[TenTec] I read this on the Omni-V group. The circuit is the same as the Omni-VI..

[Ralph Jerald 'Jerry'Volpe]

    product detector improvement
    <http://groups.yahoo.com/group/omni_V_562/message/128;_ylc=X3oDMTJxYnVqamYyBF9TAzk3MzU5NzE1BGdycElkAzIzNDUyMjIzBGdycHNwSWQDMTcwNTA2MzEwOARtc2dJZAMxMjgEc2VjA2Rtc2cEc2xrA3Ztc2cEc3RpbWUDMTI3NzU0ODg0MA-->



      Posted by: "w1eat" w1eat at yahoo.com
      <mailto:w1eat at yahoo.com?Subject=%20Re%3Aproduct%20detector%20improvement>
      w1eat <http://profiles.yahoo.com/w1eat>


        Fri Jun 25, 2010 6:05 am (PDT)



The CA3053 product detector (U3 on the IF/AF board) has been the subject 
of several mods intending to improve intermodulation distortion in the 
audio passband. W3TS has written about this at length.

The CA3028 is the same part as the CA3053, so I did some research and 
found a Harris Application Note AN5337 discussing the CA3028 in RF 
applications. In studying this info I noticed that Harris always biases 
pin 5 at 2/3 of Vcc, as opposed to 1/2 Vcc in the O-V. The datasheets 
also show this if you look close enough.

R14 and R15 form a voltage divider to provide this bias, so I put a 10K 
resistor in parallel with R14 to get the bias level to 2/3 of Vcc. The 
voltage at pin 5 in my radio is now about 5.6v, up from about 3.6v 
before the change.

The result is that the distortion goes away. Pile-ups now sound so clean 
and clear that it's hard to believe one little resistor can make such a 
difference.

Try it! You'll like it!

_____________________________

73, Jerry, KG6TT