It’s been a while since I posted again, but then I have something to report. Last year, I started experimenting with variants of a horizontal polarized omnidirectional antenna. The Cobweb, the Cobwebb and the Classic Halo. I can now tell, from my own personal experiences, which of these variants could best fit your needs. But first I need to explain the differences between these three antennas.
Circular and horizontally polarized
The Cobweb, Cobwebb and the Classic Halo are in fact dipoles where the radiators are not extended but have a square shape. This shape makes this antenna virtually circular radiating and horizontally polarized. For each band there is a dipole with one common feed point. From a mechanical point of view, these antennas are similar, but electrically totally different.
Open and folded dipoles
The Cobweb uses open dipoles, has an impedance of 12 Ohms and needs a 1:4 impedance transformer to match the 50 Ohm your transceiver. The Cobwebb (with double “d”) uses folded dipoles with open ends. Thereby, the radiators are shorted in the middle to create a T-match. This variant has an impedance of 50 Ohms and thus can be fed directly with 50 Ohm coaxial cable. The Classic Halo also has folded dipoles but with closed ends. This variant also has an impedance of 50 Ohms and can therefore also be fed directly.
Plenty of experimentation
Recently, I have experimented a lot with these three variants. I looked at the ease of self-construction, performance with transmitting and receiving, bandwidth and tunability on frequency and optimal SWR.
Cobweb
The Cobweb with single b, designed by G3TXQ Steve Hunt (sk), is an easy antenna that can even be built as a monoband or even in a 7-band version, as well as commercially available. I myself have a version built by an amateur in Poland that covers 20m to 4m, but there are also existing versions with all bands from 40m to 10m. In my commercial Cobweb, the 4m and 6m elements are not performers. You don’t have to do it for those bands. The bandwidth on HF is limited in terms of SWR, especially on 20m, 15m and 10m. To cover those bands completely, you actually need a tuner. The 1:4 impedance transformer is not easily available in stores as a ready-made product, so you have to wind it yourself.
Note that the smallest elements (6 and 4 meterd) are in fact a kind of inverted V’s.
The feed box includes a 1:4 transformer.
This antenna came pretuned and was installed in less than an hour.
The reception is quiet, especially compared to a vertical (goundplane) or half-wave EndFed. Tuning is done by folding back the ends of the dipoles and adjusting the lengths. This is not a job you do in a few minutes. Each element must be tuned separately, and the tuning of one element affects others. Commercial Cobweb’s are often delivered pretuned and can be used directly with minimal element tuning.
Cobwebb
The Cobwebb with double b, designed by G3TPW Steve Webb, is another antenna that can be built as a monoband and multiband version. The performance of the Cobwebb is better than the Cobweb in a few ways. For example, the bandwidth in which the SWR remains less than 2:1 is somewhat larger than the Cobweb. Since no impedance transformer is used, this saves in losses and, of course, the cost of an impedance transformer.
As with the Cobweb, reception is fairly quiet. The disadvantage of the Cobwebb is the tuning, which is the most difficult of the three variants. Besides the length of the dipoles, you also have to move the shorting point, the T-match.
Classic Halo
The Classic Halo, patented in 1947 and not to be confused with the modern VHF halo that is tuned through a gamma match, is mostly similar to the Cobwebb. Big difference is that the radiators are folded dipoles with closed ends. The 2:1 SWR bandwidth of the Halo is about 10% better than the Cobweb, at least according to own measurements. But still not enough to cover the whole 20m, 15m and 10m band. The Halo is 50 Ohm and an impedance transformer is not needed.
A dual band Classic Halo for 10 and 20 meters.
Reception is quiet. Although I did not do specific measurements on this antenna, I got the impression that the Halo had the best reception. Tuning is done by folding back the ends of the dipoles, as with the Cobweb. Side note with this antenna is that in the 5-band version tuning requires a lot of patience, especially 17m in terms of SWR is difficult to get under 3:1. PE4BAS reported, after an experiment, that cutting open the ends of the 17m dipole can solve this problem. Leaving the 17m elements as an open dipole with an extremely closely spaced parasitic element.
Multiband vs. monoband
It’s fair to say that all multiband antennas are compromise antennas. That’s how I experienced it with these three variants. I built them all in monoband (20m and 10m) and multiband versions. In terms of performance, I got a strong impression that the performance, both transmitting and receiving, of a 20m monoband was better than 20m in multiband.
Final verdict
If you are not a homebrewer and want as many bands as possible in one antenna then the Cobweb is the antenna to buy. It often comes pretuned out of the box and thus easy to install. There are several manufacturers such as MFJ, EAantenna and AWK.
The homebuilder does himself a favor with both variants. The extra bandwidth of the Halo and the lack of an impedance transformer is attractive. The somewhat easier tuning is another reason for a Cobweb.
The Cobwebb… I would ignore. Commercially unavailable and the tuning will take all your patience.
Want to focus on a single band or two band? Then the Halo is by far the best and easiest antenna to build. I wrote an article on how to build a 10 and 20 meter band Square Halo.
Whether you choose the Cobweb or Halo, you are going to get a lot of enjoyment from both antennas. Quiet RX and TX performance, provided your antenna is high enough above the ground.