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S-Meter Calibration Standards?
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"Avery Fineman" wrote in message ... Is there a standard RF input level per "S" Unit? If so, please post the location. Thanks. There is no "standard". You will often see it mentioned as 6 db of power per S-unit. At one time 50 microvolts into the receiver was S-9 and you went down 6 db of power per S-unit from there. I doubt that any receiver will follow that so called "standard". |
I find that most of them seem to sort of follow the rule that 4uV is S9, 3dB
down is each S-Point, that's for VHF/UHF. Sam "bviel" wrote in message ... The rule voor 50µV = S9 does still exists, this is voor HF, @50 Ohm input impedance at receiver. "They" (radioamateurs) use another rule for VHF. It's in the software MultiCalc, Google will find the adres, it's for free. Official or not, if everyone use this rule then it is a standard for me. Greetings Bas. "Avery Fineman" schreef in bericht ... Is there a standard RF input level per "S" Unit? If so, please post the location. Thanks. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.799 / Virus Database: 543 - Release Date: 24/11/2004 |
Avery Fineman wrote:
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. The Region 1 recommendation is: http://www.algonet.se/~k-jarl/ssa/IARU/smeter.html Google should also bring up the full technical paper behind this, and probably the current IARU recommendation. ISTR there's something on the ARRL website too. The 1990 Region 1 recommendation simply states that: 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. IARU functions very much like an Entmoot...only...not...quite...so...hoom...hasty. In 2004, they are just starting to think about the gap between 30MHz and 144MHz: http://home.hccnet.nl/a.dogterom/Vie...4_19_Chair.rtf But all the other comments about S-meters are true as well: that no S-meter actually conforms to this recommendation; that it makes no practical difference; and that hardly anyone cares. There's a very good web page with lots of practical measurements, at: http://www.seed-solutions.com/gregor...rimentation/SM eterBlues.htm -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
If you're wondering if S-meters are calibrated to some standard, the
answer is that they're not. S-meters simply read the AGC voltage, which is only approximately logarithmic. Therefore, the number of dB per S unit typically varies from one part of the scale to another. For example, the S-meter in my Icom 730, on 40 meters, preamp off, varies from 1.3 to 4.0 dB per S-unit depending on where on the scale you are. The "10 dB" increments over S-9 vary from 5.6 to 13.5 dB. Receiver manufacturers are free to make the sensitivity whatever they want, and seldom exceed about 5 dB per S-unit, because users complain that the meter is too "Scotch" (insensitive) if they do. There is a tendency for receivers to be calibrated to about 50 microvolts at one point on the meter, S-9, and there's often a calibration adjustment for this. Any "standard" is useless at best and misleading at worst, because it bears no relation to what S-meters really read. Roy Lewallen, W7EL Avery Fineman wrote: Is there a standard RF input level per "S" Unit? If so, please post the location. Thanks. |
On Fri, 26 Nov 2004 05:56:42 +0100, "bviel" wrote:
The rule voor 50µV = S9 does still exists, this is voor HF, @50 Ohm input impedance at receiver. "They" (radioamateurs) use another rule for VHF. It's in the software MultiCalc, Google will find the adres, it's for free. Official or not, if everyone use this rule then it is a standard for me. Greetings Bas. "Avery Fineman" schreef in bericht ... Is there a standard RF input level per "S" Unit? If so, please post the location. Thanks. 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 I installed an MC3356 log detector and calibrated it for S9 = 50uV. For about 15 years there has never been any signal of S9+30dB, most reports should be around 539....579, but again you logging problems, because everybody expect 599 and some log programs don't include the reports, they are supposed to be 599 73 Jan-Martin LA8AK (ex-G5BFV) --- J. M. Noeding, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/c.htm |
"Avery Fineman" wrote in message ... Is there a standard RF input level per "S" Unit? If so, please post the location. Thanks. My homebrew solid state receiver (see QRZ.COM) uses 5 dB per S-unit. S9 corresponds to -73 dBm available power, which is 100 microvolts open-circuit from a 50 ohm sig gen, or 50 microvolts into a 50 ohm load. Available power and open-circuit voltage are used because the input inpedance of the receiver is not guaranteed to be 50 ohms. I use 5 dB per S unit because it compresses the scale a little and it also agrees more closely with the intuitive listening test measure that I have used for many years. The upper end of the scale is 30 dB above S9, which is -43 dBm, a very strong signal. Signals stronger than S9+30 dB I don't bother to measure. At S1 the signal level is -73 - 40 = -113 dBm. Signals weaker than that S1 I don't try to quantify. My receiver has a low noise RF preamp with 8 dB of gain that I use on the 12 and 10 meter bands, when those bands are quiet. This makes the S meter less accurate but I don't worry about that. To get an S meter reading I turn off the preamp briefly. 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 |
"William E. Sabin" wrote in message ... "Avery Fineman" wrote in message ... Is there a standard RF input level per "S" Unit? If so, please post the location. Thanks. My homebrew solid state receiver (see QRZ.COM) uses 5 dB per S-unit. S9 corresponds to -73 dBm available power, which is 100 microvolts open-circuit from a 50 ohm sig gen, or 50 microvolts into a 50 ohm load. Available power and open-circuit voltage are used because the input inpedance of the receiver is not guaranteed to be 50 ohms. I use 5 dB per S unit because it compresses the scale a little and it also agrees more closely with the intuitive listening test measure that I have used for many years. The upper end of the scale is 30 dB above S9, which is -43 dBm, a very strong signal. Signals stronger than S9+30 dB I don't bother to measure. At S1 the signal level is -73 - 40 = -113 dBm. Signals weaker than that S1 I don't try to quantify. My receiver has a low noise RF preamp with 8 dB of gain that I use on the 12 and 10 meter bands, when those bands are quiet. This makes the S meter less accurate but I don't worry about that. To get an S meter reading I turn off the preamp briefly. 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 My receiver also has a 20 dB antenna input attenuator that can be switched in from the front panel. This extends the upper signal range to S9 + 50 dB. I use it very rarely. Bill W0IYH |
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. |
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