BDK ) writes:

In "pro" radios it might be true, but in hobby receivers, it's not true
that S-meters have any real correlation with signal strength in
comparing one radio to another.

Oh come on. The same model with the same factory adjustment would have
the same reading or very close. It would be reasonable to see a small
variation but a "huge" difference would indicate a problem with one of
the radios.



Obviously, your and my idea of "tolerances" isn't what theirs is. A
whole lot of radios are aligned "just good enough", or they need
touching up due to aging after a really short time.

But fundamental to all this talk about s-meters is that they never were
intended to be anything but a relative indicator. And once you have
that situation, there is little reason for the manufacturers to fuss
over them.

They are great to indicate at a glance that one station is stronger
than the other, and if you need to peak or null something they provide
a better indicator than your ears, and as I once saw suggested, they
are a great way to get a rough idea of whether your receiver is working
fine or not (just turn on the crystal calibrator when you first get the
receiver, and then record the s-meter readings on various bands. If those
start changing dramatically, then something is wrong, though it's no
indication of what might be weakening.).

Over the years, there's been lots of discussion of "how much is an
s-unit" and while some have tried to impose a value on it, there really
isn't anything to it.

Before there were actual meters attached to receivers, there were the
magic eye tubes, which had no scale at all. "You're about half open on
the magic eye tube..."

Want to give someone a better s-reading? Put up a bigger antenna, or
add a preamp ahead of the receiver. It will raise the meter reading,
but the signal as it arrives at your antenna hasn't changed one bit.


Before there were meters on receivers, there was the "RST"
system for rating signals. Readability/Signal Strength/Tone
that you'd transmit to the other guy to give an indication of
how his signal sounded at your receiver. It was all subjective,
but nevertheless likely helpful to some extent in the early days of
radio. Even today, some amateur radio contests require the exchange
of RST, though it's my impression that in those cases they
just send "59" or "599" (for code, the "T" relates to the tone of
the signal and doesn't apply to voice) to comply with the rules
and don't bother to actually send something that reflects the
state of the signal at their receiver.

From the 1961 ARRL Handbook, this is the how you are
supposed to interpret the Signal Strength code:
1 faint signal, barely perceptible
2 very weak signal
3 weak signal
4 fair signal
5 fairly good signal
6 good signal
7 moderately strong signal
8 strong signal
9 extremely strong signal

I can no longer remember if I read it outright years ago, or made an
assumption, but somewhere I got the impression that S-meters are
named after the RST system.

Given that, any attempt at defining an s-unit is retroactive, trying
to impose some absolute on something that has always been relative.

One of the silliest things I ever saw was a digital s-meter to attach
to CB sets. It was a 2-digit digital voltmeter, and you'd attach it
to the AGC line of your CB set (all s-meters are just voltmeters measuring
the voltage on the AGC line), and get flashy numbers. I can't recall
if it did anything to actual give the basic idea of s-units, or just
was a linear voltmeter. I'm sure it did sell well, because it was
the sort of gadgetry that would sell at the time, and the whole
concept of s-meters is so muddled that I'm sure the less technically
inclined would buy into the notion of digital s-meters.


Michael