WSPR at Midlatitudes from KN4NBI: A Year of Data at Solar Minimum

The Weak Signal Propagation Reporter (WSPR) is potentially a useful tool in the quantitative study of ionospheric propagation. But there are a number of factors to be considered in the use of WSPR to make propagation measurements, and it is useful to have a baseline at solar minimum to compare with measurements as we approach solar maximum in the next five years. One key measurement question is to what degree WSPR is linear, and over what dynamic range, in real-world propagation conditions. Another important issue is the role of noise in WSPR measurements. WSPR spots report SNR, not signal strength, so identification and quantification of various sources of noise is necessary. During a year of analysis of spots of my transmissions on 20 meters from a mid-latitude location (Virginia Beach), I have addressed these questions and made other observations of propagation at solar minimum. My results include:
 - a determination that WSPR spots are linear with respect to transmit power from around -25 dB SNR to over +10 dB SNR;
 - that the dynamic range may extend to more than 60 dB; however, a particular receiver’s dynamic range for simultaneous spots  may be substantially less than this;
 - there is an approximately 6 dB noise “fuzz” measured from ground wave reception, that can be averaged out, but a cost of time resolution;
 - there is especially large variability in propagation at sunrise, sunset, and at the edge of the skip zone; on the other hand, long-distance propagation (e.g., to Hawaii or the Canary Islands) can have surprisingly low variability;
 - even with zero sunspots and low K indices, there is substantial short-term variability in propagation which I have attempted to characterize. Very small changes in the K-index can have major effects on the distance of the skip zone and on nighttime propagation.