Hi,

I recently tuned up a VHF dipole, and i got
a double-dip, double resonance for the swr, and
also the minimum swr was around 1.3:1

I did some modifications, and the double
resonance was was gone, plus the swr was down
to less than 1.1:1

I'm certain that one of two things (or a
combo of both) did the trick, but i wanted to
see if any of you seasoned antenna boys could
guess what the problem was.

Thanks for your input!


Slick

On 8 Nov 2004 17:13:32 -0800, (Dr. Slick) wrote:

guess what the problem was.

Why do you think it was a problem?

73's
Richard Clark, KB7QHC

Dr. Slick wrote:
.. I'm certain that one of two things (or a
combo of both) did the trick, but i wanted to
see if any of you seasoned antenna boys could
guess what the problem was.

If it has two elements (sure, verticals can have two elements)
then a difference in resonance between the two elements could
easily have been the cause.
--
73, Cecil, W5DXP

I'm certain that one of two things (or a
combo of both) did the trick, but i wanted to
see if any of you seasoned antenna boys could
guess what the problem was.

_________________________________________________ ________

There is no problem. Dipoles and other antennas always show multiple
resonances. Just take an SWR analyzer and sweep a wide frequency range.
You'll find resonances all over the place.

--
Bill W6WRT


Dipoles are essentially harmonic devices, so they experience harmonic
resonances.

If you find resonances that are not harmonic on a dipole, then there are
loading objects that are producing them.

What exactly is your dipole? What is in proximity to it? How do you know that
the coax is choked properly?

73,
Chip N1IR

"Dr. Slick" wrote in message
om...
Hi,

I recently tuned up a VHF dipole, and i got
a double-dip, double resonance for the swr, and
also the minimum swr was around 1.3:1

I did some modifications, and the double
resonance was was gone, plus the swr was down
to less than 1.1:1

I'm certain that one of two things (or a
combo of both) did the trick, but i wanted to
see if any of you seasoned antenna boys could
guess what the problem was.

Thanks for your input!


Slick
What happened to the total bandwidth after you tuned it?

Tam/WB2TT

"Dr. Slick" wrote in message
om...
Hi,

I recently tuned up a VHF dipole, and i got
a double-dip, double resonance for the swr, and
also the minimum swr was around 1.3:1


At what two frequencies? What construction, feed type...? What method
of measurement and equipment type/numbers?

First, let's determine if there even is a problem with the antenna...



I did some modifications, and the double
resonance was was gone, plus the swr was down
to less than 1.1:1

What mods?

73,
--
Steve N, K,9;d, c. i My email has no u's.




I'm certain that one of two things (or a
combo of both) did the trick, but i wanted to
see if any of you seasoned antenna boys could
guess what the problem was.

Thanks for your input!
Slick

"Dr. Slick" wrote in message
om...
Hi,

I recently tuned up a VHF dipole, and i got
a double-dip, double resonance for the swr, and
also the minimum swr was around 1.3:1
but i wanted to
see if any of you seasoned antenna boys could
guess what the problem was.

twarnt no problem - if the dipole was 'clean' the double-dip may be due to
how close you were to it, the coax length, a nearby object, - your presence
near the antenna, the way you held your mouth while taking the measurements,
the measurement methods themselves, a passing cloaked Klingon bird of prey,
an ionized whif of exhaled air, or something none of us have ever seen.
(many causes - most just accept it is as - in Walter Cronkite's words
"That's the way it is.")


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.788 / Virus Database: 533 - Release Date: 11/1/2004

Richard Clark wrote in message . ..
On 8 Nov 2004 17:13:32 -0800, (Dr. Slick) wrote:

guess what the problem was.

Why do you think it was a problem?


A double dip is a bad sign, and your
return loss is not optimum.

S.

On 10 Nov 2004 11:36:02 -0800, (Dr. Slick) wrote:
Richard Clark wrote in message . ..
On 8 Nov 2004 17:13:32 -0800, (Dr. Slick) wrote:
guess what the problem was.
Why do you think it was a problem?
A double dip is a bad sign, and your
return loss is not optimum.

What makes a double dip a bad sign? Most antennas have many.
What does any dip have to do with non-optimal return loss? By
definition a dip in SWR indicates better return loss.

73's
Richard Clark, KB7QHC

(Fractenna) wrote in message ...

There is no problem. Dipoles and other antennas always show multiple
resonances. Just take an SWR analyzer and sweep a wide frequency range.
You'll find resonances all over the place.

Bill W6WRT



A properly tuned and positioned dipole will
be resonant at only one frequency. Double-dips
are a bad sign, and the return loss suffers.




Dipoles are essentially harmonic devices, so they experience harmonic
resonances.

If you find resonances that are not harmonic on a dipole, then there are
loading objects that are producing them.

What exactly is your dipole? What is in proximity to it? How do you know that
the coax is choked properly?


Garden variety dipole.

But you have hit on one of the factors, i believe, which
is that initially, i was only about 4 feet off the ground.
Supposedly, dipoles need to be significantly over a 1/4 wavelength
above the ground. The second time, i had it at 6.5 feet or so.

I didn't need a choke with this one.

I'm using an MFJ-259.

What do you think was the other factor?


Slick