I am getting ready to place a choke at the feedpoint of my half sloper,
hoping to lower the noise level.

Question: would the same action help with a normal beam (a 3-element
SteppIR, in this case)? I think there is a balun of some type in the driven
element of the SteppIR, and I do not know how much this rejects noise pickup
on the external shield of the coax. (The coaxes for both antennas run about
50' underground, and then about 60' up the tower.)

Bill - W2WO

On Thu, 27 Sep 2007 09:00:48 -0400, "Bill Ogden"
wrote:

I am getting ready to place a choke at the feedpoint of my half sloper,
hoping to lower the noise level.

Question: would the same action help with a normal beam (a 3-element
SteppIR, in this case)? I think there is a balun of some type in the driven
element of the SteppIR, and I do not know how much this rejects noise pickup
on the external shield of the coax. (The coaxes for both antennas run about
50' underground, and then about 60' up the tower.)

Bill - W2WO


http://audiosystemsgroup.com/RFI-Ham.pdf

On 27 sep, 15:00, "Bill Ogden" wrote:
I am getting ready to place a choke at the feedpoint of my half sloper,
hoping to lower the noise level.

Question: would the same action help with a normal beam (a 3-element
SteppIR, in this case)? I think there is a balun of some type in the driven
element of the SteppIR, and I do not know how much this rejects noise pickup
on the external shield of the coax. (The coaxes for both antennas run about
50' underground, and then about 60' up the tower.)

Bill - W2WO

Hello Bill,

Assuming a good balun, feeder in symmetry plane of beam and the 50"
under ground, I do not expect much off it.

Also when there would be noise climbing up the feeder (to the beam),
the noise could also use the (metal) mast.

You might place a signal source at your location close the coaxial
feeder. Add some common mode rejection and see whether it works. You
should source ferrite material with the highest impedance at the
working frequency.

Best regards,

Wim
PA3DJS

" Assuming a good balun, feeder in symmetry plane of beam and the 50"
under ground, I do not expect much off it.

Also when there would be noise climbing up the feeder (to the beam),
the noise could also use the (metal) mast.

Good point and that is why I am a little confused about using chokes to
lower noise --- in any situation where the coax goes up a tower.

A number of very well-written and interesting papers
describe the effective rejection of chokes (over 5000 ohms when looping the
coax
through several #31 toroids), but they do not discuss the effects on the
total antenna system. As you said, it would seem that any pickup by the coax
external shield would be mostly duplicated by the tower itself and this
would bypass the choke if the coax shield is "grounded" to the tower at the
feed point. (Yes, I know "ground" has many meanings.)

I can see where the choke would help with a dipole, where the coax is not
connected to the tower at all.

Bill - W2WO

On Fri, 28 Sep 2007 10:01:13 -0400, "Bill Ogden"
wrote:


" Assuming a good balun, feeder in symmetry plane of beam and the 50"
under ground, I do not expect much off it.

Also when there would be noise climbing up the feeder (to the beam),
the noise could also use the (metal) mast.

Good point and that is why I am a little confused about using chokes to
lower noise --- in any situation where the coax goes up a tower.

A number of very well-written and interesting papers
describe the effective rejection of chokes (over 5000 ohms when looping the
coax
through several #31 toroids), but they do not discuss the effects on the
total antenna system. As you said, it would seem that any pickup by the coax
external shield would be mostly duplicated by the tower itself and this
would bypass the choke if the coax shield is "grounded" to the tower at the
feed point. (Yes, I know "ground" has many meanings.)

I can see where the choke would help with a dipole, where the coax is not
connected to the tower at all.

Hi Bill,

The confusion may arrise from the tower's two uses. For the sloper,
it is active; for the beam it shouldn't be.

For the sloper, choke the line at the bottom of the tower. For the
beam, choke the line at the top and the bottom of the tower.

However, as far as this conventional advice goes, the lower choking
would seem to be redundant to the 50 foot run under ground. That
should choke the line just as well. If the beam comes with a choke
(I'm not sure how much they invest in that technically instead of just
for advertising's sake) then there's no point in more there either.

Take a clamp-on ferrite, build a loop of a dozen turns of fine wire
through it; terminate the wire with an LED. Attach this inside the
shack to any feed line and see if the LED lights up during a QSO. If
it does, you may want to replace the LED with a RF Current meter to
see just how much current there is, but my guess is the LED will be
dim at best. [LED current of 10-20 mA @ 2V will be quite bright.]

73's
Richard Clark, KB7QHC

For the sloper, choke the line at the bottom of the tower. For the
beam, choke the line at the top and the bottom of the tower.

However, as far as this conventional advice goes, the lower choking
would seem to be redundant to the 50 foot run under ground. That
should choke the line just as well. If the beam comes with a choke
(I'm not sure how much they invest in that technically instead of just
for advertising's sake) then there's no point in more there either.



Good advice about the sloper; and about the 50' underground acting as a
choke. I was hoping for a magic solution to a little of the "atmospheric"
noise on 80 and 160, but there may not be any magic.

I do not sense much of a noise problem with the beam, but I will try a choke
at the feed point sometime. (The coax to the beam also has the 50'
underground run, so a choke at the bottom of the tower is probably not
needed.)

Bill - W2WO

On Sun, 30 Sep 2007 14:13:38 -0400, "Bill Ogden"
wrote:

I do not sense much of a noise problem with the beam, but I will try a choke
at the feed point sometime.

Hi Bill,

The reason why you would choke or beef up an existing choke for the
beam is as to deepen the nulls that are filled by the 60 foot drop
line that might be radiating/receiving. In a sense, this choking
would lower noise coming in from what should be nulled regions in your
pattern.

73's
Richard Clark, KB7QHC