Text 11535, 87 rader
Skriven 2005-08-10 09:53:00 av Michiel van der Vlist (2:280/5555)
  Kommentar till text 11533 av Björn Forsström (2:203/614.61)
Ärende: Cell phone cost
=======================
Hello Björn,

 >>> You must have a subscription for it so the system knows
 >>> that it should be used.

 MvdV>> There is no technical need for a subscription. So it is
 MvdV>> just another trick to squeeze some more money out of you.

 > How does then the system know that it should use it?

Same as it knows how to use which cell with normal cells: trial and error.

To the handy, the "extended cell" looks the same as any other cell. So when it
can not establish contact within the normal cell because it is more than 35 km
from the base station, it will go scan again for a cell where it can make
contact and it will find the "extended cell".

Also when contact is already established, the system can initiate a handover
from the normal cell to the "extended cell" or vice versa just as it would with
normal cells.

 >>> Even if the base station have high-gain antennas the phone
 >>> doesn't and then it doesn't help how many watts you put out
 >>> at the base when it can't hear the phone.

 MvdV>> Ah, you are not a ham, otherwise you would know that a high
 MvdV>> gain antenna works to increase the signal on receive just
 MvdV>> as much as it does on transmit.

 > I know it *should' work in theory but doesn't when I have tryed it.

Then you must have done something wrong because it isn't just theory, it has
been well tested and used for nearly a century. When you have a chance go visit
a radio astronomy site and see what they can do with high gain antennas to
receive weak signals...

 MvdV>> Yes, I know. We used to have 450 MHz NMT here too some
 MvdV>> 10 years ago. That was when a car phone (That is what
 MvdV>> is was called then as the sets were too big to be carried
 MvdV>> around) was very expensive and so there were not many
 MvdV>> around. And so the cells could be big. It was phased out
 MvdV>> about then years ago I think.

 > They still have 450 in Domenican Republic when I was there in
 > March with phones just as big as any GSM.

Are you sure that was NMT? There is such a thing as GSM 450 you know.

One of the nice things of GSM is that it dispenses with the need of a duplexer.
A duplexer is bulky and expensive, do doing away with it makes the phones
smaller and cheaper.

A duplexer or duplex filter is needed if one needs to simultaneously transmit
and receive on the same antenna. With the older analog systems one either had
to use a half duplex system, where one takes turns in receiving and
transmitting, saying "over" every time, or one must have a bulky and expensive
duplexer.

GSM employs a time share method, so the transmitting and receiving are done in
a different time slot. No need for a duplexer.

So if these phones were the size of modern GSM's, I suspect they were not NMT.

 MvdV>> I can imagine it still to be useful for areas with a low
 MvdV>> population density.

 > Here, especially in the north.

Yes, but then one needs two phones when travelling. Or a dual capability phone.
Do they exist? If they do they must be bulky..

 >>> Well, I have a bluetooth headset to my Ericsson z1010 3G but
 >>> that is diconnected when I put the phone in the car-handsfree.
 >>> Even if it would work the range for bluetooth isn't more then
 >>> about 10 m so I might as well go to the other person.

 MvdV>> What if he is in the car next to you? ;-)

 > Electrical windows....

On the highway at 120 km/h? ;-)


Cheers, Michiel

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