[AMRadio] Telephone line bandwidth for AM Phone Patch

COLEMANJ at sbcglobal.net COLEMANJ at sbcglobal.net
Wed May 21 11:12:29 EDT 2003

Hi Jim:
	The majority of telephone equipment (answer 
machines, modems, fax, ect.) has filtering in it to 
bypass RF.  The bypass capacitance in these things 
causes the higher frequency components of the audio 
to be rolled off.  This bypassing also kills DSL 
signals.  The devices that you install to make your 
lines DSL ready, should be called blockers instead of 
filters, because they have inductors in series with 
each line that will keep the higher frequency 
components of any signal on the line, while stopping 
it from reaching the other telephone equipment.  
Obviously the connection that is to be used for the 
DSL modem must not have a blocker on it or the HF DSL 
signal will not reach the DSL modem.  My house wiring 
was to weird to deal with so I installed a splitter 
outside at the TELCO block and put one blocker there 
for the house telephone equipment and ran a separate 
line to the place where I wanted the DSL modem to 
be.  This way I didn't have to worry about all the 
stuff in the house.  You probably could have 
unplugged all other telephone equipment in the house 
except your computer modem and the connection rate 
would have been better as well.  I don't think  that 
matching Z on the phone patches is very important.  
As a mater of fact I think the phone patch should 
represent as high Z as posible to the phone line so 
as to not load it down.  But equilization is very 
important as is balance and isolation from ground to 
prevent common mode hum.  

Good Luck
 John, WA5BXO
-----Original Message-----
From: amradio-admin at mailman.qth.net [mailto:amradio-
admin at mailman.qth.net] On Behalf Of Jim candela
Sent: Tuesday, May 20, 2003 10:36 PM
To: amradio at mailman.qth.net
Subject: [AMRadio] Telephone line bandwidth for AM 
Phone Patch 


	This is a little off subject, but just a 
little. Sometimes when we
use a phone patch on AM, we can get better results 
matching phone line
impedances, and maybe a little lead, or lag to help 
equalize (or add
pre-emphasis) to the available bandwidth. I am sure 
this was studied years
ago when professional baseball games were broadcast 
from the announcer's
booth, and then piped for hundred's of miles down 
telephone lines, and then
using the remoted audio to modulate broadcast AM 
	This all occurred to me today when I made my 
house DSL ready. Four
lines (with a common beginning) now each have a DSL 
filter at the end before
going into a telephone, or modem. I have NEVER been 
able to connect to the
internet at a rate higher than 28.8 Kbs. Today after 
installing DSL filters
(including one at the computer modem), my connection 
is 48.8 kbs!!!! I just
might cancel the DSL which starts tomorrow, and keep 
the filters. So what
technology is in use with these filters? How do they 
apparently result in
improved connection speeds? Is it terminating the 
line in it's
characteristic impedance, or increasing the 
longitudinal balance? 

	Remember the answers to these questions need 
to be discussed in a
manner that will help us AM hams have more fidelity 
when we remote our
stations, or use a phone patch, or download the 
AMRADIO reflector's email.

Jim candela

More information about the AMRadio mailing list

This page last updated 22 Feb 2018.