Once upon a time S units had a specific meaning as part of the RST
system.

S1 Barely perceptible
S2 Very weak
S3 Weak
S4 Fair
S5 Fair to good
S6 Good
S7 Moderately strong
S8 Strong
S9 Extremely strong.

But meter readings, with the exception of a few professional receivers,
have no real meaning other than one signal is stronger than the other.

Some receivers have "Scotch" S meters which read lower than people would
like ; but most modern consumer equipment has sensitive meters which
show even weak signals as the upper end of the scale and thus make the
receiver performance look better.

Then, of course you need higher numbers because even a fair signal is
S9. Solution? add more numbers - usually as dB above S9.

The other problem is that meter deflection is also affected by antenna
gain or loss. Hook up a long wire and that S2 becomes S8 - along with a
lot more noise.

The end result is that while an S meter may show the relative signal
strength on a specific receiver with a specific antenna, they have no
relevance to the readings on a different receiver and/or antenna or to
the true strength of the signal. Which is easily demonstrated:

WWV on 15MHz is currently S5, S7, S2 and S9 on four receivers here.
CHU on 3330kHz is currently S9+10dB, S1, S7, S4 on the same four
receivers.
All receivers are similar performance in terms of sensitivy and
bandwidth, but the HF antennas are all different.

So as a measure of signal strength, antenna and receiver performance S
units are largely irellevant. They are only useful as a measure of
relative strength of different signals on a specific antenna/receiver
combination.

Dave

Dave Holford wrote:

WWV on 15MHz is currently S5, S7, S2 and S9 on four receivers here.
CHU on 3330kHz is currently S9+10dB, S1, S7, S4 on the same four
receivers.
All receivers are similar performance in terms of sensitivy and
bandwidth, but the HF antennas are all different.

So as a measure of signal strength, antenna and receiver performance S
units are largely irellevant. They are only useful as a measure of
relative strength of different signals on a specific antenna/receiver
combination.


We're lucky speedometers aren't designed with the same philosophy.




mike

m II wrote:

Dave Holford wrote:

WWV on 15MHz is currently S5, S7, S2 and S9 on four receivers here.
CHU on 3330kHz is currently S9+10dB, S1, S7, S4 on the same four
receivers.
All receivers are similar performance in terms of sensitivy and
bandwidth, but the HF antennas are all different.

So as a measure of signal strength, antenna and receiver performance S
units are largely irellevant. They are only useful as a measure of
relative strength of different signals on a specific antenna/receiver
combination.

We're lucky speedometers aren't designed with the same philosophy.

mike


There was an intriguing short story written some years ago whose premise
was precisely that. Wish I could remember the title

Dave

m II wrote:

Dave Holford wrote:

WWV on 15MHz is currently S5, S7, S2 and S9 on four receivers here.
CHU on 3330kHz is currently S9+10dB, S1, S7, S4 on the same four
receivers.
All receivers are similar performance in terms of sensitivy and
bandwidth, but the HF antennas are all different.

So as a measure of signal strength, antenna and receiver performance S
units are largely irellevant. They are only useful as a measure of
relative strength of different signals on a specific antenna/receiver
combination.

We're lucky speedometers aren't designed with the same philosophy.

mike

BION- I have a 1994 Ford factory service manual which says they
intentionally made the speedometers read a little high, apparently to
encourage drivers not to speed. When the speedometer reads '65', the car
is going about '62'. However it also makes the gas mileage look better
too because the odometer shows more miles driven for the amount of gas
used. I suspect that's the real reason they did it.
I confirmed the speedometer error by installing the next larger size
tires than the OEM ones. It made my speedometer very accurate, less than
1/10-mile error in 40-miles, compared to about 1/2-mile with the factory
tires. I measured the mileage on an Interstate highway which had newly
installed mileage markers.


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That's a good guess, but ...

S7 on its own means 7 'S' Units in strength, not "Moderately Strong"
as per standard RST.

as for strength, that'd be 12 dB less than s9 which has been set to
represent a signal at 50 µV. 10 dB over s9 would represent 500 µV.
An s7 would be 16 times less than 50 µV, about 3.125 µV.

It's classic CB ignorance and miseduation that leads to the use of
such measures as s10 or s20 ... and such reports have been
being heard more and more outside the CB service in recent years since
the FCC has dumbed down the requirements for amateur radio licenses to
just about nothing: just memorize a question pool.


On Sun, 29 Aug 2004 12:11:57 -0400, Dave Holford
wrote:

Once upon a time S units had a specific meaning as part of the RST
system.

S1 Barely perceptible
S2 Very weak
S3 Weak
S4 Fair
S5 Fair to good
S6 Good
S7 Moderately strong
S8 Strong
S9 Extremely strong.

But meter readings, with the exception of a few professional receivers,
have no real meaning other than one signal is stronger than the other.

Some receivers have "Scotch" S meters which read lower than people would
like ; but most modern consumer equipment has sensitive meters which
show even weak signals as the upper end of the scale and thus make the
receiver performance look better.

Then, of course you need higher numbers because even a fair signal is
S9. Solution? add more numbers - usually as dB above S9.

The other problem is that meter deflection is also affected by antenna
gain or loss. Hook up a long wire and that S2 becomes S8 - along with a
lot more noise.

The end result is that while an S meter may show the relative signal
strength on a specific receiver with a specific antenna, they have no
relevance to the readings on a different receiver and/or antenna or to
the true strength of the signal. Which is easily demonstrated:

WWV on 15MHz is currently S5, S7, S2 and S9 on four receivers here.
CHU on 3330kHz is currently S9+10dB, S1, S7, S4 on the same four
receivers.
All receivers are similar performance in terms of sensitivy and
bandwidth, but the HF antennas are all different.

So as a measure of signal strength, antenna and receiver performance S
units are largely irellevant. They are only useful as a measure of
relative strength of different signals on a specific antenna/receiver
combination.

Dave