JB wrote:
My take on CM chokes is that they are best on TV coax to keep energy on the
shield from bringing trouble to the TV chassis. On a transmitting antenna,
the idea is to enforce a high impedance bump somewhere to set the resonant
length other than what it wants to be. That might not contribute to
efficiency even if it prevents the coax from being part of the antenna. If
the antenna is in resonance, there won't be any coax radiation and no Choke
is really needed. My point is, you are best not needing one, but if that is
what you need to put the current out on the wire, or out of the shack. OK.
Of course high gain antennas have a pattern to protect, but does it matter
all that much for anything up to a 3 element yagi? High currents and
voltages on the coax are to be avoided because that is where your loss will
be.



That is so bizarre; I just don't know where to begin in the description
of how and how much!

Regards,
JS

"John Smith" wrote in message
...
JB wrote:
My take on CM chokes is that they are best on TV coax to keep energy on
the
shield from bringing trouble to the TV chassis. On a transmitting
antenna,
the idea is to enforce a high impedance bump somewhere to set the
resonant
length other than what it wants to be. That might not contribute to
efficiency even if it prevents the coax from being part of the antenna.
If
the antenna is in resonance, there won't be any coax radiation and no
Choke
is really needed. My point is, you are best not needing one, but if
that is
what you need to put the current out on the wire, or out of the shack.
OK.
Of course high gain antennas have a pattern to protect, but does it
matter
all that much for anything up to a 3 element yagi? High currents and
voltages on the coax are to be avoided because that is where your loss
will
be.



That is so bizarre; I just don't know where to begin in the description
of how and how much!

Regards,
JS

Ya I know, I didn't get into the how. How much is the first thing you need
to be aware of.

JB wrote:

...
Ya I know, I didn't get into the how. How much is the first thing you need
to be aware of.



Then this work:

http://www.hep.princeton.edu/~mcdona...andards_93.pdf

by Jerry Sevick, may be of significant interest to you ...

Regards,
JS

JB wrote:

...
Ya I know, I didn't get into the how. How much is the first thing you need
to be aware of.



You may also find this picture of a 1:1 guanella balun of interest.
Notice the "crossover" which alters the direction of the common winding
between sides of the core ...

Regards,
JS

"John Smith" wrote in message
...
JB wrote:

...
Ya I know, I didn't get into the how. How much is the first thing you
need
to be aware of.



You may also find this picture of a 1:1 guanella balun of interest.
Notice the "crossover" which alters the direction of the common winding
between sides of the core ...

Regards,
JS

There ya go.
One of the problems of breaking up the path to ground on the shield is that
now static can build up. If you can provide a way to bleed off the charges
that build up on both halves, while breaking up the shield currents, now you
have made it worthwhile. But when you guys start discussing off center fed
dipoles, I step aside. I have computers in the shack. I have better luck
with fan dipoles. Also running a Butternut vertical. Works a lot better
than a 4btv, but a pain to get it right on all bands.

Thanks

Also liked the other pdfs presented. I never have time to read them all
because of constant interruption around here. Back to work.

JB wrote:

...
There ya go.
One of the problems of breaking up the path to ground on the shield is that
now static can build up. If you can provide a way to bleed off the charges
that build up on both halves, while breaking up the shield currents, now you
have made it worthwhile. But when you guys start discussing off center fed
dipoles, I step aside. I have computers in the shack. I have better luck
with fan dipoles. Also running a Butternut vertical. Works a lot better
than a 4btv, but a pain to get it right on all bands.

Thanks

Also liked the other pdfs presented. I never have time to read them all
because of constant interruption around here. Back to work.



OCF antennas were not fully appreciated by me, a few of Cecils' helpful
insights and encouragement and I built one and was rather surprised ...
I do not have one right now but that is only due to neighbors/property
constraints.

Here is a URL for design/implementation of "non-standard"
baluns/transformers, but of a highly useable and desirable nature--or,
Dr. Sevick strikes again!:

http://www.highfrequencyelectronics....104_Sevick.pdf

Fig. 6(A) is very interesting. A 5-winding, 1:1.56 bootstrap
transformer which provides 50/75 ohm connections/substitutions. Perfect
for allowing one to use 75 ohm "junk" (or found in dumpsters) tv coax in
place of more expensive 50 ohm coax.

I have made good use of this since I have thousands of feet of NEW 75
ohm coax I purchased from a scrap dealer for next-to-nothing! A lot of
large dia coax and hard-line mixed in!

