Day: November 3, 2013

The measured impedance of cz={89.9733735327047, -55.8789510601876} is traslated to the feed point impedance by using a Smith Chart.

Assuming the cable length of 20m, Zant={19.398, -8.999}.

If the cable length is 20m+10cm, then Zant={20.170, -12.965}, and if it is 20m-10cm, then Zant={18.919, -5.117}.

Parameters for stub match with 75 ohm coax cables are: 531.4mm and 1182.4mm (with open end).

First, calibration of the measurement system using a dummy load. There is almost no reflected wave (in green).

This is at 28.001MHz.

gnuplot> load "gnuplot1.txt"
Freq [MHz]=28.001
V1=2.518
V2=3.539
Cursor 1=-1e-009
Cursor 2=0.0

vratio=1.4054805401112
phase1 [deg]=-10.08036
phase2 [deg]=0.0

abs(gamma)=0.455858107934516
swr=2.67551190078067
cz={89.9733735327047, -55.8789510601876}

The VSWR is 2.67, and this figure matches well with the read out from a Power Meter.

The forward power is 15 W and the reflected power is 3 W. The normalized reflect voltage is sqrt(3/15)=0.4472, thus the VSWR=(1+0.4472)/(1-0.4472)=2.61.