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Re: [TenTec] Omni VI+ receiver UHF intermod

To: tentec@contesting.com
Subject: Re: [TenTec] Omni VI+ receiver UHF intermod
From: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Reply-to: geraldj@storm.weather.net,Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Wed, 12 Dec 2007 22:43:10 -0600
List-post: <mailto:tentec@contesting.com>
On Wed, 2007-12-12 at 21:21 -0500, Jack Mandelman wrote:
> In the OmniVI only TX rf is routed through the LPFs on the LP filter 
> board; receive does not see the benefit of these LPFs.    However BPFs 
> on the front end board are used for both TX and RX.  But in the presence 
> of a very strong UHF signal, could spurious mixing could occur in the 
> switching diodes before any filtering?   These diodes are used to steer 
> rf from either the main or AUX antennas to the front end.
> Jack K1VT
One would hope that the diode on current and the diode blocking voltage
were greater than the external UHF signal could apply to the diodes. But
mixing could occur, between two or more external strong signals if the
biases weren't enough or the UHF signals were strong enough. Using true
HF PIN diodes instead of switching or 1N4007 should also help prevent
that mixing. And the external TVI filter has been proven effective in a
couple such cases.

73, Jerry, K0CQ

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