wrote:
the physical antenna stays as is and works extremely well on 75.
What has me asking the questions is that I was told a 1/4 wave piece of coax
would get it to work on 40.

Was that a parallel stub by any chance?
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

wrote:
the physical antenna stays as is and works extremely well on 75.
What has me asking the questions is that I was told a 1/4 wave piece of
coax would get it to work on 40.

Was that a parallel stub by any chance?


hmmmm, thats not what I recall being told but would it work?
one feed line?

--
I SPILLED SPOT REMOVER ON MY DOG..............AND NOW HES GONE!!

Richard Clark wrote:

On Thu, 01 Feb 2007 19:32:05 -1000, wrote:

signal reports on 80 have been very impressive.

You sound like a very good customer prospect weighed against the
testimonials offered to a German inventor of a 9 foot tall 160M
radiator.

Signal reports on 80 still doesn't make it work on 40M however. The
reasons have been explained for your difficulties, and solutions
offered. Are you looking for something different?

73's
Richard Clark, KB7QHC


Richard, I am not trying to be an ass here, but I was told BEFORE the
antenna was built it would work on 40.
So it got built and doesnt work on 40 as is. It was suggested at the time to
use a 1/4 wave section of coax to get it to work on 40, which as you know
it doesnt.

All I want to do is figure out a way to get it to work on 40 now.

Believe me this antenna works extremely well on 80. 20 over 9 reports from
ZL when the VK's there are only 10 over 9.

This configuration works well, I am sure someone could build a similar
version just for 40 and be a big gun on 40.

--
I SPILLED SPOT REMOVER ON MY DOG..............AND NOW HES GONE!!

wrote:
hmmmm, thats not what I recall being told but would it work?
one feed line?

A shorted 1/4WL 80m parallel stub will yield a
high impedance on 80m and a low impedance on 40m.
This is sometimes used with open-wire line to
achieve a match on both bands for a dipole that
is 1/2WL on 80m and 1WL on 40m. Also to open up
a 1WL 40m loop for use on 80m as a 1/2WL dipole.
--
73, Cecil, http://www.qsl.net/w5dxp

On Fri, 02 Feb 2007 05:59:56 -1000, wrote:

I was told BEFORE the
antenna was built it would work on 40.

You are a victim of poor information. That is evident in the false
assurance (it simply doesn't make sense) and the positive proof of
your measurements.

So it got built and doesnt work on 40 as is.

No one here is surprised by that outcome.

It was suggested at the time to
use a 1/4 wave section of coax to get it to work on 40, which as you know
it doesnt.

A quarter wave solution was offered by Owen which was the correct
solution. This does not mean it would turn a dog into a performer, it
simply meant it would match. Now, as to the matter of making it match
using coax, THAT is a hash pipe dream. You may eventually succeed
through luck and happenstance, but chances are that coax will glow at
night.

All I want to do is figure out a way to get it to work on 40 now.

As I offered, Owen has already done the work, but only you can build
it and discover it works.

Believe me this antenna works extremely well on 80. 20 over 9 reports from
ZL when the VK's there are only 10 over 9.

That's nice, but it doesn't solve 40M.

73's
Richard Clark, KB7QHC

Cecil Moore wrote:

wrote:
hmmmm, thats not what I recall being told but would it work?
one feed line?

A shorted 1/4WL 80m parallel stub will yield a
high impedance on 80m and a low impedance on 40m.
This is sometimes used with open-wire line to
achieve a match on both bands for a dipole that
is 1/2WL on 80m and 1WL on 40m. Also to open up
a 1WL 40m loop for use on 80m as a 1/2WL dipole.

I have seen this before, but somehow I would have to be able to connect and
unconnect the stub.

--
I SPILLED SPOT REMOVER ON MY DOG..............AND NOW HES GONE!!

wrote:
Cecil Moore wrote:

wrote:
hmmmm, thats not what I recall being told but would it work?
one feed line?
A shorted 1/4WL 80m parallel stub will yield a
high impedance on 80m and a low impedance on 40m.
This is sometimes used with open-wire line to
achieve a match on both bands for a dipole that
is 1/2WL on 80m and 1WL on 40m. Also to open up
a 1WL 40m loop for use on 80m as a 1/2WL dipole.

