Paul Butzi |||

NVIS Presentation

I’ve been asked to do a presentation on NVIS and NVIS antennas for the Microhams club. Since I’ve had further thoughts on how to improve my presentation, I’ve been going through my current Powerpoint slide deck and cleaning things up. I’m always searching for good graphics to use to make a point, and while searching for graphics I came across a pile of presentations.

Lots of good stuff in there. I’ve not looked at all of it, but in particular I found this to be an excellent presentation. Clear, well ordered. I suspect I disagree about the effectiveness of reflectors (my modeling shows more like 2.5dB gain). But I would also say that the effects of ground coupling changing the resonance of the reflector mean that the reflector must be carefully tuned to get that gain. My modeling shows that tuning the length of the reflector to get best gain and get a good SWR match at the same time is both twitchy and non-intuitive. To be honest I’m not sure it can effectively be done in a real world environment.

AI’m also highly skeptical of NEC2 modeling with conductors close to the ground… and view with considerable suspicion my NVIS modeling as well as any other modeling of NVIS reflectors, probably including W5CKs.

I suppose it’s time for me to break out 4Nec2 and start modeling again. Even more importantly, build an antenna, hang it, try to tune it along with a reflector, and test the gain, perhaps using WSPR.

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