Brian Kelly wrote:
I'm looking for a source for small inexpensive 12VDC relays which are
usable for cold-switching ~200W of RF at frequencies up to 30 Mhz. The
relays would be used to remotely select several single-band antenna
tuners and several end-fed vertical wire antennas strung up into some
tall trees. The "tuners" would be link-coupled tapped parallel tank
ciruits, one tuner per band.
There would be two relays needed per band, one to switch the 50 ohm
coax from the shack to the specific tuner and the other at the output
end of the tuner to select the particular wire. At the input ends of
the tuners the RF voltage would be around 200V @ 2 amps. At the output
ends of the tuners (depending on the feedpoint impedance) the RF
voltage could go into the 2kV range at very low currents. So basically
I need some sort of relays which can handle 2kV of HF RF at 2 amps.
Single pole NO non-latching reed switches would do the job.
I know I can use surplus vacuum relays but at $35-40 a pop that ain't
gonna happen.
Any and all suggestions will be appreciated.
By coincidence, I was reading an electronics mag over breakfast today,
and saw this press release:
"Crydom has launched a high performance miniature reed relay boosting
carry currents by 33%. Fitting a full electrostatic copper screen that
completely enshrouds the relay coil, a reduction in power loss is
achieved. Lower loss means lower self heating – enabling an increase
in carry currents to an industry leading 4A RMS at 30MHz from the
miniature 30mm x 10mm package.
"The 6 Series is designed for next generation HF antenna couplers and
filter circuits where improved RF performance and higher packing
densities are required.
"The hermetically sealed high vacuum reed switch will isolate 3kV
minimum (DC or RF peak) making it suitable for a range of Test Equipment
and Electromedical applications where high voltage, high current pulses
are generated."
Without necessarily endorsing that particular product, there are a few
interesting points:
* Switching in HF antenna couplers and filters is now a recognized
market.
* Reed relays can handle this kind of service.
* Coupling into the coil can be a problem, which may suggest making your
own. Crydom use a shielded coil, and an alternative idea ISTR is to wrap
the glass relay tube in foil instead of the coil. (In both cases the
shielding would need to be overlapping but non-shorting.) Which is the
better would depend on the application, and how much shunt capacitance
it can tolerate.
More details and a data sheet at:
http://www.crydom.co.uk/Webpages/arc...d_rf_relay.htm
--
73 from Ian G/GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek