My version of a Z-match Tuner

 

Nothing new under the sun ... this type of antenna tuner has been built many times, and is all over the internet.

But since I learned that my new QDX Digital Transceiver from QRP-Labs  doesn't like transmitting in high SWR, I wanted to have something like a ZM-2 or ZM-4, to be able to use the QDX on a piece of random wire, when a perfectly tuned antenna is not available. Probably also useful for my 3 QCX transceivers.

Other inspiration came from a post on the SOTA Reflector, where some "lockdown projects" were shown. Armin, DL6GCA posted a few pictures of what he built: a Minimal Art transceiver, and a ZM-4 ATU.

The building manual for the ZM-4 with circuit diagram is here

As always, I tried to build this project as cheaply as I could, so I took a few pieces of PCB as a chassis, and started building on the fly ... .

First I mounted all the switches, connectors and the two tuning capacitors (polyvaricons).The BNC connectors were from old Ethernet cards, and were fixed with some drops of superglue to both pieces of the chassis, after which I soldered the PCB's toghether to form an L-shaped chassis.

Then I added the SWR bridge, and finished with the rather complex coil with different taps and extra windings, and connected the tuning capacitors. I basically followed the circuit diagram of the ZM-4 , except that I did not include the 160m band.

Here the SWR bridge coil (25 turns on an FT37-43, tapped at 5 turns)

And the rather complex main tuning coil (primary 34 turns on a T130-6, with taps at 8 and 16 turns, and secundary windings with 4 and 16 turns, for low and high impedance output)

This is the final construction, before adding another "wall", and making a U-shaped cover.

Labels were made with my "quick & (not so) dirty" method, just printing them on a laser printer, and fixing them with some Scotch tape. Also two discs were printed for the tuning capacitor knobs.

It may not look really profesional, but it does the job.

And best of all .. I tested the tuner on my "random wire endfed" (9.15m wire with 4m counterpoise + 9;1 UNUN), and I was able to tune it on all bands 80m - 20m. Higher bands were not tested because of lack of time, but probably will work as well.

Good reports on RBN confirmed that this tuner works and is a keeper !

73,

Luc ON7DQ