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New Uses for old Bicycle Wheels... the 'Wheelrial'.

New Uses for old Bicycle Wheels... the 'Wheelrial'.

Postby V51JP » Wed Apr 20, 2011 1:23 pm

Here is an interesting article that reached me by mail:

Hi,

Today I finished the 'Wheelrial' a name coined by Paul MM6PMC for my proposed (at the time) dual-band bike wheel aerial.

The wheelrial uses a 700mm diameter alloy racing bike wheel rim as the resonator with a 500+500 puff variable across the horns with only the
stators connected. This halves the capacity but doubles the
flashover voltage... AND removes that wiping contact (wiper unconnected. This reduces the ohmic losses... a very good thing.

The 'horns' created by cutting out an inch of wheel-rim are stiffened and held apart with a fibreglass spreader (doubled up bare PCB material). The wooden spreader that carries the variable is bolted to the wheel-rim and the capacitor ty-wrapped in place.

My idea was for a /P aerial that was light in weight and would reliably cover 20 & 17M. I elected to use a gamma match on the grounds of physical robustness. Here's the finished deal. I jammed a lump of black PVC pipe in top of the wardrobe, propped under my guitar case to hold the loop for testing, as you'll see, with the loop sat against a wardwobe full of stuff including clothes on wire
coat-hangers. Well, It's been pissing of rain outside!!

BTW, bike rim alloy is rather like Duralumin.... tough! I made this loop with hand tools only. My most exotic tool used was my cheapo pop-rivetter. I wanted it to be reproducible by others, so I posted it on the local EARS ARS yahoo group reflector.

It works a treat on my two main bands of interest 20 & 17M and I've had a couple of QSO's with it. VSWR is not perfect at 1.5:1 but methinks the coathangers 6 inches away may be implicated in that :-) I'm sure the VSWR would be better in free space. Small loops can work remarkably well. Small, efficient and err, umm... narrowband.
Well, I *did* say you can choose only two!

Tuning is VERY sharp indeed, a sure sign of a high Q (narrow-band) resonant device. The aerial is sturdy and made to take a few knocks yet be easily repairable if it does get broken. NO AMU of course needed for my loop, a positive advantage for /P ops. Just tune for max noise and go. Should look suitably daft on top of a fibreglass pole poking out of a framed rucksack.

I'll take it to work tomorrow for some 'tests' to see if I wipe out PC's and suchlike.
It would be ideal for QRP ops from the countryside in the summer months with the FT817 and a lithium battery pack.

73 Al
GM1SXX

Finding the best match:
Image

Shorting bar soldered
Image

Testing the loop
Image
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Re: New Uses for old Bicycle Wheels... the 'Wheelrial'.

Postby zs2cx » Wed Apr 20, 2011 2:26 pm

nice one!
werner
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