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Using relays to switch rig coax cables to common antenna coax

Dec 1st 2016, 02:20

WA2P

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Hi, I'm working on a station accessory that will move the cw keyer, headphones, and station speaker between three rigs. The coax from each rig must be switched also to a common antenna coax. I'm planning to use SPDT relays to handle the coax switching. Energizing the selected rig's relay would hook the rig to the antenna, and the other rig's relays would ground their coax cables through the normally closed contact. My question is how much of a gap between the relay contacts is needed to protect the rigs with grounded coax lines? Would small open frame relays be adequate? Thanks for any suggestions. Pat - WA2P
Dec 1st 2016, 03:53

AA6E

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Depends on the power level, SWR, and frequency. Tell us more! Open frame relays are commonly used in low to moderate power equipment, where a 100 watt transmitter with a 50 ohm load and 1:1 SWR would imply a peak voltage of 100 volts or so. Vrms = sqrt(R x P).

So a relay with contacts rated for 120 vac and at least 2 Amps might be OK for HF, especially if you don't try "hot" switching. High SWR is another story.

73 Martin AA6E
Dec 1st 2016, 05:23

WA2P

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Hi Martin, I would be operating HF; two of the rigs put out 100 watts, and the third, an old HT-32, puts out less. The antennas are 50 ohm, and have SWR values in the neighborhood of 1.2 to 1.3. Hot switching is out of the question; that's asking for way too much trouble!

Pat - WA2P
Dec 1st 2016, 18:35

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
http://www.w8ji.com/rf_relay_contact.htm
AD5X and W8ZR have tested relays for projects on their respective web sites if you just want to copy something that works.

Zack W1VT
ARRL Senior Lab Engineer

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