[TowerTalk] Switching Multiple Rotors

[Jim Lux]

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.