Cecil, W5DXP wrote:
"Awwwwhhhhhh Irv, everyone has a senior moment now and then."

That`s my experience.

Arnold B. Bailey in "TV and Other Receiving Antennas" is more thorough
than most. Bailey writes on page 291:
"We have already seen that such conditions (efficient operation) can
exist for many resonant lengths of the rod. The rod if divided into two
sections and connected to a load at its center, will exhibit resonance
when the total length of the rod is any multiple of one half-wave.
----only two resonant lengths will give a simple directivity pattern ---
if the rod operates at its fourth resonant frequency, no signal is
picked up from directions broadside to the antenna in contrast to
operation at its third, second, or first resonance. Only at first
resonance is the directivity pattern as indicated by Figs. 6-20 and
6-21.

At all other resonances above the first, the pattern is going through a
progressive change which will later be more explicitly shown in a
quantitative manner."

On page 348, Bailey gives radiation resistances and drivepoint
resistances for dipole resonances 1 through 10, and shows their current
distribution patterns.

Best regards, Richard Harrison, KB5WZI

Dr. Slick wrote:
"I`ll give you the harmonics, but a double-dip at for example, 88.1 and
93.7 MHz would indicate a BIG problem!"

Does the dipper dip on one of these frequencies in te absence of an
antenna?

Is the receiver connected to the antenna, and can you move one of the
dips with the receiver tuning?

Does augmenting the antenna cable move one or both dips?

Does relocating the antenna change the dips?

There seem to be two coupled resonant circuits.

Best regards, Richard Harrison, KB5WZI

Irv Finkleman wrote in message ...


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



Explaining an antenna concept so simple to Dr. Slick after
the statement that he made seems to me akin to reading Shakespeare
to a cow.

Irv VE6BP


What if the resonant frequencies are 88.1 and about 92.0 MHz?

Not exactly harmonically related, are they! Think about it.

I think you need to change your diapers, Irv.



Slick

(Dr. Slick) wrote in message . com...

Granted, i'll give you the harmonics, but a double-dip
at for example, 88.1 and 93.7 MHz would indicate a BIG
problem!

So are you measuring _just_ the dipole, or the dipole through a
feedline? Do you have any idea at all how many coupled resonators you
are measuring? See, e.g., King, Mimno and Wing, to educate yourself
about antenna systems seen as a set of coupled resonators. Disabuse
yourself of the notion that you actually understand what your
measurements mean at this point.

Richard Clark wrote in message . ..


As for "double dipping" none of your posts to date have any facts to
test your complaint. If we are to assume these two dips occur within
the same band, that is actually to your benefit as it could only
enlarge the matching prospects. However, your paucity of details
leaves this as speculation on both sides. If the two dips occur
within and without the band, then you have offered nothing to
distinguish this from the natural order of things. Simply put, ALL
dipoles have many dips throughout the spectrum. In this regard there
is nothing special about your "double resonance."


Double dips (or even triple and more) certainly
at harmonics of the fundamental, certainly.

88.1 and 92 aren't exactly harmonically related!



As for the disparaging comment of "maximum return loss suffers," that
too is in conflict with expectation. There is nothing inherently
sufferable about having more than your share of "dips." Additional
resonances does not detract from any other resonance's capacity to
perform within its region of match. A second resonance doesn't
necessarily rob another and it could be argued that it is actually a
boon if you wish to enlarge the bandwidth of an antenna (which by your
only specification of 88-108 would be a positive feature).


A broadband antenna usually doesn't have as good a
match as a dedicated antenna. This is why when i
had two dips, the min. SWR was NOT as good as when i
had only one resonant (not incuding harmonics) freq.



Now, as to HOW you could achieve TWO SWR dips within the FM broadcast
band with a "garden variety dipole," then that is revealed by your
comments about not needing (and by inference not having) your
driveline choked. Simply put, it sounds distinctly like your
transmission line length (combined with velocity factor) added a
resonant circuit in parallel with the dipole to offer this second dip.
You munged things around with the antenna, but changed lines and the
second dip went away (as a function of a different line length, or its
becoming balanced or choked). You would have to have stumbled onto an
unique antenna design to have forced these two dips into this FM band
and this is negated by your own description of a "garden variety
dipole." On the other hand, transmission line common modality is as
common as rain in Seattle.



