TT-247 and 102 whip for mobile antenna ?
On Sat, 29 Apr 2006 07:55:47 -0400, Buck wrote:
There are a total of four antennas I have mentioned in here for
comparison sake.
Hi Buck,
They are by degrees poor, poorer and poorest.
The Hustler
You probably walked away from the best of the group here.
the 102 whip with a possible 2 foot extension
which isn't extension enough.
and two Antenna Specialists (AS)
the air-cooled resistors.
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.
These on something like 4 foot or longer extension poles would help
you for a cheap solution to the lower bands. Adding a top hat to the
stinger (yeah, impossible) would go further.
(I don't have the 102 whip yet.)
Get one, at hamfests they are cheaper than toilet paper.
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.
They would never notice on receive. The tuner made the difference.
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.
A coil loading it halfway up would go further (AKA Bugcatcher).
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.
Then using a cheap tuner (with a loaded antenna), by all means, is
part of the solution.
My question is whether or not the tuner itself can hold up to
the task without being damaged.
As an all band solution, you do stand the risk of one of them being a
fire-breather. Just which is hardly predictable with any accuracy
given the vast number of variables. There is certainly a strong
correlation with longer wavelengths and short antennas. So, you might
design two systems - cheaply, of course.
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.
Again, you should never believe everything you hear.
A quarter wave dipole should be a snap to tune. On the other hand,
using an 80M antenna on 40M could be a bear. Also, a quarterwave
dipole is only vaguely related to a quarterwave vertical - um, let's
just say that relationship is too strained to be compared.
We never discussed the use of the tuner in the mobile.
That was the first thing you said, it would be quite close to the
proposed mount. Anyway, I have always considered it part of your
cheap solution and it has a place there.
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.
This is another instance of not believing everything - but it at least
this time it offers a nugget of truth. This is the spin of the wheel
of chance I mentioned above. Don't fret so much and simply try it in
the driveway. Open the tuner, fire up the rig and tune for lowest
SWR. Let go of the key and touch components to see how hot it's
gotten. You don't need infra-red analysis and toolkit of thermocouple
probes to obtain a good understanding of the situation. Repeat on all
bands.
73's
Richard Clark, KB7QHC
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