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Author Topic: S-unit defined by IARU  (Read 1868 times)
WX7G
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« on: January 13, 2010, 04:13:31 PM »

S-unit defined by the IARU:

STANDARDISATION OF S-METER READINGS
1. One S-unit corresponds to a signal level difference of 6 dB,  

2. On the bands below 30 MHz a meter deviation of S-9 corresponds to an available power of -73 dBm from a continuous wave signal generator connected to the receiver input terminals,  

3. On the bands above 144 MHz this available power shall be -93 dBm,  

4. The metering system shall be based on quasi-peak detection with an attack time of 10 msec ± 2 msec and a decay time constant of at least 500 msec
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K0OD
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« Reply #1 on: January 13, 2010, 04:22:21 PM »

"Not all S Units are created equal. Depending upon the radio and the S Unit (S0 to S9), the value of an S Unit, as measured in dBs, changes quite a bit. It can range from less than 1 dB to almost 10 dB."

http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/SMeterBlues.htm
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W7ETA
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« Reply #2 on: January 14, 2010, 03:23:14 AM »

OK.
Now what?
73
Bob
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K0OD
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« Reply #3 on: January 14, 2010, 06:09:29 AM »

"STANDARDISATION" or is it spelled standardization? LOL

--
Flex radios are reputed to have accurate 6dB S-Units +/- 1 or 2 db on all bands. How accurate is the K3's meter?
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K0OD
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« Reply #4 on: January 14, 2010, 06:16:29 AM »

"3. On the bands above 144 MHz this available power shall be -93 dBm, "


Why should S-9 be different on 2 meters and above?
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N2EY
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« Reply #5 on: January 14, 2010, 08:42:30 AM »

"Why should S-9 be different on 2 meters and above?"

Lower noise?

73 de Jim, N2EY
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K0OD
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« Reply #6 on: January 14, 2010, 09:13:09 AM »

Now I'm REALLY confused by this "standardised/standarized" S-unit: It's an IARU REGION 1 "technical recommendation."

REGION ONE!  

Are we to have different S-Meters depending on where the radio is made/located or where a DX station we contact is located?

http://en.wikipedia.org/wiki/S_meter

Also seems to be disagreement about the frequency where the more conservative VHF scale kicks in: 144 mHz or 30 mHz?
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WX7G
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« Reply #7 on: January 14, 2010, 09:15:16 AM »

Standardisation is the English spelling of Standardization, which is the American spelling. Note that the IARU is the International Amateur Radio Union and not the ARRL.

S-units on the K3? I understand it is 5 to 6 dB per S-unit.

-93 dBm on 144 MHz and above vs -73 dBm below 144 MHz: I imagine this is so that S-1 remains near the atmospheric noise level; so that we don't need to give reports such as "you are 6 dB below S-1, OM."
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K0OD
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« Reply #8 on: January 14, 2010, 09:27:46 AM »

Some standard!

I can see why it's utterly ignored. How is an S-meter supposed to work on 6 meters which falls between the standards for <30 mHz and >144mHz.


BTW, I can't find an original copy of this recommendation from an IARU source on the web. Only secondary sources.
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WB2WIK
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« Reply #9 on: January 14, 2010, 01:28:03 PM »

I thought S-units expressed footlongs per fortnight = F/f.

At least mine are set up that way.
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WX7G
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« Reply #10 on: January 14, 2010, 03:48:08 PM »

The second cut at this standard in 1990 can be found at this link:

http://www.9h1mrl.org/VHF_Handbook_V5_35.pdf

On page 144 the 30/144 MHz descrepancy is fixed. It now specifies -73 dBm below 30 MHz and -93 dBm above 30 MHz.

