|[AMRadio] Anonymous QST Author suggests that Part 97 requires 6
jc at pctechref.com
Thu Apr 17 20:42:40 EDT 2008
I just don't get it. It has been many years since I have seen a
crowded band but who knows what the next sun spot cycle may bring! Beside's
Don, I have checked your bandwidth many times and found you to be very close
to the so called desired width of +/- 3300 Hz. I can't say with any
accuracy of course, but I have twisted the knob on the XTAL filter to a
narrow width, not very comfortable with CW even, and found your shots to be
very few and far between and weak out beyond 3.5KHZ. Not that they are not
occasionally there but another signal similar to yours could easily be
copied with a carrier just 5KHZ higher or lower than yours just by using the
phasing control a little.
What is it that makes certain folks so hateful? Let's talk about
hate. I hate those head lights with the extended blue range. One glance at
one of those and I see spots. What have I got to do, get a windshield with
a high end filter that rolls off the blues? I think there could be a song
in there somewhere. "Dem Headlites Dat Gime Da Blues"
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of D. Chester
Sent: Thursday, April 17, 2008 1:22 PM
To: amradio at mailman.qth.net
Subject: [AMRadio] Anonymous QST Author suggests that Part 97 requires 6
kHzAM Bandwidth Limit
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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