I use triplexers extensively here and they do a wonderful job of eliminating desense on Mode B (2m down, 70cm up) *The key is using good ones, not jun They key is using good ones, not junk. *If there is no reliable published spec for port to port isolation...it's junk.
All of mine are Comet CF-514J and isolate 2m/70cm/HF and can handle 500 to 800 watts on 3 segments. The port to port isolation is 60 dB, and I get 0 desense or intermode on my 2m downlink, even running 500w out on HF on the same coax that has both my 2m and 70cm Eggbeaters. I also use an ARR GASfet preamp in the 2m side...no issues whatsoever. ============================================ My main sat setup also uses Triplexers (and the unused ports are all terminated in 50 ohm loads (little bnc terminators).
70cm Tx > Triplexer 70cm Port In > 1/2" hardline Out to Tower > Dual Band Interlaced Yagi (common feed point)
HF Port on that Triplexer is 50 ohm terminated in shack. =========================================== I have even run 2 triplexers back to back for increased isolation to keep QRO HF out of my 2m Rx. Works just fine, and does not kill sensitivity for SAT work.
My Noise Floor is calibrated to -95 dBm for a 50 ohm resistor on 2m. The NF with an antenna is -91 dBm. I see passband noise on all linear sats (Mode B), with typical peak signal strength of -60 dBm. Typically,. I see 25 dB SNR when the passband noise is included.
...and not a hint of desense or intermod. I highly recommend the Comet Triplexers, even if you only need a duplexer, because the port to port isolation is higher. I found them as cheap as $28 on line...and as much as $35 on line. I bought 4 of them when I found them at $28.
Maybe this will help someone get the most out of their sat setup, and eliminate what can be a very frustrating problem.
73, N0AN
Hasan
On Sun, Nov 10, 2019 at 5:48 PM Robert Bankston via AMSAT-BB < amsat-bb@amsat.org> wrote:
Steve, I have had great success using a diplexer on the VFH side to eliminate desense on V/u satellites. I do not use a dummy load/terminator on the UHF port. Recently, I switched to a Mini-Circuits BLP-200+ as it has a smaller form factor. Note, the BLP-200+ has an advertised 0.5W power limitation. I have used mine with 10W output with no smoke released, yet. Your mileage may vary. 73,Robert, KE4AL On Sunday, November 10, 2019, 05:26:17 PM CST, Bob via AMSAT-BB amsat-bb@amsat.org wrote:
Hi Steve,
I asked myself a similar question and decided to measure things both terminated and un-terminated. Bottom line is you want to terminate that unused port.
Here is a story on my website: https://wb4son.com/wpblog/?p=2828
73, Bob, WB4SON
On Sun, Nov 10, 2019 at 6:18 PM AI9IN via AMSAT-BB amsat-bb@amsat.org wrote:
My satellite rig is two HTs running to an Arrow antenna. Trying my best to operate full duplex. When operating V/U I am using the UHF side of the Arrow duplexer as a high pass filter between the UHF antenna feed point and the UHF HT to keep the 2 m transmit signal from desensing the UHF receive.
But it only sort of works.
This set up leaves the VHF end of the duplexer open and just hanging. Would this setup work better with a 50 ohm load across that empty connection? (Sorry if this is a dumb or elementary question, but I'll never find out if I don't ask.)
All helpful insights are welcome.
Steve AI9IN _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership.
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Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb