EZnec kibitzers welcome: (corrected version)
See this model image: http://aprs.org/psat/VHF-circ-tuned-ask.gif We are placing two ¼ wave VHF whip antennas on a single feed at the corner of a 1.5U cubesat. We want them +/-45 degrees out of phase so that we get cross polarization when paralleled to a single feed point for simplicity. Modeling each one individually, we got the desired short one to -45 degrees with a coordinate of 23.4” and the long one to +45 degrees with a coordinate of 25.68”. Great… But when we connect them both to the same feed point, we get a combined29-j68 ohms and a significantly higher resonant frequency. The R Real part seems reasonable, but do not get the desired J0 term. To fix that, we lengthened each exactly the same amount to get the resonance down to 145.8 MHz and J=0 term. Good antenna…. The QUESTION IS: Are they still 90 degrees out of phase and will they work as a cross polarized antenna? And how can we verify that? The feed point is the center of a 0.1” wire between the cubesat wire frame and the combined end point of the antennas which are also 0.1” above the top of the cubesat. Maybe I should have included both wires in the original model, but only connected one at a time to a source and grounded the other one while trying to find their individual +/-45 degree lengths. This way, their passive action as a possible counterpoinse to the whole frame may be accounted for. Also, to get within the 500 data points for EZnec, we had to make all of the wire model 1” segments be a single segment per wire. Is fidelity maintained with only 1 segment per 1” wire? Bob, WB4APR _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
