I had one of those 238 matching networks once and sold it. There are
a few commercially manufactured ham feedline/antenna transmatches out
there that are decent but they are sadly no longer made. The Unique
Wire Tuner wasn't too bad for 1KW and less (all power here in terms of
CCS). It had a nice Johnson roller inductor on a ceramic form and a
good turns counter and ceramic shaft insulators. The Johnson KW
Matchbox is acceptable for balanced line, as is the TMC TAC, but that
one is almost impossible to find. I have not seen anything currently
in production that is any good. They use cheap parts and the prices
are ridiculous. There are good reasons for that from a modern
manufacturing and cost/profit standpoint, but that is no reason why a
ham has to be a consumer of these products from the likes of Pal-Star,
Ten-Tec, MFJ and the rest.
If you are going to modify an inferior network you may as well
homebrew one with vastly superior parts from a hamfest, or improve an
earlier L network such as the aforementioned Unique Wire Tuner by
simply adding a bigger air variable cap and Russian RF doorknobs. I
did that and have a great continuous duty network for 160 m. that
should handle up to 500 watts carrier. Its inductor is a popular
Johnson 22 microhenry inductor rated for 5 amps.
L networks can be easily constructed with items such as a Gates 10 amp
roller inductor, and nice wide range brass Cardwell air variables,
ceramic standoff insulators and shaft couplings, all found at hamfests
if you ever venture outside into the flea market. Brass nuts, bolts
and washers are at most hardware stores. There was a tuner discussion
recently on the 160 meter email list and it was sad to see so many
recommendations from hams for manufactured networks, instead of
designs for building one.
> Am unable to tune my 135' HB 2" ladder line fed antenna any lower then 5.2
> MHz when using a MFJ 259 Analyzer. All frequencies above 5.2 tune fine. The
> tuners rotary inductor acts like it needs >more turns to get down to 75m.
> Addng a 1000Pf cap t the back of the tuner does not seem to help. Adjustment
> of the LO or Hi Z switch does not seem to have any effect. I'm sure I'm
> overlooking >something but haven't found out what is is yet.
>
Your problem is you are using a design intended primarily for
unbalanced line or unbalanced loads to attempt impedance match _and_
transform a balanced line to an unbalanced source. I know it has a
"balun" in it so Ten Tec could advertize it as a do everything tuner
but it is really not suitable for your use. Build a link coupled
balanced network, there are designs for them on-line, or if you must,
get a pair of inductors and do the Rich Measures balanced matching
network design. There are really no substitutes. It should be
trivial to achieve a 50 ohm impedance for your ham gear with one of
these circuits. Get some parts and experiment with clip leads. This
is supposed to be one of the fun things to do in this hobby. Not
something you buy your way around.
73
Rob
K5UJ
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