Decibels - Revision history

Kitz: Category

2024-05-18T11:05:16Z

Roseway at 13:59, 27 December 2011

2011-12-27T13:59:21Z

Roseway: /* Decibels used as power measurement */

2011-12-23T15:03:31Z

‎Decibels used as power measurement

Roseway: /* Attenuation */

2011-12-19T16:24:04Z

‎Attenuation

Roseway: /* Attenuation */

2011-12-12T16:33:08Z

‎Attenuation

Roseway: /* Decibels used as power measurement */

2011-12-12T16:28:46Z

‎Decibels used as power measurement

Roseway: /* The decibel */

2011-12-12T16:19:31Z

‎The decibel

Roseway: /* The decibel */

2011-12-12T16:10:43Z

‎The decibel

Roseway: /* The decibel */

2011-12-12T10:05:14Z

‎The decibel

Roseway at 21:04, 11 December 2011

2011-12-11T21:04:54Z

← Older revision		Revision as of 11:05, 18 May 2024
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	--[[User:Roseway\|Roseway]] 13:59, 27 December 2011 (GMT)		--[[User:Roseway\|Roseway]] 13:59, 27 December 2011 (GMT)
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		+	[[Category:Technical]]

← Older revision		Revision as of 13:59, 27 December 2011
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	Most modem/routers report the upstream and downstream power levels in dBm, although in some cases this information is only available by using the telnet interface. The upstream (or local) power is the power transmitted by your modem/router, and the downstream (or remote) power is the power transmitted by the DSLAM or MSAN in the exchange.		Most modem/routers report the upstream and downstream power levels in dBm, although in some cases this information is only available by using the telnet interface. The upstream (or local) power is the power transmitted by your modem/router, and the downstream (or remote) power is the power transmitted by the DSLAM or MSAN in the exchange.
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		+
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		+	--[[User:Roseway\|Roseway]] 13:59, 27 December 2011 (GMT)

← Older revision		Revision as of 15:03, 23 December 2011
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	\|50 dBm		\|50 dBm
	\|}		\|}
		+
		+	Most modem/routers report the upstream and downstream power levels in dBm, although in some cases this information is only available by using the telnet interface. The upstream (or local) power is the power transmitted by your modem/router, and the downstream (or remote) power is the power transmitted by the DSLAM or MSAN in the exchange.

@@ Line 50: / Line 50: @@
 Ordinary twisted-pair telephone lines were never designed for the high frequencies used in ADSL transmission. Not surprisingly a lot of the ADSL signal gets lost between the exchange and the user. What may surprise you is just how much gets lost...
-Prior to 6 September 2004, the limiting attenuation figure for a UK ADSL installation was 60 dB (i.e. a gain of -60 dB). This is equal to 6 Bels, and therefore the logarithm of the power ratio is 6. In other words, the signal at the end of the line is just 10^-6 (one-millionth) of the signal transmitted from the exchange. And as from 6 September 2004 the limits were relaxed further, with 75 dB being the level of attenuation at which a usable ADSL service is considered extremely unlikely - that's a power ratio of about 32 million. Lower levels of attenuation are obviously preferable.
+Prior to 6 September 2004, the limiting attenuation figure for a UK ADSL installation was 60 dB (i.e. a gain of -60 dB). This is equal to 6 Bels, and therefore the logarithm of the power ratio is 6. In other words, the signal at the end of the line is just 10<SUP>-6</SUP> (one-millionth) of the signal transmitted from the exchange. And as from 6 September 2004 the limits were relaxed further, with 75 dB being the level of attenuation at which a usable ADSL service is considered extremely unlikely - that's a power ratio of about 32 million. Lower levels of attenuation are obviously preferable.
 === Signal-to-noise ratio ===

