Hi,
I am replacing the wire in a trap on my 3 element Tri-Band beam
antenna...
The wire is 25 turns of approximately 10 gauge on a 1.210 inch form
diameter, with a coil length of 3 inches(these numbers are
approximate).
I am unable to get the exact gauge(10 AWG) of wire and was wondering
if there would be any adverse effects in using a slightly smaller
gauge wire in place of it,say 12 gauge or so...?

Any help with this would be greatly Appreciated
Thank You

Where do you live that you can't get 10 gauge wire?

If you use 12 gauge wire, you will likely end up with the frequency of
the trap being off. If you have a dip meter, you can measure the
resonant frequency and adjust the number of turns and/or wire spacing to
get it where it needs to be.

Scott
N0EDV

Clayton wrote:

Hi,
I am replacing the wire in a trap on my 3 element Tri-Band beam
antenna...
The wire is 25 turns of approximately 10 gauge on a 1.210 inch form
diameter, with a coil length of 3 inches(these numbers are
approximate).
I am unable to get the exact gauge(10 AWG) of wire and was wondering
if there would be any adverse effects in using a slightly smaller
gauge wire in place of it,say 12 gauge or so...?

Any help with this would be greatly Appreciated
Thank You


--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

On Sep 6, 11:16 pm, Clayton wrote:
Hi,
I am replacing the wire in a trap on my 3 element Tri-Band beam
antenna...
The wire is 25 turns of approximately 10 gauge on a 1.210 inch form
diameter, with a coil length of 3 inches(these numbers are
approximate).
I am unable to get the exact gauge(10 AWG) of wire and was wondering
if there would be any adverse effects in using a slightly smaller
gauge wire in place of it,say 12 gauge or so...?

Any help with this would be greatly Appreciated
Thank You

I echo Scott's question: why is 10AWG so difficult to get?

But I also ran some numbers for you in a program I use often and
trust. Even if the absolute values are off a bit, the relative values
should be very close. Here's what I got:

3" long, 1.21" ID, 25 turns, 0.120" winding pitch = 3"/25

Parameter 10AWG 12AWG
inductance 7.148uH 7.053uH
wire length 103.1" 101.4"
Qu@14MHz 592 660
Equiv. par. C 1.68pF 1.67pF
Self-resonance 45.9MHz 46.4MHz

The inductance error could be corrected by winding it slightly larger
diameter; but it should be easy enough to just re-tune. The higher Qu
of the smaller wire is probably accurate; the larger wire is wound too
close-spaced to get the optimum Qu.

Cheers,
Tom

K7ITM wrote in news:1189193823.733779.47160
@d55g2000hsg.googlegroups.com:

Tom,

....
But I also ran some numbers for you in a program I use often and
trust. Even if the absolute values are off a bit, the relative values
should be very close. Here's what I got:

3" long, 1.21" ID, 25 turns, 0.120" winding pitch = 3"/25

Parameter 10AWG 12AWG
inductance 7.148uH 7.053uH
wire length 103.1" 101.4"
Qu@14MHz 592 660
Equiv. par. C 1.68pF 1.67pF
Self-resonance 45.9MHz 46.4MHz


I tried the same scenario in the inductance calculator at
http://hamwaves.com/antennas/inductance.html .

It suggests that the inductance is quite a bit lower (~6uH), but
interestingly, that larger diameter wire gives a lower inductance rather
than higher.

That outcome seems counter-intuitive considering an ideal solenoid, but I
suspect it is caused by a very different estimate of the self capacitance
(0.6pF).

Owen

"Clayton" wrote in message
ups.com...
Hi,
I am replacing the wire in a trap on my 3 element Tri-Band beam
antenna...
The wire is 25 turns of approximately 10 gauge on a 1.210 inch form
diameter, with a coil length of 3 inches(these numbers are
approximate).
I am unable to get the exact gauge(10 AWG) of wire and was wondering
if there would be any adverse effects in using a slightly smaller
gauge wire in place of it,say 12 gauge or so...?

Any help with this would be greatly Appreciated
Thank You

Do you want to explain why you are replacing the wire?

Tam/WB2TT

"Tam/WB2TT" wrote in message
. ..

"Clayton" wrote in message
ups.com...
Hi,
I am replacing the wire in a trap on my 3 element Tri-Band beam
antenna...
The wire is 25 turns of approximately 10 gauge on a 1.210 inch form
diameter, with a coil length of 3 inches(these numbers are
approximate).
I am unable to get the exact gauge(10 AWG) of wire and was wondering
if there would be any adverse effects in using a slightly smaller
gauge wire in place of it,say 12 gauge or so...?

Any help with this would be greatly Appreciated
Thank You

Do you want to explain why you are replacing the wire?

Tam/WB2TT
I have found that most electrical supply houses carry 10 ga solid wire..
probably covered - so that you would have to strip off the jacket..
73's Howard W3CQH

Thanks for the replies everyone

Scott,
Could you please explain how I can use a grid dip meter to measure
the
resonant frequency and adjust the number of turns and/or wire spacing
to
get it where it needs to be?
I just picked up a grid dip meter but have never used one.

