SW listening and the ability to receive stations many thousands of miles away on HF has always fascinated me. Reception on HF, more especially LF and MF has always been a challenge due to the high urban noise floor.
The doublet antenna at home while working well on 7 to 30 MHz, is a poor performer below 3 MHz. This coupled with the high noise floor makes reception of all but the strongest signals very difficult. In part the answer is a dedicated antenna for low frequency reception. Options range from very large beverage / directions arrays to small active antenna. I have no experience with large antenna on sub 7 MHz, as the average urban garden will not support such ambitions projects. The answer for many of us comes from a surprisingly small antenna.
Receive only active antenna may provide a solution, the active part providing some amplification in the receive path. Designs are available for both commercial and homebrew, the price can vary from a £20 homebrew solution to £250 commercial antenna.
I was lucky enough to spot a second hand Wellbrook loop on ebay, reasonably cheap and this gave me a chance to compare the performance with my other HF antennas. It also provided me with an opportunity to monitor WSPR signals on 472 KHz and provide some data into the WSPR network.
PA0RDT has designed a LF / MF Mini Whip antenna, you can read the fundamentals of the mini whip.
M1GEO has recently repaired a Wellbrook loop antenna, his website includes a detailed teardown.
LZ1AQ has detailed design notes on his website for his wideband active loop antenna.
PA0LUX provides a video demonstrating HF reception on his wire antenna and Wellbrook loop. You can see and hear the difference for yourself.
How well does the Wellbrook work on 472 KHz
Well it outperforms my doublet antenna by some considerable margin. Signals that I cant hear just pop out of the noise and for interest I have included some WSPR data for that band.
Monitoring 472 KHz on the evening of 15th and morning of the 16th Jan 17 provided 19 unique calls.
The best DX was LA1TN at 1346 KM
Its also interesting to look at the reception reports over time of day / night.