I was recently given a screwdriver antenna by a non ham. Can anyone give me an idea as to what brand or model screwdriver this is? Also, can you explain what is missing from its base? I'm assuming that it is the matching coil and tap points but am to new to the hobby don't completely understand myself. I'm looking for any information that will help me put this antenna back into srevice.
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What brand of screwdriver antenna is this
- Thread starter KMJensen
- Start date
I agree with Ratso, looks homebrew.
The base looks like the matching unit and looks like a matching coil should be or was in the grooves.
If the motor still works you could get that back working and learn about these antennas in the process. Problem is that exposed top coil will weather so regular cleaning would be needed.
You will need a matching coil and bypass that original design that you can make yourself out of 12 guage enameled wire which is needed for better impedance matching at lower frequencies. This will simply mount as a shunt between the antenna ground and hot side feed point.
If the bottom stud unscrews and/or if it's a 3/8 x 24 thread, it will mount to any CB style mount.
Typically these antenna motors are 12v and reversing the polarity moves the coil up or down. You just need a DPDT momentary on/off switch to control it.
At your own risk, put 12v to the antenna and see if the coil moves then reverse polarity and it should move the other direction.
If the motor works, then it would be a good project. You can get this going for less than $30 in parts minus antenna mounts.
I'm pretty knowledgeable with mobile screwdriver antennas and myself and others can help you along the way with a bit more detailed information.
First see if the motor works, if not I wouldn't bother with it.
Good luck!
The base looks like the matching unit and looks like a matching coil should be or was in the grooves.
If the motor still works you could get that back working and learn about these antennas in the process. Problem is that exposed top coil will weather so regular cleaning would be needed.
You will need a matching coil and bypass that original design that you can make yourself out of 12 guage enameled wire which is needed for better impedance matching at lower frequencies. This will simply mount as a shunt between the antenna ground and hot side feed point.
If the bottom stud unscrews and/or if it's a 3/8 x 24 thread, it will mount to any CB style mount.
Typically these antenna motors are 12v and reversing the polarity moves the coil up or down. You just need a DPDT momentary on/off switch to control it.
At your own risk, put 12v to the antenna and see if the coil moves then reverse polarity and it should move the other direction.
If the motor works, then it would be a good project. You can get this going for less than $30 in parts minus antenna mounts.
I'm pretty knowledgeable with mobile screwdriver antennas and myself and others can help you along the way with a bit more detailed information.
First see if the motor works, if not I wouldn't bother with it.
Good luck!
Fourstringburn - My thoughts were that it was home brew but was hoping that by some chance that it was manufactured with some documentation available. The motor works fine. I took the antenna apart and cleaned the windings with a electronics contact cleaner and lube. I installed a new fingerstock contact ring.
I'm sure there is some way to make a covering for the top coil. Is there supposed to be some kind of insulator between the outer tube and the mounting mounting bolt? Also do you know the specs for building the matching coil?
I'm sure there is some way to make a covering for the top coil. Is there supposed to be some kind of insulator between the outer tube and the mounting mounting bolt? Also do you know the specs for building the matching coil?
Home brew antenna no doubt.
That would depend on what band the individual built it for. Covering your coil could influence the tuning and power dissipation.
That would depend on what band the individual built it for. Covering your coil could influence the tuning and power dissipation.
The matching coil needs to be made from 12 guage enameled wire. This is the same wire used in motor or alternator windings. You can find small reels of it on Ebay if you can't find it locally from real electronics stores, not Radioshack.
Wrap the wire around a bolt the size of a spark plug thread (7/8ths?)with 9 turns and leave about 2 inches of non coiled straight excess on each side of the coil. Make a nice tight coil around the bolt threads then turn the bolt to spin off the finished coil.
Strip the enamel with a razor and smooth out with a file or emery cloth about a 1/4 inch on each end and solder 2 ring terminals on each end. Mount one ring terminal to a screw on the antenna body and the other will go to the antenna bracket which creates a shunt. Now with the antenna mounted, try to tune 40 meters by first getting as close as possible with the antenna coil, then start slowly and minimally spreading the shunt coil till you get the lowest match. An antenna annalyzer works real good here if you have one or can borrow one. Then check on 20 meters. You may have to adjust the shunt coil to find a good balance between 20 and 40 meters or you may have to take a turn or 2 out of the coil. 9 turns is a good start.
