Ron D'Eau Claire wrote:
The only historically (and in practice correct) measurement is to
listen to the signal by ear and judge the "S-reading". If the meter
doesn't agree with what you decided by listening to the signal
without referring to the meter, the meter is wrong.
I agree, Ron, in the context of giving on-air signal reports to stations as
you establish QSO with them. I always give by-ear signal reports, which
basically means going by the old established verbal definitions -- Barely
detectable (S1), Weak (S3), Fair (S5), and so forth.
Having said that, a calibrated strength meter affords the capability to make
reasonably accurate strength comparisons between different signals when doing
so makes sense. But why use S-units on the meter at all? There was a very
reasonable argument made back during the original incarnation of this thread
(by Craig, VK3HE) that a calibrated strength meter shouldn't be an "S-meter"
at all, since the original subjective, relative meaning of a strength report
couldn't possibly be meaningful when rendered by an instrument making an
absolute, out-of-context measurement -- and that the strength meter really
should read out directly in dBuV. According to Craig, all modern commercial
and military communications receivers are now doing this.
I think this argument holds a lot of merit, but my guess is that many (if not
most) hams would howl in protest at not having an "S-meter" on their rig. So
if we have to have one of the blinkin' things, it should at least read out
something that is more or less sensible. Having the no-antenna receiver noise
floor reading out at S1-S2 is not sensible IMO, so if you must have a 6-dB
S-unit, the S9 signal level has to go higher than 50 uV. In short, I think
TenTec got it right.
Bill / W5WVO
Ron AC7AC
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Bill W5WVO
Sent: Wednesday, June 06, 2007 6:39 PM
To: [Elecraft]
Subject: [Elecraft] K3: S-meter calibration (redux)
To recap: In a thread on this list back when the K3 was first
announced, there was a good deal of debate about how many dB an
S-unit should be on a calibrated S-meter. It was pointed out that if
an S-unit is 6 dB, then a signal at the receiver noise floor would be
between S1 and S2 on the meter, which seems rather high; a 5-dB
S-unit, for example, would put the noise floor a lot closer to where
it intuitively belongs on the meter. But it was also pointed out that
the 6-dB S-unit has very deep historical roots, and in IARU Region 2,
it's a published spec, not a matter of endless debate.
All this discussion was based on the universal assumption that S9 is
by definition hard-pegged at 50 uV. It was the one assumption no one
questioned.
Today, ARRL Labs' review of the new TenTec OMNI VII was published on
their website (members only), and it was revealed that the OMNI VII
S-meter is in fact accurately calibrated at 6 dB per S-unit -- but
that S9 is pegged at 67 uV, not 50 uV! Using this higher threshold
for S9 and a 6-dB S-unit, the noise floor drops down to where it
should be -- somewhere between S0 and S1. A 10 dB S+N/N signal of 0.5
uV comes in around an intuitively reasonable S2.
To me, this seems like an elegant and creative solution to the "6-dB
problem," drawing a sensible compromise between tradition and
engineering common sense. It will be interesting to see where the K3
comes down in all this. There seems little doubt that the K3 and the
OMNI VII (in that order, #1 and #2) are going to dominate the
"center" of the transceiver market for a long time. By all rights,
IKenSu should be completely shut out once both the K3 and the OMNI
VIII are in the marketplace. They will have to depend on marketing
hype and brand loyalty -- but who knows, that may be enough to keep
them in the game until they can catch up. IF they can catch up. :-)
Bill / W5WVO
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