Competition.

[VK2XSO]

This is a little competition I thought up for a few laughs as a club activity.
It has however snowballed because it is a lot of fun and it is at a level which every club member can give it a go.
We kept the prize simple. Since our club meetings are often held in the cone of silence at the local McDonalds, the prize was a McMeal.

We have access to some good test equipment for judging purposes, but we found that we didn't need to actually use it. We had so much fun
just visually judging the entries. The competition was a lot of fun and there are some very clever ideas within the ridiculous rules I originally set.

So after testing the idea at the Tamworth club meeting tonight where we fell off our chairs with laughter it was decided the concept for a club activity was worth sharing with everybody to try at their
club.

The concept is very simple... Build an antenna........ With nothing but a single coat hanger.
And you can't cut, break or unwind the neck of the hanger.


Here's a copy of the original rules.





The competition is to build an antenna.

* The judging shall be based on SWR/return loss at any chosen frequency.
* It shall also be judged on the path loss over 10 metres to a standard antenna if the SWR is not the only determining factor.
* -10dB bandwidth shall be a final determining factor if the above two factors are roughly equal.

These are the official rules, but we found visually judging the antennas was fun enough on it's own.

Now for the rules.
* You may choose any frequency you like.
* You may only use one coat hanger.
* You shall not unwind the twist in the coat hanger neck.
* You are not permitted to cut or break the coat hanger, it must remain in one piece.
* You may bend the hanger any way you like.
* You may not add any other metallic elements or reflectors.
* The feedline shall be coax and it may be any impedance and you can connect it to the coat hanger any way you like. (using a capacitor to gamma match is permitted)
* The coax must not be longer than 5m and shall have a standard connector, BNC, PL259 or N type connector etc.

----

The rules say nothing about what kind of coat hanger you can use. If you think you can make a plastic hanger work, then go for it.
But the hanger can't be cut, broken or unwound.

The constructor should nominate the target frequency of their antenna and the best result should be within half an octave of the target frequency (1/2 below and 1/4 above).
So if the target frequency is 500MHz, then the best frequency in the range of 375-625MHz. The reason for this is that the velocity factor or coat hanger wire is a little unpredictable
and given a few other factors there needs to be a bit of tolerance. This also makes it easy for novice constructors.

The gist is of course is to keep the loop in hanger. This is the handicap that makes the competition fun and interesting.

I'd post a picture of my own design which got plenty of laughs, but I don't want to ruin this for anybody else yet until a few other clubs have had the chance to try it.

Anybody up for the challenge ?
What can the members of your club come up with ?

[VK2GFR]

Hi Ash,
A bit like loading up a gum tree for optimum portable radiation?
Would this mean that if you were using a small Bonsai, it would be similar to your clubs coat hanger scenario, a frequency of the UHF region?
Maybe a weeping Willow might load at 14Mhz with a roll off at 10Mhz?
I love your thoughts & ideas as to stimulate the "grey matter".
The old XSO mind bending exercise. Keep going forward with it.

[VK3YE]

The rules say nothing about what kind of coat hanger you can use. If you think you can make a plastic hanger work, then go for it.
But the hanger can't be cut, broken or unwound.

The rules appear not to prohibit loading up the Sydney Harbour Bridge. Either whilst walking across the bridge or from a vessel underneath (via a coupling loop if a direct connection cannot be achieved).

Getting back to those intended for clothes, a metal type with coated plastic would make a fine magnetic loop with the capacitor being formed by the twist (which you wouldn't undo but would loosen to resonate on the desired frequency). Resonance on either 6 or 2 metres should be possible.

[VK2XSO]

I encourage everybody to go to the cupboard and take out a coat hanger and actually hold it in their hand and think about the task.
Don't just think about doing it. Go and get the coat hanger now and come back and while you read the rest of this thread, bend it into a shape and think about how you would connect the feed line to it.

The antenna I made has...
a return loss of -24dB. (1.1:1 vSWR)
It has a bandwidth of about 40MHz
It is directional and has more than 3dB of gain. (I've not measured the actual gain accurately yet).

Can anybody do better ?

[VK3YE]

Did just that and found its perimeter was 90cm.

Supposing one bent it out into a loop with a 70cm perimeter (ie full wave loop). The remaining bit (near the hook) would be two parallel lines. The feedline could be tapped somewhere along this for the best match. Squashing it would make a folded dipole with a little less gain than the loop.

A 2 el yagi should be possible but not without cutting the hanger in various places (there not being enough material to have both the driven element and director folded back on themselves).

[VK2XSO]

Now your thinking.
Though, you may be thinking "inside the box".
I had a lot of fun thinking up designs and I'm still thinking of more on top of what other people in our club cam up with.
I currently have 23 feasible designs on paper. About two thirds of them I've tested.

A lot of these come from actually handling the coat hanger. I drew them for record, not for design.

As an example, most members came up with this design and then moved on.
The simplest answer might be just to stretch the hanger and twist it into a single element.
Then you have a 1/4 wave antenna (without a ground plane).

A sneaky, yet acceptable trick within the rules is to put a coil in the coax 1/4 of a wave down the coax so the shield functions
as the other element of an open dipole.

A lot of members then opened the loop and progressed to a quad or loop for the next design.
Funny, that most of them considered a folded dipole but dismissed it because they could not imagine how to feed it.

It's at this point that you can see the cogs turning in peoples heads as they address the problems or think of alternatives.

My own design evolved from this kind of thinking. It would not have happened if I had just thought about doing it or drawing it.
I actually had to have the hanger in my hand and bend it and manipulate it like it was a puzzle to be solved.

New answers came to me with each bend.


This is the point of the exercise. It's educational, it's fun, it's cheap, it's easy. Anybody can give it a go.
If you're reading this.... GO GET A COAT HANGER NOW !!!

[VK5ZD]

All my coat hangers look like this.

Every time I try to bend one the wood breaks

[VK5RC]

Could you sand the varnish off, soak the two sides in a saline solution, leaving a 'dry' area in the middle and you would be getting close to a dipole! Are screws allowed?

[VK2XSO]

The you've chosen poorly haven't you Iain ?
I might you suggest you feed it with RG6 just to make it more difficult for yourself.

However, this kind of coat hanger did not escape the attention of club members who suggested straightening it out or rolling it up more to form a loop.
On person even suggested that if the hook was bent into a J-pole that it might load up correctly about 2.4GHz.
While it wasn't tested with the sweeper, I know the theory is valid and it could be made to work that way.

The plastic coat hanger was also considered. The best answer to that problem was to heat it and melt it and compress it into shape to create a dielectric antenna.
This doesn't break or cut the plastic mass so it was determined to be valid, but nobody submitted a plastic or wooden entry.