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

I didn't need a choke with this one = the other factor

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.

If something is wrong with a dip on 40m and a dip on 15m,
someone should warn all the hams who are using their 40m
dipoles on 15m. :-)
--
73, Cecil, W5DXP

Cecil Moore wrote:

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.

If something is wrong with a dip on 40m and a dip on 15m,
someone should warn all the hams who are using their 40m
dipoles on 15m. :-)

Forgot to add that dipoles are resonant near all odd
half-wavelengths, i.e. 0.5WL, 1.5WL, 2.5WL, 3.5WL, ...
They are also antiresonant (purely resistive) on all
integral wavelengths, 1.0, 2.0, 3.0, ...

Using a Smith Chart, if one plots the feedpoint impedances
of a dipole VS frequency and connects the dots, that locus
of points will describe a (very rough) spiral. (Traversing
once around that rough spiral from resonance to resonance
is one full wavelength, not 1/2 wavelength.)
--
73, Cecil, W5DXP

Cecil Moore wrote:

Cecil Moore wrote:

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.

If something is wrong with a dip on 40m and a dip on 15m,
someone should warn all the hams who are using their 40m
dipoles on 15m. :-)

Forgot to add that dipoles are resonant near all odd
half-wavelengths, i.e. 0.5WL, 1.5WL, 2.5WL, 3.5WL, ...
They are also antiresonant (purely resistive) on all
integral wavelengths, 1.0, 2.0, 3.0, ...

Using a Smith Chart, if one plots the feedpoint impedances
of a dipole VS frequency and connects the dots, that locus
of points will describe a (very rough) spiral. (Traversing
once around that rough spiral from resonance to resonance
is one full wavelength, not 1/2 wavelength.)
--
73, Cecil, W5DXP

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
--
--------------------------------------
Diagnosed Type II Diabetes March 5 2001
Beating it with diet and exercise!
297/215/210 (to be revised lower)
58"/43"(!)/44" (already lower too!)
--------------------------------------
Visit my HomePage at http://members.shaw.ca/finkirv/index.html
Visit my Baby Sofia website at http://members.shaw.ca/finkirv4/index.htm
Visit my OLDTIMERS website at http://members.shaw.ca/finkirv5/index.htm
--------------------
Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada

Irv Finkleman wrote:
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.

Awwwwhhhhhh Irv, everyone has a senior moment now and then.
--
73, Cecil, W5DXP

Cecil Moore wrote in message ...
Cecil Moore wrote:

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.

If something is wrong with a dip on 40m and a dip on 15m,
someone should warn all the hams who are using their 40m
dipoles on 15m. :-)

Forgot to add that dipoles are resonant near all odd
half-wavelengths, i.e. 0.5WL, 1.5WL, 2.5WL, 3.5WL, ...
They are also antiresonant (purely resistive) on all
integral wavelengths, 1.0, 2.0, 3.0, ...

Using a Smith Chart, if one plots the feedpoint impedances
of a dipole VS frequency and connects the dots, that locus
of points will describe a (very rough) spiral. (Traversing
once around that rough spiral from resonance to resonance
is one full wavelength, not 1/2 wavelength.)


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!

:)


Slick

Richard Clark wrote in message . ..
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.


A double dip in a very narrow band, like 88-108 MHz
for example, is a real indication of something wrong.
It has always meant that the maximum return loss suffers.

S.

Richard Clark wrote in message . ..
On 10 Nov 2004 11:42:21 -0800, (Dr. Slick) wrote:

I didn't need a choke with this one = the other factor


Incorrect. I simply didn't need it for this dipole.

Anyone else?


S.

On 10 Nov 2004 20:16:40 -0800, (Dr. Slick) wrote:

A double dip in a very narrow band, like 88-108 MHz
for example, is a real indication of something wrong.
It has always meant that the maximum return loss suffers.

Well, for openers, and by your own description of a "garden variety
dipole," you don't have the prospects of anything but a narrower band
than 88-108 MHz (even if you opt to match directly to 73 Ohms). A
"garden variety dipole" centered in this band will only match 73 Ohms
from 89.5-99 MHz - it will only match 50 Ohms from 90.5-97 MHz.

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."

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).

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.

73's
Richard Clark, KB7QHC

Cecil Moore wrote:

Irv Finkleman wrote:
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.

Awwwwhhhhhh Irv, everyone has a senior moment now and then.
--
73, Cecil, W5DXP

The devil made me do it. Aside from senior moments I also have
second childhood flashbacks!

Irv
--
--------------------------------------
Diagnosed Type II Diabetes March 5 2001
Beating it with diet and exercise!
297/215/210 (to be revised lower)
58"/43"(!)/44" (already lower too!)
--------------------------------------
Visit my HomePage at http://members.shaw.ca/finkirv/index.html
Visit my Baby Sofia website at http://members.shaw.ca/finkirv4/index.htm
Visit my OLDTIMERS website at http://members.shaw.ca/finkirv5/index.htm
--------------------
Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada