[Elecraft] K2 S Meter

Tue Apr 8 00:53:04 2003

Ron, you may have another radio in mind, but the earliest one I recall with
a calibrated gain control was the little regen made by National in the 30's.

Incidentally, the numerals on that one were termed "R" units since in those
days prior to the RST system, signal strength was informally reported on an
R1 to R9 scale, which is how the dial of the gain control knob was
calibrated.

Sorry I don't recall the model number or name of the National but it was
something like the SW-3. I believe that it had two tubes, a regen detector
and one stage of audio.

As a side note, now that our super receivers have such excellent multi-loop
AGC systems, one finds it very difficult to tell much about the strength of
a signal by how much sound it makes. The audio output may vary on a few dB
at most for a 100-dB change in signal level at the antenna terminals. Maybe
that is why the default "599" signal report obtained on all contest contacts
is as good and as meaningful as any when most signals all sound about the
same loudness.

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"In the 57th year and it just keeps getting better!"
<mailto:[email protected]>

----- Original Message -----
From: "Ron D'Eau Claire" <[email protected]>
To: <[email protected]>; "'Elecraft'" <[email protected]>
Sent: Monday, April 07, 2003 7:01 PM
Subject: RE: [Elecraft] K2 S Meter

Ha!!!

Your observation is right on, John!  All the S-meter is doing is monitoring
the automatic gain control voltage that does electrically what your RF gain
knob does manually.

Indeed, back in the 1930's when "S" meters were just starting to show up on
the most expensive receivers, some manufacturers "calibrated" the gain
control in "S" units. You set the gain for a comfortable listening level and
looked at the number under the pointer on the knob to determine the "S"
reading. Just what you can do with the K2 by looking at the bar graph as you
discovered.

The "S" from RST was, of course, part of a "by the ear" system of evaluating
the other station's signal. The RST system caught on among Hams in the
1920's as they struggled to reduce key clicks, yoops and chirps, and
tinkered with better power supplies to get the AC hum on their signals down
to something that at least sounded "musical".  A 1-5 scale for "Readability"
was borrowed from the commercial "QSA" code in which a signal is reported by
a single digit from 1 to 5 with the "5" being "armchair copy".

S for signal Strength and T for Tone were given 9 possible values,
indicating about the range of changes that an ops ear could discern.

But, just as today, us "techno-nuts" were fascinated by numeric readouts and
"graphical displays". Only in 1930 those were wiggling meters on calibrated
scales, not digital displays and computer screens. As soon as
superheterodyne receivers started using AGC to manage the gain, someone
caught the idea of measuring the AGC voltage and the S-meter was born and
became a rather useless but absolutely indispensable part of any REAL Ham
receiver.

So, at best, an "S" meter is a way to noticing if the other guy's signal is
changing up or down... assuming you can't hear it changing. VERY roughly
speaking, an "S" unit is about 6 dB or a 4:1 power change. That is, if you
up your power from 5 to 20 watts, your signal will have increased about 1
"S" unit at the receiving end. Go from 20 to 80 watts and it'll be another
"S" unit stronger.

At it's worst, it's used to decide what the other op's "S" report should be
no matter what you ears tell you.

 In any case, it's a part of Ham Radio history that few ops want to do
without.

If you want to start a real argument among Hams, just ask how an "S meter"
should be calibrated!! Once they were included in manufactured receivers,
the manufacturers had to decide how to adjust them to make sure the receiver
worked when it left the factory. Various manufacturers adopted various
standards, and those arbitrary standards have become law to some Hams.

Me, I set my K2 S-meter by tuning in an "average" signal, deciding that it
was about S-7 by ear, then I adjusted the S-meter to say S-7. Now the
S-meter and I agree so I don't have to look at it any longer.

But, you know something? If my S-meter quit working, I'd probably fix it.
After all I am a Ham.

Ron AC7AC
K2 # 1289

-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of John Lucas

Could someone plese explain the correct use of the S meter.

To this rooky it seems I can give any signal any S reading by changing the
RF gain!

thanks
John
[email protected]

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