BXO



-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of A.R.S. - WA5AM
Sent: Wednesday, February 20, 2008 5:02 PM
To: Discussion of AM Radio in the Amateur Service
Subject: [AMRadio] T3 Mod iron specs - Audio limitations, harmonics, etc.

Anyone know the approximate "designed" frequency range for a T-368
modulation transformer?

Also, if there is a website out there somewhere that has stock audio
specs on the popular commercial and military transmitters, I would be
interested in seeing it.

I think I know the answer to this, however I know there are a lot of
you out there that have a lot more knowledge than I do on the
specifics...
Let's say your transmitter is limited for 200 to 3000 cycles in the
audio section, either by coupling caps, cathode bypass, cathode
resistors, plate loading, and any transformers...  what is the result
of using an external EQ and audio chain that pumps audio from the mic
that is beyond either end of the audio range the transmitter is
allowed by design to pass?

I think this is a common mistake that a lot of us make that can cause
some serious harmonics and other artifacts.  I'd like to see a
discussion on this if any of you experts would care to chime in ;)

73
Brian / wa5am



-- 
"Money is only temporary, radios are forever" - Jim Little aka "the
old dawg"/K5BAI
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