S-meters (copied from the Homebrew newsgroup)
 

S-meters are nothing else but power (input) meters.

Amateurs and meter manufacturers long ago learned, that when giving signal
strength reports, it is more convenient to refer to meter indications in
terms of S-units rather than micro-watts or nano-watts.

At HF, when the meter reads S-9 the power entering the receiver is 50
pico-watts. There's a slight complication above S-9 when the meter scale
changes to decibels above S-9.

When the reading is S-9 plus 40 dB the meter is actually indicating about
S-16. It's just a matter of scale graduations and printing.

The S-meter does NOT measure or even indicate field strength. It indicates
nothing except that an increase in meter reading corresponds to an increase
in field strength. Which may be nice to know but by how much of an increase
is anybody's guess.

Measured field strength depends on the type of antenna, its efficiency,
ground losses, etc. It is possible, of course, to calculate field strength
in the vicinity of the antenna from S-meter readings provided the antenna,
its directivity, transmission line, tuner and ground characteristics are all
known numerically. Which in the amateur situation they are seldom not! Or
even in the professional situation.

You've all got one. To repeat - the S-meter is a power (input) meter.
----
Reg, G4FGQ

On Sat, 27 Nov 2004 18:05:48 +0000 (UTC), "Reg Edwards"
wrote:
You've all got one. To repeat - the S-meter is a power (input) meter.

BAFFLEGAB!!!! It's a reception line indicator (RLI). If the line
falls down, so do the readings. ;-)

73's
Richard Clark, KB7QHC

I think S meters should be calibrated in dB uV/m, or at least dBm input.

Frank


"Richard Clark" wrote in message
...
On Sat, 27 Nov 2004 18:05:48 +0000 (UTC), "Reg Edwards"
wrote:
You've all got one. To repeat - the S-meter is a power (input) meter.

BAFFLEGAB!!!! It's a reception line indicator (RLI). If the line
falls down, so do the readings. ;-)

73's
Richard Clark, KB7QHC

Rich, your jestful response is an absolute confirmation that my description
of the function of S-meters is the correct one.

Thank you!
----
Yours, gratefully, Punchinello.

On Sat, 27 Nov 2004 19:43:24 GMT, Frank hath writ:

"Richard Clark" wrote in message
...
On Sat, 27 Nov 2004 18:05:48 +0000 (UTC), "Reg Edwards"
wrote:
You've all got one. To repeat - the S-meter is a power (input) meter.

BAFFLEGAB!!!! It's a reception line indicator (RLI). If the line
falls down, so do the readings. ;-)

I think S meters should be calibrated in dB uV/m, or at least dBm input.

Don't the S-meters on 11 Meter radios read out in pounds?

73
Jonesy
--
| Marvin L Jones | jonz | W3DHJ | linux
| Gunnison, Colorado | @ | Jonesy | OS/2 __
| 7,703' -- 2,345m | config.com | DM68mn SK

Hello All -

This reads like a tongue-in-cheek bit of good-natured trolling... but I have
added a few comments, just in case some newbie takes it all too seriously.

"Reg Edwards" wrote in message
...

S-meters are nothing else but power (input) meters.

Actually, the tradition has been to characterize S-meter calibration
(if I may call it that) in terms of voltage, not power. Of course, the
two may be translated freely if one assumes an input impedance.

More significantly, the typical signal-strength indicators on receivers
are not ANY kind of "meters"--in the sense of comprising calibrated
test equipment. A minority of higher-end receivers MAY receive a
quick stab at meter calibration in the alignment process; and they MAY
have flat enough gain versus frequency for that calibration to apply
roughly across their frequency coverage. But I wouldn't count on it.

Amateurs and meter manufacturers long ago learned, that when giving signal
strength reports, it is more convenient to refer to meter indications in
terms of S-units rather than micro-watts or nano-watts.

Amen to that.

At HF, when the meter reads S-9 the power entering the receiver is 50
pico-watts. There's a slight complication above S-9 when the meter scale
changes to decibels above S-9.

The "at HF" qualifier is curious, since the propositions are not frequency
dependent. But 50 pW does indeed match up to the traditional 50 uV,
if I did my math right.

When the reading is S-9 plus 40 dB the meter is actually indicating about
S-16. It's just a matter of scale graduations and printing.

A very important omission here is the traditional assumption that each
S-unit should represent a 6 dB change. My FT-1000D shows substantial
departures from this ideal, BTW.

But since the S-unit scale is an attempt to quantify the S1 through S9 range
of the classic RST signal reporting scheme, there is no such thing as "S
units" above S9, the highest. Hence the "dB over" nomenclature.

The S-meter does NOT measure or even indicate field strength. It
indicates nothing except that an increase in meter reading corresponds
to an increase in field strength. Which may be nice to know but by
how much of an increase is anybody's guess.

