*Recommended Upstream signal levels are +35 dBmV to +49 dBmV (DOCSIS 3.0)
| Number of Bonded US channels | 1 | 3 |
|---|
| DOCSIS 3.0 Specification for 64-QAM channel | 57 dBmV | 51 dBmV |
| Recommended Value for good operations | 35-49 dBmV | 35-49 dBmV |
Ideally, you want to aim for a higher SNR. I'd say 20 dB or greater is good SNR. Greater than 40 dB is even better! Recommended minimum SNR for data is 18 dB and for voice over wifi it is 25 dB.
A value of -15 or worse indicates a poor downstream signal path. A tech would aim for a value close to the optimal 0 dBmV, but a good cable modem should be capable of working within the broader range of -15 to +15 dBmV, provided the downstream Signal to Noise Ratio remains good enough.
Downstream and upstream power levels are important when determining if the cable line that is connected to your cable modem or modem router is receiving sufficient power. Good Downstream power levels are within -7 to +7 dBmV. Good Upstream power levels are within 38-48 dBmV.
The three signal levels that need to be within the acceptable level are Downstream Power, SNR (Signal to Noise Ratio), and Upstream Power. Downstream Power refers to the line signal sent from the cable provider to cable modem.
Downstream and upstream power levels are important when determining if the cable line that is connected to your cable modem or modem router is receiving sufficient power. Good Downstream power levels are within -7 to +7 dBmV. Good Upstream power levels are within 38-48 dBmV.
What is the proper way to express a signal voltage of 10 mV in cable TV terms? A) 20log(10mV/1mV) = 20 dBmV.
To convert a ratio to
dB, do log and then times by
10. Example:
dB = +12.5
dB. Divide +12.5 by
10 = +1.25. Do
101.25 = 17.8 ratio.
dBW and Watts W.
| dBW scale | Watts |
|---|
| +10 dBW | 10 watts |
| 0 dBW | 1 watt |
| -10 dBW | 0.1 W |
| -30 dBW | 0.001 W |
100db is 10db louder than 90db so, yes, it's loud compared to other noise levels but quieter than others. Hearing damage depends not only on how loud a sound is but also for how long you're exposed. OSHA considers 79dbA the level of continuous exposure without damage.
A sound's loudness is measured in
decibels (dB). Normal conversation is about 60 dB, a lawn mower is about 90 dB, and a
loud rock concert is about 120 dB.
Topic Overview.
| Noise | Average decibels (dB) |
|---|
| Stock car races | 130 |
| Gun shot, siren at 100 feet | 140 |
I want more power!
| Interpreting Speaker dB Ratings |
|---|
| Speaker SPL in dB | 86 | 92 |
|---|
| 8 Watts | 95 | 101 |
| 16 Watts | 98 | 104 |
| 32 Watts | 101 | 107 |
To convert a ratio to
dB, do log and then times by 10. Example:
dB = +12.5
dB. Divide +12.5 by 10 = +1.25. Do 10
1.25 = 17.8 ratio.
dB and ratios.
| dB value | times by |
|---|
| -10 dB | 0.1 |
| -20 dB | 0.01 |
| -30 dB | 0.001 |
| -40 dB | 0.0001 |
Increasing the power tenfold will yield an increase of +10 dB and is a doubling of perceived loudness. The decibel is not an absolute measurement, but indicates the relationship or ratio between two signal levels.
| Watts | dB (rel to 1 watt) |
|---|
| 10 | 10 |
| 50 | 16.9897 |
| 100 | 20 |
| 200 | 23.0103 |
Common Sources of Noise and Decibel Levels
Sound is measured in decibels (dB). A whisper is about 30 dB, normal conversation is about 60 dB, and a motorcycle engine running is about 95 dB.What's the Impact of Increasing Power Output?
| Amplifier Power Output | Speaker Output Level Increase |
|---|
| 10 watts | 10 dB |
| 100 watts | 20 dB |
| 1000 watts | 30 dB |
The 20-watt amp is double the power of the 10-watt amp, but doubling the power only translates to an increase of 3 dB SPL. Remember, in order to sound "twice as loud," you need an increase of 10dB, so while a 20W amplifier will sound noticeably louder than a 10W amp, it will not sound twice as loud.
