Frequency Measuring Test 2004

The test format changed this year, and in my opinion not for the better. Instead of measuring a CW signal, transmitted in the CW part of the band, W1AW used SSB and transmitted an audio tone. They announced the carrier frequency ahead of time, and the exercise now involves some additional math to determine the audio tone, given the known carrier frequency.

I can see the learning advantage of this format, but it actually reduces the challenge a bit since we are bound by the accuracy of the announced carrier frequency. And, using the voice part of the 40M band means that there are many hetrodynes and other spurious signals to dig through in order to find the desired tone.

Propagation and interference didn't favor this year's FMT. We had good copy on 80M. On 40M, the signal wasn't strong and there was a huge amount of interference from a SW broadcast station. Like last year, we didn't hear a peep on 20M. Mike, WB8GXB, who operated from his own shack this year, reports hearing signals on all three bands, but he has a tribander at 90 feet, so his signal-catcher is a bit better than mine.

Band N8UR Measurement ARRL Measurement Error
80M 1 105.013 1 105.02 -0.007 Hz -- -1.75x10-9
40M 1 108.279 1 108.26 +0.019 Hz -- +2.6x10-9
Note that this is the audio, not the RF, frequency, calculated by adding or subtracting (depending on the sideband used) the measured RF frequency from the announced W1AW frequency. To calculate the fractional frequency offset, I used the frequency error vs. RF carrier frequency (rather than the ratio of the audio frequencies) since that more accurately reflects what was actually being measured.

If you're interested, here's my ARRL Submission Letter (pdf).

The test setup this year was the same as last year -- an HP 3586C selective voltmeter served as receiver, with its tracking generator looped back to the input (via an attenuator and 2-way coupler) to provide the reference tone. The external frequency reference was an HP 5065A rubidium frequency standard that was monitored against GPS at the time and was within 5x10-13.

Here are a couple of screenshots of the signals as recorded by Baudline. The signal near 1850Hz is my local reference, and the signal ~25Hz lower is W1AW. The screenshots each show an average of the signal over about 3 minutes.

80 Meters

40 Meters

Here's a close-up of the averaged 40M W1AW signal, showing two distinct peaks about 0.3Hz apart. The signal was barely discernable during much of the recording. Which is the real peak?

By contrast, here's a close-up of the 80M W1AW signal. No problem spotting the peak here!