I removed the elements of my old dipole antenna for 17m band, and build a new dipole antenna for 40m band. The elements are Al wires with 1.5mm diameter, each around 10m length. Since I only have a limited space for my antennas, the far ends of the elements are folded in a weird manner.
Impedance measurement results are:
gnuplot> load gnuplot1.txt" Freq [MHz]=7.026 V1=2.384 V2=0.272 Cursor 1=0.0 Cursor 2=0.0 vratio=0.114093959731544 phase1 [deg]=0.0 phase2 [deg]=0.0 abs(gamma)=0.885906040268456 swr=16.5294117647059 cz=3.02491103202847
# gnuplot1.txt set object 1 rectangle from screen 0,0 to screen 1,1 fillcolor rgb "#f0f0f0" behind set size square set xrange[-0.5:2.5] set yrange[-1.5:1.5] set zeroaxis set parametric # input data from measurement freq=7.026e6 v1=2.384 v2=0.272 cursor1=+0.000e-9 cursor2=+0.000e-9 vratio=v2/v1 period=1/freq phase1=2.0*pi*(cursor1/period) phase2=2.0*pi*(cursor2/period) phasedeg1=360*(cursor1/period) phasedeg2=360*(cursor2/period) I={0,1} z0=50.0 cv1=1+I*0; cv2=vratio*(cos(phase1)+I*sin(phase1)) cvfwd=cv1 cvrfl=cv2-cv1 cvr=2*cv1-cv2 cz=z0*(cv2/cvr) gamma=cvrfl/cvfwd swr=(1+abs(gamma))/(1-abs(gamma)) print "Freq [MHz]=", freq/1e6 print "V1=", v1 print "V2=", v2 print "Cursor 1=", cursor1 print "Cursor 2=", cursor2 print "" print "vratio=", vratio print "phase1 [deg]=", phasedeg1 print "phase2 [deg]=", phasedeg2 print "" print "abs(gamma)=", abs(gamma) print "swr=", swr print "cz=", cz set arrow 1 from 0,0 to 1,0 lw 2 lt 1 set arrow 2 from 0,0 to 2,0 lw 1 lt -1 set arrow 3 from 0,0 to real(cv2),imag(cv2) lw 2 lt 6 set arrow 4 from 1,0 to real(cv2),imag(cv2) lw 2 lt 2 set arrow 5 from real(cv2),imag(cv2) to 2,0 lw 2 lt 3 plot [0:2*pi] 1+abs(gamma)*cos(t),abs(gamma)*sin(t) lw 1 lt -1 notitle pause -1
The length of the coax cable is about 20m, the same as before. Please also see my previou post,
Cable Lenght Measurement (5).
Considering the coax cable length, the antenna impedance shall be around Zant=45.695-182.527j [ohm]. Sounds reasonable?