This one bothers me. Remember that there really is no such thing as ground for
RF - that ground rod is strictly for lightning / static currents. Connecting
the shield to a “grounding point” will simply combine the inner and outer
currents. That’s really not what we want to do. You need instead to choke off
the RF current on the outside of the shield.
I saw this “tip” mentioned in Dave Casler’s column in QST recently. I don’t
know which is worse - this, or his earlier information that stated there is no
loss in a tuner. The reasoning? A coil is just a wire, and the only loss will
be the negligible resistance. ARRL used to have really good engineering types
writing its columns. Not so much now.
73,
Jack, W6FB
> On Sep 26, 2025, at 2:10 PM, Brian Beezley <k6sti@att.net> wrote:
>
> Here's another offbeat idea. If you have an effective grounding point nearby,
> you may be able to shunt unwanted residual shield current to ground. The coax
> need not be severed. However, I would not trust my skill at making a
> watertight connection to the shield after slitting the outer cover to get at
> it. And what if the spot is not near a good ground? An alternative would be
> to install two quarterwave wires perpendicular to the coax. Lay them on the
> ground. To avoid a direct connection that exposes the coax to the weather,
> wrap the center of a halfwave wire around it to capacitively couple the two
> arms. The wire would need to be lengthened to maintain resonance. This is a
> single-band system. I don't think I'd want this up in the air, but if it was
> on the ground in a spot without foot traffic it might be OK. I'd model it and
> as much of the RF environment as I could using realistic ground constants to
> see how well it might be expected to work in a particular situation. On the
> other hand, if the coax was on the ground it might be worth the trouble to
> install connectors and a choke.
>
> Realistic ground constants:
>
> https://k6sti.neocities.org/hfgc
>
> Brian
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|