I have used a Scout with no problems with RF in the rig, at many Field Days,
and the only thing I can say, is we always use balanced antennas, such as
Double Zepps, ladder line fed; or horizontal loops, also parallel line fed,
and beams with dipole driven elements. Field Day is not the sort of
environment ideally suited for quarter wave verticals or mobile whips, or
other unbalanced antennas.
I think one is painting Ten Tec with a broad brush indeed, to assert they
lack RF bypassing. The use of bypassing should be designed for the majority
of applications adhering to good engineering practice, which does not
include excessive RF in the shack. My Scout has beads in it in places where
they are needed for example.
If one has very poor ground conditions such as dry desert, or wet tropics,
or stony ground, it is better engineering practice to use balanced antennas
that are independent of your earth RF impedance, than unbalanced antennas
that are either non resonant, or quarter wave types lacking "half" of the
antenna. Or bite the bullet and use 120 ground radials,as is Broadcast good
practice. Actually for short waves, often 60 will do. Recent work
indicates full quarter wave lengths may not be necessary, especially with a
loaded antenna, shorter than resonant quarter wave length itself.
In industry, bypassing is added as needed for the operations. If you use
EMC defeating aids such as beads and caps on everything, someone must pay
for the extra parts. Many of us buy Ten Tec for it is good value for the
money, and use it with an eye to optimum application. If RF becomes a
problem in the shack, you should go back to square one, and disconnect all
antennas, and see if you have RF in the shack with a dummy load on the rig.
Then, add things from there, one at a time, keeping good notes on grounds,
transmission line types and lengths, etc. to determine if the problem is a
coax fed dipole with odd quarter waves of line length or other problems that
are well known to bring RF back into the shack. Often lengthening a coax
line takes the hot spot away from where it does harm.
An 8 foot ground wire to a earth rod, is likely to cause an RF on the metal
in the shack for sure when on 10, for it is quarter wave at 10m. Heavy
pair used to a DC power supply should be twisted pair, and shielded twisted
pair may be needed. Many other combinations come to mind. Antennas too
close to other antennas can be a path for stray RF. By due attention to
spacing in terms of wavelengths of the problem bands, you can arrive at
workable solutions. I just had a case of tuning up a mobile with a bumper
mounted helical antenna for 30M. No matter what we tried with ground
straps, to the frame etc, we could not get SWR below 3:1 adjusting the whip
length adjuster at the top. This was on a van. My suspicion about coupling
of the full length helical coil to the back door was confirmed, when we used
the same mount and put a Hustler fold over mast base, and Hustler lumped
coil and top whip on the van. The coil was up away from the metal of the
door, and tuned up with 1.3:1 SWR in the desired band segment. This helical
whip would be fine on the back deck of a hatchback, or top of the roof, but
just had too much coupling of its tuning coil, along all its length, in such
a van mounting.
The Changing the length, or sensitive component, goes for tuned transmission
lines, if you have a band you cannot get to match to low SWR, add some line,
and try again with the same transmatch.
Use baluns where indicated, such as dipole feedpoint, if using coax, or
avoid odd quarter wave multiples of coax. Use a amply rated transmatch and
balun with parallel lines and untuned dipoles that are used on higher bands.
Use tuned radials to cure RF in the shack if all other measures fail. Keep
RF cables away from AC power, or audio cables. There are usually ways to
make any location RF tolerant.
73,
Stuart K5KVH
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