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Author Topic: stupid question perhaps  (Read 1372 times)
AE7IS
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Posts: 48




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« on: January 22, 2014, 05:01:23 PM »

ive been looking at a mobile antenna, something for 10 - 40 at a minimum.  I am confused tho between using a screwdriver-style or a whip.  I understand with a whip a tuner (autotuner most likely) is a requirement.  so it would be a one button push with no need to look at any meters.  if I go with a screwdriver I would most likely build my own...4 inch coil, 10 ga wire at 6 tpi, and so forth    cost would be around 500.  I have heard that a tuner is also needed or recommended.   
the question is, would a whip be similar in efficiency to a screwdriver style?
I have talked with alan and read thru his web site.  he doesn't really talk about whips to much other than 1/4 wave (10-12 meters)
thanks
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M6GOM
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« Reply #1 on: January 23, 2014, 02:03:39 AM »

If its going to cost you $500 to build a screwdriver antenna you may as well buy one. It'll have the advantage of having a turns counter in.

You do NOT use a tuner with a screwdriver antenna but use a screwdriver antenna controller if you want it automated. This can be as simple as a turns counter model or a far better SWR detecting one like the Turbotuner.

The question about efficiency isn't easy to answer as there's a lot of variables that come into play. With the screwdriver it is the efficiency of the coil and the tuner/whip the efficiency of the LC circuits.
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W5DXP
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« Reply #2 on: January 23, 2014, 05:34:13 AM »

would a whip be similar in efficiency to a screwdriver style?

Here's the compiled results of three CA 75m mobile shootouts.

http://w5dxp.com/shootout.htm

As you can see, a screwdriver (with top hat) is at the top of the list and a CB whip driven by an SG-230 is at the bottom of the list with a 25 to 1 performance difference. Of course, 80m is worst case for HF but 40m is not far behind. If you give up on 40m and go for 20m-10m operation, the whip/autotuner idea is not a bad choice. But if 40m performance is a necessity, I would go with the screwdriver which does not require a tuner. Usually, a shunt base matching coil is all that is required for low SWR readings.

My 11.5 ft whip with SGC tuner did perform very well on 17m-10m.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
AE7IS
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Posts: 48




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« Reply #3 on: January 23, 2014, 08:38:38 AM »

Thanks for the response.  Just what I needed.  I know things change , the car , the ground under the car, but with those things the same a person should be able to determine some kind of efficiency from one kind to another.  Which is just what was provided.  I know shoot outs can be less than scientific but at least it gives me something. 

Next question would be kind.  Since I'm in the northwest, which means rain most of the year, I'm leaning towards an enclosed coil, which is not exposed to outside elements.
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W5LZ
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« Reply #4 on: January 23, 2014, 10:50:06 AM »

In a 'nut shell', the bigger the antenna, meaning coil size and whip length, the lower in frequency you can go and still be 'competitive'.  If the 'size' of the antenna is limited then the largest you can manage and a very good tuner is a 'viable' alternative.
 - Paul

(and the reference antenna in those comparisons was a bugcatcher! Smiley)
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WN2C
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Posts: 447




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« Reply #5 on: January 23, 2014, 12:32:20 PM »

If you have gor the $$ buy a Scorpion screwdriver antenna. Best built (like a tank) and best warranty out there.

Rick WN2C

p.s.
I am real happy with mine and I get reports of "oh I didn't realize you were mobil, good signal"
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