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Author Topic: Homebrew Screwdriver Antennas and the Turbo-Tuner  (Read 1721 times)
XY3LON4
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Posts: 84




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« on: May 27, 2007, 01:16:01 PM »

I plan on making my own screwdriver with Don Johnson's plans. I want to be able to get on 160M. I have a few questions.
1) The whip for 160M is 8 foot long. If I have the antenna mounted on my mirror then every bridge I come to will hit the antenna. How can this be avoided? I noticed on some pics of installation that it is mounted on the handle next to the door. Will the antenna work right sitting right next to the truck like that? I imagine that it would basically turn it into a semi-directional antenna to some extent.
3) Will I have to construct the antenna in a special way to interface with the Turbo-tune?
4) I met a truck driver who had a Hy-Q mounted on his mirror with a cap-hat and the whip was bent at 90 degrees pointing towards the back of his truck. Is this advisable and what are the  pros and cons to this?
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K0BG
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« Reply #1 on: May 27, 2007, 01:24:46 PM »

Mirror? That is the WORST possible place to mount any antenna, much less a decent one. It's an inadequate ground plane even for two meters!

Go to my web site, and look under OTR trucks.

Alan, KØBG
www.k0bg.com
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XY3LON4
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« Reply #2 on: May 28, 2007, 08:33:29 AM »

Yes, I agree about the mirror not being the best place to mount an antenna and the step is a much better groundplane but it's a toss-up between being able to communicate with people on the right side of you and getting a good ground. I talked with a guy who owns a tarheel and he a bracket mounted to the front of the hood on his PB that has a square plate as a mounting surface.   Think I may do that. Then I wouldn't have to worry about the length of the whip. just have to snake the coax but that shouldn't be a problem.
I still need an answer to the turbo-tuner compatability question.
 
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K0BG
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« Reply #3 on: May 28, 2007, 10:16:57 AM »

I'd would have been delighted to take this off-line, but you didn't leave your e-mail address.

The Turbo Tuner uses RF sensing to find the resonant point. It doesn't require a reed switch like the MFJ stuff does, so it'll work even on a home brew antenna as long as you program it correctly. That is, if the current sense is within the amperage of your motor, and if the SWR is level is set correctly too. Most of the time it stops close enough, but you still might have to jog the setting manually.

The length of the whip doesn't mean much by itself. What does, is the over all length of the antenna. Length, in essence, determines the radiation resistance. Higher is better, but in your case it isn't going to make much difference. The reason being, ground losses are always high in a mobile, but especially so on 160. Adding large amounts of ground loss (mirror mount for example), makes things even worse!

Remember too, no amount of ground straps can make up for a lack of a ground plane, unless they're long enough to be radials. In other words, DC and RF grounds are not ground planes.

Alan, KØBG
www.k0bg.com
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XY3LON4
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« Reply #4 on: May 29, 2007, 09:20:33 AM »

Except for the installation thing it all might just be a mute point. I checked the kind of money that a machine shop wants to charge to do about 20 minutes worth of work to make the coil form and they claim it will take 2 hours of work and cost $100+. I have never worked in a machine shop but I know how lathes work and I can do what I need done. I am not smart but I know when I am being ripped off. I guess, if I can't find a person who owns a lathe that ISN'T a theif, I will just have to buy a hy-q or tarheel. Ya gotta love greedy capitalists.
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WW5AA
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« Reply #5 on: May 30, 2007, 08:31:59 AM »

The bad part of posting here without a call sign is that it's hard to give information not knowing someones location. You may want to email NO5E, Dean about your project. Good luck.

73, de Lindy
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XY3LON4
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Posts: 84




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« Reply #6 on: May 30, 2007, 09:14:55 PM »

Well, I think I asked at one point for my user name to be changed to my call and they said they couldn't do that. So then I tried to register a new account with my call as my username but it said I couldn't use my email address because it is already in use by someone.
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XY3LON4
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« Reply #7 on: May 30, 2007, 09:55:58 PM »

tried emailing no5e and got an error message and the email was unable to be sent. I did find a company called Windevor that has aluminum tubing in 2-1/8" dia. for about $2.30 a foot. I emailed them. I don't know if they sell short lengths or not. I will find out though. All I need now is to find someone who will mill the pvc for me. I am constantly checking the hams in the areas that I travel through to see if I can find one who has a metal shop in their garage.
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W3LK
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« Reply #8 on: May 31, 2007, 08:05:49 AM »

<< Well, I think I asked at one point for my user name to be changed to my call and they said they couldn't do that. So then I tried to register a new account with my call as my username but it said I couldn't use my email address because it is already in use by someone. >>

Follow the instructions in the eHam help section _exactly_!!! Works every time.

