Cushcraft makes a beam antenna, A14820T for both 2 meter FM and 2 meter sideband. This could be the solution to what I have been trying to accomplish with limited antenna space.
Feeding the antenna with two lines is no problem.
The archives only show one post referring to this antenna, in the "Wanted" listings.
I would appreciate any opinions from operators who have experienced this antenna.
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This antenna is similiar to the VHF twist antenna that was used in the 1980s and early 90s for 2 meter satellite work (ability to change polarization is shown in the VHF Twist manual - phasing lines)
VHF Twist manual
One caveat re this antenna:
It employs elements in the vertical plane (for FM work) and the horizontal plane (for SSB/CW, and everything else) and only works properly if installed on a
non-conductive support mast. If you install it on a metallic mast, the performance of the vertical-plane yagi suffers a great deal.
Also, with this or any vertically-polarized beam antenna: Best performance is only achieved when the coaxial transmission line is routed from the vertical driven element to the rear of the antenna, taped or tied behind the reflector element, and allowed to drop down vertically one wavelength (about 78" before bringing the cable back towards the support mast or tower and securing it there.
Reason is: If you route the coaxial transmission line down the antenna boom to the support mast and then run it down the mast, this creates the same problem as a metallic support mast, i.e., you now have an undesired vertical reflector sticking up through the middle of your yagi!
In actual antenna range testing at the Central States VHF Conference several years ago, we noted the "difference" in performance of a vertically polarized two meter yagi mounted on a metallic mast, or having its coax routed down a metallic or non-conductive mast, and using the more proper (and described above) method is very considerable -- not just a dB or two, but literally "S" units worth of difference.
Until you try it, it's hard to believe.
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I had one of the A14820T cross yagis for about 3 years with no problems. I had it mounted to a 10 ft metal mast, in a 3 foot (radio shack) roof tripod up at about 35 feet above ground level. A light weight CDR rotor moved it easily. Feed line was 2 coaxes, both 9913 and ran about 80 feet into the radio room. Feed lines ran just as the cushcraft instructions called out. Was running a TM-255 Kenwood 2 meter all mode with a mirage amp, putting out about 100 watts. It ran just fine! No problems at all. Reason I got rid of it, 2 meter side band just was not as fun as 6 meters, so I replaced the antenna with a 5 element 6 meter yagi. I had good reports on 2 meter SSB with a regular talking range of about 300 miles (alt here is 1650 ft above sea level in EN91). Ran FM on the vertical and could hit any repeater I wanted with low power (5 watts) in about an 80 mile radius. I see them around at hamfests once in a while, but not too often. Have fun!
I've had a variation of this antenna on my antenna
"stack" for a few years.. I have a 50 foot tower with a 12 foot mast out the top. My A147-22T (11 elements horizontal & 11 elements vertical) is mounted at the top of the mast with the coax running along the boom to the mast. It runs down the mast and forms a "half loop" at the top of the tower.. The height of the antenna is approximately 60 feet.. This arrangement worked very well until the 9913 coax center conductor on both coax runs broke in that "half loop".. The center conductor is solid, not stranded, copper wire and doesn't take to well to the constant flexing..
I have been using that antenna for 15 years and it is a great performer. I recently acquired a second one and want to stack it on my tower and I'm looking for the spacing requirements and feeding specs for it. And if you hve a pdf of the assembly instructions that would be great to as I have lost mine. thanks Rod email@example.com
I've had a couple of these, and used them all wrong, and they still work fine.
I'm a little surprised at WIK's comments - it was my understanding that Cushcraft designed their vertical yagis to work well on a metal mast. I vaguely remember discussions about this back in neolithic times. But, it would not surprise me at all - I usually use a wooden or fiberglass mast for vertical yagis.
When I lived in Des Moines, I could literally work repeaters all over the state with it, and it was 'OK' on SSB - it does not have the gain or directivity of a really big yagi, but it's better than a poke in the eye... I could work SSB stations all over the upper midwest.
I used one of these as my first antenna for working the Oscar 10 satellite. I whipped up a quick phasing harness and fed it as a circular antenna, propped up against a ladder in the back yard. It actually worked very well - the vertical yagi is cut for high end of the band and the horizontal one is for the low end, so feeding them this way resulted in something that worked pretty well in the middle of the band.
I've about decided to put up another one, because I need some gain on FM and it would be nice to be able to actually do something in the VHF contests besides working Eskip on 6.
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The only way to use a vertically polarized yagi on a metal mast is if the mast is behind the yagi's reflector ("end mount" antenna). When the mast protrudes through the yagi, there's no way that's going to work well -- you can't design around this: It's an untuned element in the radiation plane, and that's never good. Nor is running the coax feedline down the mast, because that's another untuned element in the radiation plane.
Originally Posted by K0RGR
It will "work," as "everything works" to some degree -- but you'll never get the full benefit of the antenna that way, not even with a lot of luck.
Using a non-conductive mast helps a lot, as does letting the coax feedline hang down from behind the reflector element for >1 wavelength before bringing it back to the support mast.
We used to mount them at the top of the mast and with the way the boom to mast bracket offset the elements I don't ever remember having a problem although I do remember some guys tilting the vertical elements about 15 degrees to help clear the boom. I never heard anyone complain about them.