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Author Topic: Problems with Turbo Tuner and Screwdriver Antenna  (Read 3010 times)
WD5GWY
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Posts: 391




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« on: July 28, 2010, 03:11:08 PM »

Hope this is not too boring a subject. BUT, about a year ago, I purchased a screwdriver antenna from
Alpine Antennas. (Model 100s) Due to work I was not able to install it until a few months ago. Before
I got around to installing it, I managed to buy a Turbo Tuner controller from a ham on eham.net.
I finally got to install the antenna on my 97 Dodge 2500 pickup. Using a manual controller a friend gave
me, I set up the antenna and just used a chart and markings on the mast to use the antenna.
I then decided I had better use the Turbo Tuner I had bought (for IC-706 MKIIG) since using the system
I had was not safe and still required me to stop in order to re-tune when changing bands.
I followed the instructions that came with the Turbo Tuner (setting up the radio and the dip switches inside)
and could not get it to work with the antenna. I emailed and later received a phone call from Bill at Turbo Tuners and he helped me check things out. It turned out that antenna was drawing 1.4 to 1.5 amps when moving up and down! Too much current draw for the Turbo Tuner. And the stall current would jump to 3 amps!
So, I gave up on the Turbo Tuner and boxed it up and put it away. And went back to using a manual controller.
That worked well one day until I was re-doing my tuning chart and the coil jammed in the extended
position (was doing the settings for 80 meters). The motor would continue to run in forward and reverse
but, the coil would not move. I contacted Wesley at Alpine Antennas and he said that even though the antenna was out of warranty , he would repair the antenna at no charge to me if I would pay shipping and handling both ways. Well, since it was out of warranty and I expected I would have to pay for parts and labor as well, I was pleasantly surprised when Wesley said he would fix it for free.
I sent it out and got it back in just about a week. (great service and turnaround)
I reinstalled it a couple of days ago and for the fun of it, I hooked the Turbo Tuner back up. (after confirming that the antenna was working with my manual controller) To my surprise, it worked!!
And did so, until today. This afternoon ( 100 degrees if that matters) I went to change bands and nothing happened. Checked connections and then it worked again.........for a bit. But, when I needed to go up with band changes ( from 20 to 10 meters for example) it would extend like it was going towards 80 meters. So, I changed a dip switch inside from normal to reverse which should have fixed the problem. Instead of fixing it, nothing happened. Rechecked all connections and everything was fine. Had power to the Turbo Tuner ( it sends R4 in code when you first power the radio up) but, it would not move the antenna at all. Even setting the dip switch back to the original setting had no effect. ( when I would stop it from attempting to tune after a long wait, it would send the letter P for Park like I had initiated the park function, which I had not)
So, has anyone any suggestions on either a way to fix this or buying another Turbo Tuner (new not used) or maybe a better method of working with the manual controller and some sort of indicator to denote when in the proper position for the frequency tuned. (there is too much RFI coming from the antenna's motor to use noise level with the receiver to pre-tune and then key up for final tuning)
What methods do other screw driver antenna users use, other than a Turbo tuner or memory controller?
(this antenna has no counter switch in it)
Thanks for any suggestions.
James
WD5GWY
 
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K0BG
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« Reply #1 on: July 29, 2010, 06:16:57 AM »

The Turbo Tuner doesn't remember where is has been, and therefore often goes in the wrong direction. Eventually, it gets all the way to the bottom (80 meters), stalls, and the moves the other way. Hopefully, if the antenna is well matched, it stops where it should.

There is a secondary issue with the antenna itself. There is a built in, base matching coil. While that works for some installations, it doesn't work for all. It is also important to remember, if the match isn't perfect, the lowest SWR won't be at resonance. Hence, an SWR bridge isn't the right tool to check the match accurately. That takes an antenna analyzer.

You might want to read the Antenna Controllers article on my web site.
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WD5GWY
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Posts: 391




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« Reply #2 on: July 29, 2010, 09:49:18 AM »

