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Author Topic: mini screwdriver or 8.5' whip  (Read 4360 times)
KD0NFY
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Posts: 75




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« on: July 07, 2011, 10:26:13 AM »

First let me preface this by saying I know that I should really be using a 25 foot long bug catcher and I'm not a real ham unless my mobile antenna is bigger than the vehicle it's installed on.  Please spare me a lecture on how either of these antennas are no where near the performance I'd get from a real antenna.  I agree with you.  It's just not an option. 

Okay with that out of the way, I'm looking for advice on what would give me better performance in a mobile station.  I have a tiny little car, a Toyota Matrix.  I'm just getting started on planning a mobile station.  If I can get decent performance on 20 meters and up I'll be satisfied.  Here's the plan so far:

mini screwdriver like a Little Tarheel II or an 8.5' whip (SG-237 tuner if using the whip)
Breedlove ball mount on driver's side rear fender
Yaesu 857D  (I want it all in one box, I don't have a lot of room inside)

40 meters and lower would be a bonus, but I know efficiency will be horrible. 

Has anyone done both, and how did it work? 

Thanks!
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AC4RD
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« Reply #1 on: July 07, 2011, 12:27:17 PM »

I've got an itty-bitty tiny econobox of a car (2006 xB) and park in a garage with low clearance, so I've been playing with the same issues.   The K0BG website is the best resource I know of for new mobilers--you definitely will benefit from spending some time there.

My own belief is that there isn't much *efficiency* difference between a screwdriver and any other type of mobile antenna, given similar lengths.  But there IS a pretty significant difference between shorter and longer antennas.  That is, the longer you can make your antenna setup, the better your performance will be.

Another completely personal opinion:  You can have PLENTY of mobile fun with a Hamstick <TM> or similar.   Buying a couple of Hamsticks, or a Hustler system, is pretty inexpensive (especially compared to screwdrivers!) and will let you have fun and see if you like HF mobiling.

The system I'm using now is 3/8x24 mounts, aluminum masts from DX Engineering (though I'm looking forward to trying to roll my own using K5LXP's website page), Hustler resonators, and whips with capacity hats.   This is fairly inexpensive, and I'm reasonably pleased with the performance.  AND it fits in my 9-foot-clearance parking garage at work.  :-)

You'll get lots of advice, I'm sure.   This is always a popular topic.   GOOD LUCK!
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K0BG
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« Reply #2 on: July 07, 2011, 03:01:19 PM »

Two things really matter. One is effective electrical length, and the other is the current distribution over that length. Base loaded antennas, like the coupler/whip combination, will have about 1/2 the efficiency of a center loaded antenna of the same length. This is true because center loading raises the current distribution within the length of the antenna. THis does not take into account any losses within the coupler, which may be significant especially on 40 meters, and down.

Add a cap hat, and you further change the current distribution. If the cap hat is big enough, and mounted correctly (at the top of the antenna, not the top of the coil), you can increase efficiency by nearly 4 times!

And, since radiation resistance is also a factor of length, increasing the length from 8 to 12 feet increases the efficiency by nearly double! Do all of these things, and you have a winner. Anything less is less.

Short, stubby antennas are a mixed bag of tricks.You can't call them base loaded, and you can't quite call them center loaded, especially if you use a long whip. Do the calculations, and you'll discover that increasing the length of a short, stubby antenna's whip length beyond about 6 feet or so, actually reduces efficiency albeit slightly. Again, it all has to do with factors in the first paragraph.

Every mobile operator has to establish his or hers level of performance. If you're willing to squeak by, fine. I'm not!
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WD5GWY
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« Reply #3 on: July 07, 2011, 07:07:05 PM »

I have used a 102" whip and an LDG Z-11 PRO autotuner in both my pickup and
big diesel rig. (2007 Kenworth) That setup was fair on 40 meters and pretty decent
from 20 meters to 10 meters. Switched to an Alpine Screwdriver antenna and it was
like night and day. (this was the pickup setup) Much better performance. I did a lot
of bonding and that really helped.
I then moved the whip & auto tuner combo to my big truck. Again, it worked Ok on 40
and decent on 20 and up. I got a good deal on a used Little Tarheel II antenna and removed
the whip & tuner combo  and installed the Tarheel. (again did a lot of bonding,,,,,,,but had other
issues with RFI from the electronic fuel injectors.......) The Little Tarheel II works pretty good on
40 - 10 meters. I feel that it is better than the whip & auto tuner setup.......but, not by a whole
lot. As Alan mentioned , the whip is short (32") and that does make a difference. I recently bought
a 56" whip from Tarheel that I plan to replace the 32" with. I'm hoping that that will improve things
even more.
   Overall, the Little Tarheel II antenna is better than the whip & tuner combo, but, not as good as
a full sized screwdriver antenna. It is almost as expensive (new) as it's larger siblings. If you can get
a good deal on a used one, then I would suggest that route. And as has been mentioned read Alan's
website. He has a lot of useful information there.
  Oh, and one good thing about the Tarheel antennas(and a few other screwdriver antennas), you can get an auto controller that will interface with your radio (Turbo Tuner) and make retuning/band switching much safer if you need to change bands while driving.
  james
 
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WA8FOZ
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« Reply #4 on: July 07, 2011, 08:34:19 PM »

"Breedlove ball mount on driver's side rear fender."

YES!!! And optimize your image ('ground") plane. Ground the shield to your chassis by as short and fat a strap as possible, and ground the door, hatch and hood to the chassis. This may also help reduce ignition noise. These things are even more important than your choice of antenna, among the options you propose.

