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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