Additions:
ARRL FMT - ARRL Frequency Measurement Test, November, 2008
Deletions:
ARRL FMT November, 2008
Additions:
I left the equipment on for a day before the test to thermally stabilize. The format of this test was different (see article linked below). The transmitting stations put out the cw notifications on their lower sideband (LSB) carrier frequency, and then output two tones between 500 and 2000 hz. The tones were 10 seconds long, alternated, and were given 3 times each for a total period of one minute. This was done on 80 and 40 meters, first by W1AW and then by WA6ZTY.
My strategy was simple. Set the receiver in LSB mode to 500 hz higher in frequency than the published carrier and use a 3khz passband. This would allow me to hear, measure and copy the cw as a 500 hz tone. The other two tones would then be in the LSB passband at somewhere between 1khz and 2.5khz. Another element of the strategy was to avoid changing the receiver frequency during the test. Modern receivers are not accurate below the few hz level, so changing the receiver at all puts unknowns into the measurement. The goal is to make all measurements with the same dial setting. Since this test only involved making DIFFERENCE measurements between carrier and the tone signals there was no need to calibrate with WWV or use a precise signal generator in the passband. All you need is a stable receiver and a way to accurately measure the tones coming out of it. The free Spectrum Lab software combined with a computer and a sound card provided that capability.
Deletions:
I left the equipment on for a day before the test to thermally stabilize. The format of this test was different (see article linked below). The transmitting stations put out the cw notifications on their LSB carrier frequency, and then output two tones between 500 and 2000 hz. The tones were 10 seconds long, alternated, and were given 3 times each for a total period of one minute. This was done on 80 and 40 meters, first by W1AW and then by WA6ZTY.
My strategy was simple. Set the receiver in LSB mode to 500 hz higher in frequency than the published carrier and use a 3khz passband. This would allow me to hear, measure and copy the carrier as a 500 hz tone. The other two tones would then be in the LSB passband at somewhere between 1khz and 2.5khz. Another element of the strategy was to avoid changing the receiver frequency during the test. Modern receivers are not accurate below the few hz level, so changing the receiver at all puts unknowns into the measurement. The goal is to make all measurements with the same dial setting. Since this test only involved making DIFFERENCE measurements between the carrier and the tone signals there was no need to calibrate with WWV or use a precise signal generator in the passband. All you need is a stable receiver and a way to accurately measure the tones coming out of it. The free Spectrum Lab software combined with a computer and a sound card provided that capability.
The oldest known version of this page was edited on
2008-11-27 12:00:19 by AlanB
[initial version]
ARRL FMT November, 2008
NEWS FLASH - the FMT results are in: WB6ZQZ (the author of this page) was one of only 3 stations that copied all frequencies with an error of less than one hz. See the link below for the full FMT results.
This was the first ARRL FMT that I participated in. I used only a warmed up Icom
ProIII, a Navigator digital mode interface (which has a usb soundcard), and a computer running the free Spectrum Lab software. It does not take a lot of equipment to do this, especially for this FMT due to the way it was designed. I spent a few evenings becoming familiar with the software (I still have a lot to learn there), and characterizing my setup. I listened to two "practice" runs by Connie K5CM and then copied the FMT signals from W1AW and WA6ZTY on the wednsday evening of the test after coming home from work.
I left the equipment on for a day before the test to thermally stabilize. The format of this test was different (see article linked below). The transmitting stations put out the cw notifications on their LSB carrier frequency, and then output two tones between 500 and 2000 hz. The tones were 10 seconds long, alternated, and were given 3 times each for a total period of one minute. This was done on 80 and 40 meters, first by W1AW and then by WA6ZTY.
My strategy was simple. Set the receiver in LSB mode to 500 hz higher in frequency than the published carrier and use a 3khz passband. This would allow me to hear, measure and copy the carrier as a 500 hz tone. The other two tones would then be in the LSB passband at somewhere between 1khz and 2.5khz. Another element of the strategy was to avoid changing the receiver frequency during the test. Modern receivers are not accurate below the few hz level, so changing the receiver at all puts unknowns into the measurement. The goal is to make all measurements with the same dial setting. Since this test only involved making DIFFERENCE measurements between the carrier and the tone signals there was no need to calibrate with WWV or use a precise signal generator in the passband. All you need is a stable receiver and a way to accurately measure the tones coming out of it. The free Spectrum Lab software combined with a computer and a sound card provided that capability.
More to come here, check back later!
Capturing the Sound File
Post Processing the Captured File
Links
AlanB