Wednesday, September 01, 2021

ZM-4 Z-match antenna tuner kit review

Years ago I built the AM-2 Z-Match antenna tuner and found that it could match pretty much any old bit of wire thrown outside. I melted the polyvaricons by running WSPR one day but they were easily replaced.

There's a German made evolution of this design with more robust variable capacitors and a larger toroid that claims to handle up to 15W.


The ZM-4 kit is available from QRP-Shop for 98 Euros. It came with an English manual but it helps to view it in colour here.

Nice spread out circuit board for easy construction.

Unfortunately a couple of component labels are missing from the board’s silk screening.


Instructions fairly clear but I started off reversing the direction of winding on the main toroid. 

It says wind to the right but neglected to say the winding should start on the bottom of the loop. At one point it says to wind over the red wire, but there’s no red wire. (I now see that it's red in the colour instruction manual).

The BNC connectors have substantial thermal mass and my little soldering iron struggled to heat the earth pins to melt temperature.

The metal case is great but it would be wonderful if the front and back panels were pre-drilled. My metal work skills are not great and I found the front and back plates to be quite hard aluminium to drill safely.


Great to see metric units with no comment.

When assembling the front and rear panels, have the circuit board close by as a guide. The instructions don’t suggest switches and plugs in the order they are on the panel and I ended up enlarging a hole that I shouldn’t have by mistake.

The kit comes with two banana sockets which I replaced with terminals so that a wire can be directly connected.

Some of the wiring, in particular the links from the panel switches down to the board is pretty tedious. I guess the solution would be a PCB behind the panel to handle that wiring but extra cost would be added by this.

Only after wiring up front and back panels did I realise that you need to slide the board in to the bottom of the case before connecting the panel wiring. I should have tried fitting the case before this but also the instructions should have mentioned it.

I unscrewed the BNC connectors and luckily had enough length of wire to the switches to be able to lift the panel out of the way and slide the board in to the lower part of the case which I had already lined with gaffer tape to try to minimise likelihood of shorts to the case as warned in the manual.

Hooked up to an end fed wire with a short counterpoise the Z-Match was able to get an excellent match by playing around with the additional capacitance switches and rocking back and forth between the variable capacitors.

Z-Matches are a versatile antenna tuner although I understand they can be lossy. This kit is well done but the switch wiring and panel metalwork takes some effort. When boxed up it's a compact and strong little tuner that will work well for portable QRP operation.

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