Hi, Everybody,
I don't think there's any question that closing down your receiver's
bandwidth will lower the noise floor and improve the receive
signal-to-noise ratio, up to a point of diminishing returns as you
finally destroy signal intelligibilty due to severely restricted
bandwidth. Even the anti-widebanders, whom I will call narrowbanders
from here on out, can agree with that.
But we aren't always in a condition of trying to copy signals close to
the noise floor. In fact, the average ham dislikes doing so and will cut
a QSO short if the S/N ratio is degraded below a certain point. Except
for contests, in which a minority of hams participate, the vast majority
of amateur radio communications takes place with at-or-close-to S9
signals at both ends.
In this case, the arguments about narrowing your transmit bandwidth to
eke out every possible dB of S/N ratio and readability don't apply. We
have plenty of signal to work with, and playing with the bandwidth to
improve reception (notwithstanding adjacent channel QRM) is unnecessary.
But then in this case, the narrowbanders argue, you should still use the
absolute minimum bandwidth necessary to avoid QRMing the adjacent
frequencies.
However, there is another consideration: if we are to follow the letter
of the law (Part 97.313(a)) and use the minimum *power* necessary for
communications, then we should never hear S9 signals on the bands,
because that implies stations using more power than needed. There are
many hams who can copy a signal at or below the noise floor. Does that
mean that those hams should *always* do so? Because if I can copy a
signal which is equal to the noise floor, then that is the minimum power
level necessary for communications for me. For that signal to increase
above the noise floor is to be at a level greater than that level that
allows me to copy it intelligibly. Do you follow me?
(I am using "S9" to describe a strong signal as compared to the current
noise floor. The noise floor varies, of course, so S9 isn't always going
to be a strong signal. So, when I say "S9", substitute whatever level
qualifies as a "strong signal" under the circumstances.)
Imagine an SSB QSO between two hams:
W6--: How's my signal over there?
W5--: You're S9. You're too strong. Reduce your power.
W6--: Okay, how's this?
W5--: I can still hear you too well. Reduce more.
W6--: Okay, how's this now?
W5--: That's about right. I can barely hear you. You're in Part 97
compliance now.
Alright, enough of this absurdity. No one, not even an FCC observer,
would impose such a stringent interpretation of this rule. *Of course*
there is room for strong signals with plenty of spare S/N ratio, isn't
there?
Actually, this is what Part 97.313 (a) really says, and I quote:
a) An amateur station must use the minimum
transmitter power necessary to carry out the
desired communications.
Please note the word 'desired'. The inclusion of that word is really
important, because without it, this rule says essentially that we would
always have to conduct communications near the noise floor. But with it,
it means something very different, doesn't it? If I *desire*
communications at an S9 level, for whatever technical reason, not just a
whim of mine, wouldn't that be legal under 97.313 (a)? Please tell me we
don't need an attorney to clarify this.
Getting back to the bandwidth question: so why doesn't this argument
apply to bandwidth? This is what Part 97.307 (a) says, and I quote:
a) 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.
But not even the experts agree on what comprises 'necessary' bandwidth.
We've heard quotes from various scientists associated with Collins
Radio, now let's turn to another accepted authority, Frederick Terman,
who in the 1937 edition of Radio Engineering (Chapter IX, section 72)
states:
Understandable speech requires the
reproduction of all frequencies from about
250 to 2700 cycles, or side-band frequencies
ranging from 250 to 2700 cycles above and
below the carrier frequency.
So already we have a discrepancy.
And what about folks with hearing loss, especially selective hearing
loss that affects certain frequency ranges more than others? I don't
know if this qualifies as a hearing loss, but I suffer from a listener's
fatigue if I have to listen to too-narrow SSB bandwidths. My minimum
bandwidth necessary for a ragchew-length QSO may be wider than yours.
Sorry, that's just the way it is, and evidently Kenwood, Icom, Yaesu and
Ten Tec agree with me (not that they nor I are authorities on this!).
Your thoughts?
Al W6LX
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