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Re: Topband: Switching Beverages

To: <n4zr@contesting.com>, <topband@contesting.com>
Subject: Re: Topband: Switching Beverages
From: "ZR" <zr@jeremy.mv.com>
Date: Wed, 2 Feb 2011 11:20:53 -0500
List-post: <topband@contesting.com">mailto:topband@contesting.com>
Im currently using a pair of Ameritron RCS 4's and their isolation is 
horrible as designed. Im working on my own design using cheap 1 GHz relays 
with 70dB of isolation at HF. Then I can also reduce the feeds from 2 to 1 
coax from each 2 wire Beverage.

At the current rate of snow this winter I'll have until May before anything 
gets installed.

Carl
KM1H


----- Original Message ----- 
From: "Pete Smith" <n4zr@contesting.com>
To: <topband@contesting.com>
Sent: Wednesday, February 02, 2011 7:30 AM
Subject: Re: Topband: Switching Beverages


> Thanks to everyone who responded.  Lee's answer seems representative of
> the bulk of the mail I received.  Back to coax switching!
>
> 73, Pete N4ZR
>
> The World Contest Station Database, updated daily at 
> www.conteststations.com
> The Reverse Beacon Network at http://reversebeacon.net, blog at 
> reversebeacon.blogspot.com,
> spots at telnet.reversebeacon.net, port 7000
>
>
>
> On 2/1/2011 9:42 PM, Lee K7TJR wrote:
>>     Pete, here is my take on switching Beverages, It is a lot harder to 
>> make
>>   a switch with very good isolation at 500 ohms than it is at 50 or 75 
>> ohms.
>>   You need very good isolation between connections so that your 20 to 30
>>   dB notches are not destroyed by leakage from another antenna. What you
>>   save on transformers will surely be spent on doubling up relays to get
>>   decent isolation.
>>      If you consider a relay with a few pf of feedthru capacitance, it 
>> will have
>>   a certain reactance at the operating frequency. This reactance will 
>> form a
>>   voltage divider with the switched impedance. If it is 500 ohms there 
>> will be
>>   a lot more feed through than if it was 50 or 75 ohms.
>>     What ever you do for switching, think it through and make sure you
>>   consider the isolation between antennas. Keep looking as there are some
>>   that have solved this problem before.
>> My 2 cents worth.
>> Lee  K7TJR
>> _______________________________________________
>> UR RST IS ... ... ..9 QSB QSB - hw? BK
>>
>>
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK 

_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK

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