Slashdot Mirror
Cell Phones - Analog vs. Digital
"The point of digital is that it takes alot less power to transmit and if you've got 1 bar or 5, the signal should sound the same.. and there in lies the problem.. with the should. With an analog phone as your signal strength begins to go below 1 bar you start to hear static but you can still understand the person your talking to, though you may need to 'yell over the static'. However, with a digital system when the signal fades, there's no yelling because the signal isn't there, and packets that should be getting to your phone, just get dropped. As a result, Aunt Martha's 'Hello' on a crummy analog connection can still be made out.. but on a digital connection of the same strength might sound like 'He...o' with a gap of silence in the middle. (See my Cell-Phone Switch parody commercial on this site for an example if you don't know what I'm talking about).
Cell phone companies are boasting about how digital is good, but is it really? Analog signals work on the 900MHz band, which goes very well through houses, trees, your neighbors dog, etc. Analog works on the 1.9GHz frequency, which does not go through houses, walls, metal, trees, well at all. The question now becomes, why are they moving to 1.9GHz? The signal length is smaller, and therefore antenas on the phones can be smaller without worrying about chopping the signal from it's full height. However, the cell phone companies need to cover the area better for there to be as much coverage, especially in the city where there is lots of Multi-path (bounces and signal inversions), and buildings to go through. This is the same reason that your 900MHz portable (land line) phone will go further then your 1.2GHz portable phone.. (or it should anyway, but alot of companies are making illegal 1.2GHz phones and putting them on the market).
In addition, back to Aunt Martha, as long as her 'Hello' usually sounds like her 'Hello' on a land line, what difference does it make right? Well, unfortunately, the digital standards we have today are from years past. And while they work, they are by no means clear. If you are looking for clarity, you'll want to stick with an analog phone. For data communications, digital is the way to go. Cell phone companies will tell you that if you're in analog you won't get your voice mail notification and such, but the truth is they COULD do it if they wanted to. They just want you to switch over to digital. Why? For one, it takes less bandwidth off of their access points, so they can get more subscribers on per access point. Each analog cell antenna can carry only 56 simultaneous phone conversations, which just doesn't cut it in heavily populated areas. With digital they compress the signal and as a result can get many more people on a sectoral antenna. Digital cell phones use extreme compression of the sound that they transmit. The compression algorithms used are lossy; they're specifically designed around transmission of human voice to human ears, and take advantage of what the human ear will tolerate and what it won't.
What about the pros for digital? Digital is a bit more secure then analog as you can't hear it just by setting a scanner to the correct frequency, you also have to un-encode it from the digital, and smooth the signal out.
On last thing, the digital system works on 1.9GHz... your home microwave works on 2.4GHz.. It's close enough, you still want to hold that phone next to your head? Remeber what happens to an egg when you put it in the microwave, and then decide.
So with all that said, which do I prefer? I prefer the analog since it has better coverage, and the analog phone will keep the connection better in fringe areas. Digital phones are an all or nothing proposition. They either work or they won't. Analog phones can swish and cut out, without dropping the call. What do Slashdot readers use and like and why?"
I don't know what the point of this article is. It is re-iterating (in some cases exaggerating) stuff we already knew. The rest of the world had this discussion at least 10 years ago. As a result, we standardized on GSM.
In Australia we discouraged the use of Analog phones in the mid 90s, and the analog networks were shutdown in 99.
Before this time GSM was gaining huge momentum, with three GSM networks rapidly expanding their coverage. The majority of the urban population were pleased with the technology, however the rural population were less than amused. As a result, CDMA technology was deployed by Telstra which is a digital system, but offering performance characteristics closer to analog.
One problem with GSM in rural areas is the timing advance issue, which limits the maximum range of dedicated mode (2-way communication) to about 35km, typically. The GSM range limitation is not, contrary to popular belief, a power output limitation.
I'm getting a little offtopic here, but I'll quickly explain the problem: The timing advance problem is a result of using fine-grained timeslots. The timing advance parameter is the number of symbol periods the MS (phone) must advance the transmission to avoid colliding with other timeslots. The maximum value is 63 symbol periods, which was chosen to allow the MS plenty of time to measure other cells when not transmitting and receiving.
