re: Phone feedback on broadband
Monday, March 27, 2006 at 7:44 am
Windows Me Annoyances Discussion Forum
Posted by Jack Gulley
(5917 messages posted)
The standard ASDL line filters are passive low frequency bandpass filters. They
block any high frequency (above audio and frequencies used by Dial-up modems) from
reaching the line and in turn block the high frequency broadband signal from reaching
the phones and being attenuated. As such they can not induce noise on the line.
However, they could be reflecting high frequency tones coming from the phone,
back to it. And this might be the source of the problem if they are low cost/quality
powered phones. Such phones sometimes have an auto gain amplifier in them that amplifies
the sound picked up by the microphone and from the phone line and power the earpieces.
Often sold to people who are hard of hearing. They usually have a volume control
or switch on them. If it has one, try lowering the volume control and see if it has
any effect.
The real problem is that the auto gain circuit on the lower cost ones usually
use a low audio frequency signal from the line to adjust the volume level. But the
ASDL filter would pass the low frequency quit will, but some of the higher frequency
sounds will not pass the filter well and part of its energy gets reflected back to
the phone. Where the amplifier amplifies it. So you get a feed back loop of high
frequency audio sounds.
Try an older non powered phone and see if it works OK.
You can also try finding a ferrite core (donut shaped) about 3/4 in to one inch
in diameter and big enough to pass the the phone jack plug through. Then pass the
phone line to the phone through it (making about three or four loops through the
core) to form a filter that will attenuate the higher frequencies on the phone line
and see if that helps reduce the feed back. They also sell noise reduction bandpass
filters that you can put in-line with the phone that might help. Just make sure you
put such ferrite cores or bandpass filters between the phone and the ASDL filter.
I would also try several different brands of ASDL filter than the one you were
supplied with. You should be able to find someone with one you can borrow to test
with.
- Written in response to:
- Phone feedback on broadband (Rik1986: Monday, March 27, 2006 at 1:56 am)
There are presently no replies to this message.
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