The 40 metre version of this antenna, installed at 20 ft above ground, was used at EI5DD's QTH some years ago. Excellent results were achieved on 40 metres where it was working very much as an omnidirectional NVIS antenna. The antenna was tuned with a KW E-Zee match. ATU. Excellent signals around Ireland and into the UK were noted. All the other bands HF of 40 metres tuned well. If installed higher above ground it would have given some interesting results and probably be more suited to DX operation. As it is a loop antenna, the band noise tends to be less than that received on a dipole or vertical antenna which is another advantage.
Most of the WAB awards were achieved using this antenna on the 40 metre band. Anytime a call was put into the IRTS news on 40 metres, it was possible to get in strong enough to be within the first 3 calls received by the newsreader located in the Dublin area. Operators calling into the news from all areas of the country were also received at good strengths and received the transmission via the loop equally well.
Some comparisons were done with G0NSL who ran QRP power of approximately 5 watts on 40 metres into a similar loop at 20 ft above ground and his signals were received 59 +20 dB any time he was on the band.
Not many are blessed with real estate large enough to acommodate the full 160 metre loop but, having tried the 40 metre version, it is certain that it will perform as well on 160 as as it did on the scaled down versions.
A final word on antenna tuning units: Some manufacturers, claim to have provided a "balanced" input by fitting a small toroidal ring balun clamped to the rear panel of the unit which surely defeats the effectiveness of the balun and at the same time has to suffer quite a mismatch between the components of the ATU and the antenna connection points. If the balanced load is near to the balun's design impedance, typically 200 ohms for the 4:1 balun found in the average ATU, then all is well. Unfortunately the typical random sized centre fed antenna with random length of ladder line has an impedance at the feed point that varies dramatically with frequency. The result can be heating and loss at the balun with possible damage.
When trying to match a balanced feed antenna it is better to use a tuner made specially for the job. The E-Zee Match, The MFJ-974H, the Palstar AT1500BAL, the AT4K or even the rare Johnson's Matchbox would be ideally suited to the task of matching balanced feed antennas.