Thanks for the reply and suggestions Allen.
 I failed to mention that I am using an MFJ 259b
antenna analyzer. When the setup was working I
checked the SWR along with the resistance with the
Analyzer after tuning with the Turbo Tuner on each
band from 80 to 10 meters, and the frequency of resonance
each time was the same on the analyzer as that shown on
my radio when the antenna was tuned with the Turbo Tuner.
The resistance was close to 52 ohms ( 48 to 49 mostly) on
each band when tuned. SWR was around 1:5 or so, since I did
not have the Turbo Tuner set to look for absolute minimum
SWR but used the default setting which gets awful close.
I was impressed with how the Turbo Tuner worked. And you are
right about it going in the wrong direction. But, there is a dip switch
that allows for that issue and is supposed to correct it. (basically saves
doing a rewire on the power cable to get the correct direction of travel
when tuning )
But, as I mentioned, once I used that switch, it quit working. It could be
that the Turbo Tuner does have a problem, or it could be something else.
Right now I'm using a manual controller I built and all is working well.
Of course, I have to stop to retune the antenna when changing bands.
I may give it another go today and if it works I will leave things alone and
let it hunt or whatever it needs to do.
Thanks for your help.
james
 
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WD5GWY
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Posts: 391




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« Reply #3 on: July 29, 2010, 12:06:55 PM »

Alan, (sorry for misspelling your name the first time)
  Are you saying that because the Alpine has the matching coil machined into the base
of the antenna that it could create problems? As I understand it, that is a copy (more or less)
of Don Johnson's design. It sure seems to work well, and my radio gives no indication of
a problem with it. Other than not being adjustable, I don't see the problem there. At first I could not see how that would work. I think I even emailed you at one time asking about it. But, it certainly does seem to work quite well having the matching coil as part of the antenna itself. The only thing i can see that might be a problem is if there is much flexing in the antenna mast. Then, the coil spacing could change and possibly effect the feedpoint resistance. I have mine mounted on the rear bumper and away from the pickup about 5" as suggested by Wes at Alpine and a brace part way up to strengthen the mast and hopefully prevent any movement by the mast below the brace.
   I have read your website and there is a lot of good info there. Thanks for your help.
james
WD5GWY

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K0BG
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« Reply #4 on: July 30, 2010, 07:18:06 AM »

The input impedance of an HF mobile antenna is reliant on several factors. Those are iterated on my web site. Suffice to say, the required reactance of the shunt matching coil will be different in each installation. Perhaps I should say, the optimal reactance, which might be anywhere between .5 and 1.5 uH.

One should remember, that the resistive component of the input impedance, changes more rapidly with frequency change, than the reactive component. As a result, you can't rely on the SWR as an indication of resonance. Thus, an antenna analyzer, properly used, will give you the requisite information to adjust a shunt coil for the best match, over several octaves.

While the fixed shunt reactance might be okay, it probably isn't when using an automatic controller like the Turbo Tuner. By the way, Bill's sold a whole bunch of these controllers, and the vast majority work as advertised if the antenna is well matched.

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WD5GWY
Member

Posts: 391




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« Reply #5 on: August 01, 2010, 10:14:21 AM »

Alan,
  As to the machined in matching coil on the Alpine antenna, would you suggest
not using it and making a coil that is adjustable and use that instead? That would
be easy enough to do. And I could even cut some aluminum tubing in half and clamp
that over the existing machined coil to add strength to the mast.
  As it is, using the manual controller, it seems to work fine. I just wish I could get it
to work with my Turbo Tuner. (I'm lazy and would like to be able to change bands and
retune the antenna without having to stop each time I change bands)
james
 
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K0BG
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« Reply #6 on: August 01, 2010, 01:12:07 PM »

The only problem is, the base of the antenna is at ground potential. if you short across the built in coil, you'll have to insulate the base. I't been a while since I played with an Alpine, so I don't remember the details of its construction.

Just to make sure..... When you set the coil, adjust the 259 for the lowest X. That should be zero, but most of the time it will be a few ohms higher for various reasons. I tell everyone to put a piece of tape over the SWR readout, and forget about it being there, as too much emphasis is put on it, instead of the actual resonant point (in this case at least).
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WD5GWY
Member

Posts: 391




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« Reply #7 on: August 01, 2010, 07:45:23 PM »

The base of the antenna has a mounting stud that fits into sleeve of some kind of gray, plastic looking, material. (I'm sure it's not plastic as it appears to be very strong and is the same thing that the coil is formed on) The antenna can be lifted off of the mounting stud once a set screw near the bottom is removed.  The mounting stud is bolted from the bottom with a  3/8's stainless steel bolt.
And the ground braid of the coax is connected to a screw at the bottom of the mast (alongside the base of the mast and not actually the bottom/underside where the mounting stud bold is located).
I have some braided flat cable ( 1") connected to the same screw that the coax ground braid is connected to on the mast as well. So, you are probably right that I would have to isolate the mast from ground in order to use an external shunt coil to match the antenna.
  Guess I have a lot of studying to do. (never to old to learn new stuff)
james
WD5GWY
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