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" <[email protected]> To: <[email protected]> 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
