"Ken Scharf" wrote in message
...
On HF there is no need for an S-meter standard because it seems to be
the rule to give report 59. If you don't you soon have a bad
reputation of giving wrong reports

A signal doesn't have to be S9 to be heard 5 by 9.
I would usually tell the guy on the other end what
the S meter read, and also how readable he was.
When the band is quiet QRN wise, I could honestly
give a 59 report to someone hardly moving the meter.
OTOH with heavy QRM+QRN someone could be pumping
30db over and still be a rough copy.

Then you are still passing out wrong signal reports. The first one would be
something like 5 x 2 or 5 x 3 and the second one would be 2 x 9 or 3 x 9.

The first number is how well you can understand what is being said and the
second is how strong the signal is.

There has been a de-facto HF standard for 60 years.

The USA military first used it in specifications of radio equipment when
placing contracts with manufacturers around the end of WW2. There may have
been some restrictions on publicity at the time.

The Standard is 6 dB per S-unit and 50 micro-volts into 50 ohms at S=9.

Therefore an S-meter is essentially a power or wattmeter.

The Standard is quite logically derived.

The 6 dB fits in very nicely between a typical receiver's internal noise
level (S=0) and a typical receiver's signal overload point (S=9+30 or 40
dB).

S=9 is about half way up the scale which is linear in dB's, or S-units, from
one end to the other.

There's nothing wrong with the standard. If your S-meter reads incorrectly
then don't blame the standard - re-calibrate the meter. If you can't
re-calibrate it blame the poor quality of the meter.

I have two relatively modern commercial transceivers plus two home-brewed
transceivers. Their S-meters are accurate enough for the intended purpose.
What more should I expect?
----
Reg, G4FGQ

In article , "William E. Sabin"
writes:

My receiver has a custom made, computer printed scale using a calibrated sig
gen, and there are two trimpot adjustments, one for the low end and one for
the high end. This circuit uses voltage regulated opamps. The S meter
dynamics are adjusted using RC time constants.

My S meter is accurate within +/- 2 dB from 160 M to 10 M, because the
receiver is designed for this accuracy. Because of the IF and RF circuit
design, the scale calibration is fairly correct and reliable, as I
mentioned.

Bill W0IYH

Thanks, Bill. I'm doing essentially the same...and expect the overall
receiver response to the flat within +/- 1 db within an octave and a
half tuning range. Accuracy of the S-Meter is only as good as the
RF level accuracy of the calibrating RF source but that's another
task and I have confidence in that. But, I have to start someplace
and that is why I asked about a "standard." I know that the U.S.
military didn't bother with any receiver S-Meter calibration standards
since around 1980, only approximate differential signal strength
readings if there was an indicator at all.

In article , Roy Lewallen
writes:

Any "standard" is useless at best and misleading at worst, because it
bears no relation to what S-meters really read.

Roger that, and I've heard all kinds of "599" reports on-air, too. :-)

In the project I have on-going, this receiver's S-Meter (there mainly
for nostalgia purposes and because I've gotten a few old-style
microammeters that I can use) will read the average carrier power
(integrated to a time-constant yet to be settled on) at the AM
detector using a half of a quad op-amp integrator. That same
detector provides the AGC control line with appropriate DC offset
for the MC1349 gain blocks, but with (maybe) different integration
time-constants. As for the RF input to the antenna connector,
that is known within +/- 2 db down to -130 dbm by separate
calibration of my HP 608 or 606 signal generator. When
completed, this particular receiver S-Meter will be as accurate,
with a custom scale plate, as that signal generator output will
allow.

Of course, to fit the "convention" of those gratuitous "599" reports,
I could borrow from the auto industry's cheapie "gas gauge" which
has a single bulb showing "low gas" on the dashboard...using an
LED driven by an op-amp integrator-comparator for high-tech.
The indicator would show "I got signal" or "I got noise" to fit... :-)

In article , "Ian White, G3SEK"
writes:

Is there a standard RF input level per "S" Unit?

If so, please post the location. Thanks.

There is an IARU recommendation, which originated in Region1
(Europe/Africa) and I believe has been adopted by IARU world-wide.

Thanks, Ian, and thanks to all others responding. A plus to Reg
Edwards for mentioning the U.S. military receiver specs which
I was hunting around for but could not find. :-(

Reason for asking is that I'm going to make a meter scale for a
little receiver a-building, using (nobody blanch, please) MS
Paint from a scanner (accurate 1:1) digitization of the removed
meter scale plate. I've done that with a normal-expanded scale
meter on a 120 W variable autotransformer box used on the
bench. MS Paint will do color in 256-color mode for a better
appearance. An inkjet printout on heavy photo paper stock
results in a fine-grain scale sturdy enough to replace the stock
plate in a little 2 1/2" microammeter.

Note: That works only on the old-style meters with removeable
scale plates (screw mounting type). Newer snap-together plastic
case types aren't recommended for that.

That method started on wondering how accurate an ordinary
scanner was...solved by scanning a 6-inch metal scale, printing
it, then comparing the real scale to the printout. By eyeball it
was dead-on! :-) I've done that for drill guides on PC board
stock used for both circuit boards and small enclosures since
and find it very time-economical. Machine shop accurate it isn't
but then my home shop drill locations were never that accurate
using scribe marks on "dye-chem" blue lacquer painted on
aluminum. :-) [rubber cement holds the paper printout on the
work, removes easily afterwards]

Most people appear to be fatally attempting to use, in reverse, their
favourite S-meter as a means of calibrating the Standard. No wonder we have
so many different standards around.

The difficulties in making an accurate power meter lie solely in the very
wide range of power levels encountered.

0 to S-9 corresponds to 9 times 6 dB = 54 dB.

S-9 to +40 dB corresponds to 40 dB.