I'm not completely understanding the math required in figuring
inductance out...
I am able to figure out that with my coil form and number of turns the
coil I have is around 6.5uH but I cant figure out how to work wire
gauge into the equation? I have been trying to find someplace that
explains it but am unable to.
Could somebody here maybe explain how the math works when you throw
wire gauge into the equation?

Tam,
I am replacing the wire in the trap because when I was cleaning the
corrosion off,the last inch or so of the wire broke off and since the
wire is aluminum I figure I would be better off replacing it then
trying to repair.

Thanks for the help everyone
Its most Appreciated
Regards

On Sep 9, 10:52 pm, Clayton wrote:
Thanks for the replies everyone

Scott,
Could you please explain how I can use a grid dip meter to measure
the
resonant frequency and adjust the number of turns and/or wire spacing
to
get it where it needs to be?
I just picked up a grid dip meter but have never used one.

I'm not completely understanding the math required in figuring
inductance out...
I am able to figure out that with my coil form and number of turns the
coil I have is around 6.5uH but I cant figure out how to work wire
gauge into the equation? I have been trying to find someplace that
explains it but am unable to.
Could somebody here maybe explain how the math works when you throw
wire gauge into the equation?

Tam,
I am replacing the wire in the trap because when I was cleaning the
corrosion off,the last inch or so of the wire broke off and since the
wire is aluminum I figure I would be better off replacing it then
trying to repair.

Thanks for the help everyone
Its most Appreciated
Regards

The link Owen put in his posting is to a pretty complete on-line
inductance calculator. The one I use is similar, in that it uses a
helical waveguide approach, though it probably does not include all
the "tweaks" mentioned on the link page. Wire gauge plays a part in
several ways. If the basic formula uses coil inside diameter, then
note that larger wire puts the current further out, on average. If
the wire spacing is much greater than the wire diameter, the current
in the wire will be nearly radially symmetric: if you look at a cross-
section of the wire, the current density will depend on the distance
out from the center of the wire because of skin effect, but will not
vary much at any angle for a given radius. But if the turns are
closely spaced, proximity effect will re-distribute the current on the
wire so it's no longer radially symmetric. That will affect the
inductance.

A grid dip (or these days, just dip) meter is used to find
resonances. You want the trap, when it's in the environment it's used
in on the beam, to be parallel resonant so it presents a high
impedance to signals at some frequency. So in a 20M-15M beam, an
element with a trap resonant at 21MHz will look like a high impedance
to 15M signals, and decouple the ends of the elements from the inner
sections, which in turn are designed to operate on 15M. On 14MHz, the
traps look inductive (the inductive reactance is lower and the
capacitive reactance higher than at 21MHz, so the _parallel_
combination looks like a net inductance), and that means they look
like loading coils. As a result, the elements on 20M including the
outer sections and the traps-that-look-like-loading-coils are shorter
than if they didn't include the traps. You can extend that reasoning
to a tri-band beam.

You'd probably do well to practice with your dip meter with some
resonant circuits "on the bench." You want to couple the meter to the
coil of the resonant circuit to get a dip. To start, you can couple
it closely, but the dip will be hard to read well, since the resonant
circuit you're measuring and the one in the dip meter will interact
strongly, "pulling" the dip frequency. So when you get a strong dip
near a reasonable frequency, pull the dip meter further away, till you
get just a gentle dip. Then the frequency readout (assuming the
frequency scale on the meter is accurate) should be accurate. As with
most instruments, it's good to get some experience with a dip meter so
you have an idea when it's giving good readings and when it's in
error.

Cheers,
Tom


Cheers,
Tom

On 10-Sep-2007, K7ITM wrote:

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From: K7ITM
Newsgroups: rec.radio.amateur.antenna
Subject: Substitute wire in Trap?
Date: Mon, 10 Sep 2007 14:18:17 -0700
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On Sep 9, 10:52 pm, Clayton wrote:
Thanks for the replies everyone

Scott,
Could you please explain how I can use a grid dip meter to measure
the
resonant frequency and adjust the number of turns and/or wire spacing
to
get it where it needs to be?
I just picked up a grid dip meter but have never used one.

.....
Its most Appreciated
Regards

.....

You'd probably do well to practice with your dip meter with some
resonant circuits "on the bench." You want to couple the meter to the
coil of the resonant circuit to get a dip. To start, you can couple
it closely, but the dip will be hard to read well, since the resonant
circuit you're measuring and the one in the dip meter will interact
strongly, "pulling" the dip frequency. So when you get a strong dip
near a reasonable frequency, pull the dip meter further away, till you
get just a gentle dip. Then the frequency readout (assuming the
frequency scale on the meter is accurate) should be accurate. As with
most instruments, it's good to get some experience with a dip meter so
you have an idea when it's giving good readings and when it's in
error.

Cheers,
Tom


Cheers,
Tom

The dials on Dip Meters are usually not very precise and may be inaccurate while loaded by the
circuit under test. You can improve your frequency determination by listening to the dip meter
signal on an accurate receiver or with a frequency counter coupled to the coil.

Ken Fowler, KO6NO