On 9/4/13 4:43 AM, Pete Smith N4ZR wrote:
In the May 2012 NCJ, I had an article on using an inexpensive
Chinese-made RF wireless relay board to switch 8 receiving antennas
without a separate cable, ~400 feet from the shack. The idea, suggested
by GM3SEK, was to couple the 300-MHz from the remote control to the coax
and pick it off at the far end, using short lengths of hookup wire as
the coupling loop. Works very reliably. I'm not sure if the hardware I
used can be programmed to switch most or all of the SPDT relays at once,
but there are lots of variations available online for peanuts.
Velleman has a nice 8 relay module for $50 with 2 wire serial input, or
and RF module that you can solder in. At least from the serial port
aspect, you can set one relay at a time, or all 8 at once. (e.g. you
send a byte that has all 8 relay positions). I use them to control RCS-8Vs
The coupling loop scheme is one way, another is a T connector with a
tiny capacitor in the "arm".
It doesn't take much coupling to make this work.
Taking 2.4GHz WiFi/Zigbee/etc as an example..
100 m through air has 80 dB loss (so radiating +20dBm gets you -60 at
the receiver)
RG-213 is about 50 db/100 meters at 2.45 GHz
So your coupling doesn't have to be all that great.
I speculate, but have not tried, that coupling to the *outside* of the
coax would probably work: all you're trying to do is get somewhat better
than free space, and launching the wave is a sort of non-critical thing.
Of course, if you wanted to be fancy, by all means, set up a G-line
launcher, etc.
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