LF: S-meter readings...]
Tue, 04 Apr 2000 14:00:49 -0400
> Steve Olney wrote:
> > G'day All,
> > I have a question about something that has puzzled me for some time now.
> > It concerns the procedure for giving signal reports. I understand the
> > scale for readability - no problem. The problem I have is with the the
> > signal strength part. The R part is a relative indication - relative to
> > QRM/QRN etc, as I understand it. But what about the S part?
> > In the case of a receiver which at the frequency and time of the received
> > signal has an S-meter reading where the needle is just moved off the stop in
> > the absence of a signal - an S-meter reading of 5 on a signal would seem to
> > warrant a report of S5.
> > However, the same receiver which might have a preamplifier added and at the
> > time and ferquency of the received which has a no-signal reading of say 3.
> > If that receiver now receives a signal which moves the S-meter up to a
> > reading of 8 - what is the appropriate report for the signal? S8 or S(8-3)
> > = S5?
> > It seems to me that it is possible to have a high level of noise with a
> > small signal which is barely readable but giving a S-meter reading of 8.
> > Isn't closer to the truth to be giving S-points above the noise or am I
> > missing the point?
> > 73s Steve Olney (VK2ZTO/AXSO - QF56IK : Lat -33 34 07, Long +150 44 40)
> Ideally one would use field strength to describe incoming signals, as
> field strength is independent of the antenna and receiver. However, the
> need for a calibrated antenna and receiver is a bit over the top for
> amateur operators. The antenna has a changing "k factor" with
> frequency. The field strength of the signal and noise could be
> determined. As well, most field strength meters have linear meter
> scales and no AGC applied to the RF or IF stages.
> A communications receiver usually has internal AGC, and an "S meter"
> that is operated by AGC voltage. A receiver with AGC can not avoid
> having a compressed S meter scale that is approximately logarithmic, and
> is an advantage if a wide range of strengths is to be displayed on a
> single meter scale, where accuracy is nominal. Ideally, the S meter
> should read S9 for 50 microvolts applied to the RF input to the receiver
> at the tuned frequency. Each S point below that is supposed to be -6
> dB per point. On most ham gear the S meter is gratuitously known by
> some as a Guess Meter.
> Bob ZL2CA