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

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

How about 1.3 meter (4.3 feet) of 450 ohm ladder-line
as a series-section-transformer?
--
73, Cecil http://www.w5dxp.com

Go back to the ARRL antenna handbooks from the 1970's or 1980's... Look
in the chapter for HF antennas for 160 and 80 meters... Somewhere in
there will be the diagram for an end fed long wire using a parallel
tank circuit - an inductor and a variable capacitor in parallel...
This will work just the same for your end fed half wave vertical on 6
meters...
The bottom end of the tank circuit goes to your ground/radials... And
the top end goes to the bottom end of your half wave vertical wire...
Your transmitter coax has the braid going to the bottom end of the tank
circuit and the center feed of the coax is tapped up a few turns from
the bottom of the coil to match 50 ohms.. Use a few turns of the coax
as a choke for common mode currents on the outside of the braid...
Obviously you will not be using components with as much inductance and
capacitance as you would for 160 meters... As a guess I would say that
for 50 mhz you will be tapping up roughly between 3/4 turn to one and
a half turns from the bottom to get a match... This of course depends
on the form factor of your coil, i.e. short/fat versus long/skinney..
Trying this on your work bench is the best way.. Make up a coil from
#14 AWG solid house wiring and a variable capacitor, use a length of
the house wiring for the radials and vertical and experiment...
Another method is the J Pole matching system.. Look in chapter 18 of
the current ARRL Antenna Handbook...


cheers denny / k8do

"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

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

How about a zepp antenna fed with open wire, with the antenna running
vertically.

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

Google WB6BLD. Or just go to http://tonnesoftware.com/piel.html Jim has
design software of both Pi and L networks that will perfectly match the
anticipated impedance to 50 Ohms. Other interesting Amateur Radio associated
software as well and free student versions.

W4ZCB

On Sat, 16 Sep 2006 14:25:35 +0200, "J. Kragh"
wrote:
In order to avoid reinventing the whee: Does anybody have some good links to
study practical realisations of the matching network?

Hi Joergen,

http://www.70mhz.org/halfwav.htm
http://www.qsl.net/dk7zb/6m/Vertical.htm
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=13226 (duplicate)

73's
Richard Clark, KB7QHC

The simplest fed is a L network with the C at the transmitter end
and the antenna at the unterminated inductor end. Works best
in the radiator is slightly capacitive looking.


Specificallly check the article "feeding the EDZ" as that
talks about the problem at hand.



Allison


Not really, the capacitor goes on the end of the coil closest to the higher
impedance. I'm certain his half wave will be appreciably above 50 Ohms.
Mine's about 2600 Ohms.

W4ZCB

wrote:
On Sat, 16 Sep 2006 17:41:01 GMT, "Harold E. Johnson"
wrote:


The simplest fed is a L network with the C at the transmitter end
and the antenna at the unterminated inductor end. Works best
in the radiator is slightly capacitive looking.

Specificallly check the article "feeding the EDZ" as that
talks about the problem at hand.



Allison



Not really, the capacitor goes on the end of the coil closest to the higher
impedance. I'm certain his half wave will be appreciably above 50 Ohms.
Mine's about 2600 Ohms.

W4ZCB



You must have missed the second sentence where I state at
resonance It's a high resistance. I think we agree.

""For a "half wave" fed at the end the sign of the reactive part will
vary depending on it's real length. If it's really resonant there is
no reactive component only a very high resistive one. ""

However in a few cases I found the radiator and mountings to be
capacitive enough to result in no additional capacitance needed.
We agree but implementation sometimes takes other forms.

One of the sites posted suggests a PI network and again with the right
values it's the most flexiable and offers a low pass characteristic
that never hurts.


Allison




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

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