Topband: W9AC's Omni VI+ key click mod

[Thomas Kuehl <ac7a@earthlink.net>]

Last year, I sought help from the list regarding key click mod's for the 
Ten Tec Omni VI + and was directed to Paul's (W9AC) mod. The Omni VI+ 
has been know for a fast leading edge (<1ms) which resulted in clicks 
that were especially noticeable when followed by an external amplifier. 
And even though I don't have an amp, I don't like the idea of being on 
the air with a wide, clicky signal. So across the holidays I delved into 
Paul's modification procedure, made the changes and put it on the air 
without knowing the end result.

This weekend I had access to a Tek 2465 oscilloscope and set it up to 
trigger off the output of my CMOS II keyer. Even though the scope isn't 
a storage scope, I was able to hold the envelope in place when sending a 
series of high speed dits. What I observed was a nearly identical rise 
and fall time; both about 4 or 5 ms. And no matter where I set the power 
level the envelope was maintained.

Paul's mod can be found at:

http://n1eu.tripod.com/Mods/omni_keying.htm

The keying mod is a bit tricky as it does involve changing surface mount 
components on the 9MHz filter board. I found that it was easier to use 
some discrete, through hole components instead of surface mounts. For 
C47, which is changed from a 0.01uF to a 4.7uF tantalum capacitor, I 
left the 0.01uF on the board and then formed the leads of a discrete 
4.7uF tantalum to terminate across the 0.01uF. I then bent the 4.7 uF 
over so that it laid to the edge of the PC board. R39 is then removed 
and replaced with a 0.22uF chip cap. The chip cap was much larger in 
width so I set it on its side and soldered it in place. Last, C37, a 
through hole 1uF electrolytic capacitor has a 10k resistor added in 
series with it. I removed the electrolytic and soldered a 1uF ceramic in 
one hole, bent it upward, and soldered a 10k 1/4w resistor in the other 
hole. The open ends were connected together and soldered.

I think think this is a very worthwhile improvement to the Omni VI+, 
that will be appreciated by other operators on the band. Thanks goes to 
Paul for his fine solution.

Regards, Thomas - AC7A (Tucson)


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