[Antennas] Remote antenna switching

Tue, 16 Apr 2002 22:45:17 +0000

Steve

I have built many home brew remote antenna switches over the years. As long 
as we are talking about frequencies below 30mhz, construction and relay 
choice is not  overly critical.

The first consideration is power handling capability. As long as you have 
reasonable SWR's then you need not worry too much about voltage breakdown 
or arch over. What is critical is the "contact current rating". Most relays 
are rated at DC or 60hz AC and not at RF frequencies where current flow 
tends to be more on the surface and not though the contact. As a rule of 
thumb I de-rate off the shelf relay current carrying capability by half. 
The only relays I ever fried were ones I inadvertently "hot switched" (i.e 
with power going to the antenna).

At 150 watts your contacts need to be able to handle about 2 amps, at 1500 
watts it is more like 6 amps. I have used the Radio Slockk 275-218 relays 
for years. I run both sets of contacts in parallel giving the equivalent of 
20 amps DC / 10 Amps RF de-rated. I connect the individual antennas to the 
center pole, the "NC" contacts are all bussed to ground  (that way any 
unused antennas are always grounded by default) and the "NO" contact is 
bused to the feed to the shack.

If your not in too big a hurry watch the auctions for relays on Ebay. a few 
years back I won a bid on  25 relays which were very similar to the Radio 
Slockk units for only $10 for all 25. The catch was they had 24 Volt coils, 
but with the money I saved it was easy to build a small 24 volt supply to 
power the remote switch.

  My most recent remote switch handles 10 antennas, I'd be glad to send you 
a couple of jpg files with pictures, but I'm not sure it would help 
much....your call

Dave
NR1DX

At 02:11 PM 4/16/02 -0400, you wrote:
>Good afternoon,
>   I am in the process of completing a couple of projects to get back on 
> the air. I have about four different wire antennas up and will possibly 
> put up one more.  I was wondering if there was a homebrew switching unit 
> I could build so that I may run one feed line into the shack.  I am also 
> open to commercial suggestions but would prefer to build it for the 
> experience.  Thanks and have a great day..
>
>73
>Steve
>N4TKP
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