The reason you are getting the error message is YOU are using the email address with your current log on name.

Edit your current log on information and replace the current email address with  xxx@xxxxx and save it. THEN create the new log on name.



Lon - W3LK
Baltimore, Maryland
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
W3LK
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« Reply #9 on: May 31, 2007, 08:39:06 AM »

FWIW, I think homebrewing your own motorised antenna is a waste of time and money. You cannot make a _good_ antenna any cheaper than buying one from High Sierra or Tarheel.

This is one area that homebrewing is not a good alternative.

Lon - W3LK
Baltimore, Maryland
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AD5X
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« Reply #10 on: May 31, 2007, 12:45:22 PM »

"You cannot make a _good_ antenna any cheaper than buying one from High Sierra or Tarheel."

Hi Lon - I built my first crewdriver antenna from Don Johnson's plans.  At the time he sold the pre-built coil for $35.  After buying everything else, I had less than $100 in it.  I used that antenna for several years mobile (you should have seen it mounted on my Geo Metro!!), and it is still being used by a friend for portable operation.  

Phil - AD5X
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W3LK
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« Reply #11 on: May 31, 2007, 05:04:01 PM »

You said the magic words - he sold you a prebuilt coil kit. That's a bunch different from homebrewing your own. Smiley

That's the killer on motorised antenas.

73,

Lon - W3LK
Baltimore, Maryland
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
RADIOGUYR2
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Posts: 1




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« Reply #12 on: June 07, 2007, 05:38:17 PM »

forget the turbo tuner-- its not all that its promoted to be in real use for the bucks it cost.  You can use a power reduction device and a wave/power meter and do just as good if not better than the turbo tuner which locks up on the wrong settings or never locks up at all, wearing out the coil on the screwdriver antenna.   It has very little provisions for overriding its control.

Again for the money, don't waist it on a auto-controller.   Go with what Don Johnson says to tune it with in his web page.

We did a compair of the leading 3 screwdriver/auto tuned by motor antennas.  One of the factors was the cost vs the effecency/useage and the other was reliability and maintenance.

DJ's came in pretty close for the effecency but failed on the maintenance and reliability.  The Q antenna (the most costly) didn't perform much better on the air than did the DJ or the HS/tH ones.   The best for the buck is the HS overall but it has its mechanical problems with the contacts.

One person tested the old Master Mobile/swan center loaded antenna at the face off.  Guess who won the best for the least.  If you can wait till your out of the car the center loaded is the best for the buck.  Then comes the off center loaded.  Hustler (ignoring all the water issues) didn't do bad with signal to cost.  However, most failed to cover the whole band in the emission range without retuning.

Finally the last catagory was the home made antenna for mobile.  Again the center loaded whips were dominating.  One used a tap system to set up the antenna.  But, again while the cost was low, the BW was also.

The one that got the prize--- HS 1800 pro. as it can take a amp, has moderate Q, and seemed to be most useable through out the range in bad enviroments.
Second was the H-Q.  It has one whopper of a coil that gets ya noticed going down the road. (doesn't help the gas mileage with all that wind resistance either) as well as it takes a much more beefy mount to keep it from dragging behind the car.  We won't even talk about the cost except to say I would not leave it on the car out in the parking lot when you go into see a movie.  It could bring a nice price at the next states swap meet after the 5 finger discount.
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KR4OW
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Posts: 43




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« Reply #13 on: June 10, 2007, 12:22:30 PM »

Do you have the full set of plans for his antenna?
I only have a couple of pages. I was wanting to do the 160 with mine as well but did not know what the mod for the antenna was
Thanks
David KR4OW
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