@@ Line 50: / Line 50: @@
 Ordinary twisted-pair telephone lines were never designed for the high frequencies used in ADSL transmission. Not surprisingly a lot of the ADSL signal gets lost between the exchange and the user. What may surprise you is just how much gets lost...
-Prior to 6 September 2004, the limiting attenuation figure for a UK ADSL installation was 60 dB (i.e. a gain of -60 dB). This is equal to 6 Bels, and therefore the logarithm of the power ratio is 6. In other words, the signal at the end of the line is just 10^-6 (one-millionth) of the signal transmitted from the exchange. And as from 6/9/2004 the limits were relaxed further, with 75 dB being the level of attenuation at which a usable ADSL service is considered extremely unlikely - that's a power ratio of about 32 million. Lower levels of attenuation are obviously preferable.
+Prior to 6 September 2004, the limiting attenuation figure for a UK ADSL installation was 60 dB (i.e. a gain of -60 dB). This is equal to 6 Bels, and therefore the logarithm of the power ratio is 6. In other words, the signal at the end of the line is just 10^-6 (one-millionth) of the signal transmitted from the exchange. And as from 6 September 2004 the limits were relaxed further, with 75 dB being the level of attenuation at which a usable ADSL service is considered extremely unlikely - that's a power ratio of about 32 million. Lower levels of attenuation are obviously preferable.
 === Signal-to-noise ratio ===

@@ Line 64: / Line 64: @@
 As described above, decibels specify a ratio between two numbers (one number divided by the other). An extension to this is the dBm, which is defined as dB referenced to 1 mW (one milliwatt). This is a convenient way to specify a wide range of power levels in fairly small numbers. So the ratio of the actual power of a device to 1 mW is converted to dB, and then the power is specified as that number of dBm. For example:
-* 1 mW  =  0 dBm
+{| border="1"
-* 2 mW  =  3 dBm
+|Power
-* 1 W   =  1000 mW    =  30 dBm
+|dBm equivalent
-* 100 W =  100,000 mW = 50 dBm
+|-

@@ Line 21: / Line 21: @@
 |Arithmetic equivalent
 |-
 |-
-|-6 dB
+| -3 dB
 |0.5
 |0 dB
 |1

@@ Line 22: / Line 22: @@
 |-
 |-
 |0 dB
-|0
+|1
 |-
 |3 dB

← Older revision		Revision as of 10:05, 12 December 2011
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	2. The log of a number less than 1 is negative, so all power gains have positive dB values and all losses have negative dB values. If the input and output powers are equal, then the gain is 0 dB.		2. The log of a number less than 1 is negative, so all power gains have positive dB values and all losses have negative dB values. If the input and output powers are equal, then the gain is 0 dB.
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		+	'''Some example values'''
		+
		+	{\| border="1"
		+	\|Decibel value
		+	\|Arithmetic equivalent
		+	\|-
		+	\|-
		+	\|0 dB
		+	\|0
		+	\|-
		+	\|3 dB
		+	\|2
		+	\|-
		+	\|6 dB
		+	\|4
		+	\|-
		+	\|10 dB
		+	\|10
		+	\|-
		+	\|20 dB
		+	\|100
		+	\|-
		+	\|30 dB
		+	\|1000
		+	\|}

	=== Attenuation ===		=== Attenuation ===

← Older revision		Revision as of 21:04, 11 December 2011
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	It should be noted that ADSL modems and routers generally report noise margin (or SNR margin), not SNR. The manufacturer specifies a SNR at which the error count reaches some threshold beyond which the connection would not be acceptably stable; the noise margin is the amount by which the measured SNR exceeds this base level of SNR. So, for example, if the minimum acceptable SNR was set at 6 dB, and the measured SNR was 10 dB, then the modem/router would report a noise margin of 4 dB.		It should be noted that ADSL modems and routers generally report noise margin (or SNR margin), not SNR. The manufacturer specifies a SNR at which the error count reaches some threshold beyond which the connection would not be acceptably stable; the noise margin is the amount by which the measured SNR exceeds this base level of SNR. So, for example, if the minimum acceptable SNR was set at 6 dB, and the measured SNR was 10 dB, then the modem/router would report a noise margin of 4 dB.
		+
		+	=== Decibels used as power measurement ===
		+
		+	As described above, decibels specify a ratio between two numbers (one number divided by the other). An extension to this is the dBm, which is defined as dB referenced to 1 mW (one milliwatt). This is a convenient way to specify a wide range of power levels in fairly small numbers. So the ratio of the actual power of a device to 1 mW is converted to dB, and then the power is specified as that number of dBm. For example:
		+
		+	* 1 mW = 0 dBm
		+	* 2 mW = 3 dBm
		+	* 1 W = 1000 mW = 30 dBm
		+	* 100 W = 100,000 mW = 50 dBm