[VHFcontesting] Coax Switch vs. Duplexer

nosigma at aol.com nosigma at aol.com
Sat Jul 9 22:28:40 EDT 2016

The below relates to FM Simplex frequencies.
If this is just for casual conversation use the diplexer it makes life very easy.  If this is a weak signal contest set up go with the switch.  After the January VHF/UHF contest I put a lot of effort into minimizing losses and getting VSWR, losses and reflected power as low as possible on my set up. I was running Yagi's on 144 and 440 with an FT8800 (dual band radio) single output.  I was using the Comet CF-4160 to let me run a single cable up the mast from the radio to the two Yagi's.  No single cable had a VSWR over 1.10 with most being 1.05 or less. With the CF-4160 inserted the VSWR to the 440 antenna jumped to 2.4  to 2.9 and the 144 was at 1.6 to 1.8 across the simplex frequencies.  Not a big deal at 144, a horrible outcome for 70cm.  I installed a coax switch (Alpha Delta) and saw the VSWR at 440 drop to below 1.4 at 144 and below 1.6 at 440.  

When I add start adding TE amplifiers,with integral pre amps, this summer I may use a triplexer between the radio's and and the amps but the added reflected power and insertion losses will be have no effect on output power and minimal effect on received signal since they are between the radio and the amps.  I will never use a triplexer or diplexer between the antenna and TX output or first stage RX amp again.


-----Original Message-----
From: Jarred Jackson <Jarred.Jackson at hotmail.com>
To: vhfcontesting <vhfcontesting at contesting.com>
Sent: Sat, Jul 9, 2016 7:01 pm
Subject: [VHFcontesting] Coax Switch vs. Duplexer

I have an IC-7000 with a common VHF/UHF output and switch between 2m and 70cm amplifiers/antennas using a Diamond CX-210A  coax switch. I am thinking of replacing the switch with a Comet CF-4160 duplexer that I have had laying around unused. I would like one less thing to do when switching between bands. It looks like there is 10dB less isolation (60 vs. 70 dB) and about 0.1 dB additional loss by using the duplexer. The radio sends the amplifiers 5W on 2m and around 28W on 70cm.

Any concerns / thoughts on making this change? It seems straightforward, but I have had the same thought on other changes that haven't turned out so well.


Jarred - KF2MR
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