🚀 go-pugleaf

In article <grahamsp02cnhq.fsf@barnowl.demon.co.uk>, Graham Murray <graham@barnowl.demon.co.uk> wrote:
>
>In article <5kirhd$eu3@news.istar.ca>, ptchat@istar.ca (Paul
>Chattaway) writes:
>
>> X2 modems do in fact work, but the actual throughput you get depends a
>> LOT on how good the wire is from your house to the local exchange, and
>> on how many other devices you have on the same line.  According to the
>> manufacturers X2 modems _are_ capable of 56Kbits, but because FCC
>> regulations limit the amount of power a modem is allowed to use,
>> 53Kbits is the highest speed they're ever likely to reach.  You might
>> find that due to line noise and other factors, 48Kbits is the highest
>> you're likely to get...  And keep in mind that these are "receive"
>> speeds; X2 modems still send in 33.6kbits.
>
>Could you possibly explain the power limit restriction to 53k?  As you
>say the high speed is receive only, so the modem will only be
>generating 33k6.  AFAIK the high speed end has to be ISDN connected,
>and so is just sending a digital bit-stream.  I am sure that there
>cannot be any restriction on the data pattern that the ISDN sends,
>even using a voice or 3.1kHz audio bearers otherwise the 'Data over
>voice bearer' that I believe is popular in the USA would not work.


The power limitation is not "power limit restriction to 53k" as you stated.  
The limitation on power, effectively limits the transmission speed to 53k, but 
you *can* get 56k even with the power limitation over pristine 
lines....something you rarely, if ever, see in real life.   The power 
limitation effect is simple....the difference between yelling across a room, 
and using a bull-horn to get your voice across the room.  

By limiting the power of the signal, you limit the signal to noise ratio.  
Thus the level of the noise is closer to the level of the carrier and thus 
they are more likely to interfer with one another.  

And why does the FCC have a limitation on the power levels...to prevent 
crosstalk...which is much less of an issue now, than it was many, many years 
ago when the power limitation was put into effect.

Don