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N8YX
06-23-2010, 07:06 PM
Okay, folks....here's a design exercise for everyone.

We have the following:

http://www.radioinc.com/oscmax/catalog/images/IC-56.jpg

which is 102" long.

We also have a 12" section of 1" dia, non-conductive material which has a 3/8-24 metal stud fitted at the bottom and a 3/8-24 metal receptacle installed at the top. The whip is screwed into the top and the completed assembly can be screwed into a standard 3/8-24 mirror or bumper mount. The mounting section originally had a piece of AirDux coil stock slipped over it and a shorting lead/clip connected to the bottom stud for manual band switching via inductance selection.

In this application, however, it's going to be attached to a mount at the top of a 40' sectional mast. The choice of components was made due to their relatively light weight, allowing one person to erect mast and antenna combination by themselves.

The challenge is this:

Design a loading/matching arrangement that incorporates the insulated mount section and

A) Is auto band-switching (no raising or lowering of mast to change coil taps possible);
B) Requires no DC drive or control voltages (screwdrivers and relay boxes are out);
C) Covers 10 and 15M. An added bonus: Include 12M in the configuration.

Four 1/4w radials per band will be used, for a nominal feed point impedance of 50 ohms.
KG4CGC
06-23-2010, 07:23 PM
Is this covered in the Extra manual?
Because it sounds like fun but I failed at math due to my undiagnosed childhood ADD/BPS.
WØTKX
06-23-2010, 09:56 PM
Run it like a vertical OCF dipole, if you can attach the base of that 40' mast to a non conductive support that gets it at least 5-6' off the ground.
Play with it with an analyzer, maybe add a small "hat" to the top of it. Get it working on 15, then use a tuner.

Presuming that's a conductive 40' mast.
N8YX
06-24-2010, 05:34 AM
Run it like a vertical OCF dipole, if you can attach the base of that 40' mast to a non conductive support that gets it at least 5-6' off the ground.
Play with it with an analyzer, maybe add a small "hat" to the top of it. Get it working on 15, then use a tuner.

Presuming that's a conductive 40' mast.
It is, but for the purposes of this exercise the mast will not be used as a radiator - just a support.
WØTKX
06-24-2010, 02:41 PM
Poopy on that then, I'd still make it electrically longer with hat wires for 15, then do matching tricks (tuner) for the higher freqs... maybe figure it out (with an antenna analyzer) so you could use fixed values. But you already have a solution... in mind.
N8YX
06-24-2010, 02:56 PM
... But you already have a solution... in mind.
Actually, I don't.

This is an exercise for the collective, and is meant to produce a workable, simplistic lightweight multi-band antenna which may be mast-mounted and easily raised by one person.

We tried this trick with a Hustler mobile mast (MO-4) and resonators a few Field Days ago. Too heavy.

We also tried this trick with a 6BTV a few Field Days ago. The resulting assembly was so heavy that it actually bent 32' of sectional mast as it was being raised; we had to use 16' instead.

For purposes of the experiment, we want the feed point at least one wavelength in the air at 10M, and a 40-footer will do this. But whatever is hung on top must be light and require no external control mechanisms. Traps are also out, but I do have a novel way to build an 80-40 and 20-15-10 vertical "pair" using the masts, whips and embedded traps - which I'll describe later on.
ka4dpo
06-25-2010, 08:37 PM
Actually, I don't.

This is an exercise for the collective, and is meant to produce a workable, simplistic lightweight multi-band antenna which may be mast-mounted and easily raised by one person.

We tried this trick with a Hustler mobile mast (MO-4) and resonators a few Field Days ago. Too heavy.

We also tried this trick with a 6BTV a few Field Days ago. The resulting assembly was so heavy that it actually bent 32' of sectional mast as it was being raised; we had to use 16' instead.

For purposes of the experiment, we want the feed point at least one wavelength in the air at 10M, and a 40-footer will do this. But whatever is hung on top must be light and require no external control mechanisms. Traps are also out, but I do have a novel way to build an 80-40 and 20-15-10 vertical "pair" using the masts, whips and embedded traps - which I'll describe later on.

Oh hell, just hang an SGC-230 on it and hoist it up. Might want some radials too.
suddenseer
07-04-2010, 08:35 PM
http://www.modelroundup.com/images/hm63fd4.jpg