This may be a dumb question for some of you, but.....

I understand what a choke does at the feed point (I use an air wound one at
my feed point) However, I am having trouble understanding the purpose of one
near your rig.

Also what effect happens in the coax between the two chokes?

Thanks
Joe

On Sat, 3 Mar 2007 16:41:07 -0500, "merlin-7"
wrote:

This may be a dumb question for some of you, but.....

I understand what a choke does at the feed point (I use an air wound one at
my feed point) However, I am having trouble understanding the purpose of one
near your rig.

Also what effect happens in the coax between the two chokes?

Hi Joe,

The one near your rig would be opportunistic (on the chance it was
needed). However, as it could satisfy a need then that leads us to
your second question.

The portion of the line beyond the choke at the antenna is still in a
strong field that "could" couple energy into it and reestablish the
common mode currents the choke was there to prevent. If you were to
place a second choke a quarter wave from the first, that would snub
this coupling (and thus the one at the rig, if it were harmonically
related, would also tend to snub common mode current).

I use a 20 foot line section with about 60 ferrite beads distributed
along it to make for a more multiband, or general purpose second
choke.

73's
Richard Clark, KB7QHC

In article ,
Richard Clark wrote:

On Sat, 3 Mar 2007 16:41:07 -0500, "merlin-7"
wrote:

This may be a dumb question for some of you, but.....

I understand what a choke does at the feed point (I use an air wound one at
my feed point) However, I am having trouble understanding the purpose of one
near your rig.

Also what effect happens in the coax between the two chokes?

Hi Joe,

The one near your rig would be opportunistic (on the chance it was
needed). However, as it could satisfy a need then that leads us to
your second question.

The portion of the line beyond the choke at the antenna is still in a
strong field that "could" couple energy into it and reestablish the
common mode currents the choke was there to prevent. If you were to
place a second choke a quarter wave from the first, that would snub
this coupling (and thus the one at the rig, if it were harmonically
related, would also tend to snub common mode current).

I use a 20 foot line section with about 60 ferrite beads distributed
along it to make for a more multiband, or general purpose second
choke.

73's
Richard Clark, KB7QHC

hi Richard

on that 20footer of yours, do you coil it up or leave it straight

and are the beads spaced random or did you calculate each location

On Sat, 3 Mar 2007 16:41:07 -0500, "merlin-7"
wrote:

This may be a dumb question for some of you, but.....

I understand what a choke does at the feed point (I use an air wound
one at
my feed point) However, I am having trouble understanding the purpose
of one
near your rig.

Also what effect happens in the coax between the two chokes?

Hi Joe,

The one near your rig would be opportunistic (on the chance it was
needed). However, as it could satisfy a need then that leads us to
your second question.

The portion of the line beyond the choke at the antenna is still in a
strong field that "could" couple energy into it and reestablish the
common mode currents the choke was there to prevent. If you were to
place a second choke a quarter wave from the first, that would snub
this coupling (and thus the one at the rig, if it were harmonically
related, would also tend to snub common mode current).

I use a 20 foot line section with about 60 ferrite beads distributed
along it to make for a more multiband, or general purpose second
choke.

73's
Richard Clark, KB7QHC

Thanks, I get it now. Sometimes I miss the simple things (not seeing the
trees thru the forest)

Now to make things more complicated.....

I use a modified fan dipole for all bands from 10m to 80m so how to figure
out where to place the beads would be pretty hard to figure out. I really do
not favor any frequency on any band.

I do not seem to have any problems with the feed or the antenna but hell I
am all for trying different ideas.

I will be moving soon and starting over with my set-up. So now is a great
time to plan everything.

Would placing the beads, 1/4 wave apart, midband for every band, have any
benefit?

Also, where is a good place to buy them? I use airwound chokes now but they
have there limits along with the added loss of more coax....

Thanks
KI4ILB

On Sun, 04 Mar 2007 12:14:59 GMT, ml wrote:

hi Richard

on that 20footer of yours, do you coil it up or leave it straight

and are the beads spaced random or did you calculate each location

Hi Myles,

The beads are spread evenly along the length, and I generally use it
to lead away from the choke so that it is in the highest field.

73's
Richard Clark, KB7QHC

On Sun, 4 Mar 2007 12:59:50 -0500, "merlin-7"
wrote:

I do not seem to have any problems with the feed or the antenna but hell I
am all for trying different ideas.

Hi Joe,

Well, if you are trying new ideas, how do you test how effective they
are if there is no problem to solve?

I will be moving soon and starting over with my set-up. So now is a great
time to plan everything.

Truly, truly.

Would placing the beads, 1/4 wave apart, midband for every band, have any
benefit?

It would certainly add more isolation for all bands. You might want
to focus on connector strain relief.

Also, where is a good place to buy them? I use airwound chokes now but they
have there limits along with the added loss of more coax....

Amidon, Fair-rite are two brands that come to mind. There are others
certainly, but having bought and scavenged all that I've ever needed
some 10 - 15 years ago, I wouldn't know just where to purchase (google
can undoubtedly point you in that direction). The harder part is
choosing which formula and form factor. I will leave that to others
to chime in, providing you aren't inundated by theorists.

73's
Richard Clark, KB7QHC