Standards change and improve over time. The NIST definition of the VOLT has changed several times in the past 40 years. The NIST definition of the unit of length the METER has changed from a physical artifact to an electronically derived measurement.
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WX7G
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« Reply #11 on: January 14, 2010, 03:57:21 PM »

K0OD,

As noted the Flex is calibrated for 6 dB S-units and the Elecraft K3 for 5-6 dB S-units. These are the two highest performance amateur receivers, according to the Sherwood Engineering reports. These two manufacturers are evidence that the 6 dB/S-unit spec is not totally ignored.

Your assertions that standardisation is mispelled, that there is a 30/144 MHz descrepancy, and that the S-unit is totally ignored have been refuted. Have you other assertions to voice in your attempt to discredit the S-unit?
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K0OD
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« Reply #12 on: January 14, 2010, 04:49:27 PM »

I never said "standardisation" was misspelled. Its spelling just isn't standardized.  

The IARU "technical recommendation" is for Region One which includes only "Europe, Africa, Middle East and Northern Asia." I live in Region Two. My equipment was made in Region Two and Region Three (Japan).

That R-E-C-O-M-M-E-N-D-A-T-I-O-N was adopted in 1981. I remember reading about S-units being 6 (or sometimes 5) dB in the 1950s. The IARU, for God-Knows-What-Reason simply attempted to codify a long recognized but rarely realized goal.

I doubt that obscure 1981 IARU Region One recommendation amounts to a Hill of Beans. The internationally recognized "Hill of Beans" is defined as 1.5 Imperial Hogsheads.
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K0OD
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« Reply #13 on: January 14, 2010, 05:10:19 PM »

That EUROPEAN vhf manual does contain this interesting insight on page 136



http://www.9h1mrl.org/VHF_Handbook_V5_35.pdf


"8.6.1 SIGNAL REPORTING ( Recommendation R.1; R.2)
Although from the beginning of amateur radio signal reports have been essential, no formal standard for
the reports exists. But the "Readability, Strength, Tone" system with R,S and T values between 1 and 9 is
in widespread use. Several handbooks gave and give in words indications how the values are to be
understood.
The readability and tone reports are in principle "subjective" but the strength report can be objective as a
simple measurement of the received signal in voltage or power is possible. Such reports are in particular
at the VHF and higher frequencies useful for more precise evaluation of propagation, antenna properties
and receiver sensitivities.
At the IARU Region 1 Conference in Hungary 1978 the need for a harmonised standard for the "S-meter
scale" was expressed and a proposal was accepted for publication in society journals. The essential
recommendation was 1 S-point is 6 dB . At the Brighton Conference in 1981 the recommendation was
formally adopted as a standard for amateur radio equipment manufacturers.
At the 1990 Torremolinos conference an amendment was adopted which reconfirmed the -93 dBm
reference level for frequencies above 144 MHz, but no statement was issued for the bands between 30
and 144 MHz.
Although not explicitly stated the implication of the recommendation is that on VHF and higher frequencies
the S-meter will deviate on the thermal noise only ( S2 in 3 kHz bandwidth, S3 in 12 kHz bandwidth).
Although the recommendation is not too complex it seems to be rather difficult to implement by
commercial manufacturers.
Another matter is the Atone@ report. This is a subjective measure. It was important in the Aold
days@when rather primitive oscillators were used in the TX. Modern transmitters, even on the millimeter
bands, have in most cases a very good oscillator, resulting in a Apure tone@ and a T9 report is generally
given. On VHF and higher, however, the characteristics of the propgation medium can significantly
Amodulate@the signal ( doppler shift, spreading) and a T9 report is not possible. Definitions of tone
reports below 9 are rather vague. At the Region 1 conference 1999 in Lillehammer a recommendation
(R.2) has been accepted to use special letters for signal tone reports when the influence of the
propagation is detectable. Such reports can support propagation studies."
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WB2WIK
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« Reply #14 on: January 15, 2010, 05:32:08 PM »

Interesting it has a recommended definition, but I certainly don't care.

On HF, I guess the conversation would go like this:

"Your signal strength here is S7 to S9+10 dB.  Let me adjust the ionosphere to level that out and I'll get back to you."

:-)
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