Clark,
The Ten-Tec mod does help the in-passband intermod of the product
detector.
I don't have a manual here at work, but as I recall you increase the lower
capacitor of the divider capacitor pair after the IF amp buffer transistor
just before the signal goes into the product detector. This reduces the IF
level to the product detector and the intermod. The original capacitor is
a
1000pf and they have you increase it to 2200pf. Then to make up for the
loss
of gain you change a resistor on the opamp section of the manual notch
filter from 33K to 100K.
I'm very sensitive to inband intermod and I think this type of
intermod -if
very low- is what makes for a clean clear sounding receiver, more so than
a
very high front end intermod number, because all signals in the passband
generate phantom signals in the IF or product detector if they have a poor
intermod spec. This in-passband rating is not given in most reviews but is
very important to how clean a receiver sounds.
I have done this mod. to my older OMNI-V and it makes the receiver sound
much better.
I have the G4PKT product detector in my OMNI-VI option 3 and it is even
better. It is a much more involved mod. And the detector chip, an SL6440
is
no longer available.
73,Mike W3TS
-----Original Message-----
From: tentec-bounces@contesting.com
[mailto:tentec-bounces@contesting.com]On Behalf Of Clark Savage Turner
Sent: Monday, January 17, 2005 12:43 AM
To: tentec@contesting.com
Subject: [TenTec] OMNI VI product detector IMD
Hey all -
Anyone with an early OMNI VI do the Ten Tec modification to improve the
in-passband performance of the product detector? I do not mean the 2nd
order IMD mod that is done on the RF board (I have done this one and it
does not help).
If you have a fairly early OMNI VI, check with 2 stations in the
passband with S9 or so, see if you can hear the beat note. G4PKT
produced a daughterboard product detector to cure the problem and Ten
Tec did a fix for later OMNI's to take care of this problem.
I spoke to Ten Tec and got some instructions to add two caps to the
IF/AF board, I did what was suggested and got no improvement. I'll
call back to see if I have it correct, but just wonder if anyone has
taken care of this and knows exactly what the remedy is. I have the
G4PKT board but would rather not install it if the Ten Tec remedy is
sufficient.
Clark
WA3JPG
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