Again, didn't need a choke for this one.

Someone infered the first problem, not high
above off the ground.

Anyone else?


S.

(Richard Harrison) wrote in message ...
Dr. Slick wrote:
"I`ll give you the harmonics, but a double-dip at for example, 88.1 and
93.7 MHz would indicate a BIG problem!"

Does the dipper dip on one of these frequencies in te absence of an
antenna?


???? The MFJ-259 is obviously infinity to one when you
have an open....



Is the receiver connected to the antenna, and can you move one of the
dips with the receiver tuning?


not using a receiver.


Does augmenting the antenna cable move one or both dips?


Didn't try this. Didn't have to change this
to fix the problem.


Does relocating the antenna change the dips?


Again, one of the two things i did to fix this
problem was to increase the height above the ground
from 3.5 feet to about 6.5 feet.

Can you guess what the other factor was?

Hint: no inductive choke was needed, and the radial
lengths remained the same.


Slick

Dr. Slick wrote:
What if the resonant frequencies are 88.1 and about 92.0 MHz?

Log Periodic?
--
73, Cecil, W5DXP

On 11 Nov 2004 12:11:26 -0800, (Dr. Slick) wrote:

Double dips (or even triple and more) certainly
at harmonics of the fundamental, certainly.

88.1 and 92 aren't exactly harmonically related!

Never said they were, and until these recent posts, we all had to
guess. And besides, not all antennas are harmonically resonant.

A broadband antenna usually doesn't have as good a
match as a dedicated antenna.

You have too little exposure to the world of antennas to paint them
with that broad brush. A simple example is a discone antenna which is
a variant of the biconical antenna, which is the genesis of ALL
dipoles. Either the discone or the biconical display a very wide
bandwidth (octaves) and are eminently matchable by definition.

This is why when i
had two dips, the min. SWR was NOT as good as when i
had only one resonant (not incuding harmonics) freq.

You have yet to disclose what SWRs were present to make this a
problem.

Again, didn't need a choke for this one.

You have yet to show that it is not your problem, much less the lack
of need (which is a strict requirement for tuning). "Not needing" it
can be accomplished through one of two means:
Luck,
or
a hardwired solution (the customer, like with CB whips, cannot
vary the length without causing a major shift in dynamics).
Either way, the two are probably the same solution, an even halfwave
multiple length line. The longer the line, the more tenuous the
solution.

Someone infered the first problem, not high
above off the ground.

Which will broaden the response (lower the SWR) if too close.
Proximity to ground will shift resonance too, but not add resonances.

Your problem was feedline related. You simply (and without taking
note of it) changed that along with the melange of other activity and
pushed the "problem" up/down the spectrum. The addition of the other
dip is harmonically related to a structural issue that has a physical
dimension related to the wavelength and velocity factor. There is no
other way to accomplish this with "a garden variety dipole" except
with a short transmission line to a SWR tester (I will bet your test
cable was a generic 3 foot coax). Any coax line that is as long as an
odd multiple quarter wavelength (1/4, 3/4, 5/4...) of the unusual dip
will do the same thing if it is not snubbed at the drivepoint.

73's
Richard Clark, KB7QHC

On 10 Nov 2004 11:42:21 -0800, (Dr. Slick) wrote:
Garden variety dipole.

On 11 Nov 2004 12:20:02 -0800, (Dr. Slick) wrote:
Hint: no inductive choke was needed, and the radial
lengths remained the same.

What do you grow in your garden?

(Tom Bruhns) wrote in message om...
(Dr. Slick) wrote in message . com...

Granted, i'll give you the harmonics, but a double-dip
at for example, 88.1 and 93.7 MHz would indicate a BIG
problem!

So are you measuring _just_ the dipole, or the dipole through a
feedline?

Through about 20 feet of RG-58.


Do you have any idea at all how many coupled resonators you
are measuring? See, e.g., King, Mimno and Wing, to educate yourself
about antenna systems seen as a set of coupled resonators. Disabuse
yourself of the notion that you actually understand what your
measurements mean at this point.

I understand it quite well... two non-harmonically
related resonances in a very narrow band (88-108 Mhz) is
a bad sign if you didn't design you antenna for broadband.


S.