Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
db relation TX/RX
www.qsl.net/k5lxp/projects/SMeter/SMeter.html
Check the chart to see actual input readings. I've always used the (6db per S unit) as a general rule-of-thumb. |
#2
|
|||
|
|||
db relation TX/RX
Rollie wrote:
.. . .I've always used the (6db per S unit) as a general rule-of-thumb. Which is fine if you don't mind possibly being off by a factor of 50 or more, mistaking the gain of a 3 element beam for the gain of a 150 element one. Or you might only be off by a factor of 10, thinking the 3 element beam only has the gain of a 30 element beam. Shucks, what's a few dB anyway. Roy Lewallen, W7EL |
#3
|
|||
|
|||
db relation TX/RX
On Jul 19, 5:36*am, Roy Lewallen wrote:
Rollie wrote: . . .I've always used the (6db per S unit) as a general rule-of-thumb. Which is fine if you don't mind possibly being off by a factor of 50 or more, mistaking the gain of a 3 element beam for the gain of a 150 element one. Or you might only be off by a factor of 10, thinking the 3 element beam only has the gain of a 30 element beam. Shucks, what's a few dB anyway. Roy Lewallen, W7EL All of my radios are at least 15 years old before DSP. I was wondering manufactureres that had gone to DSP were using it to make S meter indications more accurate. I am seeing this type of signal correction being made in some of the equipment that I work on that has gone to DSP. Jimmie |
#4
|
|||
|
|||
db relation TX/RX
On Sun, 19 Jul 2009 03:00:51 -0500, "Rollie"
wrote: www.qsl.net/k5lxp/projects/SMeter/SMeter.html Check the chart to see actual input readings. I've always used the (6db per S unit) as a general rule-of-thumb. More receiver S-meter testing: http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/SMeterBlues.htm# http://www.smeter.net/slc/signal/strengths.php -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#5
|
|||
|
|||
db relation TX/RX
Thanks for the references.
Where does the fiction come from that an "S-unit", presumably the marks on our S-meters, is or for some reason should be, 6 dB -- that this is a "correct" or "ideal" value? To me it's the same as "defining" pi to be 3.2, as the Indiana House of Representatives once did. "Defining" an S-unit to be some value has no effect on our S-meters, any more than the proposed Indiana law changed the ratio of the circumference to diameter of a circle. Roy Lewallen, W7EL Jeff Liebermann wrote: On Sun, 19 Jul 2009 03:00:51 -0500, "Rollie" wrote: www.qsl.net/k5lxp/projects/SMeter/SMeter.html Check the chart to see actual input readings. I've always used the (6db per S unit) as a general rule-of-thumb. More receiver S-meter testing: http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/SMeterBlues.htm# http://www.smeter.net/slc/signal/strengths.php |
#6
|
|||
|
|||
db relation TX/RX
On Sun, 19 Jul 2009 12:20:40 -0700, Roy Lewallen
wrote: Thanks for the references. One more (in German): http://www.s-meter.de This one is rather interesting in that you can use the site to make an S-meter scale. Software to convert a perfectly good digital receiver data output, into marginally useful S-Units: http://www.seed-solutions.com/gregordy/Software/SMeterLite.htm Where does the fiction come from that an "S-unit", presumably the marks on our S-meters, is or for some reason should be, 6 dB -- that this is a "correct" or "ideal" value? Using S-Units is its own punishment. I couldn't find anything on the history of the S-Meter that would substantiate my guess that long ago some major radio company incorporated a signal meter into their receiver. Soon after, everyone had to have one. Whether they did anything useful is probably debatable. I guess it's not considered a proper ham radio unless it has an S-meter. For example, the new Elecraft K3 now has a software S-Meter for those that just can't live without one: http://www.sight.net/K3Meter/ My guess(tm) is that the 6dB per S-Unit was probably fairly close for the early tube type receivers. Below S-9 was probably below the AGC threshold. Above S-9 was more compressed above the knee in the AGC curve. AGC thresholds in old tube radios was probably a fairly strong signal, mostly because the RF/IF chain didn't have much gain. 6dB per S-Unit was probably fairly close and fairly linear below the AGC threshold. Roll forward 90 years and we have sensitive receivers that have an AGC knee at a few dB above the noise floor, with lots of overload handling ability to maintain a wide AGC range, and sensitivities much better than tube radios. If I maintain my assertion that S9 is the AGC knee, there would be perhaps one or two S-Units below S9, and the rest of the scale would be highly compressed "dB over S9" units. That would be a rather strange looking S-Meter, but might also be more useful than the current dual range meter. I'll give cellular designers minimal credit for replacing the inaccurate S-Meter with a less accurate 5 bar graph. Not satisfied with the bar graph abomination, they also invented that rather non-linear RSSI indication, and then cut it in half again by using 0-100 instead of 0-255. I suspect