QRP PROJECT ZM-4, Manual

2

The  Z-Match

Other than most ATU the Z-match is not based on a High Pass or a Low Pass 

but due to it´s parallel circuit it´s a Bandpass. The benefit of the Z-Match 

principle is that there is no need for tapped coils. Due to it´s bandpass cha-

racteristic it also attenuates off frequency signals, a fact that helps if your 

RX tends to have intermodulation problems.

If you use the ZM, you do not need a seperate SWR Meter because during 

tuning, the Z-Match uses a 50 Ohm Wheatstone-Bridge. This is another 

great help because your TX-PA everytime has a real resistive load. The SWR 

never can exceed 2,0 because if the atenna port is shorted, the bridge resi-

stance is 25 Ohm and of the antenna port is open, the bridge resistance is 

100 Ohm.

During years the Z-Match has become one of the most used ATU for the QRP 

Community. Lot´s of us have been happy with the ZM-2 kit of EMTECH USA.

Some time ago I started the development of ZM-4. The reason was not that 

I have not been satisfied with the ZM-2, but during time I had found 2 

problems which I tryed to solve:

1. The ZM-2 „did not like“ Antennas with a very low feed impedance 

2. The ZM-2 could not handle 160m Band

Another idea was to use a PCB to make it easier to build a Z-Match for 

HAMs with less expierience.

Using a lot of papers I found in the internet, at the end I got a design 

which solved all my problems. Mainly I used the really good papers of 

Charlie Lofgren, W6JJZ, und Lloxd Butler, VK5BR. The complete ZM-4 could 

be realizes on one PCB. Stability and useability compared to the old design 

could be improved which helps a lot for hard outdoor useage.

The new ZM 4 easyly tune my 2x20m doublett between 28 and 28 MHz. 

The two diefferent coupling windings help to tune Antennas with very low 

impedance as Antennas with very high impedance. 

The resonate coil compared to the old ZM-2 coil has some extra windings. 

This extra inductivity together with switchable capacitors add the 160m 

Band.

We wish you a lot of fun building and using your ZM-4

Peter, DL2FI

QRPproject

Assembling the ZM4

Please take the time and read the manual before you start soldering. It 

contains some information that will be helpful for success.

If you find something to be written better, please contact Peter, DL2FI. He 

will be happy if you help him to make a manual better. Use the email adress

support@qrpproject.de. 

The same email adress is good if you need any help!

Because the big Torroid coil is the heart of our ZM, we start the project by 

winding it. To make it easy for you we use wires of different colours for 

each part of the complete winding. Those who are not familiar with Torro-

ids should at least read the following introduction. A very helpful article in 

english language about winding torroids can be found on W8DIZ homepage: 

http://kitsandparts.com/wtoroids.html 

Torroid winding tips:

Count the turns while you are winding them. ATTENTION: every time 

the wire is feed trough the torroid counts as 1 turn, so allways coun 

INSIDE the core!!!

Every time you start a new turn, pull the old turn tight to the torroids 

body. The turns should lay as near to the torroits body as possible.  

Never cross an old turn with a new turn, each turn must be parallel to 

the other.

If you finnished a particular winding count the turns again. Use a 

small screwdriver or your fingernail to help counting,  Again, always 

count INSIDE the core