[AMRadio] Anonymous QST Author suggests that Part 97 requires 6 kHz


D. Chester 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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