A Note on Performance of the Short Misek-SWA

Jeff VE1ZAC Sept. 09

While testing a newly erected Pennant antenna, I had reason to compare the performance of the SW pointing Pennant against my short phase controlled SWA antenna. SWA is an acronym coined by Vic Misek to describe his steerable wave antennas designed for urban locations. I put one together last spring aimed at helping reception during low band fox hunts. It is 60 feet long and sits on three pole about 6 feet high. It is fed in the center with two RG-6 coax lines which run to a Dallas Lankford designed phasing control unit. In this unit is a 12 dB Norton common base transformer feedback rf amplifier. This unit works superbly and does everything claimed and more.

Listening to the West with the Pennant and the SWA on 160, 80 and 40 gives the edge to the Pennant when a very broad band null aperture will suffice. The null is pointing to the NE in my case and cannot be moved (very much). This works perfectly for helping increase the SNR of weak QRP signals in the US and Canada. Compared to the SWA, it provides a no-tune solution to fox hunting and QSO party style contesting.

The SWA , however, is capable of some very impressive signal tuning feats. With a 360 degree steerable null I can depress stations in the South over the West by 4 or 5 S units. Or vice versa. This can sometimes make a big difference in a pile up with a weak signal.

Last evening, after making comparison notes with the Pennant, I turned my attention towards a more DX friendly environment using the SWA. On 160M, there is lots of interesting DX opportunities from Nova Scotia in the evening and during early morning greyline sessions. Too test out its DX capabilities it is fun to try a hand at MW DXing. By pointing the null SW of Halifax, stations from Europe pop up all over the place. I can copy UK and Eu stations on 1377, 1215, 1134, 1107 and 1053 KHz quite well after suppressing the splatter from the West of me. Further the established null stays stable over a very wide frequency range. The station frequencies listed above needed no tweaking of the null from 900 KHz to 1400 KHz. That is impressive by itself. Listening with a vertical, a Windom and Pennant in omni directional mode did not show the presence of these signals.

Reduction of noise, both local and distant, is also possible with the SWA, and in the right direction with the Pennant. Noise power is something that receivers are very good at detecting and can easily overwhelm weak signals. If the weak signal is in the same direction as the noise source, it is harder to do anything with it, but if the noise is local or from a different direction, the kind of null available from a terminated loop or from a SWA style antenna is invaluable. Beverages can have this affect as well, but have the disadvantage of needing lots of real estate. They also tend to have narrow null apertures and some have big lobes off the sides which do not help with noise reduction from those directions. When compared with the modest footprints of 30 or 60 feet for a terminated loop, it’s a win win situation for these modest antennas, especially in urban locations.

Reliability of these antennas is also good, when an inside phase control and preamp is used. The Pennant is likely very reliable with a fixed termination resistor, which is something that may work just fine in my case. ( See previous article on Pennant construction). The reliability of the Vactrol remote termination device remains to be seen. If it survives a winter of low band use, I will be pleased. Time will tell. A few report all sorts of problems while others claim it is 100% reliable over several years of use. In my case, the Pennant null is fixed and pointing at my transmit antennas, which could help with reducing self induced large RF currents on the elements. I don’t use an amplifier very much, but when I do, it will be interesting to see how well the Vactrol device stands up.

These two antennas enable low band utilization that would not be possible for me with my regular transmit antennas.