On 14 Jul 99, at 11:01, Branch T SMSgt AFRS
<Tom.Branch@rs.af.mil> wrote:
> Been trying to track down a problem that has plagued me for months. I
> have a large amount of RF coming into my shack via the coaxial shields and
> the rotor cables
[snip]
> 73 de Tom, K4NR
I had a similar problem here and I accidentally fixed it in my quest
for good lightning protection.
Could I suggest you consider implementing a "single point
grounding system". PolyPhaser has good information on how to
construct them. www.polyphaser.com
The basics are these:
1. Provide a low resistance ground for the tower (many ground rods
spaced apart at a distance slightly greater than their length, see
PolyPhaser information), the single point location in the wall or just
inside the wall where the feedlines enter the building, and the
building service entrances for telephone, cable, water and electric.
All bonded together with 4 ga. underground, bare, solid copper wire.
2. Use wide, solid copper strap from the single point ground to the
tower ground at the base of the tower. The width of the copper strap
must be equal to or greater than the total of the circumferences of all
the coaxes. This may require several straps--two six inchers in my
case.
3. For tower mounted antennas, bond the shields of all coaxes to
the tower at the top of the tower and the bottom of the tower. For
wire antennas, skip this step. Otherwise the tower will be part of the
antenna circuit.
4. All feedlines then come to a single point ground plate (I used a 2'
by 2' by 1/8 inch piece of aluminium) and run through it. Use a
double female SO-239 bulkhead connector (or N connector as
necessary) for coaxes not protected from lightning. Use a bulkhead
mount lightning protector for those always connected to radios.
5. Use small, light weight copper strap from each radio chassis
ground to the single point ground plate.
6. Use a Polyphaser rotor control lightning protector mounted on
the single point ground plate. The rotor control wire runs down the
tower and through the protector and then to the control box.
All lightning and RFI stops at the single point ground location and is
shunted to ground. This stopped all my RFI problems.
It's a bit of work, I admit. And it can be very expensive if you buy a
large number of lightning protectors. But it will do the job.
I have attached a picture of my dusty, messy single point ground
plate. Omitted from the SIG's copy.
Sorry there is no simple fix.
73, Dave, N3EOY
mailto:daveh@erie.net
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