[TowerTalk] antenna relays

[Jim Lux]

On 7/22/11 7:18 PM, Rik van Riel wrote:
> On 07/22/2011 08:35 PM, Felipe Ceglia wrote:
>
>> For 50 ohms switching I usually use Omron G2R relays.
>
> Thank you Felipe,
>
> It looks like the G2RL-24 relays are the DPDT relays
> that I want.  They are available in various coil voltage
> ratings, but it's easy to find the 12V DC ones.
>
> Looks like Mouser has these for sale for just over $2
> each.  Building an antenna array might be cheaper than
> I expected :)
>


Here are the things you need to think about (and unfortunately, most of 
them are not in the datasheet for the relay, so testing/trial and error 
is usually how it goes)

1) What's the capacitance of the relay signal circuit when "open" and 
"closed"?  At 2MHz it probably isn't a big deal, but at 30 MHz a few pF 
makes a difference.

2) What's the AC resistance (the relay may be fine for 10Amps at DC or 
60Hz, but not so great for 30MHz)

3) What's the breakdown voltages  (you can take the DC/60Hz ratings 
here.. it's different for RF, but not hugely different.  Just don't 
choose a 500V relay for a 450V application

4) Leakage C between signal circuits and coil..  This is actually 
potentially troublesome, although at the "few watts" power it's not as 
big a deal, but at 1kW levels..  RF will couple into the surface of the 
coil and work back along the control leads.


Here's some notes collected a few years back
http://home.earthlink.net/~w6rmk/relay.htm