5 Aug 2015

2m/70cm beam down

After about a year of service, I have taken down my beam for 2m and 70cm which was not working as it did. In the near future I want to erect big-wheels instead. According to Wimo literature they have an omni pattern and a single big-wheel has a gain (horizontal) of 3dBD. Spacing between a 70cm big-wheel and a 2m big wheel needs to be 1.5m. This gain is a little down on the beam but needs no rotating. At the moment I think I'll install a single big-wheel for 2m and one for 70cm both fed with low loss coax on a single mast as high as I can. These should suit my operating fine. I monitor beacons and take part in some 2m and 70cm contests from home in a non-intensive way. A couple of big beams would be nice but these would need a rotator.


Paul Stam said...

Hi Roger,
I understand your considerations. I have the same thoughts. I almost do not work very often on 2 m FM. But it is my only VHF antenna. I also looked at Wimo Big Wheel antennas for SSB and CW on 2 meter. I don't want a big yagi on my roof. I live near the coast and we have often strong winds here. 73 Paul PC4T

Roger G3XBM said...

Paul, exactly right. If you don't want a large yagi, then the big-wheel seems to offer a useful alternative for casual VHF/UHF SSB/CW operating with a useful horizontal gain in all directions. These antennas are lightweight so wind should not be a problem.

G1KQH said...

I don't believe a Big wheel will deliver the same thump and penetration as the beam for DX?

It will be an interesting experiment..

73 Steve

Roger G3XBM said...

No Steve, I agree. The horizontal gain (in nearly all directions) of a single big wheel is 3dBD. My small 2m beam (3el) may be 5-6dBD in the best direction. The advantage of big wheels is no rotation needed (horizontal omni pattern). Often, one is working stations not on the main lobe of the beam where the horizontal gain is far down on the gain with the antenna pointing in the right direction. No, in most situations, a large beam would be better. However I have worked GM from my old QTH (lower) in this village with a halo and poor feeder coax and a big wheel should be at least 3-4dBD better than a halo. It is all a compromise.

Todd Dugdale said...

If a beam is hand-rotated, you lose a lot of the advantage because there's a strong inclination not to make the effort to optimise its direction. Having said that, if you upgrade the coax for the Big Wheel, then it's not a fair comparison.

I've been amazed how much difference using LMR-440 coax makes over RG-58 on UHF -- even on 20-foot runs.

If you have localised RFI, a beam can let you "null out" interference. But on UHF that might not be a big consideration.