RogerTango.com - Install a screwdriver fixed
|Install a screwdriver fixed|
Posted on Tuesday, 11/20/2007
This article will detail the install of a screwdriver antenna to be used in a fixed location. I have pretty much given up on
QRO auto tuners, I spent a lot of money on one only to find it had "weird behavior". On low power CW I would tune up my
doublet and as soon as I switched to QRO (500w) and start to transmit, the tuner would "klick" (one of the latching relays)
and either my C or L would go off setting (I don’t know which) and the SWR would jump from the nice 1.5:1 to over 5:1.
Something strange- so at any rate, some extensive research led me to conclude a SCREWDRIVER antenna in a FIXED install would
suit. At least I hoped it would work out.
I got the screwdriver antenna, $250 worth of home built craftsmanship. All was good, until I got my "new" amp and ran QRO in
it. On the first run with 500w I could NOT get it to tune low SWR like I did at 100w. I took it apart to find the top screw
that should contact with the whip nut was NOT making contact, what so ever. I fixed the problem by redrilling and
repositioning a NEW screw that went INTO the brass nut that held the whip. I put it all back together and put it up. Great!
Works perfectly fine now! From close inspection I found the previous screw was about 1/16" away from the nut which held the
whip, so it was not a direct contact. When I contacted the builder on this he got defensive about his "craftsmanship" so I
just let it go.
Next came the B&D screwdriver which would NOT stay together. By admission I ran the antenna down too far and it binded a
bit, but this caused the clamshell design of the B&D screwdriver to separate and the gears jumped out! So once again I am
tearing down an antenna that should have been perfect when I got it, and redoing the gears.
Flash forward 2 days later, without running the coil too far into a bind, the screwdriver once again jumps gears! This is
getting tiresome so I put in new rods that hold it all together firmly and will keep the unit from coming apart and thus the
gears jumping out.
Coupled with the fact the coil cover was PVC tubing and not the Lexan cover that was dipicted in the builder's web page, I
have decided to NOT mention the builder as I cannot in honesty recommend one of his antennas.
After over 3 tear downs, I have for the sake of argument rebuilt this antenna. And the job is not finished. I will soon
have to devise some new fingerstock since the ones installed are flimsy junk.
This does not mean I would not recommend a screwdriver for a fixed install, rather do the screwdriver but pick a GOOD one to
I will get the ugly out of the way before I put good up- There is no reason anyone should have to tear down a new antenna for
repairs jut to get it to work right.
Here you can see how the clamshell gets cock-eyed and the gears jump out of place.
This was fixed by running pins that go all the way through the screwdriver.
I am not in the least impressed with the fingerstock, it is working fine now but I am devising some new ones.
Meter shows that after the fix I am getting contact between the coil and the nut which holds the whip.
Details of what was needed to fix the poor design and build.
Okay, so now lets move on with the good-
Here are some of the supplies I got for the fixed install.
I am going to put the 3-way socket at the antenna, this will allow me to use a standard extension cord for the control cable,
and since the plug of the cord will be outside at the antenna, it cannot be plugged up by accident to mains in the shack.
Just hooking up the socket.
The socket for the control cable is ready to go.
Now for an insulator for the brace. I found a pipe cap with a hold clamp at the hardware store, perfect!
Cut it up, get it ready.
How it will go on.
Finished! Ready to go mount it up and try it out.
I predefine which lead will be pos and neg, so I can lable the up/down switch with labels.
My first install was more or less a temp install, just for the sake of trying it out.
As you can see, I am using the chain link fence for the counterpoise & ground.
A little "cheat sheet" in the shack so I can remember which way to run the coil as I QSY.
Installed in it's new configuration. Works fine and is plenty sturdy.
A close up shot of the mount and brace system I came up with. I have other ideas, but for now this works FB.
I thought the view was nice, so I am posting it…
A little more stealth mode, the cover is now painted OD Green. :-0 It is less noticable from the street. I just hope the
neighbors like ham radio!
Listed is minimum achieved SWR with this particular install
80m - 1.5:1 Entire Band
60m - Not an option with IC-718
40m - 1.2:1 Entire Band
30m - 1.1:1 Entire Band
20m - 1.2:1 Entire Band
17m - 1.7:1 Entire Band
15m - 1.3:1 Entire Band
12m - 1.2:1 Entire Band
10m - 1.5:1 Bottom / 1.2:1 Top
Measurement was conducted with a cross needle Watt/SWR meter
using 10w CW carrier.
I have had several really good contacts with it, so at this point I am pleased. I am just thankful that I had the ability to
fix it up and make it operational or else I would have been out some money- Projects like this are not for the inexperienced
operator, a little knowledge and a lot of determination is needed to make sure it all works as you intented.