I'm planning to get a Yaesu FT-857D and operate mobile HF on as many
bands as possible. I see two options so far for my Jeep Wrangler- a
102" whip with a tuner or a screwdriver antenna. Which is the better
way to go?

Given the choice of ONLY those two options, the screwdriver!

KE5MBX wrote:

I'm planning to get a Yaesu FT-857D and operate mobile HF on as many
bands as possible. I see two options so far for my Jeep Wrangler- a
102" whip with a tuner or a screwdriver antenna. Which is the better
way to go?

On Feb 27, 12:54 pm, "KE5MBX" wrote:
I'm planning to get a Yaesu FT-857D and operate mobile HF on as many
bands as possible. I see two options so far for my Jeep Wrangler- a
102" whip with a tuner or a screwdriver antenna. Which is the better
way to go?


Do you need fast tuning from band to band?

Can you see the antenna from where you operate?

Do you want to operate while actually driving, or just when you're
parked.

I had a screwdriver on the roof of my VW Passat for a while. It was
tedious to adjust because I didn't have feedback about where it was
set. I then moved it to the front bumper, and it was a lot easier to
do band changes (you can quickly see when you're in the right
region). Worked greate for 10,12,15,17, and 20, because you can tune
to a visible mark, and then just check SWR. However, it's still a bit
tedious to tune for 40 and 75, because it has a pretty sharp
resonance, so if you QSY very far, you have to readjust the antenna.

There are some newer screwdriver antennas with automatic controllers
that make life much easier. They can count turns, or actually look at
the reflected power and adjust up and down for the match. However, you
still have the "tuning speed" issue.. that motor only moves so fast.

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.

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.

I didn't have very good luck with a single whip on a SGC tuner, (as
far as getting a match on all bands) but when I improvised a dualband
whip by wrapping another wire around the first whip (say, 25-30 ft of
AWG 16 hookup wire) and connecting them at the base, it works quite
well. (this is similar to what's inside the SGC whips and other
similar wideband whips... essentially it's like having two verticals
in parallel, with widely varying resonant frequencies... when you're
close to the resonance of one, the other just looks like a lumped L
or C in parallel, and the tuner takes it out)

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

KE5MBX wrote:
I'm planning to get a Yaesu FT-857D and operate mobile HF on as many
bands as possible. I see two options so far for my Jeep Wrangler- a
102" whip with a tuner or a screwdriver antenna. Which is the better
way to go?

Depends on what you mean by better.

One caveat on autotuners; most I've looked at will be marginal at
tuning a 102" whip on 40 and won't tune lower than that.

If you decide on an autotuner, read the specs carefully before you buy.

--
Jim Pennino

Remove .spam.sux to reply.

Jeep? I'd go for the 102" whip and tuner, or a set of tuned hamsticks
on spring mount. Wouldn't even consider the screwdriver unless you
always stay on the pavement and don't live in an area with trees next to
the highway/street. Now here's why...

I have a Yaesu FT-857 with the digital option (nearly the same as the
857D, which is newer) and when I initially installed it, I had the Yaesu
Atas-120 Screwdriver, which I mounted on a "rollbar loop" behind the cab
on my Toyota Tacoma 4x4 pickup. It worked fine, auto-tuning under
command from the 857 merely by pressing the tune button, for bands from
40 meters up (even underway at speeds up to 55, which is the speed limit
here in Hawaii). However, I eventually took if off after replacing the
whip three or four times (the last time, I drilled out the mount for a
larger diameter whip from a hamstick antenna). Yep, you guessed it
already, overhanging trees killed the whips, over and over.

The other problem I had was that I had to re-solder the "matching base"
to it's internal PCB twice, as vibration would cause the solder joint to
fail. Nothing fatal, but clearly a pain in the butt.

