A Loop Experiment

On 15th March I set out for a business meeting in the US and decided that as an experiment I would leave my 40m coax loop that we made at the club connected to my FT817 receiving WSPR. The receiver ran almost continuously for the 14 days that I was away. I say almost continuously, I have a bug in the computer that keeps resetting the the audio port from line-in (which is the audio input port I am using) to mic in (which interestingly still receives the stronger signal due to audio cross talk between the ports) and I needed to remotely log on from time to time to correct this. Because I could not be sure that I would have good internet connectivity whilst I was away I did not attempt to rin the system as a remote transmitter.

Please excuse the mess in the shack, but the loop in use is shown below.



This rather saggy loop is in my loft shack which is constructed with aluminum foil covered plasterboard, although as it is not bonded together I am nit sure what effect it has. It was oriented in a plane exactly East-West.

Over the 14 days on 40m (which is not the most popular WSPR band) I logged 120 unique call signs from 19 countries. To get some assessment of the range groupings I grouped the number of unique contacts into range buckets 1.414 time the previous max range as shown below:

0 to 50Km 2
50 to 121Km 2
121 to 221Km 6
221 to 362Km 9
362 to 562Km 19
562 to 845Km 23
845 to 1245Km 26
1245 to 1811Km 10
1811 to 2611Km 6
3742 to 5342Km 1
5342 to 7605Km 8
7605 to 10805Km 1
10805 to 15330Km 1

The contacts in the range 0 to 500Km were most probably NVIS which is about 38 out of the 120 contacts meaning that about 1/3 were NVIS and 2/3 were contacts that required F layer skip.

I then took a look at number of unique contacts by country, and did a by eye estimate of the baring from my QTH. The results I got were as follows:

Country # Range(Km)
Australia 1 60
Austria 3 111
Belgium 3 102
Brazil 1 220
Denmark 1 47
England 14
Finland 3 45
France 6 160
Germany 35 70 to 110
Italy 9 130
Netherlands 7 76
Norway 1 28
Poland 5 80
Scotland 4 330
Spain 4 190
Sweden 2 47
Ukraine 7 84
USA 3 290

I did not do bearing for UK because they were spread over such a wide arc that I did not feel that the results would contribute much to understand how the antenna behaved.

I then classified the results into front and back (315 deg to 45 deg plus 135 deg to 225 deg) and side (45 deg to 135 deg and 225 deg to 315 deg). The result was that 16 unique reports were made on the front back and 81 off the side. Even if I discount all of the NVIS contacts the majority of contacts were still off the sides. This distribution is heavily skewed by the distribution of round the world stations, but the results would suggest that the small tuned loop probably receives off the side, or omni-directionally rather than off the face which I believe is common wisdom.

Just one final observation I took a look at the powers (in Watts) that various stations that I received were advertising.

Power #
0.05W 1 (Germany)
0.1W 1 (Netherlands)
0.5W 5
1W 12
2W 12
5W 64
10W 8
20W 1 (Italy)
100W 1 (Spain)

I leave you to draw your own conclusions.

It will be interesting to see how this compares to other antennas that I have available and to get a feel for their patterns. I will run some other tests and report what I find.

73

Stewart/G3YSX