Omni VI 2nd order IMD Mod

Clark Savage Turner WA3JPG
Thu, 28 Mar 1996 10:01:14 -0800

> Would appreciate hearing from anyone who ever installed the subject 
> modification in their Omni VI.

Hi John:

I got a late model OMNI with the mod installed by the factory...and 
apparently the newer firmware.  I called them about installing RF
PIN diodes throughout (they use PIN like diodes not designed for that
purpose...and some hams think that they are inferior to the other
PIN diodes designed for the purpose), and they sent me the mod kit.
I looked and found it already done, the factory said it is standard
since about a year ago.  It looks very, very simple to do. 
Ten Tec sent me the parts for nothing after I had asked.  Can't 
beat that.

I read some articles from a UK ham journal about the diodes and
second order IMD.  The article says that the diodes used by Ten 
Tec are very good in the application there, and replacement by the
HP diodes everyone else is using is not called for, and in fact,
degrades performance.  It seemed to say that installing the HP
diodes (I think they were HP, they are the standard RF switching
PIN diodes)  -- increased losses over the ones Ten Tec used.  This,
of course, increases other specs of receivers, as any attenuator
does.  SO, if you want to increase the IMD performance of your 
receiver, use the attenuator, hi hi.  If you are interested, I can
dig out the reference for you.  There are more than one article
mentioning 2nd order IMD in the OMNI VI and other radios.