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.

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

On Mon, 01 Sep 2008 16:07:39 GMT, "JB" wrote:
How's this for testimony

It isn't.

Oh it's you again. You don't seem to do much other than poke the fire.

There weren't even sparks left in those dead ashes.

73's
Richard Clark, KB7QHC

JB wrote:
Just because God knows how everything will turn out, doesn't mean our
choises are of no value.

Actually, if God knows the future, the future is fixed,
everything is predestined, and we do not have free will.
If God already knew everything about this posting of
mine before I made it, I had no choice but to make it
using these exact words.
--
73, Cecil http://www.w5dxp.com

JB wrote:
In the end you will have to be open to the Holy
Spirit before anything can come of it.

Please prove that the "Holy Spirit" exists outside
of the human mind.
--
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

wrote:
A common mode choke is used in RF applications, very true, but it
serves a filtering purpose, not a conversion of unbalanced to
balanced energy transfer or vice
versa. A common mode choke that operates well will turn
unwanted RF into heat or cause it to dissipate in its core or a
resistor etc..

The common "W2DU balun" works well as both choke and
balun function.
--
73, Cecil http://www.w5dxp.com

Readers interested in baluns might take a look at "Baluns: What They Do
and How They Do It" in the _ARRL Antenna Compendium_, Vol. 1 or at
http://eznec.com/Amateur/Articles/Baluns.pdf.

Roy Lewallen, W7EL

Cecil Moore wrote:

...
Actually, if God knows the future, the future is fixed,
everything is predestined, and we do not have free will.
If God already knew everything about this posting of
mine before I made it, I had no choice but to make it
using these exact words.

Actually, I have heard this argument(s)/discussion(s) since a very early
age.

I see no conflict between me having complete free choice and the ability
to control my destiny exactly as I see fit, or change my mind to fit
me--right along side an all-knowing mind who has already seen every
decision and change of heart I will have in my lifetime (the future is
there for me to discover and make my decisions to influence--but
he/she/it/the-aliens has/have already "been there, seen that!" ... )

What am I missing?

Regards,
JS

Cecil Moore wrote:
JB wrote:
In the end you will have to be open to the Holy
Spirit before anything can come of it.

Please prove that the "Holy Spirit" exists outside
of the human mind.

Well, "Grain Spirits" exist outside my mind (and body), until I drink
them--then suddenly, I feel like I am "FILLED WITH THE HOLY
SPIRIT!"--well, if I drink enough anyway ... ;-)

Obviously, in the above, that "HOLY SPIRIT" was not originally there, so
it had to be outside, somewhere! :-|

Regards,
JS