[TowerTalk] RF Relay Question

Dr. James C. Garland 4cx250b at muohio.edu
Sun Dec 16 09:32:51 EST 2007


Thanks to those replying to my question about RF relays. Many helpful
suggestions. My application is for an indoor switching unit to select HF
linear amplifiers.  The relays are for an intermittent duty cycle, will
never be hot-switched, but should be good up to 50MHz, and should easily
handle 1.5kW with a reasonable safety margin.  They will normally work only
into 50 ohms, but should have enough RF insulation to handle mistakes, such
as accidently transmitting into an open circuit.


The best open-frame relay I've found is the Deltrol 100RF series. They have
a special dielectric that will withstand high RF voltages, with contacts
rated at 10A.I bought ten of them at Dayton for $0.50/ea a few years ago,
and now wish I'd bought a hundred.  Unfortunately, they're rather scarce and
expensive. Some are for sale now on eBay
QQitemZ160179799014QQcmdZViewItem )  but the guy wants $25 each. Last time I
checked, Surplus Sales had the SPST version for $15. 


Some people suggested vacuum relays. A couple of years ago I built a couple
of switching boxes using inexpensive vacuum latching relays. Latching relays
are nice because they require only a momentary pulse to activate them. My
switchbox runs off a small 24V wall wart, but three 9V batteries will power
it almost indefinitely. The box shown uses SPST relays, so the port-to-port
isolation isn't high. This was not important for my application. You can see
it at





Jim W8ZR

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