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

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

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.

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

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.

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