EZNEC predicts the feedpoint impedance of an 80m half-wave at 30ft over
average ground as 51 Ohms at resonance - that was close enough for me to
call the RG213 "matched" ;)
But you raise a very good point about bandwidth: in my model the
half-wave dipole was resonant at 3.6MHz; by 3.8MHz the SWR on the coax
had risen to 5.7:1, increasing feedline losses by 0.5dB. On the other
hand the 100ft ladderline-fed system losses hardly change, so the "gap"
between it and the half-wave is considerably narrowed. If you care to
run the sums with 600 Ohm open-wire line feeding the 100ft dipole,
rather than commercial ladderline, you can close the gap completely.
On 17/01/2012 17:51, Gene Fuller wrote:
> Hi Steve -
> You 've made a good point , however:
> an 80m dipole at 30 feet isn't going to be 1:1 on 50 ohm line and,
> how does it look off resonance out towards the band edges ?
> Gene / W2LU
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