An additional 20dB of isolation can be realized by replacing the antenna Tee connector with a circulator. Port A to B tuned to the TX frequency, Port B to C tuned to the RX frequency. Connect TX to port A, antenna to B, Receiver to C.
I'm using a set of WP-639 and with this setup I am seeing approx 102dB of rejection from the TX to RX port and 97dB the other way. On Wed, Sep 8, 2010 at 8:40 PM, Scott Zimmerman <[email protected]> wrote: > Rich, > > The short answer is: You need to find a bigger duplexer. Four 8" cans > would work well such as a Wacom WP-641. You could simply call and order > one if Wacom was still in business. (RIP) Unfortunately Tx/Rx bought > them years ago for the name and to quash competition. They can be found > occasionally for around $600 or so on the used market. > > Other alternatives are as follows: > 1) You can use two antennas and split the 639 duplexer so that 2 cans > are in series between the TX and the TX antenna, and the other two are > in series between the RX and the RX antenna. Terry WX3M a list member is > doing this with VERY good results on one of his VHF machines. Of course > this involves the expense of additional feedline and a second antenna. I > think you said you had this machine on an 80' mast. 50' or so of > vertical isolation coupled with the additional isolation of splitting > the duplexer *may* be enough isolation to get rid of all the desense. TX > goes on bottom, RX on top. > > 2) Buy additional Band Pass / Band Reject (BPBR) cans. You can add these > additional cans between the Tx and/or Rx and the duplexer. These cans > will give additional isolation. Even if you can find just Pass or Notch > cavities, tune them and put them in the correct place. > > With both of the above options, you are looking to add to the isolation > between your transmitter and receiver. You'll find you'll do best by > adding cans to your transmitter that notch side-band noise at your > receiver's frequency. In other words, do what you can to insure your > receiver is not hearing your own transmitter's sideband noise on it's > input. Pass cans tuned to the TX frequency or NOTCH cavities tuned to > your *RX* frequency placed in the transmit line are your best hope. > > Good luck, > Scott > > > > Scott Zimmerman > Amateur Radio Call N3XCC > 474 Barnett Road > Boswell, PA 15531 >
