A quarter wave center fed wire has low radiation resistance and is very
capacitive. Bad phase angle. You run that through a 600 ohm line about a
quarter wave long, converts low R to high R and C to L. So your balun
sees high impedance that may be causing core saturation (for sure in a
voltage balun) and you see high Z at the tuner.
More wire at the antenna will shift the results, a quarter wave more
feed line would shift the results, but the easiest change is to lower
the characteristic impedance of the feeder by going to fatter wires or
closer spacing. I take you are using 6" spacers. For 300 ohms you need
only 1/2" spacers. A quarter wave of 600 ohm transforms a 20 ohm load to
18,000 ohms. A quarter wave of 300 ohm transforms that 20 ohm load to
4500 ohms which is somewhat easier to match. That 110 feet of feed line
is close to a half wave or multiple of a half wave on higher bands, so
the characteristic impedance has much less effect on the impedance seen
at the tuner.
73, Jerry, K0CQ
On 4/8/2011 12:13 PM, Art Trampler wrote:
It's on-topic, as I am using a 238B...
New antenna, 140' sloping dipole...apex about 50 to 55 feet, ends about 30
feet, so not quite an inverted vee,
Feedline: 600 ohm (or thereabouts) 14 gauge stranded, insulated wire using
73CNC spreaders, Guesstimated length: 110 feet. Feedline and antenna are
continuous pieces.
Tuner: 238B, followed by 10 feet of LMR600 to a 1:1 current balun from Balun
Designs (to get out of the shack).
On 160 meters, I wound up in Hi-Z "5" position to get a 1.8:1 match. Am I
looking at Hi-Z because the antenna length is about 1/4 wave? If so, would it help so add
20 feet to each end, even if it went at nearly a right angle to the antenna? Or is this
really unimportant/not an issue as long as I get a match?
Also, what recommendations do other owners have for additional capacitance if
necessary? I have not replaced the internal capacitors with the Russian
doorknobs but might at some point.
Interested in your thoughts. If the Pegasus S-Meter is at all accurate, I was
hearing Russians a full S-unit better on 20 meters last night with this antenna
than with my AV640 vertical. Japan is off the end, so the vertical is better in
that direction.
73,
Art
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