One of my long-term experiments involves receiving on HF. Transmitting on these bands works well with a Cobweb antenna for 10m to 20m and a wire with a CG-3000 automatic tuner for 30m to 160m. Reception in my densely populated area on the lower bands is challenging, often facing up to S9 noise, especially on 60m to 160m. On these lower bands, I use active antennas, such as the Wellgood active loop by M1GEO. Now, I wonder if the way such an active loop antenna is positioned affects reception in such a way, that it would perform better.
Horizontal instead of vertical
Active receive loops are in most cases positioned vertically. I have rarely seen one positioned horizontally? Why not? I have two identical Wellgood loop antennas and two identical receivers, so it comparing reception performance on HF seemed like a good experiment to conduct. FT8 mode signals produce quite some data that can be easily retrieved and through the PSKReporter.info webiste database.
Active loop antenna setup
To measure accurately, I set up a test with the two identical active antennas. Both Wellgood v4 loops are mounted 10m AGL, spaced 2.4m (8 ft) from eachother. One loop is positioned vertically and the other horizontally. Both antennas are connected via equal lengths of RF240UF (50 Ohm) coaxial cable to a bias tee injector. Both bias tees are powered by the same 13.8V stabilized QRM-free power supply.
Receiver and WSJT-X decoder setup
From the bias tee injector, an identical short length of RG-316 (50 Ohm) coaxial cable runs to an SDRplay RSPduo with harbors two identical receivers. The RSPduo is connected to a Windows PC running SDRuno software and WSJT-X v2.6.1. The audio is routed through two identically setup SoundBlaster USB sound cards.
My station is located at JO21ev, just west of Rotterdam in the southwest of The Netherlands.
Collecting test data
I collected data by simultaneously monitoring FT8 spots on each HF band (excluding 12m and 17m) with both antennas over a 24-hour period. This data was gathered using PSKreporter.info and screenshots were taken of the displayed maps.
Test results
Below are the test results for each band with a brief explanation. First screenshot is data produced witht he vertically positioned Wellgood loop, the second with the horizonally positioned one.
10 meters
On this band the vertically positioned loop (top image) was a clear winner. It produced 1710 spots against 960 for the horizontally positioned loop. You see more long distance (DX) spots for the vertically positioned. But a lot more spots were decoded within a 1000km distance, which is mainly weak backscatter. I am not sure why this is.
15 meters
Here on 15 meters the vertically positioned Wellgood loop performs better with 1253 spots vs. 1046 spots for the horizontally positioned. It also looks like the vertical loop managed to pull out a little more DX.
20 meters
However the vertically positioned loop produced 4817 spots vs. 4001 spots for the horizontally positioned, that difference was mainly due to a lot more short skip European spots. Is the vertically positioned loop more sensitive to high angle signals here?
30 meters
On this wavelength, the tipping point turns to the horizontally positioned loop with 3113 spots vs. 2660 spots for the vertically positioned. The images below clearly show a lot more DX spots when the loop is mounted horizontally.
40 meters
The longer the wavelength the better the horizontal loop performs. In this 24 hour run it produced 7023 spots vs. 6093 spots for the vertical loop. However not very well visible, the horizontal Wellgood received especially more signals from North America.
60 meters
There is a lot less activity on 60 meters compared to other bands. Most activity is from European stations. So the main part of the spots are within Europe. Here is where the vertical loop does best. The difference between vertical (723 spots) vs. horizontal (741 spots) is not very big. But there is a bit more DX for the horizontal loop.
80 meters
More or less the same results here as on 60m. More spots (1820) for the vertical loop compared to the horizontal (1600). That difference is also caused by many more European spots, which are high angle signals. The horizontal loop did much better at DX with quite more stations from North America, which are low angle signals.
160 meters
On this band, in fact a medium wave band, the horizontal loop did much better with 468 spots vs. 304 spots for the vertical Wellgood loop. It was actually the first time on this band I received a station from the US west coast (Washington state)! Thanks to the horizontal Wellgood loop.
The results tabulated
| Band | Vertical loop spots | Horizontal loop spots |
|---|---|---|
| 10m | 1710 | 960 |
| 15m | 1253 | 1046 |
| 20m | 4817 | 4001 |
| 30m | 2660 | 3113 |
| 40m | 6093 | 7023 |
| 60m | 723 | 741 |
| 80m | 1820 | 1600 |
| 160m | 304 | 468 |
Final conclusions
This experiment produced very interesting insights, but also a bit confusing. Why the loops perform different on the high and low bands remains subject for further research. I believe low angle performance and sensitivity to manmade noise (QRM) are in some ways responsible for the performance difference.
Low angle performance
Especially on the lower amateur bands, the horizontally placed loop receives more DX than the vertically placed one. This difference is quite clear. I can’t immediately explain why this is. DX signals generally come in at a low angle. It is possible that the horizontal loop is more sensitive to signals at a low angle on those lower frequencies. I cannot explain why the horizontal loop does not have this advantage on the higher amateur bands.
Manmade noise and sensitivity
Another possible explanation is that the horizontal loop is less sensitive to man-made noise. This is something that is present here in my densely populated location during the day and to a lesser extent at night. Now, man-made noise is a bigger problem on the higher amateur bands here, especially during the day. So, would the horizontal loop only be sensitive to man-made noise on the lower bands?
New noise floor comparison experiment
To test the difference in sensitivity to man-made noise, I will conduct an experiment to compare the noise floor on all amateur bands between the horizontal and vertical loop.
In the meantime, I will intensively use all the advantages of the horizontal loop on the lower bands this coming winter!