I have a 10m dipole in the attic connected to my ic718. Is it possible to tune
it to 20m using the mfj 901b that I have? Does the dipole need to be 20m
length and then tuned down or can tuners tune to a resonance higher than that
of the existing dipole. I do not have a balun on it. On 10m I have an SWR of
1:1

Thanks
73
G. Doughty
KI4BBL

G. Doughty wrote:
I have a 10m dipole in the attic connected to my ic718. Is it possible to tune
it to 20m using the mfj 901b that I have? Does the dipole need to be 20m
length and then tuned down or can tuners tune to a resonance higher than that
of the existing dipole. I do not have a balun on it. On 10m I have an SWR of
1:1

You have a problem. Extend the dipole to 33ft and use it on 20m-10m by
feeding it with ladder-line. Use a 1:1 choke/balun between the tuner
and the ladder-line.

I have a 33ft rotatable dipole fed with 300 ohm window-line. It works
very well on all bands between 20m and 10m.
--
73, Cecil http://www.qsl.net/w5dxp



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On 23 Sep 2003 13:59:49 GMT, ojunk (G. Doughty)
wrote:

I have a 10m dipole in the attic connected to my ic718. Is it possible to tune
it to 20m using the mfj 901b that I have? Does the dipole need to be 20m
length and then tuned down or can tuners tune to a resonance higher than that
of the existing dipole. I do not have a balun on it. On 10m I have an SWR of
1:1

Thanks
73
G. Doughty
KI4BBL

Hi OM,

You would have a harder time tuning a 20M dipole to 10M. But, really,
why don't you simply try? Transmitter limited (no 20M)?

The issue of to BalUn or to not to, depends on do you suffer from not
doing it? Seems not, or you would have said so.

More wire, less wire, BalUn or no; changes are unlikely to be
observable in your day-to-day activities. If you really want a 20M
dipole in the attic (and it fits reasonably well) simply add it in
parallel (use the same drive point connections) to the one already
there (you may even be able to get rid of the tuner). 6 inches
separation between them out 10 feet and beyond will do just fine. No
Rocket surgery is required.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
You would have a harder time tuning a 20M dipole to 10M.

Why? An odd number of quarter-wavelengths of ladder-line will
result in a near-perfect match.
--
73, Cecil http://www.qsl.net/w5dxp



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"Cecil Moore" wrote in message
...
.............................
I have a 33ft rotatable dipole fed with 300 ohm window-line. It works
very well on all bands between 20m and 10m.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil,
Why didn't ypu use a 15 or 17 m dipole and get away from the impedance
extremes?

BTW, Parallel dipoles work great, I had 40, 17, and 12 m on the same
feedline and SWR at resonance was better than 1.5 on all three bands.

Tam/WB2TT

Tarmo Tammaru wrote:
Why didn't ypu use a 15 or 17 m dipole and get away from the impedance
extremes?

The impedance extremes don't bother me. A 50 ohm antenna gives an SWR of
9:1 with 450 ohm ladder-line. An 4050 ohm antenna gives an SWR of 9:1
with 450 ohm ladder-line. The impedance at a current maximum point is
the same 50 ohms for both of those antennas.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil,
He didn't say he was using ladder line. Then again,
he didn't say what he was using for a feed line. I'd
be willing to bet it's coax, though...
'Doc

'Doc wrote:
Cecil,
He didn't say he was using ladder line. Then again,
he didn't say what he was using for a feed line. I'd
be willing to bet it's coax, though...

Me too. That's why I suggested he switch to ladder-line if he is
not already using it.
--
73, Cecil http://www.qsl.net/w5dxp



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Bob Miller wrote:
Cecil, I have a 44-foot dipole with 42 feet of ladder line -- I can
tune it for 30m-10m easily with my tuner. I can't get it to tune on
40m, though. If I shorten the ladder line to 33 feet, or lengthen it
to 99 feet, would that give me a near-perfect match on what is a 3/8
wave dipole for 40m?

Nope, it wouldn't, Bob, because the SWR is too high. EZNEC says a 44'
dipole fed with 450 ohm ladder-line will have a current maximum feedpoint
resistance of about 10 ohms. I define "near-perfect" as a feedpoint resistance
of 25-100 ohms giving a 50 ohm SWR of less than 2:1. However, you can
probably match that 10 ohms with your tuner.

In general, to use the variable ladder-line length approach that I use,
a dipole needs to be at least 1/2WL on the lowest frequency of operation.
For dipoles shorter than 1/2WL, as the dipole is made shorter, the resistance
goes down and the reactance goes up, causing the resistance at a current
maximum point to go lower and lower with increasing SWR.
--
73, Cecil http://www.qsl.net/w5dxp



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On 23 Sep 2003 13:59:49 GMT, ojunk (G. Doughty)
wrote:

I have a 10m dipole in the attic connected to my ic718. Is it possible to tune
it to 20m using the mfj 901b that I have? Does the dipole need to be 20m
length and then tuned down

Yes. Make the dipole twice as long, and then, with your tuner, you'll
be able to get a good swr from 20 meters through 10.

Bob
K5qwg

or can tuners tune to a resonance higher than that
of the existing dipole.

Cebik says a dipole needs to be at least 3/8 wavelength long on its
lowest frequency. I find 1/2 wavelength works a lot better.

I do not have a balun on it. On 10m I have an SWR of
1:1

Thanks
73
G. Doughty
KI4BBL