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Ian Jackson[_2_] · October 13th 15, 02:37 PM posted to rec.radio.amateur.antenna

In message ,
writes
Feedline is sealed (commercial antenna), but I think I can break it
open Ill let you know how it goes.

Why do you need to 'break it open'? At the TX end, isn't there some sort
of connector which connects it to the TX? If so, that's where I would
attach the additional length of feeder. [Also, what (if anything) is
connecting the balanced feeder to the (presumably) unbalanced output on
the TX?]

Assuming it's a plastic twin feeder, its velocity factor will be (say)
0.9 - so the physical 75' will be equivalent to around 88' electrical.
The 105' each leg of the antenna, plus 88' of feeder, adds up to 188' -
or 57.3m.

On 30m, a halfwave is 15m, so 57.3m is 3.82 halfwaves, or 7.6
quarterwaves. So on the face of it, the impedance looking into the twin
feeder is unlikely to be extremely high (which I understand some
auto-tuners don't like) or extremely low (which I understand they are
reasonably happy with).

However, as others suggest, adding a few additional feet of feeder will
probably bring the feed impedance to something that the tuner accepts.
--
Ian