A Tiny Z-match Tuner

Z-match vs MFJ-945E

Cosy MUTO, JH5ESM
6 July, 2005

Japanese


Introduction

I made some field operations in May and June, 2005. During these field days, MFJ-945E (above, left) consumed large amount of volume in my backpack.
For this reason, I recently built a compact Z-match tuner (above, right) for field usage with my 7T9521 TX and 7R3357 RX.


Circuit description and implementations

The schematic is shown in Fig.1.
Based on WB3GCK design (and his design was based on G3YCC's), I only made a small modification on the tuning inductor.
In addition, though Craig made it as it can handle both balanced and unbalanced antenna, I only implement unbalanced output.
For details of previous designs, see References section shown below.

Z-match schematic
Fig.1 Schematic of the Z-match tuner (click figure to enlarge, or download PDF version)

The tuner consists of two parts; SWR bridge and Z-match sections. A high luminous intensity LED shows mismatch (i.e. the LED is light off when tuned). 

I assembled the whole circuit into a 100×70×50[mm] aluminum enclosure as shown in Fig.2. Note that the VC1 shaft must be insulated from the enclosure.

Fig.2 Z-match tuner implementation (click each photograph to enlarge)
fornt view rear view inner view
(a) Front view (b) Rear view (c) Inside the enclosure

Experimental results

Table 1 shows experimental matching test results for several load conditions. A 20[dBm] function generator output is applyed as source signal.

The tuner perfectly made impedance matching except 10[Ω]+47[pF] load on 3.5[MHz].  As not shown in the table, 1.8/1.9[MHz] band is out of tuning range.

Table 1 Macthing results.
Load  |  Band 3.5 7 10 14 18 21 24 28
10[Ω] O.K. O.K. O.K. O.K. O.K. O.K. O.K. O.K.
10[Ω]+47[pF] Not perfectly mathced O.K. O.K. O.K. O.K. O.K. O.K. O.K.
10[Ω]//47[pF] O.K. O.K. O.K. O.K. O.K. O.K. O.K. O.K.
10[Ω]+4.7[μH] O.K. O.K. O.K. O.K. O.K. O.K. O.K. O.K.
10[Ω]//4.7[μH] O.K. O.K. O.K. O.K. O.K. O.K. O.K. O.K.
300[Ω] O.K. O.K. O.K. O.K. O.K. O.K. O.K. O.K.
300[Ω]+47[pF} O.K. O.K. O.K. O.K. O.K. O.K. O.K. O.K.
300[Ω]//47[pF] O.K. O.K. O.K. O.K. O.K. O.K. O.K. O.K.
300[Ω]+4.7[μH] O.K. O.K. O.K. O.K. O.K. O.K. O.K. O.K.
300[Ω]//4.7[μH] O.K. O.K. O.K. O.K. O.K. O.K. O.K. O.K.


References

  1. Craig LaBarge, WB3GCK, "Homebrew Z-Macth Tuner," http://www.qsl.net/wb3gck/zmatch.htm
  2. Frank, G3YCC (Silent Key) "A Single Coil Z-Match," http://www.g3ycc.karoo.net/zmatch.htm or  memorial site http://www.zerobeat.net/g3ycc/zmatch.htm maintained by K3HRN.

back to home