[AMRadio] Relay rating


Bernie Doran qedconsultants at embarqmail.com
Tue Dec 15 08:40:00 EST 2009


Hi John:
yes, easily on the lower freq. I have used power relays for antenna 
switching on 80 and 40 meters, that said, it is a low impedance(50 and 75 
Ohms)  and power in excess of 1200 watts  carrier.  the relays I used are 
the standard guys about 1.5 x 1.5 x 2.25  or so with a clear plastic case. 3 
PDT. do not switch under power. do not use for hi z as the voltage could be 
practically anything.   if you compare the contact size with the old 
dedicated antenna relays you will find contacts are larger, silver coated 
contacts are desirable for receive use and it would not hurt to use a set of 
contacts to ground the rx antenna term on transmit.  I think all of these 
guys are silver plated.  The only problem I have had is in winter, outside, 
they tend to get moisture in them and frost occures causing them to be a 
little sluggish. a small resister in a box with them would probably stop 
that.  I also have some open frame relays that I use for plate xformer 
primary power switching. they are double pole single throw and have a large 
gap when open, they would be satisfactory for open wire feeder.   I do not 
think there would be an issue up to 10 meters, above that there might be a 
impedance bump that could be an issue... all of these are available on ebay 
rather cheap. I tend to go with the DC relays as it becomes so easy to add a 
delay with just a fat cap across them.  you should have seen what happined 
to a Dow Key relay  when the AC power quivered one time.  another nice 
aspect of DC is that you can switch two different relays  with only two 
wires and two diodes  +  for one and - for the other relay. you can even use 
the coax and feed DC into and out with chokes.  They are not going to work 
with break in but if you are here, I do not think that is an issue, 
Bernie W8RPW
----- Original Message ----- 
From: "John King" <k5pgw at yahoo.com>
To: <amradio at mailman.qth.net>
Sent: Monday, December 14, 2009 10:45 PM
Subject: [AMRadio] Relay rating


> Will 10 amp rated contacts on a relay handle 300 watts of carrier  from an 
> AM transmitter? Your opinion based upon your experience will be 
> appreciated. Thanks and 73, John, K5PGW
>
>
>
>
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