I just put up a prototype full-wave wire dipole for VHF and it is working great - thought I'd share some thoughts before I commit this to tubing for the elements.
It is extremely easy to make, and has a direct connection to the 75-ohm feedline without any impedance transformer. I'm now trying a few different prototypes cut for different bands and they are all working as expected. Like the ocfd it is fed off-center, but it is not really an "ocfd" designed for multiband operation. Essentially it is a 3/4 wave over 1/4 wave antenna.
I started out in the aircraft band centered on 127 mhz:
1) Overall length for full-wave: 936/127 = 7.37 feet or roughly 88.5 inches total.
2) Cut the wire at the 1/4 wave point for attachment to coax: 234/127 = 1.84 feet, or roughly 22 inches. Center conductor of coax to long leg.
So after the cut I have a 66" length and a 22" length, which is a little over 7 feet tall. But I have the vertical room. Aircraft operations are great.
Since this is a full-wave, it has a cloverleaf pattern rather than the standard donut-pattern for a half-wave. This is good for me, since I can't mount the antenna very high, and need a little upward look angle to get above my neighboring surroundings. It is very similar to the directional pattern of a 1/4 wave groundplane, although it has a bit more gain than a 1/4 wave - about 4db.
(This is the reason the antenna is not really that popular commercially - but if you live down low like I do, why not provide some gain in the angles you can see?)
I topped it off with a simple rf-choke made out of 5 closely-spaced turns of the feedline coax wrapped around a plastic water drink-bottle near the feedpoint. I ran out of clamp-on ferrites, and was too lazy to build a pawsey-stub. Seems to be working well on my 2-meter amateur version of the antenna which is a little bit shorter.
(With the full-wave version on the amateur 2-meter band, I ran an mfj analyzer on it and got 3:1 swr on the band edges and about 1.5:1 on the center)
Anyway, I'm really happy and there don't seem to be any surprises compared to my 1/4-wave groundplanes - other than stronger signals! So the directional pattern seems to be holding like the books and modeling say.
Now I just need to put these in the attic or maybe on the side of the house eves - but amazingly it is working very well indoors near ground level.
(Need to take a break since with a little bending, you can turn this into a vertical "half-square" with some directivity....another day perhaps...)
It is extremely easy to make, and has a direct connection to the 75-ohm feedline without any impedance transformer. I'm now trying a few different prototypes cut for different bands and they are all working as expected. Like the ocfd it is fed off-center, but it is not really an "ocfd" designed for multiband operation. Essentially it is a 3/4 wave over 1/4 wave antenna.
I started out in the aircraft band centered on 127 mhz:
1) Overall length for full-wave: 936/127 = 7.37 feet or roughly 88.5 inches total.
2) Cut the wire at the 1/4 wave point for attachment to coax: 234/127 = 1.84 feet, or roughly 22 inches. Center conductor of coax to long leg.
So after the cut I have a 66" length and a 22" length, which is a little over 7 feet tall. But I have the vertical room. Aircraft operations are great.
Since this is a full-wave, it has a cloverleaf pattern rather than the standard donut-pattern for a half-wave. This is good for me, since I can't mount the antenna very high, and need a little upward look angle to get above my neighboring surroundings. It is very similar to the directional pattern of a 1/4 wave groundplane, although it has a bit more gain than a 1/4 wave - about 4db.
(This is the reason the antenna is not really that popular commercially - but if you live down low like I do, why not provide some gain in the angles you can see?)
I topped it off with a simple rf-choke made out of 5 closely-spaced turns of the feedline coax wrapped around a plastic water drink-bottle near the feedpoint. I ran out of clamp-on ferrites, and was too lazy to build a pawsey-stub. Seems to be working well on my 2-meter amateur version of the antenna which is a little bit shorter.
(With the full-wave version on the amateur 2-meter band, I ran an mfj analyzer on it and got 3:1 swr on the band edges and about 1.5:1 on the center)
Anyway, I'm really happy and there don't seem to be any surprises compared to my 1/4-wave groundplanes - other than stronger signals! So the directional pattern seems to be holding like the books and modeling say.
Now I just need to put these in the attic or maybe on the side of the house eves - but amazingly it is working very well indoors near ground level.
(Need to take a break since with a little bending, you can turn this into a vertical "half-square" with some directivity....another day perhaps...)
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