Unequal dipole legs on shortened antenna
 

I have a shortened all-band dipole with two loading coils on each leg.
On 80 and 160 it has a very narrow resonance bandwidth that requires a
choice between data (low end) and phone (hi end). I am using a
wide-range manual tuner.

By changing the length of two segments on each side, I can move the
resonant "passband" where I want it on 80 and 160.

Using the antenna outside the passband results in unacceptably huge
(like 99%) feedline losses -- when the feedline is coax. I suspect
that if I shift to ladderline, the losses will just move to my tuner.

What would happen if I adjust one leg for resonance on phone and the
other for resonance on data?

If this would give me 50% of the resonant signal of a balanced
antenna, that would be acceptable.

Ken KC2JDY
Ken
(to reply via email
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Hi Ken -

You have a couple of wrong ideas. One relates to the feedline losses.
At the frequencies in question, it is extremely unlikely that they could
reach 99%--even with some SWR--unless your line is bad, or your
antenna is in the next county. Also, your half-wave resonance is deter-
mined by the TOTAL length, not by each side independently. So your
unequal sides should produce just a single resonance (per band), but with
an off-center feed. There's nothing wrong with off-center feed, though.
Some folks (including yours truly) have found that off-center feed can be
a very useful technique for improving the match--especially if the antenna
is in an asymmetrical environment, and/or too low (like mine). BTW,
I move up and down in the 80m band using plug-in stubs to change the
overall length. Works FB.

Good luck with your tuning, and 73,

Ed

"Ken" wrote in message
...
I have a shortened all-band dipole with two loading coils on each leg.
On 80 and 160 it has a very narrow resonance bandwidth that requires a
choice between data (low end) and phone (hi end). I am using a
wide-range manual tuner.

By changing the length of two segments on each side, I can move the
resonant "passband" where I want it on 80 and 160.

Using the antenna outside the passband results in unacceptably huge
(like 99%) feedline losses -- when the feedline is coax. I suspect
that if I shift to ladderline, the losses will just move to my tuner.

What would happen if I adjust one leg for resonance on phone and the
other for resonance on data?

If this would give me 50% of the resonant signal of a balanced
antenna, that would be acceptable.

Ken KC2JDY
Ken
(to reply via email
remove "zz" from address)

Ken wrote:
Using the antenna outside the passband results in unacceptably huge
(like 99%) feedline losses -- when the feedline is coax. I suspect
that if I shift to ladderline, the losses will just move to my tuner.

Not necessarily. Since a ladderline with an SWR transforms impedances
simply have it transform the impedance to something that is acceptable
to your tuner. That's what I do.

What would happen if I adjust one leg for resonance on phone and the
other for resonance on data?

Your antenna would resonate half way between phone and data. Maybe
not a bad idea. Try it and see if the SWR is still unacceptable.

If this would give me 50% of the resonant signal of a balanced
antenna, that would be acceptable.

Measure the SWR and calculate the losses to see if they are acceptable.
--
73, Cecil http://www.qsl.net/w5dxp



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