Re: LF: Tuning inductance for 137kHz receive.

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

Hi Martin

 

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

From: Martin Evans <books@mollies.freeserve.co.uk>
To: rsgb_lf_group@blacksheep.org
Sent: Wednesday, 11 January 2012, 20:44
Subject: LF: Tuning inductance for 137kHz receive.

I use a decade inductance bridge to series tune my  (approximately) 50m end-fed  inverted U wire for 137kHz.

It uses 3mH - 2mH is too little, 4mH is too much. Obviously I need to be able to vary this inductance rather more finely and I thought of using a small variac (don't laugh!) as a variable inductance, connecting one end, and the tap, in series with the wire.

Anyone know what the "inductance per turn", or total inductance, of such an animal might be?

Any idea if it would work?

Yes, I know I should wind a coil & tap it, but I like to be different!

Martin  GW3UCJ  Swansea, South Wales.