On Feb 27, 6:34 pm, wrote:
On Feb 27, 12:54 pm, "KE5MBX" wrote:


And, no matter how you look at it, you're only adjusting one parameter
(series L), which limits the best possible match you can get.
Granted, with the lossiness of a typical screwdriver, and the usual
clever 4:1 transformer with leakage C, you can do pretty well. better
than 2:1 from 10-40 is no problem and you can probably do somewhat
better.

Not all screwdrivers are the same though.. Some are pretty close to
a bugcatcher as far as efficiency. Some are horrible due to excess
coil loss. In general, a screwdriver will usually be one notch down
from
a bugcatcher, which I consider king of the hill. The bugcatcher is
often better due to it's often better coil location. Most screwdrivers
have the coil fairly low, which limits them as far as current
distribution.
I don't use transformers to match per say.. I usually use an
inductor,
and this inductance can be included with the main lumped loading coil.


A whip and auto tuner at the base of the antenna, on the other hand,
is virtually instantaneous to tune and requires no manual intervention
on the part of the operator. Squeeze the pickle and you're matched
and ready to go. I suspect that the loss in the tuner is not
materially different than in the variable loading coil, particularly
when you consider the mismatch from only having one adjustable device,
and besides, the dominant efficiency issue is going to be from having
a physically short radiator on lower frequencies, which is the same
regardless of how you tune it.

The screwdriver is likely to be much more efficient than the tuner/
whip.
The efficiency is most certainly not the same for a given size whip.
A tuner/whip is likely to be 10-12 db down from a good bugcatcher,
or high quality screwdriver.
The current distribution through the whip effects the efficiency
greatly.
If you feed a whip with a tuner, maximum current is at the tuner.
If this tuner is in the car, maximum current is in the car with you.
A center fed antenna will be a good bit more efficient than a normal
base
fed for a given short height.
The tuner/whip can do semi ok on the higher bands, because it doesn't
take much there to begin with. On the low bands, they will be fairly
horrible.
Anyway, as far as the OP, the screwdriver would be much better, as
long as it's a decent screwdriver. Some screwdrivers have lousy coil
design, some don't.
MK

Cecil Moore wrote in
et:

Dave Oldridge wrote:
Yep....a GOOD screwdriver with a really high-Q coil will run rings
around most other short antennas. Especially if you use a capacity
hat. But for mobile operation while travelling, that gets a bit
bulky and hard to tame, physically.

Not at all, Dave. $5 worth of PVC pipe works wonders.

It's those 5-inch coil diameters that give the problem!!! Takes a sturdy
mount for those.


--
Dave Oldridge+
ICQ 1800667

On Apr 13, 9:13 pm, Dave Oldridge
wrote:
Cecil Moore wrote .net:

Dave Oldridge wrote:
Yep....a GOOD screwdriver with a really high-Q coil will run rings
around most other short antennas. Especially if you use a capacity
hat. But for mobile operation while travelling, that gets a bit
bulky and hard to tame, physically.

Not at all, Dave. $5 worth of PVC pipe works wonders.
It's those 5-inch coil diameters that give the problem!!! Takes a sturdy
mount for those.

--
Dave Oldridge+
ICQ 1800667

HAs anyone ever tried using a long whip with a screwdriver matching
network. For example I have a telescoping 18ft whip and I was
wondering how it might work with it. I have never used a screwdriver
antenna before and the whip collapses to a little over 6ft.

JIMMIE wrote:
HAs anyone ever tried using a long whip with a screwdriver matching
network. For example I have a telescoping 18ft whip and I was
wondering how it might work with it. I have never used a screwdriver
antenna before and the whip collapses to a little over 6ft.

It's done quite often for non-mobile antennas,
fixed and portable. Mobile antennas are limited
to about 12.5 ft above the ground.
--
73, Cecil http://www.w5dxp.com

"JIMMIE" wrote in
ups.com:

On Apr 13, 9:13 pm, Dave Oldridge
wrote:
Cecil Moore wrote
.net:

Dave Oldridge wrote:
Yep....a GOOD screwdriver with a really high-Q coil will run rings
around most other short antennas. Especially if you use a
capacity hat. But for mobile operation while travelling, that
gets a bit bulky and hard to tame, physically.

Not at all, Dave. $5 worth of PVC pipe works wonders.
It's those 5-inch coil diameters that give the problem!!! Takes a
sturdy
mount for those.

--
Dave Oldridge+
ICQ 1800667

HAs anyone ever tried using a long whip with a screwdriver matching
network. For example I have a telescoping 18ft whip and I was
wondering how it might work with it. I have never used a screwdriver
antenna before and the whip collapses to a little over 6ft.

Should work fine. I know a fellow who put a wire on the end.

Just which frequencies you'll cover will vary, though.

--
Dave Oldridge+
ICQ 1800667