that in the future, when we're all carrying FTL sub-space communicators, Tricorders, and direct thought transmission radios, the associated projection or heads up display will probably include an S-Meter. To me it's the same as "defining" pi to be 3.2, as the Indiana House of Representatives once did. "Defining" an S-unit to be some value has no effect on our S-meters, any more than the proposed Indiana law changed the ratio of the circumference to diameter of a circle. So it is written, so it must be. Actually, I didn't think of it much until you mentioned it, but 6dB/S-Unit is rather improbable. The base line noise level for an antique AM radio is probably about 10uv which I presume is S1. S9 is loosely defined as 50uv. 6dB per S-unit implies a: 9*6 = 54dB range, which is considerably larger than the: 20 log (50/10) = 14dB range. If the 14dB range from S1 to S9 were considered the basis for calibration, then: 14dB / 9 S-Units = 1.5dB per S-Unit nowhere close to 6dB per S-Unit Or, if 6dB per S-unit, and S9=50uv are considered sacred, then 54dB below 50uv (-72dBm) = -72dBm -45dBm = -117dBm = 0.3uv, which is rather improbable. However, that will work for a modern receiver, with fairly good front end sensitivity and gain. Roy Lewallen, W7EL Jeff Liebermann wrote: On Sun, 19 Jul 2009 03:00:51 -0500, "Rollie" wrote: www.qsl.net/k5lxp/projects/SMeter/SMeter.html Check the chart to see actual input readings. I've always used the (6db per S unit) as a general rule-of-thumb. More receiver S-meter testing: http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/SMeterBlues.htm# http://www.smeter.net/slc/signal/strengths.php -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#7
|
|||
|
|||
db relation TX/RX
"Roy Lewallen" wrote in message ... Thanks for the references. Where does the fiction come from that an "S-unit", presumably the marks on our S-meters, is or for some reason should be, 6 dB -- that this is a "correct" or "ideal" value? Might be IARU Region 1 Technical Recommendation R.1. See http://www.algonet.se/~k-jarl/ssa/IARU/smeter.html Do we have to adhere to it? No, but if enough equipment makers implemented it, we might have a tough time ignoring it. Sal |
#8
|
|||
|
|||
db relation TX/RX
Hello,
Roy, with all the respect i owe you, you are barking up the wrong tree. 1 S-point should be 6 dB. Manufacturers choose not to do this for obvious cost reasons. Yet this is the definition, and they should work on it, especially so now, with digital techniques. Remains the definition of S9, supposedly different on HF & VHF. I am not so sure about this, but strongly support HF S9 = 50 uV. Thanks for your enlightening comments on this newsgroup. Olivier, HB9CEM / AE7AL Roy Lewallen wrote: Thanks for the references. Where does the fiction come from that an "S-unit", presumably the marks on our S-meters, is or for some reason should be, 6 dB -- that this is a "correct" or "ideal" value? To me it's the same as "defining" pi to be 3.2, as the Indiana House of Representatives once did. "Defining" an S-unit to be some value has no effect on our S-meters, any more than the proposed Indiana law changed the ratio of the circumference to diameter of a circle. Roy Lewallen, W7EL Jeff Liebermann wrote: On Sun, 19 Jul 2009 03:00:51 -0500, "Rollie" wrote: www.qsl.net/k5lxp/projects/SMeter/SMeter.html Check the chart to see actual input readings. I've always used the (6db per S unit) as a general rule-of-thumb. More receiver S-meter testing: http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/SMeterBlues.htm# http://www.smeter.net/slc/signal/strengths.php |
#9
|
|||
|
|||
db relation TX/RX
"Rollie" wrote in message ... www.qsl.net/k5lxp/projects/SMeter/SMeter.html Check the chart to see actual input readings. I've always used the (6db per S unit) as a general rule-of-thumb. The chart is interesting. Where the "S-Meter Standard" numbers come from, in blue on the left? If I were to create such an "S-Meter Standard" chart myself without source or authentication, I might be inclined to set S-9 equal to -73 dBm/50 uV and extend the S-values down from there at the popular rate of 6 dB per S-unit. Chart values do decrease at 6 dB per S-unit but the chart sets -72 dBm/56.8 uV as S-9, vice 73 dBm, 50 uV. 1 dB isn't much to quibble about, but it does make me inquire about the source of the data. Can anyone elaborate? TKS BTW, http://en.wikipedia.org/wiki/S_meter provides a similar chart based around 73 dBm as S-9. It sources IARU Region 1 Technical Recommendation R.1. I looked for it; no luck. Sal |
#10
|
|||
|
|||
db relation TX/RX
"Sal M. Onella" wrote in
: .... Chart values do decrease at 6 dB per S-unit but the chart sets -72 dBm/56.8 uV as S-9, vice 73 dBm, 50 uV. 1 dB isn't much to quibble about, but it does make me inquire about the source of the data. Actually, it is 146dB lower than that... 50µV in 50 ohms is -73dBm. Owen |
Reply |
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
dB relation TX/RX | Antenna | |||
Orthogonality relation between modes in Dielectric-Lined Circular Waveguide (or with concentric dielectric layers) | Antenna |