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What does this mean?... General Blackberry forum

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    pthomas11's Avatar
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    why does singal strength read a negative number?



    What does this mean?

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    Re: why does singal strength read a negative number?

    I'm curious about that as well

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    Re: why does singal strength read a negative number?

    Because signal strength/radio waive is measured in decibel (dB).

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    Re: why does singal strength read a negative number?

    Yea that's what I was thionking but wasn't sure. On a TV the volume is in decibels also. So it reads like -30 dB on a TV and its the same concept with signal strength but its just measured in how many signals you are getting.

    Hope this helps,

    COJO 24

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    Re: why does singal strength read a negative number?

    It is a measure of signal strength as a loss from what was transmitted. If you received the same level of power that was transmitted there would be no loss so your strength would be 0 dB. As you move further and further away from the source of the transmission, your reletive power is decreased. Therefore your signal strength goes negative.

    Hope this Helps
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    Re: why does singal strength read a negative number?

    Just to add on a teeny bit, with probably more detail than anyone cares about (sorry, I'm a ham radio operator, K2DBK, so this is something I'm pretty familiar with), the reason why it's a negative number is because it's a logarithmic relationship, with a negative sign indicating that the ratio is less than zero. Specifically, the units used are dBm, which means decibels compared to one milliwatt. When you see a signal like -80, that means that it's -80dBm, which means that the signal being received is 100pw (picowatts). By comparison, a typical cellphone transmits at about 500mw (milliwatts), or 1/2 watt, which equates to +27dBm.

    There's a really nice chart at Wikipedia that shows a bunch of relative signal levels with the power levels and dBm equivalents.
    David

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    Re: why does singal strength read a negative number?

    thanks guys. that was something i was curious about late last night....

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    Re: why does singal strength read a negative number?

    ...just to add more useless information (boy do I have a lot of *that* crammed upstairs) the typical cellphone works within the range of -50dBm (sitting on top the tower, 5 bars) to -98dBm (utter loss of signal, 1 bar). I'd love to link where I read that, but the memory is failing me right now.

    For the life of me I can't find it, but there's an excellent article explaining this range in relation to SAR of the handset (see here: http://www.mobile-phones-uk.org.uk/sar.htm) and why it doesn't go beyond a certain point in relation to what the tower is broadcasting. You'll never see "near zero" types of signal strength on a mobile device.

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    Re: why does singal strength read a negative number?

    ^ im confused does this mean lower negative numbers are better? (-50dbm better than -98dbm)

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    Re: why does singal strength read a negative number?

    Quote Originally Posted by husnain1
    ^ im confused does this mean lower negative numbers are better? (-50dbm better than -98dbm)
    yup! 100% correct, the closer you move towards zero ("less negative") the better. You can use this same knowledge and apply it to WiFi connections as well, they're all radio waves (see dkozinn's post above). For example, the statistics sitting here with wifi on my laptop:

    Link Quality=93/100 Signal level=-34 dBm Noise level=-89 dBm

    ...so you see having a Signal level closer to 0 and a Noise level further from 0 is a good thing for my WiFi connection. Life would be sad if they're reversed.

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    Re: why does singal strength read a negative number?

    ~via BB (wap.pinstack.com)~ my berry is nearly always at -80 or so, but always has perfect reception so I'm a little lost here. Does that mean that it requires less signal to do its job than other phones? I used to sell phones and they were decidedly not all created equal in reception and call stability, some dropping calls like Terrell Owens in a playoff game while others were rock solid while standing in the same place. Is it that some had stronger antennas or did they simply use the signal they had more effectively?

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    Re: why does singal strength read a negative number?

    Quote Originally Posted by Yellowfin
    Is it that some had stronger antennas or did they simply use the signal they had more effectively?
    The number that you're seeing (which on typical cellphones, including BB are normally just represented as "bars") represents the signal strength as received by the device. Below a certain value, you will have no service at all. On most devices, the strength that's displayed isn't necessarily updated constantly, so if you're in an area where the strength is variable, such as when you're moving, the value that you'll see isnt' necessarily accurate for that precise moment in time. (Though we're not talking about minutes between updates or anything like that.)

