On Fri, 28 Apr 2006 22:07:00 -0700, Richard Clark
wrote:

On Fri, 28 Apr 2006 22:57:40 -0400, Buck wrote:
I would like to use it for 75-6
meters as I am not worried about 160 meters. I would like to use it
on 75 meters, as it is the band most likely to meet the coverage I am
interested in,

Hi Buck,

All reports of short, mobile antennas on 80M generally cry crippled.
That is, unless, they are augmented by center loads under top hats a
dozen feet high or more. Even then, hardly remarkable unless you can
stand to be down 2 S-Units out the gate. For some, this knowledge is
a killer. For others who ignore it, they simply work those who can
hear them.

I realize this. I have used a Hustler on 75 before. I was definitely
a weak signal station. I can only imagine that a tuned whip would
generate similar results, or more likely, poorer results.

but also to operate all bands as I would like not to
change antennas all the time. I have loaded the 20 meter and 40 meter
antennas with it to see how it works on other bands, but they really
suck!.

Well, again, you are short on details. These two antennas (I presume
you have introduced two more to the discussion) may be air cooled
resistors for all their qualities you suggest. You might find an
object lesson here.

There are a total of four antennas I have mentioned in here for
comparison sake. The Hustler, just mentioned above, the 102 whip with
a possible 2 foot extension, and two Antenna Specialists (AS) (look
exactly like HamSticks). I haven't had the Hustler for over a decade.
I will introduce another antenna in this message later.

The AS antennas are thin fiberglass poles with long stingers on the
top. The fiberglass poles, of course, have copper wound around them
from bottom to top, above which is a whip (stinger) about the same
length as the pole. The hustler was a center loaded trap that was
several inches in diameter and about 10-12 inches tall (the trap part)
with a stinger on top. (You are probably familiar with the Hustler.)
I also have a Volvo brand CB whip. It is a thin fiberglass whip
similar to the bottom portions of the AS antennas, but it does not
have a stinger. Like the AS antennas, the fiberglass has copper wire
wound from bottom to top with the top tightly wound and the bottom
section loosely wound. There is no stinger on top of the CB antenna.

I previously did a little experimenting with the two AS antennas and
the Volvo CB antenna (I don't have the 102 whip yet.) I used the tuner
to compare receive signals on various active bands. the results
weren't very good. Basically, each antenna performed best on the
frequencies for which they were designed (no big surprise here) but
they performed terribly on any other band. In fact, they were not
even acceptable for use on other bands. The signal strength on 20
meters, for example went from s-9 on the 20 AS antenna to less than
s-2 on the other antennas. I know others who have used the 102 steel
whip/auto-tuner combination that I have talked to never complained
that they only received s-2 signals with the system. Therefore, my
theory is that the winding of the coil on the fiberglass poles is
adversely affecting the radiation on out-of-band operation. I am
hoping that the steel whip, with or without the extension, will
perform better on all bands than any of these antennas tested. I
realize it is a compromise but the loss of an s-unit or two in
exchange for all band coverage for my mobile without having to switch
antennas or get out of the car and change taps is an acceptable
trade-off.

Remember, too, that in the original post, money is a big issue. The
purchase of a screwdriver (the best known mobile antenna design for
all band coverage) is not an option at this time. My theory is that I
should be able to mimic the 102 whip/auto-tuner results using a manual
tuner. My question is whether or not the tuner itself can hold up to
the task without being damaged.





I don't know if it is the way they are wound or what, but
tuning the 20 for six works well, but not with other bands. Going
lower doesn't help.

Barring details....

I think I addressed that above, the fiberglass poles are wrapped
tightly at the top and then loosely to the bottom, a stinger extends
from the tops of the AS antennas, and the Volvo antenna doesn't have a
stinger.


As for the mobile vs base antennas, there may be some difference. The
problem occurs when using a quarter wave or shorter dipole.

Mobile quarterwave dipole?
base. The suggestion I was given was not to use the antenna tuner on
a 20 meter dipole to tune a 40 meter frequency. This would be a 1/4
wave dipole on 40 meters. I don't know what the impedance of such an
antenna would be, but I do know that a 1/4 wave vertical is a
reasonable match. We never discussed the use of the tuner in the
mobile.



However,
a quarter wave vertical is a match! This is part of my questioning.

Aside from this being natural, what could the question be?

Also, the fact that the tuner will be virtually at the antenna rather
than the coax, may make some difference, although, technically, I
think the coax would lower the reflected power to the tuner.

Many antennas are designed with a match external to them, but quite
close by. Why would this be detrimental? Even more, many antennas
are built with the match as part of them. They go by many names,
Gamma being one. Certainly nothing is lost in their use.

The theory i was hearing was that the loading coil takes all the
missing length of antenna and heats up.

I should have clarified that this statement. The internal inductor of
the tuner makes up the missing length of the antenna and heats up
which can cause damage to the antenna tuner's inductor. This is how
it was presented to me, or how I understood it. Again, the discussion
was using the tuner to tune short dipoles to transmit on lower
frequencies.


Dare I say you can't trust everything you hear (read here)?

Myself, I taught RF communications in the Navy and had no trouble
whatever with the concept that a coil replaces the electrical length
missing in a short antenna. However, the Navy was never a slave to
fashion nor strict interpretation in this matter, and it was enough to
observe this quid-pro-quo as symbolic, and not literal.

I can't imagine auto-tuners
having as large a coil as this manual tuner. (It uses a wire wrapped
around a toroid of some sort. ) I imagine an autotuner uses much
smaller inductors tied together thru relays.

Indeed.

I am trying to think of a type thurmometer that I could use that
wouldn't interact with the tuner to see if it heats up.

Yuri might suggest aquarium thermometers (Liquid Crystal) - but you
would have to make sure the entire surface fit the entire strip (or
versa vice). If you have a very old digital camera, then they were
sensitive to IR. You could take a picture in the dark and resolve hot
spots.

I will probably test the antenna this weekend if I can get the parts
and time....

Further reports would be interesting.



I have been scheduled to work this weekend. I hope to be off Sunday,
If I can, I will try testing the whip idea using the side mount on the
van and if it appears to be promising, I will drill the holes in the
roof to mount the whip there near the radio and tuner.


73's
Richard Clark, KB7QHC
73 for now

--
73 for now
Buck
N4PGW