On Thu, 2 Dec 2010 20:34:09 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

This still sounds like the vagaries of propagation. Do you keep logs?

It's not needed. I have two coaxes going outside, one to the folded dipole,
one to the J-Pole. If I tune in a station in the "dead" range (7.0-7.3mHz),
using the J-Pole as my antenna that reads s-5, when I switch to the folded
dipole, it barely moves the s-meter at all.

Hi Geoff,

That confirms propagation - more a matter of polarization. We keep a
variety of antennas to suit just situations. Polarization diversity
is what that is called.

Your lead out to the antenna could have a short/open in it.

Possible, but at 14mHz, it comes in great, far better than the J-Pole.

I presume by this response, your antenna/line being "dead" at 15 MHz
(it should be a busy band) is quite alive at 14 MHz (which, too,
should be a busy band).

My bad, I was speaking of a null, as in a frequency range with zero
(or close to it) signal.

The following is pedantic for its own sake:
Null in engineering denotes the indication offered in a balanced
situation - the meter indication in a bridge - where two potentials
are equal (no current flows in the meter). As you adjust the arm on
one side of the bridge, the approach of equality reduces the potential
between both side of the meter, and its indication "nulls."

If you are referencing a null in tuning, then that would occur at
either resonance, or anti-resonance (broadly speaking). If this is
your intent, then, yes, "nulls" would represent impedance matching
issues which in turn would put a block to signals. A tuner is a
design tool for this situation.

Thanks, that's easy to try. Would it work on the near end of the system?
radio - tuner - 10 meters of coax - balun - 300 ohm feedline - 300 ohm
folded dipole.

That is good solution; the perfect topology would have the tuner at
the 300 Ohm folded dipole with coax back to the radio.

Some of the 10mm rods were broken into pieces in shipping. Does that affect
their performance? Can I just use the pieces as they are?

Magnetic performance is impacted by air gaps. In some situation this
is an asset where saturation is an issue. Super glue the pieces for
the closest fit.

Sorry, I wasn't clear. Someone on another mailing list said that breaking
a ferite rod could magnetize it. I don't want to glue them together
again, I would use the pieces as they are.

Someone on another mailing list has mixed priorities. So what? (Not
to say I buy their guff.)

Feel fine to use them as they are, but if you were to use them as
stock for choking purposes, more bulk ferrite offers more bulk
isolation.

Maybe a better question would of been to start from the begining and ask "I
have a 300 ohm twinlead folded dipole resonant at 15mHz, with an aprox 6 foot
twinlead feed line. I need to feed that with 10-15 meters of 75 ohm coax.
How do I get that to appear resonant to my transmitter on 14 mHz, and hopefully
7 and 28 mHz and get some signals in and out?".

The fold in the dipole, the approx 6 foot twinlead feed line, the 75
Ohm coax, and the BalUn are unnecessary elaborations. The combination
of all sounds like complexity squared to achieve a goal by applying
nebulous charms.

Resonance is resonance and the rest is unnecessary. You put up an
ordinary dipole, connect an ordinary line to it (OK, so it can be 75
Ohm line if that is what is handy) THROUGH a choke (AKA 1:1 BalUn),
and to a tuner at your radio. The tuner solves resonance. Sometimes
a tuner cannot cope with extreme natural resonances such as a fullwave
dipole presents you on the band you want. Cut the size of the dipole
and move on.

The combination of folded dipole, odd twinlead line, and high ratio
BalUn (almost always of the wrong construction) suggests the desire
for an "all band antenna." That and unicorn horns for aphrodisiacs
are sought by many and claimed real by liars or fools. Marrying the
term "resonate" or seeking resonance from these antennas compounds the
lie or the foolishness.

The usual (and inverted wish from seeking resonance) is that this
solution of dipole/tuner dashes the SWLer's desire for frequency
agility (no time to tune an optimal signal when chasing the bands).
The simple solution is the Fan Dipole. This new solution being too
easy and lacking the mystique of charms, amulets, and complexity to
fuss over, SWLer's quickly reject simple success to cozy up to the
oddities of their failure in contrast to the glowing (lying or
foolish) reports of others (liars or fools) using the (presumably)
same contorted design.

It's not like any of these contorted designs bring any gain to the
table. And the gain differences between them and a simple dipole
wouldn't move the S-Meter more than a needle's width!

The reason why I am quick to dismiss "frequency agile" requirements is
that I know full well that SWLing demands your full attention on one
frequency to pick up that interval ID signal, or just recognize the
style of programming if you are going to catch that DX. The agility
race is won by the patient listener.

However, if you really want an "all band" antenna that is "frequency
agile" then the Fan Dipole will do that on every band you cut an
element for. All it takes is wire (and it would seem you, and others,
made that investment with the fold).

73's
Richard Clark, KB7QHC