View Full Version : 2M yagi question
04-25-2006, 12:32 AM
Just built a 6 element 2M Yagi antenna. #Planning on using a 23' painters pole to get it up in the air for portable operation. #It is supposed to be resonant across the entire 2M band. #When I am using it vertically polarized for FM, will the aluminum painters pole distort the radiation pattern or change the impedance? #I am thinking I will need to use a plastic or wood extension to raise the antenna away from it. #Thanks,
# # # # # Sam kb1LLY
04-25-2006, 01:05 AM
Yes it will. Use the non-metallic pole for vertical polarisation. If you turn it horizontally you won't have such an issue with the metal mast, but for vertical, absolutely, use plastic/wood, etc.
04-25-2006, 01:06 AM
When going vertical a metal mast may affect the radiation pattern. When horizontally polarized it will not have any effect.
You might build another yagi and "phase" it with your first antenna. Then you would have an antenna on each side of the mast (on a "cross" mast) and there would be basically no interaction (theroetically there would be some but in the "real world" . . . ) when vertically polarized. Again, when horizontally polarized there would be no interaction.
04-25-2006, 01:59 AM
When I had my beams, I spent a LOT of time taking them down and putting them back up, and moving the mast mount from center to off center from inbetween elements and it does affect the performance. Too bad a guy can't extend the boom behind the reflector element and have the mast mounted there. But then of course it would be way too front heavy.
So I just left it in the spot where it affected it the least. I was thinking the same thing, to use something non metalic. I didn't have anything that would be light enough and sturdy.
04-25-2006, 03:35 AM
What I have is what was described; two yagis, stacked, verticle.
No issues doing it this way.
But, I'll note that I didn't really see anything bad in the way of performance when I had just one up. Might have been lucky placement on the top mast, I don't know..
04-25-2006, 03:51 AM
Try to put the elements and the mast on opposite sides of the boom, that will help.
04-25-2006, 08:24 AM
Quote[/b] (ve2nsm @ April 24 2006,20:51)]Try to put the elements and the mast on opposite sides of the boom, that will help.
That will probably make the beam "squint".
04-25-2006, 01:19 PM
I use the white pvc? plastic water pipe for the upper4' for so, with another tube inside for strength. Seems to work.
TOM K8ERV Montrose Colo
04-27-2006, 05:42 AM
Yes, The metal pole will affect your antenna pattern when you install the beam vertical.
As already pointed out, The best cure for a base station is to just get another antenna and phase them on a cross boom to get the vertical pole out of the antenna pattern, And almost double your gain at the same time!
For a temporary portable set up with only a single beam, The fiberglass or plastic pipe is a good solution. (However NOT a good solution for a base station! #NO lightning protection ground from that plastic pipe!)
04-27-2006, 10:51 PM
Hi Sam and all,
Any metal including the coax in the same plane as the antenna elements will affect the pattern. Most of us don't really consider it because the polar pattern of a vertical beam is pretty sloppy to begin with. It tunes a bit differently but you have to adjust it anyway, no big deal so don't be picky, just do it.