Why WSPR?

As an avid SOTA activator, I have taken many portable antennas into the field; searching and probing for the 'perfect' antenna for portable operation; easy to pack, easy to deploy, lightweight, multi-band capability, and high performance/efficiency.  While I have yet to find such an ideal antenna, I have sought out techniques currently practiced by hams to evaluate performance of antennas to assist me along my journey.

On the transmitting end, antenna analyzers can give valuable information at the antenna feedpoint which help you to minimize SWR and adjust the antenna into resonance.  But it cannot tell you how well your signal is heard in the far-field. Many operators will do a A-B antenna comparison of two antenna with far-field on-air RST reports. These are useful, but are only accurate to +/- 3db (S-meter reading) and only give a view at point-specific receiver locations. I was then drawn to the Reverse Beacon Network (RBN) as a way to get a view into a wider window of receiver locations through a world-wide network of beacons listening and reporting Signal-to-Noise ratios (SNR) from on-air QSO's or tests. This was more intriguing, but as I conducted my own studies I found that the SNR values reported by a single receiver station from my setup showed significant variaiblity in time. How was I to process that information and draw meaningful conclusions?  

I then moved on to WSPR and found that I could take advantage of automated transmitting and receiving tools (such as WSJTX) to run semi-automated testing scenarios.  Furthermore, the weak-signal capability enabled me to reach more receiver stations and at significantly greater distance. OK great, so now what? Going back to my original desire to evaluate antenna performance what I was searching for was a way to do an A-B antenna comparison that resulted in a tangible quantity to compare the antennas. In short, I was looking for a way to evaluate the relative gain of antenna "B" to antenna "A". Further searching led to the discovery of a paper by J. Zender entitled "Simple HF anntena efficiency comparisons using the WSPR system". The paper demonstrated that under a controlled test environment, far-field SNR data at a receiver station from two antennas A&B can in fact be used to calculate the relative gain between the antennas.  My quest was on.