Highland Ham wrote:
Also: http://www.hamuniverse.com/balun.html (many pictures)
================
Nice URL with excellent info

The problem with ugly baluns is their limited frequency
ranges. In the following measurements, the choking
impedance was over 1k ohms for only small ranges of
frequencies, 19-29 MHz, 10-22 MHz, 16-25 MHz, 8-16 MHz,
5-8 MHz - frequency ranges of 2/1 or less. HF covers
a 10/1 frequency range.

http://www.k1ttt.net/technote/airbalun.html
--
73, Cecil http://www.w5dxp.com

On Aug 28, 8:45*am, Cecil Moore wrote:
Highland Ham wrote:
Also: *http://www.hamuniverse.com/balun.html*(many pictures)
================
Nice URL with excellent info

The problem with ugly baluns is their limited frequency
ranges. In the following measurements, the choking
impedance was over 1k ohms for only small ranges of
frequencies, 19-29 MHz, 10-22 MHz, 16-25 MHz, 8-16 MHz,
5-8 MHz - frequency ranges of 2/1 or less. HF covers
a 10/1 frequency range.

http://www.k1ttt.net/technote/airbalun.html
--
73, Cecil *http://www.w5dxp.com

I noticed the use of a lot of tie wraps. Its never a good idea to use
these exposed to sun light.



Jimmie

"JIMMIE" wrote in I noticed the use of a lot of
tie wraps. Its never a good idea to use
these exposed to sun light.

Most of the white tie wraps will not withstand sunlight. The black ones are
more UV ray resistant and do beter.

I sometimes use the white ones, but cover them with tape.
Scotch 33 tape.

JIMMIE wrote:

I noticed the use of a lot of tie wraps. Its never a good idea to use
these exposed to sun light.
=============================
Black tie wraps contain carbon black and are hence UV resistant and
almost last forever.

Coloured or non pigmented plastic will indeed deteriorate due to UV
radiation.

Polypropylene rope , for example ,is usually coloured but never black.
Reason : If black it would not deteriorate due to exposure to UV ,hence
it would last far too long and the manufacturers would only need to
produce a fraction of their current production.
That's commercial life.

If you use rope other then polyester (sailing boats etc) try to find a
black plastic variety (not easy).
My 40 ft mast has (blue)polypropylene guys which need to be replaced
every 8 -9 years (even here in northern Scotland) ,but it is cheap
compared with polyester rope.

Frank GM0CSZ / KN6WH

I use an ugly balun with an attic GRrV and do not suffer significant
back-RFI to my transceiver in the regular frequency ranges. I think
that by chosing 1Kohm that may be a bit conservative. In (old)
engineering school, we tended to use an order of magnitude (X10) as
our highly arbitrary cut-off point for impedances that have a
significant effect. You are doing that too but by using 1000 ohms, you
are using (X10 times 2) as your arbitrary cutoff point. Since the
filter is an exponential curve, if you chose 500 ohms instead of 1000
ohms, you might even get a 4 or 5 to 1 frequency range. In my case I
use two different turns chokes so that is why I think I am covered
pretty well. Your information is very interesting; good to see people
are actually measuring things!


On Aug 28, 8:45*am, Cecil Moore wrote:
Highland Ham wrote:
Also: *http://www.hamuniverse.com/balun.html*(many pictures)
================
Nice URL with excellent info

The problem with ugly baluns is their limited frequency
ranges. In the following measurements, the choking
impedance was over 1k ohms for only small ranges of
frequencies, 19-29 MHz, 10-22 MHz, 16-25 MHz, 8-16 MHz,
5-8 MHz - frequency ranges of 2/1 or less. HF covers
a 10/1 frequency range.

http://www.k1ttt.net/technote/airbalun.html
--
73, Cecil *http://www.w5dxp.com

wrote:
I use an ugly balun with an attic GRrV and do not suffer significant
back-RFI to my transceiver in the regular frequency ranges. I think
that by chosing 1Kohm that may be a bit conservative. In (old)
engineering school, we tended to use an order of magnitude (X10) as
our highly arbitrary cut-off point for impedances that have a
significant effect. You are doing that too but by using 1000 ohms, you
are using (X10 times 2) as your arbitrary cutoff point. Since the
filter is an exponential curve, if you chose 500 ohms instead of 1000
ohms, you might even get a 4 or 5 to 1 frequency range. In my case I
use two different turns chokes so that is why I think I am covered
pretty well. Your information is very interesting; good to see people
are actually measuring things!

Actually, 1000 ohms is pretty liberal. For instance, on
15m, the G5RV coax sees 36+j230 ohms or about 233 ohms.
The balun needs to be 10x that value or 2330 ohms.
--
73, Cecil http://www.w5dxp.com

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