Antenna tuner

I woke up this morning to extremely heavy rain.  Under these conditions, the resonance of my 20 m vertical delta shifts fairly significantly.  Not enough to require an ATU, but it would be nice to match out the small error when necessary.

The basic lesson of this post is one that many people have issued before: an antenna matching unit is extremely easy and relatively cheap to make.  For example, it's well worth having a look at this clear, simple article by AA5TB.  This site by VK6YSF also very clearly shows the underlying simplicity of a T-match ATU that anyone can copy - even an electronics non-expert like me!

A commercial non-continuous inductor ATU, such as the actually very robust MFJ 941E I've used for many years, costs a shade under £160 in the UK at the moment.  Not a bad investment at all, but it is slightly limited in having only a fixed number of inductor positions from which to choose.

If you want a continuously-variable 'rollercoaster' inductor, then the cost goes up to around £250.

So here is what I threw together as a proof-of-concept prototype this morning, to see if what I had lying around in the junk cupboard could make an effective and, above all, efficient ATU.  The capacitors (one encased in a PVC tube for earlier use on a magloop) typically cost about £10-£20 second hand on E-bay, and a roller coaster inductor, though much rarer, is about £40. 

Origins of a homebrew ATU...

Of course, it looks awful, with all those spade connectors and loose wires.  But it works!  Looking at the WSPR reception reports from IZ0FKE before and after connecting to this rat's nest shows an already increasing signal continued on-trend, and certainly shows no obvious sign of any deterioration due to the introduction of the circuit.  The blue vertical line shows when the ATU was put in-line:

Before and after reports from IZ0FKE.  200mW, 14MHz.

So, even if you have to buy used components for this ATU, it will only come in at around £80-£100, or not more than about 2/3rds the cost of a fairly basic commercial unit, or less than half the cost of a roller-coaster unit.  OK, there's no matching meter, but that's not really necessary, and can be added at a later stage, again for pocket money if you haven't already got the parts.