[TowerTalk] Multiple Rigs switch isolation .

[Jim Lux]

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.