Balun. Yes. You should use one. See my posting on the previous page.Some thoughts to consider:
- Balun of some sort should be used
- Impact of pipe dia?
- Should the loop measurements be inside, centre or outside circumfrence? (I used outside)
Pipe diameter. Greater diameter will mean broader bandwidth; smaller diameter will mean narrower bandwidth.
Loop measurements. Authors can be sloppy about mentioning this. If they don't mention it, go with pipe centre measurement. If you used outside circumference on the one you built, while the article's author used pipe centre, then your loop will be slightly short and this would explain why your hentenna's resonant frequency was higher than you expected (and why shifting the feedpoint tap/s only marginally changed the VSWR curve).
Another 2c.
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