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christofire · January 28th 09, 01:03 PM posted to rec.radio.amateur.antenna

"Ian Jackson" wrote in message
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In message
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writes
What about ribbon cable? I've got a fair length of ribbon cable
(something like 25 wires - the sort used in PCs to connect hard drives
and the like) put away for a rainy-day loop antenna project. While I
could make one large loop using all 25 wires for the really low
frequencies, I'll almost certainly cut it up and make several smaller
loops with fewer wires for the higher frequencies.
--
Ian- Hide quoted text -

Hello Ian,
I have used 16 core ribbon cable, with each core connected in series
for an AM broadcast band loop antenna. It was about 1 metre long in
circumference which gave me a total length of 16 metres. I used a
cheap tuning variable capacitor with a switch which connected another
capacitor to increase the total capacitance so I could tune down to
the bottom of the AM band. It is coupled through the internal ferrite
antenna in the radio. On my main tuner in the house, it has
connections for an antenna on the back, so I made another ribbon cable
loop antenna and put a single wire with it as a pick up wire. Each end
of the pick up wire is connected to the antenna inputs on the tuner. I
have made four of them. They are easily made, not too fiddly and they
work well. Cheers
Max

Ah! Thanks for that info. It does seem to conflict with the previous
advice. I was thinking about a somewhat larger loop - maybe using 2 or 3m
of ribbon, but with fewer turns - but I can't see why 'working well'
should no longer apply.

I have no preference for using ribbon - it's just that is seems like a
simple way of getting several turns 'in one go' (if you know what I mean).
Obviously, you will reduce the self capacity (and have a greater potential
tuning range) by using a loop with the turns well spaced - although the
inductance will probably be a bit less, and you'll need to add a turn or
two to compensate.

My next question is about using varicap diodes to tune the loop. Most
designs use a conventional capacitor, but a varicap would enable the loop
to be located (say) in the loft, and the tuning varied from the shack
downstairs. Is this technology worth perusing (ie Googling)? Or has it
been found to be a waste of time?

Thanks again.
--
ian

Varicaps are fine and you will find devices containing pairs like the BB212,
specifically intended for tuning domestic receivers. They're used in all
the modern radios that are digitally controlled. The trick is to use them
in balanced pairs so strong signals don't push a single diode into
conduction.

Chris