[Signalone] MilSpec 1030 VOX

[signalone@mailman.qth.net]

This is a copy of my response to Uli posted to the group...

In a message dated 12/21/01 2:49:40 AM, Ulrich.Graf@ulm.siemens.de writes:
>Just by chance I wanted to try vox operation I normally don't use and found
>the modulation level to be less than half of the average level needed to
>feed the rig correctly. I could't even get sufficient output in vox mode. My
>first investigation did not show any impact of the PTT/VOX switch control
>onto the mic level. Do you eventually have an idea?

Usually the VOX does not work well with a low impedance microphone.  Using a 
Hi-Z microphone does wonders for VOX operation and there should be plenty of 
drive for proper operation.  If not, I'd first look for proper gain from U5A, 
U5B, and U7A on the power supply board.  Also, R35 on the inverting input to 
U5B (pin 6) should be changed to 4.7 K from 2.7K.  This should make the DC 
output of U5B (pin 7) read +5.18 volts no signal and +9.53 volts with signal.

>The radio works very satisfactorily now, particularly after the integration 
of
>a relay switched highpass filter box to avoid the strong 2nd order intermod
>distortion caused by the large BC signal density here in Europe.

I have had to do much the same thing here with my early 1030 also - and i'm 
only in michigan!  The first 30 units (or so) they made did not perform well 
at all.

Outside of the IF improvements, the biggest improvement to the 1030 is to 
open up the receive audio and put an audio low pass filter in line (like the 
service bulletin on the Collins KWM-380).  Run a frequency response graph on 
the audio stage and you'll see what i mean.  I can advise what components to 
change to save you the work if you'd like.  Also, with the scarcity of the 
Collins 380 mod boards, i use the toko low pass filter chip.  If memory 
serves me right, I found out about that chip from you !

Thanks & 73,
-paul   w8zo
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