David,
Amidon makes a very effective tool to match the impedance of 50 ohm coax to a
variety of possibilities of do it yourself antennas. Their W2FMI UNUN
(UNbalanced to UNbalanced transformer) model number 1.78:1-HMMU50 can match
50 ohm coax to impedences of:
36 ohms 1.36:1
28 ohms 1.78:1
22 ohms 2.25:1
16 ohms 3.06:1
12.5 ohms 4:1
5.6 ohms 9:1
4 ohms 12.25:1
3.1 ohms 16:1
My Inv L for 160 meters had a poor SWR (4:1 at resonance) due mismatched
impedences until I inserted the UNUN and now I have a flat match at
resonance. The UNUN box is about the size of a deck of cards in aluminum
casing and inserts between the coax at the feedpoint using PL259 females. It
works well with shotened verticals, vertical beams, shunt fed towers, slopers
and Inverted L's. These devices are awesome and you can run high power
through them-
I think I paid like $50 for mine a few years back. Amidon can be contacted
at 714-850-4660. I got my UNUN back in 1995. I assume that Amidon is still
around-
If anyone is using a vertical whereas the minimum SWR reading is higher then
2:1, you might consider using a UNUN to better match your feedline to the
antenna- They are remarkable devices that don't get a lot of attention- They
make low power UNUN' for matching beverages too- and a whole bunch of other
devices for matching ladder line to coax etc.........GL
73 Paul N0AH
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