[Milsurplus] RT-68/GRC - the continuing saga

[WA5CAB at cs.com]

Actually, speaking both as an EE and as a military radio collector rather 
than a 50's surplus converter, the book is poorly and sloppily written.  I traded 
a useful piece of mil gear for one and discovered that I had made a bad deal. 
 Its treatment of nomenclature is abysmal.  I didn't get far enough into it 
before I put it out with the other trash in disgust to find the paragraph 
quoted below but I'm not at all surprised.  The whole treatment reminded me of the 
immediate post-war Surplus Conversion Manuals.  "sneak up on the radio chassis 
and remove everything in sight".

If your goal is interoperability with Jap transceivers, the proper place to 
insert a deviation control is between terminal 2 of L-137 and the top of R-130. 
 However, if your monitor receiver is a narrow band one and you can hear a 
carrier but no audio when you key the RT-68 and speak into microphone or 
handset, the transmitter deviation is not the problem.  Even if you speak loudly 
enough for full deviation of the RT-68, the narrow band receiver would hear 
something, just maybe not intelligibly.  Check the two 1R5 modulators first.  And 
your handset or microphone.  If the transmitter is being modulated at all, any 
FM receiver tuned to it will hear something.

And on the receive side, the solution is not to turn up the gain.  There 
isn't enough available.  What you need to do is to realign the IF and 
discriminator .  In the alignment procedure given in Section V of TM 11-289 dated 12/53, 
substitute 1.405 for 1.430 and 1.395 for 1.370 throughout.

In a message dated 1/30/2007 6:33:20 PM Central Standard Time, 
bsugarberg at core.com writes: 
> 1. Get a copy of "Mil Spec Radio Gear" by Mark Francis KI0PF.
> 
> 2. Quoting from that book:  "The standard transmit deviation is too wide
> for use with modern FM ham gear.  BUT there is a quick and dirty fix. Just
> put a resistor in series with the mic input.  You can do this inside the
> handset switch, or inside the radio itself.  Start with a haywired 5K pot
> to determine the value you want, and replace it with a corresponding fixed
> resistor.  Make up for the distant station's lower deviation by simply
> turning up the volume."

Robert Downs - Houston
<http://www.wa5cab.com> (Web Store)
MVPA 9480
<wa5cab at cs.com> (Primary email)
<wa5cab at houston.rr.com> (Backup email)
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