Pi were to directly drive the antenna selection? Then the question becomes
whether these relay assemblies are capable of handling 1 KW RF.
These relays assemblies are: inexpensive, SPDT, opto-isolated from the
CPU, include reverse diode protection on the coils, rated for 220VAC at 10
amps, and the PCBs have been notched to physically isolate the relay
common from the two outputs (hard to see that from the photos).
http://www.amazon.com/gp/product/B0057OC5WK
Will these work? How would I test them?
Larry,
DC or LF relay ratings do not mean much.
There are five problems (not just one or two):
Ground loops (related to current paths)
Capacitive coupling
SWR changes
Voltage breakdown
RF heating
Arcing is an instantaneous failure on peaks. It is usually a frequency
independent voltage breakdown.
Heating (usually from current through the switch unless a poor dielectric is
involved) causes a time and duty cycle failure. Heating and current ratings
are almost always frequency sensitive.
One obvious compromise in the board link you posted is the relay physical
layout. The problem is it uses an in-line layout and connects through wire
terminals. While the connectors are good connectors at low frequencies, they
are not so good for radio frequencies.
This doesn't mean the system will not work. If the relays are adequate, the
board might work OK if mounted over a groundplane with connectors passed
through the groundplane. This is especially true on 160 where layout is
least critical, but ten meters will almost certainly show problems with an
in-line layout. My guess would be it has a chance of working OK on lower
bands, but would likely be falling apart on upper HF.
I have no idea if the relays are good enough or not, my comments are only
concerning the physical layout of relays pictured at the link you posted.
73 Tom
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