The more you spread the coil the less inductance value and the tighter the coil and higher number of turns, the more inductance. More inductance is needed if the feedpoint is less than 50 ohms or an SWR well above 1.8 if you don't have an analyzer. Less is needed if the the inductance value gets above 50.You have to keep checking between the 2 bands to see which way to adjust the coil.
What you are doing here is adding some extra inductance at the antenna feedpoint since mobile antennas are way short of any HF band and even with a loading coil in the screwdriver, the feedpoint impedance is too low, typically under 25 ohms and this extra coil will bring it back up to near 50 ohms.
Yes there needs to be an insulator between the antenna body and where it mounts to a bracket. Post a pic of the bottom of the antenna with and without that bolt.
It looks like a typical bolt and coax ring terminal style bolt might work or the more common CB 3/8 x24 threaded stud will work for a mirror mount style bracket or similar. Both these have the nylon insulator bushing.
Other than that just wire it up to DPDT monentary ON switch where the motor leads pick up a positive and negative on on side of the switch and reverse polarity of the motor wires on the other side.
It maybe easier and safer to buy a motor switch wired and ready to go from Tarheel antennas.com
Wrap the wire around a bolt the size of a spark plug thread (7/8ths?)with 9 turns and leave about 2 inches of non coiled straight excess on each side of the coil. Make a nice tight coil around the bolt threads then turn the bolt to spin off the finished coil.
Strip the enamel with a razor and smooth out with a file or emery cloth about a 1/4 inch on each end and solder 2 ring terminals on each end. Mount one ring terminal to a screw on the antenna body and the other will go to the antenna bracket which creates a shunt. Now with the antenna mounted, try to tune 40 meters by first getting as close as possible with the antenna coil, then start slowly and minimally spreading the shunt coil till you get the lowest match. An antenna annalyzer works real good here if you have one or can borrow one. Then check on 20 meters. You may have to adjust the shunt coil to find a good balance between 20 and 40 meters or you may have to take a turn or 2 out of the coil. 9 turns is a good start.
The more you spread the coil the less inductance value and the tighter the coil and higher number of turns, the more inductance. More inductance is needed if the feedpoint is less than 50 ohms or an SWR well above 1.8 if you don't have an analyzer. Less is needed if the the inductance value gets above 50.You have to keep checking between the 2 bands to see which way to adjust the coil.
What you are doing here is adding some extra inductance at the antenna feedpoint since mobile antennas are way short of any HF band and even with a loading coil in the screwdriver, the feedpoint impedance is too low, typically under 25 ohms and this extra coil will bring it back up to near 50 ohms.
Yes there needs to be an insulator between the antenna body and where it mounts to a bracket. Post a pic of the bottom of the antenna with and without that bolt.
It looks like a typical bolt and coax ring terminal style bolt might work or the more common CB 3/8 x24 threaded stud will work for a mirror mount style bracket or similar. Both these have the nylon insulator bushing.
Other than that just wire it up to DPDT monentary ON switch where the motor leads pick up a positive and negative on on side of the switch and reverse polarity of the motor wires on the other side.
It maybe easier and safer to buy a motor switch wired and ready to go from Tarheel antennas.com
Good point.
My guess is that antenna has enough coil inside to tune between 10 and 40 meters with a 4 ft. whip.
looks to me like the base of the tube has been helical cut to form a 9 turn coil to ground with various holes for shorting screws.
That's what I was thinking too but hadn't figured out WHY yet unless it was meant to include it as a base matching shunt coil.
So that spiral cut would act as the coil that fourstringburn described above? if so that's a pretty slick design.
It most likely is for a matching coil but it doesn't look to go to ground. I guess you can run a ground up to the lower adjustment screw. It looks like there are upper and lower clamps to hold the coil form in place. My guess would be 14 guage wire.
Maybe that would be the way to go. I would try rebuilding that first before using a shunt coil.
