[plug] Interference

[HILL Walter]

	> Software Engineers..sheesh   :)
	> 
	> Seriously though David, insulation won't stop radio waves,
screening may.
	> You could have well hit upon your problem though and I would
suggest a
	> filter in series with the phone line.  Not sure if you can buy
them, supect
	> not.  Basically an inductor in series with each wire with 2
caps at each
	> end of the inductor. Ground the center connection of the 2
caps.  If there
	> are any radio hams in the area talk to them. You may get
lucky.

	This may or may not work. Assuming that you are trying to
achieve 56k, this 
	would require a signal of 56+ kHz while your friendly local
transmitter will be 
	pumping out 700-740 kHz (720[6WF]+/-20kHz). Some calcs will be
required to get 
	the parameters just right. Any filtering WILL degrade the signal
performance.

I think that you'll find that the underlying signalling rate for a
56kb/s is 9600 baud.

Encyclopaedia Britannica says...

"In addition to the elementary forms of digital modulation described
above, there exist more advanced methods that result from a
superposition of multiple modulating signals. An example of the latter
form of modulation is quadrature amplitude modulation (QAM). QAM signals
actually transmit two amplitude-modulated signals in phase quadrature
(i.e., 90<Picture: {degree}> apart), so that four or more bits are
represented by each shift of the combined signal. Communications systems
that employ QAM include digital cellular systems in the United States
and Japan as well as most voiceband modems transmitting above 2,400 bits
per second. 

A form of modulation that combines convolutional codes with QAM is known
as trellis-coded modulation (TCM), which is described in Channel
encoding. Trellis-coded modulation forms an essential part of most of
the modern voiceband modems operating at data rates of 9,600 bits per
second and above, including V.32 and V.34 modems."

Regards,
Walter...
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Walter Hill                                   ,-_|\
w.hill at computer.org                          /     \
walter.hill at customs.gov.au                   \_,-._/
+ 61 8 9430 1505 (Voice) + 61 8 9430 1391 (Fax).