On 6/1/2014 11:17 AM, Jim Allen wrote:
I may have a ground loop issue here.
Ain't no such thing as a ground loop.
The new to me Omni VI+ with 962 power
supply has an odd quirk, in that the power supply quits as I increase
power, but only on 40M, with either of my two antenna, but not with the
dummy load, and does the same thing with either the Omni VI+ or the Omni VI
opt3 I have had for awhile. This quirk does not happen when using another
power supply, non-Tentec 23 or so amp. On other bands, either radio,
either antenna, the power supply does not shut down.
You have an RF in the shack problem.
I have an "Ugly choke" (20+' RG8X around a 4" PVC pipe) on the dipole at
the feedpoint of the AH-4 tuner.
That's a very poor choke, because it's purely inductive. A good choke
should be RESISTIVE.
There is a 4:1 UNUN on the new vertical,
with an RT-100 remote tuner.
I also get some hum in the computer speakers and now and then the computer
keyboard goes offline and has to be unplugged adn plugged back in.
The ground system is an 8' copper ground rod, in 36" or rock and dirt,
A connection to earth is NOT part of a solution to RF in the shack
problems, nor does it make antennas work better. it only matters for
lightning protection, which IS important.
Ferrites have been suggested but I don't know what kind or how many.
See the Choke Cookbook (Chapter 8) in k9yc.com/RFI-Ham.pdf for specific
recommendations, see Appendix One for part numbers and places to buy the
parts. For a balanced antenna fed with 50 or 75 ohm coax, one of the
simple bifilar chokes wound with 10-12 turns of a pair of #12 THHN
(house wire) will work fine from 80M up to at least 20M, with slightly
increased loss up to 10M. Cut two lengths of #12 THHN to 4 ft each, tape
them together, wind that pair 10 turns around a #31 Fair-Rite 2.4-in
o.d. toroid. Cut the left over ends to whatever length works
mechanically, and put that in series with the transmission line at the
feedpoint.
Notice that I said a BALANCED antenna. Un-balanced antennas create lots
of common mode voltage (and current on the line) that CAUSES the sorts
of problems you are having. And because the common mode voltage is high,
it tends to blow up chokes with high power. In today's world, badly
unbalanced antennas (off-center fed dipoles are the most common) are a
REALLY BAD idea.
Caps added for emphasis. :)
73, Jim K9YC
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