WiFi signal strength is tricky. Ultimately, the easiest and most consistent way to express signal strength is with dBm, which stands for decibels relative to a milliwatt. Since RSSI is handled differently by most WiFi adapters, it's usually converted to dBm to make it consistent and human-readable.
10.00 watts. 36 dBm. 4.00 watts. { Maximum ERP allowed by FCC in U.S. 30 dBm.
The unit dBm denotes an absolute power level measured in decibels and referenced to 1 milliwatt (mW). To convert from absolute power "P" (in watts) to dBm, use the formula dBm = 10*log (P/1 mW). This equation looks almost the same as that for the dB. However, now the power level "P" has been referenced to 1 mW.
dBm is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt. It is used in radio, microwave and fiber optic networks as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form.
dBW value in dBm is always 30 more because 1 watt is 1000 milliwatts, and ratio of 1000 (in power) is 30 dB, eg 10 dBm (10mW) is equal to -20 dBW (0.01 W). Input a value above, select the type of unit you wish to convert, and click the 'Convert My Power' button. All calculated values will be shown.
The decibel watt or dBW is a unit for the measurement of the strength of a signal expressed in decibels relative to one watt. Although the decibel (dB) is permitted for use alongside SI units, the dBW is not.
I want more power!
| Interpreting Speaker dB Ratings |
|---|
| Speaker SPL in dB | 86 | 101 |
|---|
| 32 Watts | 101 | 116 |
| 64 Watts | 104 | 119 |
| 128 Watts | 107 | 122 |
- 1 W = 1000 mW = 0 dB = 30 dBm. Or.
- 0 dBm = -30 dB = 0.001 W = 1 mW. Another common variation on dB in antenna theory is dBi which means "decibels relative to an isotropic antenna".
- Gain of 10 dB = Gain of 10 dBi.
- Antenna with a gain of 10 dBi = 10 dB = 7.85 dBd.
3dB rule and the doubling of sound energy
In a work context, this means that a small increase in the number of decibels results in a huge change in the amount of noise and, as such, the potential to cause damage to your hearing.dBu measures decibels relative to 0.775 volts with an open or unloaded circuit. ( The “u” in “dBu” stands for unloaded.) While 0.775 volts may seem rather arbitrary, it is the voltage level that delivers 1 mW in a 600Ω resistor, which is the standard reference impedance in a telephone audio circuit. (
Doubling of the volume (loudness) should be sensed as a level difference of +10 dB − acousticians say. Doubling of sound intensity (acoustic energy) belongs to a calculated level change of +3 dB. +10 dB is the level of twice the perceived volume or twice as loud (loudness) in psychoacoustics − mostly sensed.
Nominal levels
| Use | Nominal level | Nominal level, VRMS |
|---|
| Professional audio | +4 dBu | 1.228 |
| Consumer audio | −10 dBV | 0.316 |
The most basic form for deciBel calculations is a comparison of power levels. As might be expected it is ten times the logarithm of the output divided by the input. The factor ten is used because deciBels rather than Bels are used.
But any sound that is loud enough and lasts long enough can damage hearing and lead to hearing loss. A sound's loudness is measured in decibels (dB). Normal conversation is about 60 dB, a lawn mower is about 90 dB, and a loud rock concert is about 120 dB.
Decibel Level?
Sounds at or below 70 dBA are generally considered safe. Any sound at or above 85 dBA is more likely to damage your hearing over time. Researchers have found that people who are exposed over long periods of time to noise levels at 85 dBA or higher are at a much greater risk for hearing loss.Abbreviation for decibels as referenced to voltage. Similar to dBu, dBV specifies a relative voltage level without regard for impedance and is used to measure input and output levels for electronic audio equipment. -10 dBV = . 316 volts. You can prove that by checking it against the 1-volt reference.
