Home |
Search |
Today's Posts |
#31
|
|||
|
|||
Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
"Michael A. Terrell" wrote in message
... You need to do a lot of studying on how to use the dB. I know full well what a logarithm is; don't patronize me. My point was that some otherwise ambiguous dB scales (at least one) have a defined absolute basis. Tim -- Deep Fryer: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |
#32
|
|||
|
|||
Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
In article ,
"Tim Williams" wrote: "Michael A. Terrell" wrote in message ... You need to do a lot of studying on how to use the dB. I know full well what a logarithm is; don't patronize me. My point was that some otherwise ambiguous dB scales (at least one) have a defined absolute basis. Like Michael stated dB is a logarithmic reference-less ratio value. You can use dB for things like amplifiers that have a gain or attenuators that have a loss for example. The gain of an amplifier can be expressed in dB because the reference value is the input value of the amplifier, which will allow you to calculate the output value but if you are speaking of a value of power or voltage by itself then you need an absolute scale with a reference quantity. Absolute scales would be dBV, dBuV, and dBm. In those terms the reference is 1 volt, 1 micro-volt (0.000001 volt), and 1 milliwatt (.001 watt). The reason you need a reference value is noise prevents you from measuring 0 Volts and 0 watts accurately so you need to use a small reference value in its place and so everyone agreed to use these values. Definitions a dBV = 20 * log (volts / 1 ) dBuV = 20 * log ( volts / 0.000001 ) dBm = 10 * log ( power / .001 ) So for example: 30 dBm = 1.0 watt 0 dBm = 0.001 watt (the reference value) -30 dBm = 0.000001 watt Most of the time in radio dBm, dBuV, and watts are used. -- Telamon Ventura, California |
#33
|
|||
|
|||
Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
Tim Williams wrote:
"Michael A. Terrell" wrote in message ... You need to do a lot of studying on how to use the dB. I know full well what a logarithm is; don't patronize me. My point was that some otherwise ambiguous dB scales (at least one) have a defined absolute basis. I'm not "Patronizing" you. You were using it in the wrong context. -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida |
#34
|
|||
|
|||
Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
"Telamon" wrote in message ... Absolute scales would be dBV, dBuV, and dBm. In those terms the reference is 1 volt, 1 micro-volt (0.000001 volt), and 1 milliwatt (.001 watt). The reason you need a reference value is noise prevents you from measuring 0 Volts and 0 watts accurately so you need to use a small reference value in its place and so everyone agreed to use these values. Given you are discussing use of the dB, I think the above leaves a bit out. You can't use 0W as your reference because, given the definition of the dB, you'd need to divide by 0 which, as I'm sure you know, isn't acceptable. -- 73 Brian www.g8osn.org.uk |
#35
|
|||
|
|||
Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
On 2006-09-13, Don Bowey wrote:
On 9/12/06 3:57 PM, in article , "Radium" wrote: In fringe areas, analog cell phones could be well understood despite the poor signal-to-noise ratio. Digital cell phones in a fringe area just quit working, or lose sync and you hear bits of other conversations. with GSM phones I got a "guitar sounding" effect in marginal areas Bye. Jasen |
#36
|
|||
|
|||
Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
On 2006-09-13, Radium wrote:
Easy for you to ask. I doubt any store has the device. And the equipment required to amplify .00000000001 dB to an audible level would take up the entire room. There is no such thing as a .00000000001 dB signal Whats stops a .00000000001 dB signal from existing? Nothing, it's just indistinguishable from a 0db signal. In other words it's about half the amplitide of a 3db signal... It's a logarythmic scale. Bye. Jasen |
#37
|
|||
|
|||
Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
jasen wrote:
On 2006-09-13, Radium wrote: Easy for you to ask. I doubt any store has the device. And the equipment required to amplify .00000000001 dB to an audible level would take up the entire room. There is no such thing as a .00000000001 dB signal Whats stops a .00000000001 dB signal from existing? Nothing, it's just indistinguishable from a 0db signal. In other words it's about half the amplitide of a 3db signal... It's a logarythmic scale. Bye. Jasen No, without a reference, its use is meaningless. He was trying to use dB for an absolute signal level, not a ratio. -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida |
#38
|
|||
|
|||
Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
"Telamon" wrote in message
... My point was that some otherwise ambiguous dB scales (at least one) have a defined absolute basis. Like Michael stated dB is a logarithmic reference-less ratio value. So what is acoustic dB? http://home.new.rr.com/trumpetb/audio/dBexamp.html SPL, I should say. There it lies, x dB on the left scale. Tim -- Deep Fryer: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |
#39
|
|||
|
|||
Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
Tim Williams wrote:
"Telamon" wrote in message ... My point was that some otherwise ambiguous dB scales (at least one) have a defined absolute basis. Like Michael stated dB is a logarithmic reference-less ratio value. So what is acoustic dB? http://home.new.rr.com/trumpetb/audio/dBexamp.html SPL, I should say. There it lies, x dB on the left scale. That is a SPL chart with the dB levels referenced to 0 dB SPL = 0.0002 µbar. -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida |
#40
|
|||
|
|||
Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
Tim Williams wrote:
"Telamon" wrote in message ... My point was that some otherwise ambiguous dB scales (at least one) have a defined absolute basis. Like Michael stated dB is a logarithmic reference-less ratio value. So what is acoustic dB? http://home.new.rr.com/trumpetb/audio/dBexamp.html SPL, I should say. There it lies, x dB on the left scale. Read this Sound Level Meter manual if you want to understand that chart. http://rsk.imageg.net/graphics/uc/rsk/Support/ProductManuals/3304050_PM_EN.pdf -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|