Everyone knows that a vertical yagi must be mounted on a non-conducting mast or end-mounted on a metal mast. Nevertheless, last night during an eme run just for fun I decided to try turning my 2M9SSB vertical, because I was vertical to the guy on the other end and I was not copying him (although he was copying me when I was horizontal). Not surprisingly, he did not hear me at all when I went vertical. This suggests that a cross-polarized horizontal beam is more effective than a vertical beam with a metal mast in the middle. Interestingly, the metal mast had no effect on the SWR, so apparently just the pattern was distorted.
Easiest way to do this effectively is to use a second identical beam and stack the two side by side on a horizontal crossboom whose center is clamped to the vertical rotating mast.
This gets the vertical conductive mast completely out of the field of the vertically polarized beam antennas and the mast simply "disappears" electrically.
Otherwise, simply using a 3'-4' piece of wood above the vertical conductive mast does not provide a good solution: (1) It's too short, and really needs to be a wavelength long (about 6-1/2' at 144 MHz); and (2) if your coaxial feedline still runs down the yagi boom to the vertical support mast, and then down that mast, you STILL have the same problem as you have with a conductive mast: The shield of the coax becomes an undesired parasitic element in the middle of your beam. The only way to prevent this problem when using a single vertically polarized beam is to either end-mount the beam (clamp it to the mast behind the reflector) or to route the coax backwards from the driven element to behind the reflector, tie it there to the boom behind the reflector, and let it drop at least one wavelength vertically (behind the reflector) before pulling it back to the supporting structure below the rotator, to make a very large loop.
Hope this helps/// 216 aka Turbo Conway South Carolina.:bdh:
Easiest way to do this effectively is to use a second identical beam and stack the two side by side on a horizontal crossboom whose center is clamped to the vertical rotating mast.
This gets the vertical conductive mast completely out of the field of the vertically polarized beam antennas and the mast simply "disappears" electrically.
Otherwise, simply using a 3'-4' piece of wood above the vertical conductive mast does not provide a good solution: (1) It's too short, and really needs to be a wavelength long (about 6-1/2' at 144 MHz); and (2) if your coaxial feedline still runs down the yagi boom to the vertical support mast, and then down that mast, you STILL have the same problem as you have with a conductive mast: The shield of the coax becomes an undesired parasitic element in the middle of your beam. The only way to prevent this problem when using a single vertically polarized beam is to either end-mount the beam (clamp it to the mast behind the reflector) or to route the coax backwards from the driven element to behind the reflector, tie it there to the boom behind the reflector, and let it drop at least one wavelength vertically (behind the reflector) before pulling it back to the supporting structure below the rotator, to make a very large loop.
Hope this helps/// 216 aka Turbo Conway South Carolina.:bdh:
