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From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <593F4C0651144C339855AFC49ED4329E@computereebf79> <1326365524.91314.YahooMailNeo@web28108.mail.ukl.yahoo.com> <00e101ccd119$b7755790$ae01a8c0@youry0mkaz8jaq>
Date: Thu, 12 Jan 2012 12:20:24 -0000
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Subject: Re: LF: Tuning inductance for 137kHz receive.
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Martin here is a relatively quick and dirty way of making a largish variable
inductor.
http://www.alan.melia.btinternet.co.uk/lfaecoil.htm
varying the pie spacing changes the inductance

However for recieve only switch you sub' box to the next biggest value and
connect a multigang variable cap in series to "tuneout" the excess (I use a
2 gang 500pF) You can easily find the tune as the noise peaks in the middle
of the swing somewhere.

Alan
G3NYK

----- Original Message ----- 
From: "Martin Evans" <books@mollies.freeserve.co.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, January 12, 2012 11:02 AM
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.
>
> ########################################
>
> 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
>
>