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Amateur Radio

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  • $\begingroup$ So, I could do the measurement earlier than I thought. So, here's the Smith chart: freeimghost.net/images/2025/07/09/vna2.png Do you need anything more? Why in MININEC3 and NEC2 there's no impact on far-field? Are theese programmes poorly simulates current distribution along antenna? I knew the fact, that MININEC3 takes it better than NEC2, and sometimes even NEC4. The 2m DE is 986 mm long. 70 cm DE is 330 mm long. D1 70 cm - 319 mm. D1 2m - 925 mm. $\endgroup$ Commented Jul 9, 2025 at 16:36
  • $\begingroup$ And what do you mean by writing "De-tune the 2m driven element intentionally"? $\endgroup$ Commented Jul 9, 2025 at 16:47
  • $\begingroup$ Just quickly for now. The impedance looks consistent with what I anticipated, given the narrowband nature of Yagi. If you electrically de-tune the driven element of 2m Yagi with a reactance, that interference may be lessened. It may or may not be a good enough solution by itself. Yeah the simulator may be a disappointment. If your simulation was run on a wider frequency range from 130 to 500MHz or something (just on the 70cm Yagi part) it may give some more insight, but may not be very fruitful. But regardless of how simulation gives us, I think the interaction is a good suspect in theory. $\endgroup$ Commented Jul 9, 2025 at 17:44
  • $\begingroup$ If you somehow fix or optimize away from this problem, it is likely that you want to reoptimize 70m reflector and D1 length/placement as they are probably strongly influenced by the presence of 2m driven element. You run optimization that probably did something given correct or wrong constraints (since the sim apparently failed to capture the interaction) and then when you fix that, the design is certainly not optimized, without re-work. It may simply that your 70cm yagi is not properly optimized due to failure to consider the interaction. $\endgroup$ Commented Jul 9, 2025 at 17:47
  • $\begingroup$ Thank you very much for all advances. Maybe I just move the DE 2m 5 cm away (it will be 94 mm in distance between DE's) and place wide reflector, 50 mm before DE for 70 cm? Is this 94 mm could be enough with reflector behind them? Or maybe more distance? I will need to reposition D1, D2, D3 and maybe D4 afterwards. Moreover, will need to reconsider feeding this 2m DE. This will be around 14 cm distance between N socket and dipole... $\endgroup$ Commented Jul 9, 2025 at 18:33