Chinese Manual Tuner

 

I have seen this cheap little tuner pop up in newsgroups, and on numerous websites, so finally decided to "see for myself" what this tuner is worth. I ordered a kit for just 12€, shipping included. If all went wrong, I would at least have a nice plastic box and some components to use in another project.
This is what I got before assembly.

There is an updated manual on the internet here. But I got most help from a video by Carol KP4MD, that you better watch before starting.

The important points are the orientation and grounding of the main coil of the T-match network, the correct mounting of the SWR transfomer T1, and how to fix the buttons to the polyvaricons without them coming loose.

Another point is that you better remove the plastic stubs inside the box, where you want to mount the polyvaricons. I did that with a Dremel tool with a grinding wheel.

Here is my final circuit diagram:

As you wil notice, I wound my coil with a slightly different scheme, here are my data:

switch     total       measured total
position   turns       inductance (µH)  

A          37          18.0 µH

B          27          8.6

C          24          7.4

D          21          6.1

E          18          5.0

F          15          4.0

G          12          3.0

H           9          2.1

I           6          1.35

J           4          0.90

K           2          0.56

L           1          0.49

(or if you like, the turns between the switch tabs are 10 - 3 - 3 - 3 - 3 - 3 -2 - 2 - 2 - 2 -1)

NOTE : 'L   1'  above means that there is still one coil winding from the last switch tab to the connection between the polyvaricons. Also, the inductance was measured with 3cm leads at both ends of the assembly, before mounting. The wires were cut shorter when mounted in the box, so the total inductance will be somewhat less, especially the low inductance values. I did not re-measure them.

I replaced the rotary switch from the kit by one from my stash, that I trusted somewhat more.

Therefore I also had to find another button.

And after carefully drilling all the holes, winding the main coil, and mounting all the other stuff, this is the finished tuner. I put some labels over the Chinese text, see top picture for the end result.  

And now the question : does it work?

I took the tuner for a POTA activation, and I can testify that, if built correctly, it does work!

I was able to tune my random endfed (length 9.15m with 9:1 UNUN + 4m CP + coax 5m of RG-58) on all bands from 60m to 10m.

80m and 6m didn't tune very well.

I made 18 QSO's by calling CQ myself, on 20m and 40m, SSB and CW.
But then I wanted to hunt for some park-to-park QSO's, and it became obvious that a manual tuner slows you down, having to retune after each band change.
So I switched back to my ATU-100 automatic tuner, which is in the picture below.
I forgot to take a picture of the Chinese tuner in action, but you can see it in the background, hi.

73,

Luc ON7DQ