[plug] phone line interference

[John Summerfield]

On Wed, 25 Nov 1998, David Campbell wrote:

> Date sent:      	Wed, 25 Nov 1998 09:12:38 +0800
> To:             	plug at linux.org.au
> From:           	Tony Clark <tony at ballist.net.au>
> Subject:        	RE: [plug] Another (Possibly) Redhat specific squid tip
> Send reply to:  	plug at linux.org.au
> 
> > 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.

Take care here. BPS (data rate) is different from BAUD (signal frequency).
Do remember, to, that 56K modems are 56K in one direction. Outbound data is
sent at the same speed as achieve by my 33k6 modem.

two 55K modems talking to each other will be no more speedy than two 33k6
modems (unless they have better error recovery).

IAPs achieve 56 outbound by using fancy digital hardware to connect to
Telstra's digital network. Those of use using modems talk analog to
Telstra's digital network and our analog signal has to be converted to
digital. This A/D conversion costs speed.


I suggest you talk to Telstra about the problem and ask whether a second
phone point might help.



Cheers
John Summerfield
http://os2.ami.com.au/os2/ for OS/2 support.
Configuration, networking, combined IBM ftpsites index.