fremont Posted October 24, 2022 Report Share Posted October 24, 2022 This antenna is 1/2 wavelength at 155 MURS and 5/8 at 460 (e.g., GMRS). I am going to use it as a base antenna on top of a NMO mount. For GMRS, it'll primarily be used for simplex communications, but there will be instances whereby it'll go through repeaters. I had a couple of questions--which I subsequently tested: 1) Would the GMRS (5/8 wave) frequencies benefit from elevated radials and, if "yes," then 2) how long should they be? Question #1 gets debated a fair amount from what my cursory review of the interweb uncovered.....it seemed as the antenna would benefit from some type of radial. To answer Q #2, I went to this website to get the radial length. (By entering 465.200--halfway between GMRS duplex Tx and Rx frequencies, I was given the answer of 6" radials. I cut mine from 1/8" alum. rod.) The results on MURS (155)--again, a 1/2 wave antenna at 155--were consistent: The commercial (Blue4, Green5) channels near 155 performed better than Ch 1-3 near 152, with SWRs of 1.35 and 2.19, respectively. For UHF, including GMRS, the results were interesting. By adding the radials, the SWR graph became the traditional very steep parabola which helped the UHF frequencies especially near repeater inputs, e.g., 440 (3.05), 445 (2.35), 450 (1.84), 462.800 (1.55), 465.200 (2.06) and 467.600 (2.68). Without radials, it was a mildly meandering, relatively flat but downward sloping line, e.g., 440 (2.98), 445 (2.54), 450 (2.36), 462.800 (1.95), 467.200 (1.59), 467.600 (1.64). So, I concluded that I would use the radials, since a) I want to use the antenna to hit both FM and DMR UHF repeaters and b) the majority of my GMRS QSOs will be via simplex. The antenna is definitely tuned for what it says on the label: 155 and 460. Not 155 and 465. Does this sound right to the RF engineers of the world? Quote Link to comment Share on other sites More sharing options...
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