11m Tuner for 2m Antenna

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Samuel Bartholomew Fox:
I know the title sounds strange, so I'll explain. 

I am about to install a VHF radio and a CB in a disaster relief trailer.  I want the setup to be easy to use, and I want to keep external antennas to a minimum due to certain restrictions.  I would like to use a Hustler SF-2 antenna for both radios. I know it will be very inefficient on 11m, but I just want something for communication with non hams during a deployment.

I want to build a permanent value tuner for the CB.  How should I go about this this? 

Thanks,
Sam

Dale Hunt:
OK, that is a 5/8 wave whip with a series loading coil at the base.

First you need a diplexor to keep the 11m RF out of the 2m receiver and vice
versa.  With that much separation you might get by with just a series
coil on the 11m side and a capacitor on the 2m side, but a better approach would
be to use series capacitor / shunt inductor / series capacitor on the 2m side and
series coil / shunt capacitor / series coil on the 11m side.  Specific values would
be chosen for a loaded Q of perhaps 2 to 5 on each band - we can figure that when
we get down to details.

You'll need an additional loading coil for 11m, probably around 2uH, likely with one
end grounded and the 11m coax tapped onto it to get a match.  This would go
between the 11m port on the diplexor and the 11m radio, preferably as close to
the antenna as possible.  Actually since the L-C-L circuit for the diplexor can also
work as an antenna tuner we might be able to chose those components accordingly,
but I think a better approach would be to add an extra variable coil and capacitor
to provide adjustable matching at that point.  A screwdriver adjust mica compression
trimmer capacitor should work.

SWR bandwidth is likely to be narrow - perhaps 400kHz at 2 : 1 SWR, depending
on the details of the circuit.  As long as the circuit can be installed RIGHT AT the
antenna mount it might actually be almost as efficient as a base-loaded CB antenna
of the same overall height.

Chris J. Smith:
You would be better off making a wire dipole for the CB.  Something that you could toss up into a tree or string between the trailer and a near by support.  The range you'll get trying to use it on a 2 meter antenna will be nil--that is, nobody beyond a few hundred feet will hear you.  Been there, done that.

:
My opinion:  Trying to do 11m and 2m on the same antenna is ridiculous!  The gear, limitations and procedure for using this gear makes it ridiculous.

I've also found from experience than 11m doesn't like dipole antennas, unless they're strung vertically.  To use a horizontally polarized antenna like a dipole for a primarily vertical polarized service is very inefficient.

If you do try the dipole, string it as vertical as you can.  Opt for separate antennas.  Hams are noted for their ingenuity when it comes to adapting to complicated situations.

Barrett de Visser:
I agree that trying to match an 11m rig to a 2m antenna for diplex use would probably end up being a headache.
If you are able to get a match, your usible bandwidth would be limited to a couple channels or so before requiring adjustment
to the tuning.

If space and quick setup are are key features. (which I assume they are) A 5/8wave 4 foot loaded fiberglass whip would be a choice. There are also fold over mounts that can be had from ebay for about $12. They threat onto the stud and allow the antenna to be released and folded for storage. Add one of those wall clamps used to hold mops and brooms to hold the antenna securly in its folded position for storage or transport of the trailer.
This will also eliminate the need for a nearby supporting struction for a dipole if the trailer is deployed on a large open parkinglot or field. Would take litterally seconds to deploy the antenna.


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