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Antenna switch question

Jul 17th 2012, 19:41

KF7SXD

Joined: Dec 13th 2011, 23:51
Total Topics: 0
Total Posts: 0
I want the ability to use more than one radio with the same antenna without having to pull my rigs out and swap coax cables. Can I use a coax antenna switch in reverse (use the multiple port side for radios and the single port side to the antenna)?

I haven't found anything in the manufacturers info yet that says I can or can't use the switches this way, so I'd like some information before I order a switch.

Thanks.
Jul 17th 2012, 22:12

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

It is certainly possible, but may not be a good idea, as it is very easy to accidentally transmit into an open circuit or ground (if the switch shorts the unused contacts to ground).

What normally works better is a patch panel--in which you connect all your gear to a panel filled with UHF bulkhead connectors. The connectors should be arranged logically--perhaps three antennas on one side and three rigs on the other--so it is very easy to visually check that you don't have two rigs hooked up together.

But, if you are really talented, it is certainly possible to build some electronic circuitry to insure that a radio will only transmit when connected with the proper antenna--this can be as elegant or as complex as your skills allow.

Zack Lau W1VT
ARRL Senior Lab Engineer
Jul 18th 2012, 04:10

KF7SXD

Joined: Dec 13th 2011, 23:51
Total Topics: 0
Total Posts: 0
Me? Electronically talented? LOL

Thank you for the advice, I'm glad I asked before spending money. I like the patch panel solution as it will prevent any mistakes I might make. I really don't want to damage any equipment.
Jul 20th 2012, 13:18

K0BG

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
You could use what is often referred to as a cross switch. MFJ sells one, advertised as an amplifier bypass switch. In one position it is A in to 1 out, and B in to 2 out. In the other position it is A in to 2 out, and B in to 1 out. Put a dummy load on the used out port, and you're in business. However.......

As Zack mentioned, unless the switch in question has very good port to port isolation (>60 dB), you run the risk of damaging the unused transceiver, even though a dummy load is essentially shorting it out. I haven't a clue how much isolation the MFJ has, and MFJ doesn't say either.

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