Making a very high total range of 94 dB for a power meter.

That explains why S-9 usually appears just over half way up the scale.

For a range of 94 dB it is not beyond modern technology to make a linear dB
scale out of it. The limitation is manufacturing cost. But who wants to pay
an extra hundred dollars to replace a receiver they are already happy with.

Of course, if you MUST have an accurate S-meter, the cheap way is to obtain
a blank meter scale, a fine-nibbed pen, a bottle of black ink, a signal
generator, and a 0-100 dB switched attenuator. You will proudly end up with
a work of art and a beautifully cramped scale at the bottom end. But when
done it's as accurate as you like!

Hint: There's no need to obtain a new blank scale if the existing scale can
just be turned over to its white side. Such small divergencies can make
restful breaks in between investigations of skin depths at 1 to 10 Hz of the
ocean bottom of transatlantic submarine cables.
----
Reg

Just to tidy up.

And I've been through this before but I'm just a bloody foreigner who
favours French wine.

The S-meter is a power meter.

The standard receiver input impedance is 50 ohms.

That's why you get a conjugal match when you switch the transmit tuner from
transmit to receive but you don't get such a match when you switch back.

The standard, HF, 50 microvolts at S-9 into 50 ohms corresponds to 50
pico-watts which is an inconvenient quantity to refer to in signal strength
reports. Hence the popular S-units.

S-9 requires a standard 50-ohm signal generator, set to a standard
open-circuit 100 micro-volts, to be connected to the receiver. Receiver
manufacturers in their maintenance manuals usually prescibe this at the
non-descript frequency of 7 MHz.

The internal thermal and other noise level of a typical receiver with an
input stage consisting of a balanced modulator (the first frequency
changer), referred to the receiver's input terminals, with a receiver SSB
bandwidth of 4 KHz, is of the order of 60 dB below S-9. That is a little
less than S-zero on the meter. A signal level of the same order as the noise
takes the meter to S-zero.

A signal level of S-9 plus 40 dB, or 40 dB above 50 pico-watts, corresponds
to a signal input voltage of 50 micro-volts times 100 which equals 5
milli-volts. At which point a good receiver begins to overload and suffers
from non-linear intermod products.

Hence we have a meter range of 54 + 40 = 94 dB as displayed on a typical
meter.

All this fits in very nicely with the recognised S-meter Calibration
Standard.

(I do hope I have not made an arithmetical error. But I'm sure you Americans
get the general idea nevertheless.)
----
Reg, G4FGQ

"Reg Edwards" wrote in message
...

Most people appear to be fatally attempting to use, in reverse, their
favourite S-meter as a means of calibrating the Standard. No wonder we
have
so many different standards around.

We have seen a dozen or so posters indicate that S9=50uv

Nowadays, very few rigs have analog meters. Instead, they have a computer
that can take that AGC voltage and display it however the computer decides.

In the Icom calibration procedure for the 706, there are three calibration
points known by the computer ... S0 (0 uv), S9 (50 uv), and S9+60 (50 mv).
The calibration procedure sets these three with known inputs, and presumably
the computer interpolates from there. That really isn't a bad calibration,
and I'd be surprised if other modern rigs were much different.

Now it is quite likely that there is some dependence on the AGC voltage with
frequency, but again, in a modern rig that should be manageable.

What isn't so constant, of course, is the antenna. The voltage at the
receiver could range over several orders of magnitude for the same signal
depending on the antenna. So in terms of providing input to the sender, the
S meter reading is still of limited usefulness, even if we all had
calibrated radios and agreed that S9=50uv.

...

The 756 pro is "properly" calibrated, each S-Point is individually
calibrated.

Sam
"xpyttl" wrote in message
...
"Reg Edwards" wrote in message
...

Most people appear to be fatally attempting to use, in reverse, their
favourite S-meter as a means of calibrating the Standard. No wonder we
have
so many different standards around.

We have seen a dozen or so posters indicate that S9=50uv

Nowadays, very few rigs have analog meters. Instead, they have a computer
that can take that AGC voltage and display it however the computer
decides.

In the Icom calibration procedure for the 706, there are three calibration
points known by the computer ... S0 (0 uv), S9 (50 uv), and S9+60 (50 mv).
The calibration procedure sets these three with known inputs, and
presumably
the computer interpolates from there. That really isn't a bad
calibration,
and I'd be surprised if other modern rigs were much different.

Now it is quite likely that there is some dependence on the AGC voltage
with
frequency, but again, in a modern rig that should be manageable.

What isn't so constant, of course, is the antenna. The voltage at the
receiver could range over several orders of magnitude for the same signal
depending on the antenna. So in terms of providing input to the sender,
the
S meter reading is still of limited usefulness, even if we all had
calibrated radios and agreed that S9=50uv.

..




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Ralph Mowery wrote:
"Ken Scharf" wrote in message
...

On HF there is no need for an S-meter standard because it seems to be
the rule to give report 59. If you don't you soon have a bad
reputation of giving wrong reports


A signal doesn't have to be S9 to be heard 5 by 9.
I would usually tell the guy on the other end what
the S meter read, and also how readable he was.
When the band is quiet QRN wise, I could honestly
give a 59 report to someone hardly moving the meter.
OTOH with heavy QRM+QRN someone could be pumping
30db over and still be a rough copy.


Then you are still passing out wrong signal reports. The first one would be
something like 5 x 2 or 5 x 3 and the second one would be 2 x 9 or 3 x 9.

The first number is how well you can understand what is being said and the
second is how strong the signal is.


If you mean the actual strenth of the signal in uv at the antenna,
then you are correct. If you mean the strength of the signal in your
EARS that's another story. One is an actual measurement, the other
is subjective. (How would you measure signal strength if you
were using a receiver without an s meter, such as an old SW3?)