Measuring Frequency Off-the-Air:
The ARRL Frequency Measuring Test
There are some unique challenges in measuring the frequency of signals being received from distant stations. Interference, signal strength, and the vagaries of the ionosphere all conspire to make it quite a challenge to determine the frequency of an HF signal (in the range of 3 to 30MHz) more accurately than a few parts in 107.
For decades up until 1981, the American Radio Relay League ("ARRL"), the US national amateur radio organization, ran tests by transmitting a carrier from its headquarters station, W1AW, and inviting hams to measure its frequency; certificates were given for those who came close to the official frequency. This activity ended when the frequency synthesizers and digital displays used in ham equipment became accurate enough that inadvertent out-of-band operation was no longer a significant problem.
In 2002, however, the ARRL re-introduced the Frequency Measuring Test ("FMT") as an annual affair. Information about the FMT is available at www.arrl.org/w1aw/fmt. I've been an enthusiastic participant in all the recent tests (what a surprise!).
Here are details of the technique I use for high-resolution measurement of received signals.
The ARRL graciously gave me access to the raw data submitted for the 2005 FMT (scrubbed to protect the privacy of the entrants) and I've done an analysis of the FMT 2005 data here.