Thanks everyone who responded - I think I know enough to proceed.
I had wondered about the need to open the shield side of the coax - I
have 16 turns of RG-400 on a Type 31 core right at the base of the
inverted L. If the darned rain/snow ever stops, I think I'll
temporarily re-connect the shield and compare, but my expectation is
that a single pole will do the trick.
73, Pete N4ZR
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On 12/10/2019 1:54 PM, Guy Olinger K2AV wrote:
The need to disconnect the feedline shield is to block common mode signals.
A K9AY approved **EXCELLENT** common mode block (not a regular "balun" with
likely awful blocking on 160m), or (GASP) an isolation transformer will
take care.
In the case quoted, with the coax center contductor opened, the
stinky-on-160-blocking "balun" is how the noise gets in. Further since Pete
saw a 4 S unit drop by simply disconnecting the TX wire, it's likely that
his common-mode provision, even if not intended as such, would appear to be
satisfactory, and therefore a double pole relay (lot more expensive) is not
called for.
73, Guy K2AV
On Sun, Dec 8, 2019 at 7:30 AM Rob Atkinson <ranchorobbo@gmail.com> wrote:
If you open the tx antenna feedline for rx, from my experience, you
need to completely open the entire feedline, namely the coaxial cable
shield as well as the center conductor. coaxial relays that maintain
conductivity of the shield when N.O. won't detune/isolate the tx
antenna. I use a pair of open frame relays for this. Fortunately on
1800 kc the Z bump is almost nonexistent. What will govern your
choice of relay is tx power and tx time, and whether or not you
require QSK. I do not, but if you do, you may have to consider
something like multiple paralleled reed relays tor speed and power, or
vacuum relays.
73
Rob
K5UJ
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