Regards,
JS

Here is a URL for design/implementation of "non-standard"
baluns/transformers, but of a highly useable and desirable nature--or,
Dr. Sevick strikes again!:

http://www.highfrequencyelectronics....104_Sevick.pdf

Fig. 6(A) is very interesting. A 5-winding, 1:1.56 bootstrap
transformer which provides 50/75 ohm connections/substitutions. Perfect
for allowing one to use 75 ohm "junk" (or found in dumpsters) tv coax in
place of more expensive 50 ohm coax.

I have made good use of this since I have thousands of feet of NEW 75
ohm coax I purchased from a scrap dealer for next-to-nothing! A lot of
large dia coax and hard-line mixed in!

Regards,
JS
A little mismatch isn't such a problem. At least if you can get the loss
down. I wouldn't even worry about it, the internal tuner would make short
work of that. Look out for water damage on that stuff though. Especially
the Aluminum braid/foil shield stuff like LMR. Even a little bit of
moisture percolates all through the braid.and turns it into aluminum oxide
powder and extremely noisy with power on it. It could look brand new and
you would keep cutting it back, then find a foot of new braid but keep
cutting and its back to chalk. We would routinely assume it bad and throw
it away. At least with the Hardline, you can sweep it and put some power to
it to check the loss Only hardline allowed on towers.

JB wrote:

...
A little mismatch isn't such a problem. At least if you can get the loss
down. I wouldn't even worry about it, the internal tuner would make short
work of that. Look out for water damage on that stuff though. Especially
the Aluminum braid/foil shield stuff like LMR. Even a little bit of
moisture percolates all through the braid.and turns it into aluminum oxide
powder and extremely noisy with power on it. It could look brand new and
you would keep cutting it back, then find a foot of new braid but keep
cutting and its back to chalk. We would routinely assume it bad and throw
it away. At least with the Hardline, you can sweep it and put some power to
it to check the loss Only hardline allowed on towers.


Since it was on spools, and dusty, had no concern with that. LOL

Regards,
JS
--
It is like a nightmare where the public servants are people which the
police are supposed to protect you from!

In message , John Smith
writes
JB wrote:

...
There ya go.
One of the problems of breaking up the path to ground on the shield is that
now static can build up. If you can provide a way to bleed off the charges
that build up on both halves, while breaking up the shield currents, now you
have made it worthwhile. But when you guys start discussing off center fed
dipoles, I step aside. I have computers in the shack. I have better luck
with fan dipoles. Also running a Butternut vertical. Works a lot better
than a 4btv, but a pain to get it right on all bands.
Thanks
Also liked the other pdfs presented. I never have time to read them
all
because of constant interruption around here. Back to work.


OCF antennas were not fully appreciated by me, a few of Cecils' helpful
insights and encouragement and I built one and was rather surprised ...
I do not have one right now but that is only due to neighbors/property
constraints.

Here is a URL for design/implementation of "non-standard"
baluns/transformers, but of a highly useable and desirable nature--or,
Dr. Sevick strikes again!:

http://www.highfrequencyelectronics....104_Sevick.pdf

Fig. 6(A) is very interesting. A 5-winding, 1:1.56 bootstrap
transformer which provides 50/75 ohm connections/substitutions.
Perfect for allowing one to use 75 ohm "junk" (or found in dumpsters)
tv coax in place of more expensive 50 ohm coax.

I have made good use of this since I have thousands of feet of NEW 75
ohm coax I purchased from a scrap dealer for next-to-nothing! A lot of
large dia coax and hard-line mixed in!

Regards,
JS

What about the loss in the balun? You need to decide if the loss in the
balun is less than that you would get if you simply used the 75 ohm coax
direct. And ask yourself 'In my application, why would 75 ohm be more
lossy?' Also, with similar physical dimensions, construction etc, 75 ohm
coax is slightly less lossy than 50 ohm (current is less, so 'I squared
R' loss is less).
--
Ian

Ian Jackson wrote:

...
What about the loss in the balun? You need to decide if the loss in the
balun is less than that you would get if you simply used the 75 ohm coax
direct. And ask yourself 'In my application, why would 75 ohm be more
lossy?' Also, with similar physical dimensions, construction etc, 75 ohm
coax is slightly less lossy than 50 ohm (current is less, so 'I squared
R' loss is less).

Simple solution, I trust my S-meter!

Regards,
JS

--
It is like a nightmare where the public servants are the people which
the police are supposed to protect us from!