Hello, I have a vertical antenna that is tuned via taps on a coil at
the base. As I was moving the tap the other day I had the idea...why
not replace the tapped coil with a roller inductor? This would
certainly make tuning easier and as long as the roller is protected
from the elements should work as good as a fixed coil. Is there any
reason why this wouldnt' work? Has anybody else modified or built an
antenna using such a system? (For the record, the antenna is a Hy-Gain
AV18VS. I used to use it only on the low bands and as such rarely had
to move the tap, but now that I have an amp and this is the only
antenna I have that can handle power, I've been using it more often and
on more bands).
73, Craig KB8FGC

wrote:
Hello, I have a vertical antenna that is tuned via taps on a coil at
the base. As I was moving the tap the other day I had the idea...why
not replace the tapped coil with a roller inductor? This would
certainly make tuning easier and as long as the roller is protected
from the elements should work as good as a fixed coil. Is there any
reason why this wouldnt' work? Has anybody else modified or built an
antenna using such a system? (For the record, the antenna is a Hy-Gain
AV18VS. I used to use it only on the low bands and as such rarely had
to move the tap, but now that I have an amp and this is the only
antenna I have that can handle power, I've been using it more often and
on more bands).
73, Craig KB8FGC

Yes it has been done but not without its problems. Stopping the coil in
the right place, roller contact with the coil... can all be a problem.
I had good luck using a tapped coil and using relays to switch the taps
much as is done with an auto tuner. Some radios would allow the coil(s)
to be switched automatically with the help of a little extra equipment.
Just using manual control is not too bad. I think I saw a circuit to be
used with ICOM radio that controls relays by utilizing a DC voltage
that changes with band selection/frequecy. This was fed to a group of
comparator circiuts that drove the relays. I know of at least one
person who has tried this and it proved to be a good route for
lightning to get in his radio so my preference is the manual switch
controling relays. I dont know how this would work with your radio. The
only one I am familar with using this arrangemet was a 30+ ft whip
using a big flat metal roof as a couterpoise.

ORIGINAL MESSAGE:

On 28 Jul 2006 08:30:43 -0700, wrote:


Is there any
reason why this wouldnt' work? Has anybody else modified or built an
antenna using such a system?

------------ REPLY SEPARATOR ------------

I've done it myself and been quite happy. I used a low RPM reversible
DC motor to tune it remotely from the shack. Works great.

The only suggestion I would make is to not tune it with any
significant power to it or you could damage the coil by arcing as the
roller moves along. Up to ten or twenty watts should be ok. Keep the
roller clean.

Bill, W6WRT

"Bill Turner" wrote in message
...
ORIGINAL MESSAGE:

On 28 Jul 2006 08:30:43 -0700, wrote:


Is there any
reason why this wouldnt' work? Has anybody else modified or built an
antenna using such a system?

------------ REPLY SEPARATOR ------------

I've done it myself and been quite happy. I used a low RPM reversible
DC motor to tune it remotely from the shack. Works great.

The only suggestion I would make is to not tune it with any
significant power to it or you could damage the coil by arcing as the
roller moves along. Up to ten or twenty watts should be ok. Keep the
roller clean.

Bill, W6WRT

Hi Bill, can you tell m something about your setup with the roller inductor.
I tried it and was not very happy with it. I guess I could have tried a
slower motor and it seemed like it require cleaning a couple of times a
month. I still have the old stuff around and may try it again if I thought I
could get it to work better.

ORIGINAL MESSAGE:

On Wed, 2 Aug 2006 11:11:08 -0400, "Jimmie D"
wrote:

Hi Bill, can you tell m something about your setup with the roller inductor.
I tried it and was not very happy with it. I guess I could have tried a
slower motor and it seemed like it require cleaning a couple of times a
month. I still have the old stuff around and may try it again if I thought I
could get it to work better.

------------ REPLY SEPARATOR ------------

At the time I lived in the Seattle area so waterproofing was a must. I
built a plywood box with a plexiglas front and sealed it with
silicone. I used it for a couple of years and never had to clean the
roller inductor. One thing I didn't mention but should have is to have
most of the loading inductance in a separate high Q coil, and use the
roller only for tuning. IOW, don't try to use the roller for the
entire loading coil or it will tune too fast and probably won't be
very high Q either. As with mobile antennas, a center coil is best, or
at least as high off the ground as practical. If you don't have an MFJ
SWR analyzer or the equivalent, buy or borrow one. I would not attempt
this kind of project without one!

The motor was one I got from All Electronics in California. They seem
to have lots of surplus ones available. Something around five RPM
would be about right. They call them "gearhead" or something like that
because they have the reduction gears built in.

Does that answer your questions?

Bill, W6WRT

"Bill Turner" wrote in message
...
ORIGINAL MESSAGE:

On Wed, 2 Aug 2006 11:11:08 -0400, "Jimmie D"
wrote:

Hi Bill, can you tell m something about your setup with the roller
inductor.
I tried it and was not very happy with it. I guess I could have tried a
slower motor and it seemed like it require cleaning a couple of times a
month. I still have the old stuff around and may try it again if I thought
I
could get it to work better.

------------ REPLY SEPARATOR ------------

At the time I lived in the Seattle area so waterproofing was a must. I
built a plywood box with a plexiglas front and sealed it with
silicone. I used it for a couple of years and never had to clean the
roller inductor. One thing I didn't mention but should have is to have
most of the loading inductance in a separate high Q coil, and use the
roller only for tuning. IOW, don't try to use the roller for the
entire loading coil or it will tune too fast and probably won't be
very high Q either. As with mobile antennas, a center coil is best, or
at least as high off the ground as practical. If you don't have an MFJ
SWR analyzer or the equivalent, buy or borrow one. I would not attempt
this kind of project without one!

The motor was one I got from All Electronics in California. They seem
to have lots of surplus ones available. Something around five RPM
would be about right. They call them "gearhead" or something like that
because they have the reduction gears built in.

Does that answer your questions?

Bill, W6WRT

Ok, that helped. My motor turned even slower than yours but I was using only
the roller inductor. The next time I try this I may use a stepper motor.