|[AMRadio] Anonymous QST Author suggests that Part 97 requires 6 kHz
k4kyv at charter.net
Thu Apr 17 14:22:26 EDT 2008
On p. 64 of the May issue, the anonymous writer of the monthly Q-A
"Workbench" column in QST entitled "The Doctor is In", responds to a report
by the coordinator of the ARRL OO program regarding "wide AM signals with
bandwidths of up to 30 kHz on 75 m."
He briefly explains the relationship between signal bandwidth and the
frequency response of the audio that modulates SSB and AM transmitters, then
states that Bell Labs concluded many years ago that high quality voice
transmission (toll quality in telco terminology) can be carried over a
300-3300 Hz frequency response, but that "This worked better for the
grey-haired Bell scientists who were likely to have lost some of their high
frequency hearing". He goes on to allege that an AM signal occupies "a bit
more spectrum" than two SSB signals, based on the notion that there is no
need to transmit audio frequency components of the voice that fall below 300
Hz, and that the "usual approach" with SSB is to transmit frequencies from
300 to 2700 Hz.
He then cites §97.307 of the FCC rules that states "No amateur station
transmission shall occupy more bandwidth than necessary for the information
rate and emission type being transmitted, in accordance with good amateur
practice." Since voice is what is being transmitted, he suggests that the
rules require AM to occupy a bandwidth of "no more than about 6 kHz".
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