I have seen this before, but somehow I would have to be able to connect and
unconnect the stub.

No you don't. The stub is a high impedance on 80m in
parallel with a low feedpoint impedance and therefore
has a negligible effect on 80m. It can be left in the
circuit.

The stub is a low impedance on 40m in parallel with
a high feedpoint impedance which lowers the SWR and
makes your transmitter happy. On 40m, the stub acts
as a low impedance load that eventually delivers most
of its stored energy to the high impedance antenna
(assuming the stub is made from low-loss transmission
line).
--
73, Cecil http://www.w5dxp.com

In message , Cecil Moore
writes
I have seen this before, but somehow I would have to be able to
connect and
unconnect the stub.

No you don't. The stub is a high impedance on 80m in
parallel with a low feedpoint impedance and therefore
has a negligible effect on 80m. It can be left in the
circuit.

The stub is a low impedance on 40m in parallel with
a high feedpoint impedance which lowers the SWR and
makes your transmitter happy. On 40m, the stub acts
as a low impedance load that eventually delivers most
of its stored energy to the high impedance antenna
(assuming the stub is made from low-loss transmission
line).

I don't understand that, Cecil. Yes, the stub will be a halfwave on 40m,
and therefore add a low impedance in parallel with the antenna
feedpoint. Depending on the exact resonant length of the stub, the
impedance will be either a very low value resistor, a low value
inductor, or a large value capacitor. None of these is going to help to
convert the resistive part of the input impedance of the antenna to
something around 50 ohms.

However, I suspect that what the matching arrangement actually consists
of a stub which is connected across the feeder AT SOME DISTANCE from the
antenna feedpoint. If the antenna feedpoint presents a high impedance on
40m, there will be a point at some distance (less than a quarterwave)
back along the feeder (towards the TX) where the resistive part of the
impedance (at that point) is 50 ohm, in parallel with a considerable
capacitive reactance. By choosing the correct length of stub and the
correct distance between the connection of the stub and the antenna
feedpoint, you can probably get a 'reasonable' match for both 80m and
40m.

If this IS the actual physical arrangement, it's time to get the Smith
Charts out!

Ian.
--

Ian Jackson wrote:
I don't understand that, Cecil. Yes, the stub will be a halfwave on 40m,
and therefore add a low impedance in parallel with the antenna
feedpoint. Depending on the exact resonant length of the stub, the
impedance will be either a very low value resistor, a low value
inductor, or a large value capacitor. None of these is going to help to
convert the resistive part of the input impedance of the antenna to
something around 50 ohms.

You're right, Ian. I was trying to apply the same
principles that causes the stub to turn a full-wave
40m loop into a 1/2WL 75m dipole and had a senior
moment. But that idea would work with RG-174. With
a 3 dB loss in the stub, the impedance looking into
the stub would be around 50 ohms. :-)
--
73, Cecil http://www.w5dxp.com

In message , Cecil
Moore writes
Ian Jackson wrote:
I don't understand that, Cecil. Yes, the stub will be a halfwave on
40m, and therefore add a low impedance in parallel with the antenna
feedpoint. Depending on the exact resonant length of the stub, the
impedance will be either a very low value resistor, a low value
inductor, or a large value capacitor. None of these is going to help
to convert the resistive part of the input impedance of the antenna to
something around 50 ohms.

You're right, Ian. I was trying to apply the same
principles that causes the stub to turn a full-wave
40m loop into a 1/2WL 75m dipole and had a senior
moment. But that idea would work with RG-174. With
a 3 dB loss in the stub, the impedance looking into
the stub would be around 50 ohms. :-)

I'm not an antenna person, Cecil. Are you going to do the hono(u)rable
thing and calculate the dimensions?
Ian
--