hi Kenny,
you wrote:
> Back to the hairpin... The hairpin coil is a step up transformer and is
> attached across your hot & ground of your feedline. This is the vertical
> section (hot) and radials (ground). The hairpin coil turns should be in
the
> same direction of the base loading coil, and use solid wire so the coil
> keeps its shape. We either use 1/4" aluminum tubing for the hairpin coil,
> or copper refrigerator (water line) tubing. 10 or 12 gauge solid wire
will
> work OK for temporary installations, but may move too easily for a
permanent
> installation. Starting off with a coil of around 3-4" diameter, and about
6
> turns should get you close. Squeeze or spread hairpin coil for best match
> (you can easily get a 1:1 match with a hairpin). If your coil is squeezed
> all the way for the best (but not yet perfect) match, you will need to add
> another turn or two. If spread as wide as practical to get the best (but
> not yet perfect) match, then you need to remove a turn or two from the
coil.
this is exactly the idea of the original Titanex matching unit...
the bottom part of the coil (i.e. the turns between the feedline tap and
ground) works as what you call a "hairpin coil"... you obtain the necessary
C for the LC-matching circuit by not fully compensating the capacitive
reactance of the (short) vertical (i.e. by adjusting the upper part of the
coil)...
if a good match cannot be obtained, either the taps are not set properly or
the (upper part of the) coil is not large enough...
IMHO it might be just a problem of SWR-measurement... because of the
inevitable stray pick up of the relatively long vertical I'd never try to
match a low band vertical using an MFJ-type SWR-bridge, but by a
reflectometer-type SWR-meter at the input of the ATU (i.e. at the base of
the vertical) using just enough power for reliable readings...
presumably, Jim has meanwhile solved the problem after so much good advice!?
regards
Uli, DJ2YA
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