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Coax Collinear Element Materials and Velocity Factor
K7ITM wrote in news:9b6a34a7-9578-4660-b4f0-5cf02e3ee862
@z14g2000yqa.googlegroups.com: The other thing that the free-space length of the elements will affect is the feedpoint impedance. I'd suggest, again, that you model it to make sure the net impedance of the paralleled feedpoints is something you don't mind matching to. An interesting point. I cannot recall any of the online articles discussing feedpoint Z, and by assumption it is 50+j0... but that doesn't happen by accident. Here is a deck for 8 halfwaves at 435MHz with a single stub tuner. CM 8 half waves coaxial collinear on 435MHz CM Assumes lossline TL, VF=0.667, effective choke at bottom of array. CM Matched to 50 ohms with single stub tuner. CM Owen Duffy 2009/04/05 CE GW 2 20 0 0 -0.23383 0 0 0 0.0045 GW 3 20 0 0 -0.46766 0 0 -0.23383 0.0045 GW 4 20 0 0 -0.70149 0 0 -0.46766 0.0045 GW 5 20 0 0 -0.93532 0 0 -0.70149 0.0045 GW 6 20 0 0 -1.16915 0 0 -0.93532 0.0045 GW 7 20 0 0 -1.40298 0 0 -1.16915 0.0045 GW 8 20 0 0 -1.63681 0 0 -1.40298 0.0045 GW 9 10 0 0 -1.87064 0 0 -1.63681 0.0045 GW 200 1 -0.01 0 -2.25634 0.01 0 -2.25634 0.001 GW 201 1 -0.01 0 -2.35634 0.01 0 -2.35634 0.001 GE 0 GN -1 EK EX 0 200 1 1 0 TL 3 1 2 1 -50 0.350745 0 0 0 0 TL 4 1 3 1 -50 0.350745 0 0 0 0 TL 5 1 4 1 -50 0.350745 0 0 0 0 TL 6 1 5 1 -50 0.350745 0 0 0 0 TL 7 1 6 1 -50 0.350745 0 0 0 0 TL 8 1 7 1 -50 0.350745 0 0 0 0 TL 200 1 8 1 50 0.42855 0 0 0 0 TL 200 1 201 1 50 0.0837 0 0 1e99 0 FR 0 0 0 0 435 0 XQ EN The antenna bandwidth is quite narrow as might be expected from so many resonant lengths. It reaches about 7.8dBi gain, well short of the much touted 9dBd or 11.2dBi. Owen |
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