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Author Topic: Use of Transfer Relay for 2 Transceiver/2 antenna switching  (Read 1801 times)
N1JR
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Posts: 15




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« on: December 16, 2011, 04:12:06 PM »

I have two transceivers, a 600 watt THP K1.1 amp and two HF antennas (HEX and 40m End Fed) to manage.  I have a few new heavy duty Dow Key Latching Transfer relays (412AR-3801a).  My design uses the Dow transfer relay to alternately switch the two antennas between the two transceivers such that each antenna alternates between each of the transceivers but the same antenna cannot ever be seen by both transceivers at the same time.  I have a manual push button switch box employing a small secondary latching relay to manage colored LEDs to indicate which antenna is connected to which transceiver.  The specs for the Dow Key Relay shows 85 db isolation and at least 800 watts rf power capacity in the 0-1 Ghz range.

As far as risks, the biggest risk I would foresee is that the wrong antenna than expected is connected to a particular transceiver.  An unexpected SWR would signal the problem.   

I would like to ask for thoughtful and knowledgeable feedback on this idea.  My concerns are whether I am overlooking something which could result in damage to either transceiver.  (I've been a ham long enough-54 years-to know that I don't always foresee everything:)  Many thanks for your thoughts.  Jim, N1JR
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AI7RR
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« Reply #1 on: December 16, 2011, 09:44:47 PM »

A problem that I've experienced personally with multiple transceivers and antennas has to do with rf coupling from one antenna to the other. I've inadvertently taken out the front ends of 2 ( I'm a slow learner) transceivers by transmitting 600 - 800 watts on one and forgetting to ground or otherwise isolate the other rig. If you have room to adequately seperate your antennas, you should have no problem. Test and measure should surely be done.

73, Roger
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K2DC
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« Reply #2 on: December 17, 2011, 06:44:35 AM »

Jim,

    I don't see a problem there.  The switch will open-circuit the unused antenna and transceiver so coupling will not be an issue.  It will take the power with no problems.  And the isolation is 85 dB up to 1 GHz, so even at 600W there shouldn't be a risk to the front end of unused transceiver.

73,

Don, K2DC
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N1JR
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« Reply #3 on: December 17, 2011, 08:26:31 AM »

Many thanks Roger and Don for your comments.  I should clarify that the current design will always have one antenna connected to one (or other) transceiver, and will not ground or open the input of either transceiver.  In other words,  the transfer relay just flips the antennas between the rigs.  I think Roger may have a point about one antenna feeding rf into the other antenna and into the other rig (whether it is turned on or not).  Perhaps the safer approach is to use one relay to switch antennas and to consider using a second relay to ground the antenna connection of the unused rig (even if the antenna itself is not disconnected). Many  thanks for getting me thinking.  73, Jim, N1JR
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