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 Previous: Dayton Hamvention® Says Better Communication a Key Goal for 2006 Show |  Next: White House Nominates New FCC Commissioner, Copps Tapped for New Term |
NEWINGTON, CT, Nov 9, 2005--Returning to the airwaves November 17 at 0245 UTC (Wednesday, November 16 in US time zones), the 2005 ARRL Frequency Measuring Test (FMT) will repeat the challenge of last year's successful event. This year's FMT again calls on participants to measure the frequency of an audio tone modulating the carrier.
"Measuring the tone frequency, as opposed to that of the carrier, reinforces the understanding of the relationship between carrier frequency and the actual components of a transmitted signal," Engineer and ARRL Contributing Editor Ward Silver, N0AX, says in "Tune In the 2005 Frequency Measuring Test," in November QST. "With the carrier largely suppressed for SSB signals, only the sideband components remain. A single modulating tone results in a single transmitted component." But, Silver notes, the frequency of the absent carrier is what the operator sees on the radio's display.
The FMT signals will emanate from Maxim Memorial Station W1AW this year on 160, 80 and 40
meters. The 20-meter transmission has been dropped this year because of the
generally poor conditions during evening hours on that band. The frequencies
will be 1855, 3990 and 7290 kHz, and all transmissions will be on lower
sideband (LSB). The FMT will replace the W1AW phone bulletin normally
transmitted at 0245 UTC on November 17 (November 16 in US time zones).
 Indirect measurement: The components of an SSB signal--shown here as LSB--form a sideband above (USB) or below (LSB) the carrier frequency. An SSB signal modulated by a single audio tone appears as a single transmitted signal offset from the carrier by the audio tone's frequency. |
Participants may utilize either direct or indirect techniques to determine the tone frequency. "Direct measurements assume a carrier frequency and measure the audio tone frequency directly," Silver explains. "Indirect measurements obtain the transmitted frequency of the tone component at RF, then compute the difference between the published carrier frequency and measured frequency."
Silver notes that a frequency counter display of the audio tone frequency using direct measurement techniques also will include receiver carrier-frequency errors as well as errors from noise and ionospheric Doppler shifts. "Please note that since the exciters are independent units (and not fed with a single local oscillator), expect the measured tone frequency to be slightly different on each band," he advised.
His article "The ARRL Frequency Measuring Tests," includes additional details on indirect and direct measurement methods.
Silver recommends that FMT participants listen to the W1AW CW or digital bulletin transmission prior to the FMT to determine which band will provide the best conditions for reception and measurement purposes. The test itself will consist of three 60-second tone transmissions on each band, followed by a station identification. The whole test will run for about 15 minutes and will end with a station ID.
Submitted report should include the time of reception and the tone frequency. "If you used an indirect method of measurement, show your calculation of the tone frequency," Silver requests. Participants should include name, call sign and location in their reports, and they may submit separate reports for each band. A Certificate of Participation is available to all entrants.
Those entrants coming closest to the measured frequency as determined by the ARRL Laboratory will be listed in the test report and will also receive special recognition on their certificate. Entries must be received via e-mail or postmarked by December 16, 2005. Send hard-copy entries to W1AW/FMT, 225 Main St, Newington, CT 06111.
The ARRL resurrected the FMT--an ARRL staple for nearly 50 years--in 2002. The first FMT, held in October 1931, employed three transmitting stations--W1XP at Massachusetts Institute of Technology, W9XAN at Elgin Observatory in Illinois and W6XK at Don Lee Broadcasting System in Los Angeles--and drew more than 200 measurement reports.
The increasing technical quality of amateur gear was one
of the primary reasons that the FMT was suspended in 1980. Even so, the fact
that operators continue to stray occasionally outside the amateur bands
suggested a need to revive the FMT.
| Previous: Dayton Hamvention® Says Better Communication a Key Goal for 2006 Show | Next: White House Nominates New FCC Commissioner, Copps Tapped for New Term |
