Re: LF: Tuning inductance for 137kHz receive.

[M0FMT <m0fmt@yahoo.co.uk>]

Hi again Martin

 

The two other replies are from of the most experienced 136 ops (James and Stefan) and constructors around. I only play at it. Rather than use my slide rule oops sorry a scientific calculator for calculating coils I use software down loaded from  http://dl5swb.de/html/mini_ring_core_calculator.htm  it covers cored and aircored inductors. You can do a lot of "what  ifs" quickly I find and the measured result is pretty close to.

 

Keep at it.

73 es GL Pete M0FMT IO91UX

From: Martin Evans <books@mollies.freeserve.co.uk>
To: rsgb_lf_group@blacksheep.org
Sent: Thursday, 12 January 2012, 11:02
Subject: Re: LF: Tuning inductance for 137kHz receive.

Morning, Pete.

Thanks for this.

Yes, this is what I should do. My problem is that I get carried away -  I
begin by thinking of making a variometer - then I decide that it *must* be
the biggest one ever - so I search for a *huge* former - which I can't
find - and so it goes.

Pathetic really.

Maybe my resolution for 2012 should be to stop daydreaming and actually *do*
something!

Martin  GW3UCJ.

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Just make a variometer two inductors one inside the other like piston and
cylinder and adjust in and out to resonance (I think this design is the
simplest form of variometer mechanically). I use a couple of plastic paint
buckets, mine are 200mm diameter. 3mH looks about right for the antenna
described but fine inductance adjustment is necessary and it is best to get
as high a 'Q' as you can. The band is very narrow and 'Q' helps reduce out
of band high power signals. I am in fact describing my TX setup the primary
inductor is a large 600mm diameter coil tapped. All my inductors are air
cored.

For RX you can tune the inductor with a large variable capacitor strapped
across because there are no flash over issues. It is quite simple to make
these tuning coils from scratch a lot of wire though, but I would recommend
it.

Try Rick Strobbe ON7YD's site highly recommended
http://www.strobbe.eu/on7yd/136ant/#Introduction

Hope this helps.

73 es GL Pete M0FMT IO91UX