    If the signal strength is at some particular level or greater, you will not hear any difference in the call quality. Current cellphones are digital, which means that if there's a good enough signal so that all the digitized voice data makes it to (and from) your phone, the call will sound as close to perfect as you're going to get. Getting a better quality signal won't change the quality of the voice signal. However, for data transmissions, you will possibly see higher throughput with better signal strength.

    As for your question, there are a couple of things: First, yes, some phones do receive better. If you've got a phone with an external antenna, it may receive better than one with an internal antenna. However, the technology available in newer phones is such that they are able to successfully pull out the weaker signals and process them correctly. (In other words, yes, some phones just work better with weaker signals). There's actually a whole lot more to this than I've gone into (for instance, how strong is the signal compared to the noise that's also being received; how well does the device do in the presence of other strong signals, etc.) but in a nutshell, what it comes down to is this: If you've got a few bars on your phone, it's probably going to work just fine.

    The dBm display on the phones is interesting to look at, but you're probably better just leaving the display set to bars and remembering "more is better".
    David

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    Re: why does singal strength read a negative number?

    In addition the the internal vs. external antennae quality and so forth, there's also the issue of how the code (firmware) is written and designed for that device. For example, almost everyone agrees that Nokias have the best RF reception quality (in general, there are some models that suck) -- this is partly because of the hardware used, but also because a Nokia constantly scans for better "channels" (cells) to attach to on any given tower; the side effect is that it uses a lot more battery when you're in a less-than-5-bar area - the battery takes a beating and drains a lot faster.

    I've noticed my Pearl scans for better links a lot further spaced apart (think like every 2 minutes instead of every 30 seconds), which is actually good -- in my city we have a lot of dead spots, so it seems I have a lot better battery life on my Pearl because it's not wasting a lot of time re-scanning when I go out of range (like in my underground garage) for a minute or two. This gives the user-appearance that it always seems to have signal and be locked on, when in reality it might not be (until you'd try and make a call, or wait a minute for it to rescan and find no towers).

    It can also be carrier-specific branding optimized; T-Mobile branded firmware on a Nokia is set to scan for towers on 1900 MHz *before* 850 MHz, since this is their official wavelength for a lot of the US (CA and NV especially). This means that typically a branded handset will waste less battery power scanning through 850 if a 1900 signal is found, and it limits it's searches there (which results in increased battery life and a more constant signal as it's scanning only one band). It'll "pick up" service a lot faster than an unbranded (generic) Nokia, as these handsets start in 850 and scan outwards towards 1900 (so they cycle through all the 850 Cingular towers in my area first, uselessly).

    Then we can talk handset design -- the hardware engineers can choose to use a more sensitive antennae to pick up weaker signal at the cost of a little more noise in the signal. Again, a Nokia does this as the firmware engineers take this into account and have a very robust set of algorithms to pull in weak signals and scrub out the noise from the pattern. This is why you'll see a lot of comments from Nokia people about how their handset will pick up a signal where other phones won't (e.g.).

    NOTE: to see a lot of the things above for yourself, you have to have "Netmon" enabled on a Nokia, or unlock the Engineering menu on a Moto. This is not how the come officially or how you can buy them.

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    Re: why does singal strength read a negative number?

    Quote Originally Posted by husnain1
    ^ im confused does this mean lower negative numbers are better? (-50dbm better than -98dbm)
    -98 is lower than -50 but, yes, -50 would be better.

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    Re: why does singal strength read a negative number?

    Quote Originally Posted by takeshi
    -98 is lower than -50 but, yes, -50 would be better.
    Actually, -50 is "less negative" than -98. (Anyone remember the "number line" from elementary school? It had zero in the middle and was "more positive" to the right, and "more negative" to the left?)

    If it's easier to think of it this way, for the purposes of this discussion, the closer the signal value is to zero, the better. (That assumes that the signal value won't be greater than zero, which it won't be, for the stuff we're talking about.)
    David

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