Topband: K9ay loop not performing

N4ZR n4zr at
Tue Dec 10 14:22:57 EST 2019

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 at> 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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