[TenTec] TVI Problem

[rohre]

OH NO!  A LONG WIRE ANTENNA.

OK, LET US CONSIDER WHAT YOUR " RIG WELL GROUNDED' MEANS?

If it is just water pipe and ground rods, forget it, it is not an RF ground.
It will help with lightning discharge protection to the rig, maybe.

I had a 400 foot long wire in 9M2 land, and in the tropics you can't get a
good RF or DC ground for the conductive salts wash out of soil in the daily
rains.
I did not know that at the time.

There was lots of RF on everything in the shack.  End fed wires are voltage
fed antennas, with high impedance right where you do not want it, the end
coming into the rig.  The matching box, (tuner) only tries to make the best of
that bad situation, but does not keep the high voltage from apppearing at the
end inside.

What can you do?  Try some quarter wave counterpoises for each band you use
from the ground post of the tuner, and make sure the rig and tuner case
grounds are bonded with wide flat condutors.  Run the quarter wave wires out
as far from each other as you can, but along the base boards if nothing else
available. Are you using the single wire position of the matching box?

Keep your ground rods and water pipe connection, if it is a short run from the
shack.  Avoid attic pipes, quarter wave ground rod leads, long runs of wire,
even if of #8 often suggested for electronic equipment grounds like TV
antennas, etc.  Copper sheet as straps would be ideal.  You want low lead
inductance, and good conductivity of copper. 8 feet for example is a bad
length grounding conductor length on 10M.  (Quarter wave and thus high voltage
at rig end!)

If you have coax from the tuner to the rig, see if it is hot with RF on outer
shield.  Make a simple diode probe, of a germanium or silicon diode, 100 or
500 microamp  DC micorammeter, bypass cap across the meter of anything handy
from 0.001 mf to 0.01 disc ceramic.  Polarity of diode to match meter
polarity, other end of diode to a probe wire, or even to several turns of
hookup wire and back to ground side of meter, to make a pickup coil.  You want
to move it along the coax, and even rig chassis looking for hot spots of RF
during transmit.  If you have a keyer, you can send short dashes, or a test
message briefly on the air.

Probably your rig is clean if operated into a dummy load of 50 ohms, but if in
doubt, check that way first to verify connections to match box, coax to rig,
and your power leads effects re RF.  Any water gotten into the coax to cause
"green" effects in the shield?  Replace if so, this appears back from
connectors a short way, and may form a diode like joint, causing RF
interference elsewhere.

IF you need a stealth antenna, and you must have end fed long wire, get it up
high and at right angles to house length so as to not couple to house wiring
longer runs.  You can use small gauge wire down to no. 24 or even less for the
power you have. 

Check bonding of all connectors, coax and power lead grounds.  Use shielded,
twisted pair of large enough conductors for DC power to the rig.  Use of no.
12 is good for 20 amp rigs, yours would be OK with no. 18 gauge. Twist a
couple times every inch if you can, ie a tight twist. Ground the power leads
shield to station earth ground point.  Use a single run of copper flashing, or
plate as central ground point behind the match box, rig, and accessories, to
keep common lead impedance low and non inductive.

For the best results without RF in the shack, and for low antennas that bring
RF close, the dipole or other balanced antennas like beams are better.  A
stealthy dipole could be fed with TV twin lead to a balun and matching box. 
Even small coax could be used such as RG 58 without it being very noticed, if
you buy White coax from Belden or other vendors with colored outer jackets.
This is sometimes used in computer networking and cast off reel bits might be
free from Network intstallers!  Any unbalanced antenna can bring high RF
voltage near shack, thus causing TVI.  All single or long or random wires are
unbalanced antennas. Place the antenna so it blends into the background like
foliage, shrubbery, etc.  Use small light blue insulated wire against sky
background, etc.

But, one good stealthy antenna is a simple quarter wave vertical wire, or even
an ell shaped wire, vertical then horizontal to fit.  Use with coax feed to
base, and use quarter wave radials.  At least one, and four or more in the
four directions if you can .  Elevated radials high enough to walk under are
best.  Ground mounted radials often do not have equal RF currents in the
radials, which causes lopsided patterns. If quarter wave is too long for you,
many find that anything over 1/8 th wave is better than a ground rod alone.

Many true TVI cases are found in Cable tv systems to home sets.  Break the
coax continuity from the outside system with baluns to 300 ohm back to back,
and back to coax to set.  Ideally, you want an RF transformer coupling the TV
signals. No DC or continuous connection for common mode RF currents.

I suffered long wire problems in the desert where I lived another time, same
deal, no good RF earthing.  Earth is poor RF conductor at best.  I so suffered
from these extremes I would not put up anything but dipoles for years.

I have now an elevated Gap Titan vertical with which I am well pleased, thus a
vertical can work well for DXing and be RF feedback free.  I have also had
very good experience with G5RV home made to have the ladder line portion up in
the air horizontal as part of the radiating wire.  Then coax to shack.  No RF
in shack at 100 watts.  Short thru wall connection to copper water pipe for
bonding chassis of rigs.  Twisted no. 12 actually unshielded DC power leads of
5 feet long from DC supply.  But I do use surge arrestor at single wall outlet
that feeds power strip on operating desk.  Another important point. Power all
shack AC items off same phase of power line!!!  Ie, go to a heavy 20 amp
outlet single phase with a cord to a power strip for everything.  This can be
fused and surge protected for more benefit.

Disconnect everything from power and antennas however, during non operating
periods, and storms!

Good Luck, and let us know how it comes out,
Stuart K5KVH

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