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Re: [TenTec] Omni VI+ receiver UHF intermod

To: "tentec@contesting.com" <tentec@contesting.com>
Subject: Re: [TenTec] Omni VI+ receiver UHF intermod
From: "Jim Brown K9YC" <k9yc@audiosystemsgroup.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 13 Dec 2007 09:36:14 -0800
List-post: <mailto:tentec@contesting.com>
On Thu, 13 Dec 2007 11:51:10 -0500, Jack Mandelman wrote:

>One might expect that the 600MHz energy 
>would not make it through my antenna tuner (an L-network in LP 
>configuration).  However, at 600MHz parasitic lead inductance in the 
>tuner may make it behave not at all as a LP filter.  Thus 
>600MHz energy could be transferred to the Omni.

Yes. It must be remembered that 1) ANY non-linear device can do this 
mixing; and 2) ANY network has stray components that make it act very 
differently from what is expected far from its design frequency. It 
is well known that transmitter output stages produce intermod from 
other nearby transmitters if RF from those other transmitters is 
allowed to enter the transmitter. Devices called circulators are used 
at VHF and UHF transmitter sites to prevent this from happening. 
Major UHF TV stations are licensed for 3MW or more ERP. If you're 
close, and in the main lobe, they can easily put enough RF in your 
radio to excite intermod. 

I work in pro audio (and am Chair of the AES Technical Committee on 
EMC). I regularly preach about the misconception that because an 
audio stage or device has a low impedance (and may be balanced) at 
audio frequencies, its impedances and balances are VERY different at 


Jim Brown K9YC

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