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Author Topic: Sharing one antenna with two radios in different rooms at same QTH - ? switch  (Read 6986 times)

Posts: 2

« on: April 29, 2013, 02:10:00 PM »

A simple question - how to safely share one antenna with two radios in different rooms at the same QTH?

Is there a safe way to do this rather than using a 2:1 switch in reverse and risk transmitting to ground?

Thank you very much.

Posts: 876

« Reply #1 on: April 29, 2013, 04:48:20 PM »

A few questions:
(I'm assuming both radios are similar, e.g. HF transceivers)
1. how much power do you intend to run (the answer will help determine which switching device(s) that you need)?
2. what is the distance between the rooms; are they on the same or different floors?
3. will both radios need both transmit and receive switching?

There is equipment that can easily do this.  Start by checking out (for the high-end products) and this

GL, 73, Rich, K3VAT
« Last Edit: April 29, 2013, 05:13:23 PM by K3VAT » Logged

Posts: 2

« Reply #2 on: April 29, 2013, 07:57:15 PM »

Thanks for your reply. Here are answers to your questions:

1. No more than 200 W
2. Distance between rooms - about 100 ft; rooms are on the same floor
3. Both radios will need both transmit and receive switching.

I looked at as you suggested. It seems that their "Transco Type Switch" might work. Would you happen to know what the control signal needed for this switch would be?

Thank you very much.

David, WD7I

Posts: 22

« Reply #3 on: April 30, 2013, 07:38:59 AM »

You might want to look for a transfer relay and wire it up so that the unused transceiver is connected to a dummy load just in case you accidentally transmit with the switch in the wrong position.  You can do the same thing with a couple of standard switches or relays, but a transfer relay is best.

Be sure to check isolation between ports to ensure that you don't get enough transmit RF leaking through the unused port to damage the other transceiver.  I've heard that 10 mW (10 dBm) is a decent rule of thumb for what the RX port of a transceiver can withstand.  Since 200W equates to 53 dBm (10 log P1/P2) you need at least 43 dB (53 dBm-10dBm) of isolation to keep the receive port at 10 mW.   More would be better and I personally would aim for no more than 1 mW leakage into the unused transceiver.

You could go by the relay or switch specifications but I prefer to verify when the consequence of failure is a toasted radio.  This is easy to test if you have a lab type power meter that can measure milliwatts like an HP-432 or HP-435.  Though not a typical ham shack power meter, lots of of radio techs and ham microwavers use these or similar meters so you may know someone with the appropriate test gear.

Perhaps the simplest, cheapest and most robust solution is a simple patch panel.  Two ports for the radios, one port for the antenna and one for the dummy load.  Just be careful to never connect the radios together.  If you're prone to mistakes when tired or in a hurry, you might want to arrange things so the cables won't reach far enough to hook it up wrong. If you used quick connectors like BNC it would only take a few seconds to swap the cables around but it would not take long even if you used PL-259 connectors.

Posts: 14788

« Reply #4 on: April 30, 2013, 07:53:06 AM »

If you are talking about HF then it should be pretty obvious if the antenna is not connected to the transceiver you are using - no noise or signals in the receiver.

Personally, I prefer patch panels. Better isolation, if arranged properly its easy to see which radio is connected, and it provides an easy point to patch in other options or test equipment in the future.


Bob  AA4PB
Garrisonville, VA

Posts: 18072

« Reply #5 on: April 30, 2013, 08:29:35 AM »

I think there is a solution similar to a 3-way light switch in a hallway (where it can
be turned on or off from either end) but that will require a couple length of coax
between the rooms:  if they are 100' apart that might not be a good solution.

The simplest approach is a coax relay with an extra set of contacts.  Dow-Key and
others made these years ago, and there are still some around if you can't find
a new one.  (At HF you could also use a standard relay with heavy-duty contacts.)
Or you can use a standard relay in parallel with the coax relay to get the extra

Using a SPDT coax relay, one room would have a push button that applies power to
the relay, using the auxiliary contacts to latch it in the ON position.  The other station
has a momentary push button in series with the power lead (hot or ground side) that
disconnects power and unlatches the relay, causing it to switch to the feedline to
that station.

Then either station just pushes the button at their end and the antenna is attached
to their rig, regardless of the state it was in previously.

Personally I wouldn't worry about transmitting into an open circuit:  the rig should have
adequate protection, and the high SWR should be an immediate clue that the antenna
isn't connected properly if the lack of signals didn't do the job.  You can, as suggested
previously, add a dummy load for the other transmitter, though that complicates the
switching a bit more (if you can't find a "transfer" relay) and also doesn't give you the
high SWR indicator that you don't have the antenna connected.

Posts: 91

« Reply #6 on: April 30, 2013, 06:21:37 PM »

+ on patch panels...I use bnc connectors on everything these days.

Posts: 76

« Reply #7 on: April 30, 2013, 07:47:23 PM »

Another source for good ideas comes from the ham contesting world.  Search the web for SO2R (Single Operator Two Radio) station designs and you'll see what I mean.  Basically you can partially or fully automate the switching process to make it much safer for your radios to coexist.  The goal is to eliminate human error as much as possible.  Otherwise sooner or later you just might accidentally feed the output of one radio into the input of the other.

If you're going to use those radios for separate bands (like using one radio only on 40 meters and the other only on 20, 15, and 10) then I'd seriously investigate putting bandpass filters on their inputs.  The filters add cost but rebuilding the front end of a modern transceiver is much more expensive.

Good luck and 73,  Jim W.

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