Many hams will recommend you try a home-made balun, multiple turns of coax
cable wound neatly around a cylindrical form. Exact requirements and
effectiveness may vary with frequency and the antenna as installed.

I saw an interesting talk at a local ham-club, at which the presenter
gave an explanation for one reason that the "effectiveness may vary"
with these sorts of choke baluns.

The common-mode impedance created by many such chokes is primarily
inductive (below the choke's self-resonant frequency, at least).

The impedance of the unwanted current path (e.g. from the antenna
feedpoint, back along the outside of the feedline, to the transceiver
chassis or to the point at which the coax is grounded) will depend on
the frequency and the length of the coax. It'll have a resistive
component (from loss resistance and from radiation resistance) and
will usually have a reactive component as well... either inductive or
capacitive.

If the feedline-path reactance is inductive or near zero, all is
well... the choke balun's inductive reactance will (if sufficiently
high) block most current flow along this path.

On the other hand, if the feedline-path reactance is capacitive, and
happens to be close in absolute value to the inductive reactance of
the choke... then you've got a series-resonant circuit. The two
reactances will largely cancel, the choke will "vanish", and you can
actually have more current flow back along the feedline than you would
without the choke.

If you change the length of the feedline, the choke's performance can
get better, or worse.

His prescription: if you want choking that's going to be effective at
a wide range of frequencies and won't be sensitive to the feedline
length, you need to use a choke which will introduce a significant
amount of resistive loss into the choked path (but not, of course,
into the differential path that feeds the antenna). The usual
solution is a ferrite.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dave Platt wrote:
On the other hand, if the feedline-path reactance is capacitive, and
happens to be close in absolute value to the inductive reactance of
the choke... then you've got a series-resonant circuit.

This is one reason why an ugly choke only works well over
approximately a 2:1 frequency range. Below that range,
the inductive reactance is too small and above that
range, series resonance defeats the purpose.
--
73, Cecil http://www.w5dxp.com

Dave Platt wrote:

...
I saw an interesting talk at a local ham-club, at which the presenter
gave an explanation for one reason that the "effectiveness may vary"
with these sorts of choke baluns.
...

In 1982, when I worked for Boeing, they flew us to New York to attend
some lectures ...

Anyway, I remember one guy who gave an hour-and-a-half talk, complete
with slides, charts, models and other presentation aids on why the
bumblebee can't possibly fly ... it was totally fascinating, the data
looked absolutely real!--even though everyone (well, most) in the room
realized they were being "put on."

To anyone who has wound and used a few dozen chokes/baluns/ununs of
varying designs, I highly recommend the "Bumblebee Lecture."

Now, I am off to watch a few bumblebees crawl about ...

Regards,
JS

On Aug 28, 5:10*pm, John Smith danced
around naked pulling on his meat:
snip a lot of John Smiths bull**** diatribe

Now, I am off to watch my momma crawl about ...

Momma still selling her pussy on the corner huh John? I bet she still
has nightmares over your conception from the guy that donated her his
half of your egg! I guess the old saying that you get what you pay
for is true and its a shame your momma had to pay for the other half
from some old whino in Bakersfield, living under the freeway ramp in a
box!

Regards,
JS

John Smith wrote:
On Aug 28, 5:10 pm, John Smith danced
around naked pulling on his meat:
snip a lot of John Smiths bull**** diatribe
Now, I am off to watch my momma crawl about ...

Momma still selling her pussy on the corner huh John? I bet she still
has nightmares over your conception from the guy that donated her his
half of your egg! I guess the old saying that you get what you pay
for is true and its a shame your momma had to pay for the other half
from some old whino in Bakersfield, living under the freeway ramp in a
box!
Regards,
JS


Does make you wonder:

1) Some disgruntled ham with mental problems?

2) Some wino with a stolen laptop and wifi link?

3) Individual that is a product of the current school system?

4) Local/county/state/federal politician?

5) Religious devotee of the arrl?

6) Someone bored with the traffic on a moderated news group?

7) Retarded relative/family-member of a group member here--sneaking
about and gaining unauthorized access to his/her computer?

8) ...

plonk ...

Regards,
JS