[Milsurplus] TBX Modulation

[Bob Wilder]

 From what I have observed for the past few years since becoming interested 
in Naval radio gear, that almost ALL equipment was originally designed to 
operate CW and AM was an after thought. Viable communications was expected 
to be on CW and if voice was needed for VERY short range then AM was 
used.  60% modulation would be about the maximum you can expect.  Go back 
and look at just about any navy transmitter of the period and you will find 
ratings such as 200W CW and 25 watts AM, or 100 watts CW and 15 watts 
AM.  This says a lot on what was expected of the RM aboard.  CW first and 
voice later on.


At 05:21 AM 3/27/2005 -0500, Robert Flory wrote:

>Hi,
>I'm flying without a manual, here, and beating my head against the wall to
>get more than about 50 percent modulation out of TBX-4 and TBX-6 units.
>It seems that theory ought to allow for 80 or 90 percent, but since both
>run about the same, I'm wondering if the low modulation is normal.
>
>Operating conditions:
>Self-Excited Mode
>Ep=500V
>Eg2=200V
>Eg1= -75/80V
>Eg3= -30V
>
>The modulator drives the suppressor g3 well into positive range which
>suggests that modulation audio is wasted.  RCA 837 spec sheet wants a
>larger bias on a suppressor modulated amp, like -65V.  When I look at the
>voltage divider that derives the suppressor bias from the grid bias, there
>is no way to significantly increase the magnitude of the bias by moving the
>tap.
>
>Any thoughts?
>
>Rob Flory
>www.home.earthlink.net/~navyradio
>
>
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Bob & Carole Wilder
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Asst USAF State MARS Director- Alabama
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