My friend Andreas, N6NU has been kind enough to “peer review” my meanderings through LowBandVille. After yesterdays discovery that I can get 160 and 80M to work very well with the Inverted U, Andreas suggested that I only bring the far end of the “bent over” Inverted L so that it is 15 – 20′ above ground. Since the Inverted U was too long, I followed his advice, and with a quick and dirty model confirmed what he found – that keeping the far end off the ground drops the take off angle from 45 to 30 degrees and adds in almost 1 dB of gain.
I will drop the takeoff angle from 45 degrees to 30 degrees and also pick up almost 1 dB gain . . The loss showing is a bit worse than I expect it really is since I only have modeled one radial underneath. WHen I use my AA-30 and look at the SWR curve – if I find that the curve is fairly narrow banded, then the ground loss is not bad. If the curve makes the antenna SWR look a lot more broad banded, then its time to see what I can do radial wise. Fingers crossed . . .
Furthermore, Andreas just uses a hairpin match across the radials and vertical – so I must try this when I get home. If I could use just the inductor to match the antenna on 160 and 80M, that would be awesome!
Thanks Andreas – I feel like this is the best 160M TX antenna I could put up on a small lot.
The Mod Bob was a very interesting antenna if you have small space and want 160 – 30M in one antenna, but if you want best performance on 160 and 80M, then the Inverted L rules. I also learned why – although it seems easy to try an Inverted U – that the far side should not come so close to ground – and that its no more convenient support wise than to just fold the wire down and keep it 20′ above ground.
Finally, I like this solution much better than severely shortened antennas where you use hats and coils or other top loading because the antenna will stay up – and the voltage isn’t as severe as a really short vertical. I had experienced enough arcs and sparks on very short 160M antennas to stay away from that territory. And also – getting something up high that is strong and can withstand winds is also another design parameter where I had to experience and do the best I can on my small lot. I’m quite happy with the fact that I’ve gone “full circle” on the RX antennas, and now am closing in on wrapping up the TX antennas.