After putting up with the issues of periodic soldering and whip
replacement, I moved to a Hamstick mounted at the left rear corner of
the truck, using 1 1/2" square steel tubing bolted to my hitch receiver.
The tubing has a 3/8-24 adapter connected to it, with about 18" of
pipe with another adapter, and a spring on top with a quick disconnect
for the ham sticks. Moving it up 18" from the bumper level made the
hamstick get out better, and gave them both a wider bandwidth and lower
swr, but of course, they had to be retuned when I added the 18" pipe
extension. I've had the whip bend back a bit in the wind, and at
"passing speeds" the entire hamstick leans back about 20 degrees or so,
but still gets out just fine. I haven't broken a whip on the hamstick
yet, though it does take a minute or so to pull over, jump out and swap
antennas to do a band change. Oh yeah, going through a drive-through
gets me some really wierd looks if I forget to hop out and unplug the
whip, because it drags over the ceiling of their drive-through awning if
I don't (looks sort of line the power bar above a bumper car at that
point). I keep the bands of choice (usually 40, 20 and 15 or 17
depending on mood) in the pickup bed, so I don't need to mark the whip
to make them fit inside. Normally run on 40 meters because we have a
daily net here on 7.088 at 0200 Zulu. (4 pm local time in Hawaii).
Bandwidth on 80 is pretty narrow, but usable if you have a relatively
narrow interest there. The 40 meter and higher frequency bands get out
pretty well, I've had contacts to mainland US (2300 miles minimum) on
40, with world class contacts (Russia, Australia, South America, Japan,
etc.) on 20 meters, and up. Used to talk to east coast on 10 meters in
the morning hours a couple of years ago, but haven't been out in the
truck much lately, working on building a house right now...

Another thing about the screwdriver: When I had the Atas-120 screwdriver
on, I made it a snap-lock mount, so I could fold it over the bed of the
truck when I parked in the garage. It also snapped over when I forgot
to lower it before I drove into the garage, so I didn't kill the antenna.

If you ever enter a parking garage you'll have to have a way to fold or
remove the screwdriver or youll kill it. A jeep with a 102 can just be
pulled over and held down with a short cord you can remove after you get
back outside.

KE5MBX wrote:
I'm planning to get a Yaesu FT-857D and operate mobile HF on as many
bands as possible. I see two options so far for my Jeep Wrangler- a
102" whip with a tuner or a screwdriver antenna. Which is the better
way to go?

Both!!


"KE5MBX" wrote in message
oups.com...
I'm planning to get a Yaesu FT-857D and operate mobile HF on as many
bands as possible. I see two options so far for my Jeep Wrangler- a
102" whip with a tuner or a screwdriver antenna. Which is the better
way to go?

"Pro Shop at Home" wrote in message
...
Both!!


"KE5MBX" wrote in message
oups.com...
I'm planning to get a Yaesu FT-857D and operate mobile HF on as many
bands as possible. I see two options so far for my Jeep Wrangler- a
102" whip with a tuner or a screwdriver antenna. Which is the better
way to go?



For those selling them :-)
As far as efficiency, screwdriver will beat the pants off whip with base
tuner, especially on low bands.

Yuri, K3BU.us

Yuri Blanarovich wrote:
For those selling them :-)
As far as efficiency, screwdriver will beat the pants off whip with base
tuner, especially on low bands.

To the tune of a measured 12 dB difference in 75m
mobile shootouts.
--
73, Cecil, w5dxp.com

"Yuri Blanarovich" wrote in news:096Th.6$na.4
@newsfe12.lga:


"Pro Shop at Home" wrote in message
...
Both!!


"KE5MBX" wrote in message
oups.com...
I'm planning to get a Yaesu FT-857D and operate mobile HF on as many
bands as possible. I see two options so far for my Jeep Wrangler- a
102" whip with a tuner or a screwdriver antenna. Which is the better
way to go?



For those selling them :-)
As far as efficiency, screwdriver will beat the pants off whip with
base
tuner, especially on low bands.

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.


--
Dave Oldridge+
ICQ 1800667