[Antennas] Only dumb question is the one not asked

2002年3月29日 11:00:46 -0600

Short answer:
1. The current we are trying to block flows along the outside of the coax
braid.
2. By winding the coax into a coil, we create an inductance with the outer
braid - it has no effect on the inner braid and center conductor which are
carrying the desired signal to the antenna - and the inductive reactance of
this coil acts to reduce or eliminate the current by placing a relatively
high impedance in its path.
3. You can earth-ground the outer braid at any point and that will provide
another path for the outer-braid current to take: one path to the shack and
another to the "ground." How much current goes to each path depends upon
the impedance of each path. "Grounding" does not automatically eliminate
all outer-braid current although it is usually very effective.
73/72/oo, George W5YR - the Yellow Rose of Texas 
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe 
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121 Kachina 505 DSP #91900556 Icom IC-765 #02437
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[email protected] wrote:
>> Hi Gang,
> I hear so many times (and I have done it myself) make a choke buy winding 6-8
> turns of coax at the feed point to keep RF from coming down the feed line.
> OK,
> RF is on the line.
> You make 6-8 turns and there is no more RF coming down the line.
> How does this work?
> What keeps the RF from just traveling around the turns and keep on going?
> Also what if I exposed a bit of the braid right after the last turn and
> grounded the coax there.
> I know this list has some smart EE's and antenna experts.
> My other question is a brain basher so i'll save that and post it on Monday.
> Happy Easter to all.
> Bob
> WA2HOQrp <tm>........Soon to be AF2Q