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Re: [TenTec] Isolation of diode T/R Switch on Corsair

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Isolation of diode T/R Switch on Corsair
From: Ken Brown <ken.d.brown@hawaiiantel.net>
Reply-to: ken.d.brown@hawaiiantel.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 07 Jun 2009 13:54:47 -1000
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
> I'm seeing voltages at the RX ANT jack that are 1/1000 of the ANTENNA output 
> voltage on 80 and 40 meters, and only 1/165 at 10 meters.  These tests were 
> made using a 50-ohm dummy load connected to the ANTENNA connector.
How are you measuring the voltages? Oscilloscope with 10X probe, 10 
Megohm impedance, properly compensated? A poorly compensated scope probe 
might explain differences in your measurements on 80/40 versus 10 
meters. Even if the compensation of the probe is adjusted properly for 
correct voltage division at 3 MHz and at 30 MHz, the capacitive loading 
of the probe connected to the circuit under test may have a lot more 
effect on 10 Meters than at 80 Meters. Are all of your voltage 
measurements above the noise floor of your measuring setup?

Voltage ratio of 1/1000 is power ratio of 1/1,000,000, or 60 dB. That 
seems like pretty good isolation to me. Voltage ratio or 1/165 is power 
ratio of 1/2275 or 44 dB, which is maybe good enough too.


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