[Elecraft] K3: S-meter calibration (redux)

[Bill W5WVO]

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: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] 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
>