Additionally, GSM offers Short-Messaging-Service, GPRS (packet switched data), far more efficient spectrum use, EDGE (high speed GPRS using 8PSK modulation).
The population and population density of the US is far better for deploying GSM networks than Australia, so if Australia can do it, I can't see why the US can't.
While one will indeed find this "fact" listed in many places, including a few physics texts, it may well be a fallacy. I've looked up the frequency absorption spectrum of water, and 2450 MHZ was not a peak. Unfortunately my "classic" paper link is now dead (I'd really appreciate a currently active and stable link even if it supercedes the paper I had and proves me wrong)
The best I can do right now is " Absorption Spectrum of H2 18O in the Range 12 400...14 520 cm-1 [Journal of Molecular Spectroscopy 216, 77-80 (2002)]
Moreover, anyone with equipment to measure the relevant range can see that microwaves are not tuned to a tight band. The frequency of any one oven varies far more than any the reasonable expectation for an absorption band in that range (depending on temperature, use, etc.) and the variance between ovens is greater still.
That's actually one specific reason why a resonance frequency is not used: the increase in efficiency that would result from picking an absorption peak (vs. simply reflecting the microwaves around inside the cavity 10-1000 times until a significant fraction is absorbed) simply wouldn't have been worth the effort and cost of precisely tuning each unit (at the time when microwaves first came out) Further, we are all aware of the accounts (admittedly potentially apocryphal) that relate the discovery of microwave cookery to an accidental exposure to a military radar dish. Military radars (excluding weather radars) generally avoid the water bands, because water vapor in the air would limit range.
I don't mean to criticize the Original Poster, since that "information" can indeed be found in reputable sources. I'd simply rather not see it repeated if it obscures and incorrectly explains the operation of microwave ovens and EM radiation.
Finally, even if the microwave radiation from a oven *did* operate on a resonance absorption band for water, the total power of a cell phone is tiny (mW-W). One would get orders of magnitude more tissue heating by stepping out into the sun or even another person (both things some techie types seem to avoid). In the absence of any specific epidemiological or other significant evidence of specific tissue or cellular disorders caused by the specific frequency bands used by cellular phones, their radiation can *only* be expected to produce nonspecific tissue heating.
Before you worry about microwaves, worry about other sources of energy like sunlight. Microwaves onlt *seem* "spookier" to certain people, while sunlight is far stronger in many, many specific bands than celphones over their entire range.
It might be wise to say say IANAMD, but I *am* an MD (with a degree in molecular biology). That doesn't make me an authority on epidemiology or molecular properties, but I like to think it does give me a small edge.
So many things are misinformed/wrong about this...
Most have been posted by others, such as:
a) Digital can be in the 800 MHz band (same as analog) in addition to 1.9 GHz, and most of Verizon's CDMA network is low-band. 1.9 GHz is used because we ran out of 800 MHz spectrum.
b) Analog typically takes 3x as much power. Digital is good for the handset battery and good for your head. Digital phones peak at 200 mW, analogs are 600 mW for handsets, and some portables are 3W units. Analog is actually better for the provider power consumption wise - Analog FM signals can be amplified with around 70-80% efficiency or more, as opposed to around 14% for the absolute latest CDMA amplifiers. (FM signals do not need a linear amplifier, while CDMA requires an ultra-linear amplifier.)
c) RF cannot directly harm your body. (i.e. changing DNA nucleotides) The only way RF can harm your body is by heating it. Who cares if 1.9 GHz is close to 2.4 GHz? It's 200 milliwatts, which will cause negligible heating even if it is more efficiently absorbed than 800 MHz radiation. If RF were that dangerous, half of my coworkers would be dead after 10+ years of developing microwave transmitters and amplifiers. Yes, you have to be careful, and 45W of microwave directly into your body can do serious damage, but 200 milliwatts can't do diddly, even if you directly touch the antenna.
d) The author is severely wrong about quality vs. signal strength with analog vs. digital. Even at 4 bars of signal, an analog signal will have static. At 1-2, it will be almost unintelligible. I can get crystal-clear connections at 1 bar of signal, sometimes even 0 (i.e. on the verge of losing a connection) with my CDMA phone.
retrorocket.o not found, launch anyway?