No, Dave, I was told long ago by Steve, to short the coax at the bottom
end and feed both sides off the top of the variometer. When I did that my
reception really improved. That has never changed since then. the antenna
is an inverted L where the riser is coax shorted at its base.
The coax is OK I find no problem with it by using the Ohm meter on the
shield portion.
Everything is back together. Today, however, I am finding that the antenna
is consistent and shows a resonant point at about 98 kHz which is changing
in relationship to the amount of inductance. There is another problem which
I mentioned in my last message, however... At resonance the voltage waveform
becomes a mess. I am following Scotts advice and building an isolating
transformer. Once that is in play, I may be able to tune the antenna, and
YES it looks like I had WAY too much inductance.
J.
----- Original Message -----
From: "Dave Brown" <[email protected]>
To: <[email protected]>
Sent: Friday, 2006/07/07 22:49 PM
Subject: Re: Antenna Tuning
So how did the coax look?
I was going to ask if you could provide a rough sketch of the
interconnections of everything as its so easy to misinterpret a written
description and make assumptions that are wrong about these sorts of
things-but just to confirm-
I understand this is the setup.
You have a coax feedline (for LF) that has its outer grounded at the
tower base to the common ground point there. The coax inner is connected
to either a tap on the loading coil or the 'hot' end of a link winding
wound over the cold end of the loading coil.
The bottom end of the link, if you are using one, is also grounded to the
common grounding point.
The loading coil has its cold end grounded to the common tower base
grounding point and the top end is connected to the vertical part of the
LF antenna-be it the coax or a semi-vertical random wire etc- and
either/both of these have some/none top loading.
The cable 'radiator' is spaced from the tower with what sort of clamps and
what are the details of the insulation at the clamp points? These need to
be able to sustain very high voltages even with quite low power.
I understand the tower can be ungrounded or grounded at the base, to the
common grounding point. Normally it is grounded.
Re the coax 'radiator', is the inner bonded to the outer at both the top
and bottom of the cable, or what configuration do you have?
Just using the braid should work fine (ie inner not connected to anything
at both top and bottom) but it's worth knowing what you have done with
the inner as one possibility is all or part of the inner-outer cable
capacitance is somehow appearing in series with the top loading, so
details of the connections at top and bottom of the cable may be
significant.
Hope reviewing these details helps some.
73
Dave
ZL3FJ
----- Original Message -----
From: "J. Allen" <[email protected]>
To: "LF (RSGB)" <[email protected]>
Sent: Saturday, July 08, 2006 5:41 AM
Subject: LF: Antenna Tuning
Mike and All,
The reason the tower has been bonded to ground is that the tower supports
HF antennas as well. The feed lines, rotor cable, and remote antenna
relay control cable would need to be decoupled at LF which I am
unfamiliar with accomplishing. My attempt to decouple was to put the
feedline out at 4 feet from the tower. I do not want to get too far from
the tower, because my ground system is tied to two 10 foot ground rods at
the tower base. These ground rods are required by local electrical code
for grounding the tower. If I unground the tower for LF, I have to find a
way to connect the rods but have them decoupled at LF.
Yesterday, to make sure that the HF wire antennas were not part of the
problem, I took them all down. The only antenna left on the tower is a
small A4 tribander. When this was done, it made no difference at all on
the LF tuning.
Does anyone know how far out from the tower will be the best distance for
a 100 foot vertical riser of 1/2 inch coaxial cable? Would I be better
off by making the vertical riser a single #11 wire instead of the coaxial
cable?
Mike, you said that this may not be the problem at all, because you had
done a similar installation without these problems. What is different
about your installation?
Anyone who has been following, please brainstorm and think of any
possibility which I should be looking for. Because I get confused, I
could have made just about any kind of mistake imaginable in the
construction of the antenna, but whatever it is, that antenna sure works
on receive!
I will be leaving for Edmonton for neuropsychological testing related to
early Alzheimer's on July 9 and will be back on July 12. Please think
about the antenna problems. I hope that someone can find the little fox
in my antenna vineyard.
J.
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