This is more realistic, although nits could be picked.

Measured field strength depends on the type of antenna, its efficiency,
ground losses, etc. It is possible, of course, to calculate field
strength in the vicinity of the antenna from S-meter readings provided
the antenna, its directivity, transmission line, tuner and ground
characteristics are all known numerically. Which in the amateur
situation they are seldom not! Or even in the professional situation.

You've all got one. To repeat - the S-meter is a power (input) meter.

S-meters are relative signal strength indicators. Some of them MAY match
the "ideal" response at a few input levels and input frequencies.

----
Reg, G4FGQ

So I cant resist

We had a similar discussion on the VK-VHF NG (a closed NG). The general
consensus for VHF/UHF SSB use as summarized by Gordon VK2ZAB was;
--------------
The scale is:
S9 = -93 dbm = 5 uV into 50 ohms.
S8 = -99 dbm = 2.5 uV
S7 = -105 dbm = 1.25 uV
S6 = -111 dbm = 0.625 uV
S5 = -117 dbm = 0.313 uV
S4 = -123 dbm = 0.156 uV
S3 = -129 dbm = 0.078 uV
S2 = -135 dbm = 0.039 uV
S1 = -141 dbm = 0.02 uV - Note that this fortuitously corresponds to the
level, on Earth, of the power due to thermal noise in a bandwidth of
2000 Hz.
And if you like:
S0 = -147 dbm = 0.01 uV
S-1 = -153 dbm = 0.005 uv
S-2 = -159 dbm
S-3 = -165 dbm
S-4 = -171 dbm
S-4.5 = - 174 dbm Note that this fortuitously corresponds to the level,
on Earth, of the noise power due to thermal noise in a bandwidth of 1Hz.
Those that wish to do so may exercise their arithmetic skills by
determining what S point and /or dbm level corresponds to the noise
power at say one [1] degree above absolute zero - which may exist
somewhere in space.
-------------

Note that there was a lot more discussion about the use/misuse of S
meter reports. I thought the scale the more useful though.

Cheers Bob VK2YQA



Old Ed wrote:
Hello All -

This reads like a tongue-in-cheek bit of good-natured trolling... but I have
added a few comments, just in case some newbie takes it all too seriously.

"Reg Edwards" wrote in message
...

...... etc

"Frank" wrote in message
news:wN4qd.217617$9b.158132@edtnps84...
I think S meters should be calibrated in dB uV/m, or at least dBm input.

Frank


You cannot do that. Even on a good meter (like a spectrum analyzer or an EMI
receiver), the meter is calibrated only for input power at its front panel
connector. You still have to add a frequency dependent correction factor for
cable loss and antenna efficiency. Very expensive measurement systems
operate under computer control, with a calibrated analyzer and the computer
adding the appropriate factors for cable loss and antenna factor. (This
allows for flexibility; a different coax or antenna can be substituted at
any time, so long as the computer has a table of factors for the new
device.)

As for how you mark the S-meter scale, I agree that we use an archaic system
with S-units. It would be more rational to use a simple dB scale referenced
to something like 1 picowatt (which would then become 0 dBpW). OTOH, the
purpose of an S-meter is not to provide absolute measurements. It is used as
a tuning indicator and for relative signal strength comparisons. And the
archaic marking system works fine for that need.

Ed
wb6wsn

"Old Ed" wrote in message
nk.net...
Hello All -

This reads like a tongue-in-cheek bit of good-natured trolling... but I
have
added a few comments, just in case some newbie takes it all too seriously.

"Reg Edwards" wrote in message
...

S-meters are nothing else but power (input) meters.

Actually, the tradition has been to characterize S-meter calibration
(if I may call it that) in terms of voltage, not power. Of course, the
two may be translated freely if one assumes an input impedance.

More significantly, the typical signal-strength indicators on receivers
are not ANY kind of "meters"--in the sense of comprising calibrated
test equipment. A minority of higher-end receivers MAY receive a
quick stab at meter calibration in the alignment process; and they MAY
have flat enough gain versus frequency for that calibration to apply
roughly across their frequency coverage. But I wouldn't count on it.

Amateurs and meter manufacturers long ago learned, that when giving
signal
strength reports, it is more convenient to refer to meter indications in
terms of S-units rather than micro-watts or nano-watts.


Hams can use S-units, but I really prefer antenna manufacturers to stick
closer to physics and give me real gain in dB or numeric.

Ed
wb6wsn

Hi Other Ed -

I have to agree that S-units have little or no role in specifying antennas.

Ed

"Ed Price" wrote in message
news:Vnbqd.4491$KO5.2116@fed1read02...

Hams can use S-units, but I really prefer antenna manufacturers to stick
closer to physics and give me real gain in dB or numeric.

Ed
wb6wsn