How do all these various matching schemes affect bandwidth?
73,
Tom Donaly, KA6RUH

For the "L", it depends on the Q of the "L" network. You're not in charge
of that, you have to take the Q that the transform gives you. With a
constant inductor value, I can get pretty close to 1:1 clear across the band
just by varying the capacitor value for the frequency. Of course, if you
don't have any adjustable "C", YMMV. I'd think you need to get to a pretty
high frequency before you didn't have to add "C" to whatever exists, but the
big advantage of Voltage feed is that the current to the "Ground" is
minimal. When you don't know that your ground is zero Ohms, you're better
off putting as little current into it as possible.

W4ZCB

J. Kragh wrote:

Togethere wih a fellow amateur I am trying to design an endfeed halfvawe
vertical antenna for 50 MHz.

We have encountered som problems regarding the impedance match in the
feedpoint. I have surveyed the ARRL Antenna Book and Antennebuch (a German
antenna book very popular in Europe). The properties of the antenna and its
impedance is well understood. The missing point is how to realise the
matching network

In order to avoid reinventing the whee: Does anybody have some good links to
study practical realisations of the matching network?

vy 73

Joergen, OZ7TA



I am curious as to what the expected use will be. I am not familiar
with 6m in Europe, but 50 megahertz vertical in the US is not something
you will work much on.

If you are looking to work SSB on 6m, you will be better off with a
horizontal antenna. There are many easily built 6m beam plans available.

tom
K0TAR

Tom Ring wrote:

I am curious as to what the expected use will be. I am not familiar
with 6m in Europe, but 50 megahertz vertical in the US is not something
you will work much on.

If you are looking to work SSB on 6m, you will be better off with a
horizontal antenna. There are many easily built 6m beam plans available.

tom
K0TAR

Respond if you'd like some.

tom
K0TAR

wrote in message
...
On Sat, 16 Sep 2006 14:25:35 +0200, "J. Kragh"
wrote:

Togethere wih a fellow amateur I am trying to design an endfeed halfvawe
vertical antenna for 50 MHz.

snip

Look at a J-pole antenna. Its really a stub section feeding a halfwave
antenna.

The impedence transformation has to go from coax (60-75 ohms) to
a much higher and possibly reactive load in the range of
1500-3000j(+/-)0-100 depending on dimensions of the halfwave antenna
relative to the actual frequency.

Yes. I have built three copper-pipe j-poles for 6 M. The overall length is
about 13 feet (4 meters) long. I made them predominantly from 3/4-inch
copper water pipe, which comes in 10-foot lengths in the US. I used a
reducer and about three feet of 1/2-inch pipe for the top part of the long
section. All of the connections are standard water-pipe fittings and the
soldering is with a propane torch on sanded and fluxed surfaces. These
three are among about twenty j-poles I've made for VHF/UHF. They seem to be
indestructible.

I was able to match about 80 percent of the 6 meter band under 3:1. My best
SWR was about 1.2:1 with a short length of coax and nothing special at the
feed point. A choke consisting of four turns of the coax is recommended for
decoupling.

I am a j-pole lover. I intend to try a flagpole or two at HF, someday.

Good morning all

I take the opportunity to answer all of you at once.

Thank you for a lot of suggestions. I had thought about the J-pole the
problem however the problem is that we have some glass fibre tubes only
about 25 mm in diameter, so we are somewhat constrained with respect to
realise a J-pole.

Regarding a groundplane as suggested by some, the idea is to mount the
antenna on top of a mast much like an ordinary 2 meter or 70 cm vertical
antenna. In these circumstances a ground plane is not feasible.

Tom Ring asked about 6 metres in Europe. In some counties among them Denmark
there are few FM repeaters in operation. A number of amateurs have either
old army radios or modified Land Mobile Radios (LMR), typically salvaged
from taxis, fire engines and so on. All these radios operate in FM. Our idea
was to operate in this segment of 6 meter operation, not to operate in the
DX part of the band. Together with som fellow amateurs we have also tried 6
metre mobile. It actually works!

vy 73 and once again thanks for the responses

Joergen, OZ7TA
"J. Kragh" skrev i en meddelelse
k...
Togethere wih a fellow amateur I am trying to design an endfeed halfvawe
vertical antenna for 50 MHz.

We have encountered som problems regarding the impedance match in the
feedpoint. I have surveyed the ARRL Antenna Book and Antennebuch (a
German antenna book very popular in Europe). The properties of the antenna
and its impedance is well understood. The missing point is how to realise
the matching network

In order to avoid reinventing the whee: Does anybody have some good links
to study practical realisations of the matching network?

vy 73

Joergen, OZ7TA

"Tom Ring" wrote in message
.. .
Tom Ring wrote:

I am curious as to what the expected use will be. I am not familiar with
6m in Europe, but 50 megahertz vertical in the US is not something you
will work much on.

If you are looking to work SSB on 6m, you will be better off with a
horizontal antenna. There are many easily built 6m beam plans available.

tom
K0TAR

Respond if you'd like some.

tom
K0TAR

If he plans on working Es, Aurora, F2 etc. vertical polarity will work just
as well as horizontal, except for maybe more man made noise p/u on the
vertical.

Dale W4OP

If he plans on working Es, Aurora, F2 etc. vertical polarity will work
just
as well as horizontal, except for maybe more man made noise p/u on the
vertical.

Dale W4OP

If that's the plan Dale, he really ought to use something besides a half
wave dipole no matter what the polarization!

W4ZCB

Jeff Caird wrote:
"J. Kragh" wrote in
k:

Togethere wih a fellow amateur I am trying to design an endfeed
halfvawe vertical antenna for 50 MHz.

We have encountered som problems regarding the impedance match in the
feedpoint. I have surveyed the ARRL Antenna Book and Antennebuch (a
German antenna book very popular in Europe). The properties of the
antenna and its impedance is well understood. The missing point is how
to realise the matching network

In order to avoid reinventing the whee: Does anybody have some good
links to study practical realisations of the matching network?

vy 73

Joergen, OZ7TA



An endfed halfwave has inductive reactance, ISTR. If you add another 1/8
wave to it, you reverse the sign of the reactance, thereby allowing an
inductance to tune out the reactance. Ground one end of the inductor and
tap down with the coax center conductor for a 50 ohm match--Voila! A 5/8
wave vertical!

Jeff

I think the 5/8ths is much more practical on 50 than the 1/2
wavelength. You will find the matching unit much easier to build. The
down side is you have to have radials.

J. Kragh wrote:
Togethere wih a fellow amateur I am trying to design an endfeed halfvawe
vertical antenna for 50 MHz.

We have encountered som problems regarding the impedance match in the
feedpoint. I have surveyed the ARRL Antenna Book and Antennebuch (a German
antenna book very popular in Europe). The properties of the antenna and its
impedance is well understood. The missing point is how to realise the
matching network

In order to avoid reinventing the whee: Does anybody have some good links to
study practical realisations of the matching network?

vy 73

Joergen, OZ7TA

Joergen, I was working along the same lines for a 60M/5MHz antenna
several years ago. I asked the coded Extras on RRAP for suggestions
and got some pretty nasty replies. I hope that you are able to find
the help that you need.

Best of Luck!

bb

J. Kragh wrote:
Good morning all

snip

Tom Ring asked about 6 metres in Europe.

K8MN, from Africa, managed to snag a bunch of out of band Frenchmen on
6M.

Perhaps he could shed some light on 6M DX Operations.