 "Overall, the Little Tarheel II antenna is better than the whip & tuner combo, but, not as good as
a full sized screwdriver antenna. It is almost as expensive (new) as it's larger siblings. If you can get
a good deal on a used one, then I would suggest that route."
This makes sense.

 "And as has been mentioned read Alan's website. He has a lot of useful information there."
If anything, an understatement!

I like my bugcatcher. You can see it on k0bg,com (thanks, Alan). It's big, but I can take all or parts of it down very quickly, since the base and the whip are equipped with quick-disconnects. To do this, or to change bands, I must stop and get out of the car. This doesn't bother me; the combination of cheapness, light weight, simplicity, and efficiency are worth it to me.  If it's important to stay in your car, screwdriver + Turbo Tuner makes sense. Hey, whatever floats your boat - it's all fun.
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M6GOM
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« Reply #5 on: July 08, 2011, 02:10:06 AM »

I'm for the Little Tarheel II however with the following caveat. Take the supplied whip and throw it in the bin. Replace it with a 72" CB whip. You'll lose the ability to use 6m but on every other band it will be a massive improvement over the original. In my experience it was at least 6dB on 20m - a fourfold improvement. A received S7 went to S9+ and its reciprocal with TX.

Also don't use magmounts or stupid lip mounts but drill a hole in the roof. When I used mine on a triple magmount, on the 80m band if I tried to put more than 50W through it, the common mode currents were so bad due to the poor grounding that it rebooted the radio. Mine is mounted via a 3/8 mount drilled in the middle of the roof. With the 72" whip on, its still fine doing 80MPH fully extended on 80m into a 50MPH headwind.

I regularly work the USA from east coast England on 100W on phone on 20m and had no problem getting hold of CO6LC the other night at 10pm - a distance of 4500 miles.
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WA2LLN
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« Reply #6 on: July 08, 2011, 06:34:13 AM »

I'm using a 102-inch whip and SGC-237 with an IC-7000 in my minivan. The whip is on a Breedlove mount on the rear driver-side pillar, about as high as I could get it and still have the tuner close to the mount and inside the pillar.

I'm really impressed with the Breedlove mount. I feel like you could almost pick up the car with it.

The SGC 237 tuner is OK. There are times it seems to take forever to find a coupling solution, particularly on 20m. And sometimes it never seems to converge. When that happens, if I turn the rig off and back on and re-tune, it works OK.

As far as performance, well, its OK. No, I'm not able to reach the Australian stations I can hear sometimes early in the day on 40m, and I'm not busting big pileups for the rare stuff on 18m, but I have been able to talk to stations all over the globe under the right conditions.

I am considering switching to a screwdriver, mostly because I want better performance on 40m and I don't want to compromise automatic band switching. I'm pretty sure that even with the Breedlove mount, I'll need some additional support for a large screwdriver.

--
Art
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K0BG
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« Reply #7 on: July 08, 2011, 06:35:23 AM »

The ability to work a DX station has nothing to do with the antenna in use. It has to do with band conditions. Nothing more, nothing less.

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HS0ZIB
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Posts: 410




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« Reply #8 on: July 08, 2011, 06:58:57 AM »

Quote
The ability to work a DX station has nothing to do with the antenna in use. It has to do with band conditions. Nothing more, nothing less.

Ah OK... I'll replace my mobile ax with a dummy load and wait for some good band conditions for my next QSO... Smiley

Simon
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KD0NFY
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« Reply #9 on: July 08, 2011, 07:08:12 AM »

I think what Alan's getting at is unless you have a beam on your car, atmospheric conditions are what is doing all the work. 

Thanks everyone for your help.
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AA4PB
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« Reply #10 on: July 08, 2011, 07:27:06 AM »

The ability to work a DX station has nothing to do with the antenna in use. It has to do with band conditions. Nothing more, nothing less.

The band conditions have a whole lot to do with it, but a more efficient antenna is certainly going to improve your odds of making the contact. I expect that on 20M and up, there is not all that much difference between a properly installed Hamstick and a full sized screwdriver.

The bottom line is that one cannot use a few DX contacts as proof that any antenna is a particularly great performer. Propagation can have a lot more effect than antenna efficiency differences on the higher bands.
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K0BG
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« Reply #11 on: July 08, 2011, 01:25:55 PM »

One thing is for sure, you can tell who uses DX contacts as a justification.

You can indeed work DX on a dummy load. Under the right circumstances, you can circle the globe with just a few microwatts of ERP. Most cheap dummy loads leak more than that!

I further suspect, if most amateurs really found out what their ERP was, they wouldn't believe how low it is.
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W9PMZ
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« Reply #12 on: July 08, 2011, 02:30:07 PM »

sometimes listening to 20m i can't believe how high some amateurs ERP could be...
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N6AJR
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« Reply #13 on: July 08, 2011, 05:00:03 PM »

In my car, I use an ft 857 d with an ATAS antenna.  it is small and will work ok vfom 2m/440 up to 40 meters.  I tie a piece of fishing line to the tip to bend it over when pulling in the garage. ( it hangs up on the metal garage door.  I have an electric tilt over mount for it, but am just to lazy to install it,  the fishing line works.  in my truck I have a DK 3 and it does 6m to 80 m. and i rund a 2/440/6m fm whip for those bands.  bothe are compromises, but what the hay.  and the ATAS is designed to autotune with the ft 857.  works for me.   a big antenna works better but the ATAS 120 fits in the garage.
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K0BG
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« Reply #14 on: July 09, 2011, 04:26:13 AM »

Carl, when you put legal limit (or more) into 6 over 6 over 6 with the top antenna at 200 feet, you might be surprised just how loud some folks are!
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