On 5/26/13 11:06 AM, johne tds.net wrote:
I just checked a multiple rig switch port that would connect on to the
other HF radio and with the other HF rig keyed up (500w cw) I did measure
500 ma on the section of coax that would go to the other rig. I am worried
about the isolation of the two HF rig's. Any better way to check this ? or
is the 500ma ok ? The switch is a ice 512-12 antenna switch.
half an amp? or half a watt? Into what kind of load?
30dB isolation (500W on one port, 500 mW on the other) isn't bad for a
relay, although not that great for a switch. 500 mW (+27dBm) is a lot
of power to be putting into a receiver antenna port, though..
the ICE website doesn't seem to give an isolation spec, but, for
instance, MFJ manual switches are 50-60dB, and the coax relays from
DowKey typically are 80-85 dB below 1 GHz. (MFJ doesn't give any specs
on the RCS-8V)
I suspect that people tend to use these switches with one transceiver
and multiple antennas, so having crummy isolation isn't a big deal. 30dB
would be plenty in that application.
For a multiple rigs to multiple antennas, you might want a design that
has two relays in series (figuring you probably get around 30dB/relay,
if the layout isn't bad).
The DowKey relays, internally, are pretty sophisticated, with a lot of
attention to good isolation.
With a conventional AC/DC power relay (as used in the RCS-8V, for
instance) you've got leakage from capacitive coupling across the relay,
as well as through the coil.
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