1. audio_engr's Avatar
    I have with me 2 BBs, side-by-side, having SIM cards both from the same carrier, and both in EDGE operation for Blackberry BIS service.

    (1) 9900 reads -47 dBm (running OS

    (2) 9780 reads -70 dBm (running OS

    Can someone interpret what's happening ? Why the different readings on the BBs ?
    03-07-12 10:40 PM
  2. audio_engr's Avatar
    no one here to clarify ?
    03-08-12 12:53 PM
  3. Schufly's Avatar
    My guess would be a different radio versions, or possibly a different antenna configuration. I'm not too familiar with the 9780. Maybe someone else will have a better idea.
    03-08-12 04:56 PM
  4. kevinnugent's Avatar
    Zero dBm equals one milliwatt. A 3 dB increase represents roughly doubling the power, which means that 3 dBm equals roughly 2 mW. For a 3 dB decrease, the power is reduced by about one half, making −3 dBm equal to about 0.5 milliwatt. To express an arbitrary power P as x dBm, or vice versa, the following equations may be used:


    where P is the power in W and x is the power ratio in dBm. Below is a table summarizing useful cases:

    dBm level Power Notes
    80 dBm 100 kW Typical transmission power of FM radio station with 50-kilometre (31 mi) range
    60 dBm 1 kW = 1000 W Typical combined radiated RF power of microwave oven elements
    Maximum RF output power from a ham radio transceiver allowed without special permission

    50 dBm 100 W Typical thermal radiation emitted by a human body
    Typical maximum output RF power from a ham radio HF transceiver

    40 dBm 10 W Typical PLC (Power Line Carrier) Transmit Power
    37 dBm 5 W Typical maximum output RF power from a handheld ham radio VHF/UHF transceiver
    36 dBm 4 W Typical maximum output power for a Citizens' band radio station (27 MHz) in many countries
    33 dBm 2 W Maximum output from a UMTS/3G mobile phone (Power class 1 mobiles)
    Maximum output from a GSM850/900 mobile phone

    30 dBm 1 W = 1000 mW Typical RF leakage from a microwave oven
    DCS or GSM 1800/1900 Mhz mobile phone. EIRP IEEE 802.11a (20MHz-wide channels) in either 5Ghz Subband 2 (5470-5725 MHz) provided that transmitters are also IEEE 802.11h-compliant, or U-NII-3 (5725-5825 MHz). The former is EU only, the latter is US only.

    27 dBm 500 mW Typical cellular phone transmission power
    Maximum output from a UMTS/3G mobile phone (Power class 2 mobiles)

    26 dBm 400 mW
    25 dBm 316 mW
    24 dBm 250 mW Maximum output from a UMTS/3G mobile phone (Power class 3 mobiles)
    1880-1900 MHz DECT (250mW per 1728kHz channel). EIRP for Wireless LAN IEEE 802.11a (20MHz-wide channels) in either the 5Ghz Subband 1 (5180-5320 MHz) or U-NII-2 & -W ranges (5250-5350 MHz & 5470-5725 MHz respectively). The former is EU only, the latter is US only.

    23 dBm 200 mW EIRP for IEEE 802.11n Wireless LAN 40Mhz-wide (5mW per MHz) channels in 5Ghz subband 4 (5735-5835 MHz, US only) or 5Ghz subband 2 (5470-5725 MHz, EU only). Also applies to 20Mhz-wide (10mW per MHz) IEEE 802.11a Wireless LAN in 5Ghz Subband 1 (5180-5320 MHz) if also IEEE 802.11h compliant (otherwise only 3mW/MHz=>60mW when unable to dynamically adjust transmission power, and only 1.5mW/MHz=>30mW when a transmitter also cannot dynamically select frequency).
    22 dBm 160 mW
    21 dBm 125 mW Maximum output from a UMTS/3G mobile phone (Power class 4 mobiles)
    20 dBm 100 mW EIRP for IEEE 802.11b/g Wireless LAN 20Mhz-wide channels in the 2.4GHz ISM band (5mW per MHz).
    Bluetooth Class 1 radio. Maximum output power from unlicensed AM transmitter per U.S. Federal Communications Commission (FCC) rules 15.219.[1]

    15 dBm 32 mW Typical Wireless LAN transmission power in laptops.
    10 dBm 10 mW
    6 dBm 4.0 mW
    5 dBm 3.2 mW
    4 dBm 2.5 mW Bluetooth Class 2 radio, 10 m range
    3 dBm 2.0 mW More precisely (to 8 decimal places) 1.9952623 mW
    2 dBm 1.6 mW
    1 dBm 1.3 mW
    0 dBm 1.0 mW = 1000 W Bluetooth standard (Class 3) radio, 1 m range
    −1 dBm 794 W
    −3 dBm 501 W
    −5 dBm 316 W
    −10 dBm 100 W Typical maximum received signal power (−10 to −30 dBm) of wireless network
    −20 dBm 10 W
    −30 dBm 1.0 W = 1000 nW
    −40 dBm 100 nW
    −50 dBm 10 nW
    −60 dBm 1.0 nW = 1000 pW The Earth receives one nanowatt per square metre from a magnitude +3.5 star[2]
    −70 dBm 100 pW Typical range (−60 to −80 dBm) of wireless received signal power over a network (802.11 variants)
    −73 dBm 50.12 pW "S9" signal strength, a strong signal, on the S-meter of a typical ham or shortwave radio receiver
    −80 dBm 10 pW
    −100 dBm 0.1 pW
    −111 dBm 0.008 pW = 8 fW Thermal noise floor for commercial GPS single channel signal bandwidth (2 MHz)
    −127.5 dBm 0.178 fW = 178 aW Typical received signal power from a GPS satellite
    −174 dBm 0.004 aW = 4 zW Thermal noise floor for 1 Hz bandwidth at room temperature (20 C)
    −192.5 dBm 0.056 zW = 56 yW Thermal noise floor for 1 Hz bandwidth in outer space (4 kelvins)
    −∞ dBm 0 W Zero power is not well-expressed in dBm (value is negative infinity)

    The signal intensity (power per unit area) can be converted to received signal power by multiplying by the square of the wavelength and dividing by 4π (see Free-space path loss).

    In United States Department of Defense practice, unweighted measurement is normally understood, applicable to a certain bandwidth, which must be stated or implied.

    In European practice, psophometric weighting may be, as indicated by context, equivalent to dBm0p, which is preferred.

    The dBm is not a part of the International System of Units and therefore is discouraged from use in documents or systems that adhere to SI units (the corresponding SI unit is the watt). However the straight decibel (dB), being a unitless ratio of two numbers, is perfectly acceptable.[3]

    Expression in dBm is typically used for optical and electrical power measurements, not for other types of power (such as thermal). A listing by power levels in watts is available that includes a variety of examples not necessarily related to electrical or optical power.

    03-08-12 05:59 PM
  5. Phill_UK's Avatar
    dBm - Wikipedia, the free encyclopedia

    Nicely quoted, but didn't really answer the OP's question
    03-08-12 06:30 PM
  6. albee 1's Avatar
    The bottom line the smaller the negative number the greater the signal received.
    03-08-12 06:43 PM
  7. aqw955's Avatar
    sometimes I got -101dbm with only GSM enbled... that scares me a lot
    03-08-12 07:31 PM