Day: September 21, 2013

For a single band, stub matching is relatively an easy job. A short wire of length 30cm, described in my previous post (A little bit longer), is removed from each far end of the element, and Zant should be aound 14.025-49.337j [ohm]. (See Folded Weirdly for the detail.)

Now let’s try single stub matching using two 75 ohm coax cables, which I have in abundance. (Of course, you can use 50 ohm coax cables, if you prefer.)

gnuplot> load "gnuplot1.txt"
Freq [MHz]=7.026
V1=3.008
V2=3.731
Cursor 1=8.4e-009
Cursor 2=2.72e-008

vratio=1.24035904255319
phase1 [deg]=21.246624
phase2 [deg]=68.798592

abs(gamma)=0.47580332514932
swr=2.8153618593054
cz={42.3068002762323, 49.1623697140194}

The VSWR now becomes 2.81. Note that the length of 75 ohm coax cables is not adjusted yet, and is somewhat longer for both the cables than the values shown in the Smith chart.

A short wire of length 30cm is added at each far end of the element.

gnuplot> load "gnuplot1.txt"
Freq [MHz]=7.026
V1=3.653
V2=6.169
Cursor 1=1e-009
Cursor 2=2e-009

vratio=1.68874897344648
phase1 [deg]=2.52936
phase2 [deg]=5.05872

abs(gamma)=0.69113364433374
swr=5.47529251182366
cz={252.437028893358, 72.0354980323906}

The VSWR is now estimated to be 5.475, which coincides well with the measurement by CMX-200 SWR meter.

Considering the coax cable length of 20m, Zant is estimated to be 9.491+9.744j [ohm].