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I need some help. I've been trying to solve an interference problem with my
neighbors Nutone Intercom for some time now. He has an extensive system
with 19 speakers. At first, I thought the RF was coming in through the
speaker leads. I investigated what it might take to eliminate that. By
chance, during a test, I removed the doorbell module, and the RFI stopped.
The doorbell module connects to the doorbell with a two conductor cable.
One side is ground and the other side is the input to the module. I have
tried the following:
.01 uF cap across doorbell - no effect
.01 uF cap across input terminals to doorbell module - no effect
put 10 ferrite beads on each lead at doorbell module - some reduction, but
still audible
I also noticed that both the ground and input leads must be disconnected to
eliminate the RFI. If either wire is left connected, the RFI is present. I
tried a clip lead between the doorbell module ground wire and the intercom
chassis - no effect.
I have hope in that it appears that the RF is not coming in through the
speakers. I have isolated it down to two wire. This should be simple.
Can anybody help?
Thanks,
Tim K8XS
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<BODY>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV class=3DSection1>
<P style=3D"MARGIN: 6pt 0in"><SPAN=20
style=3D"COLOR: blue; FONT-FAMILY: Arial; mso-bidi-font-size: =
10.0pt"><SPAN=20
class=3D370460100-08122001><FONT color=3D#000000 size=3D2>I need some =
help. I've=20
been trying to solve an interference problem with my neighbors Nutone =
Intercom=20
for some time now. He has an extensive system with 19 =
speakers. At=20
first, I thought the RF was coming in through the speaker leads. I =
investigated what it might take to eliminate that. By chance, =
during a=20
test, I removed the doorbell module, and the RFI stopped. The =
doorbell=20
module connects to the doorbell with a two conductor cable. One =
side is=20
ground and the other side is the input to the module. I have tried =
the=20
following:</FONT></SPAN></SPAN></P>
<P style=3D"MARGIN: 6pt 0in"><SPAN=20
style=3D"COLOR: blue; FONT-FAMILY: Arial; mso-bidi-font-size: =
10.0pt"><SPAN=20
class=3D370460100-08122001><FONT color=3D#000000 size=3D2>.01 uF cap =
across doorbell -=20
no effect</FONT></SPAN></SPAN></P>
<P style=3D"MARGIN: 6pt 0in"><SPAN=20
style=3D"COLOR: blue; FONT-FAMILY: Arial; mso-bidi-font-size: =
10.0pt"><SPAN=20
class=3D370460100-08122001><FONT color=3D#000000 size=3D2>.01 uF cap =
across input=20
terminals to doorbell module - no effect</FONT></SPAN></SPAN></P>
<P style=3D"MARGIN: 6pt 0in"><SPAN=20
style=3D"COLOR: blue; FONT-FAMILY: Arial; mso-bidi-font-size: =
10.0pt"><SPAN=20
class=3D370460100-08122001><FONT color=3D#000000 size=3D2>put 10 ferrite =
beads on each=20
lead at doorbell module - some reduction, but still=20
audible</FONT></SPAN></SPAN></P>
<P style=3D"MARGIN: 6pt 0in"><SPAN=20
style=3D"COLOR: blue; FONT-FAMILY: Arial; mso-bidi-font-size: =
10.0pt"><SPAN=20
class=3D370460100-08122001><FONT color=3D#000000=20
size=3D2></FONT></SPAN></SPAN> </P>
<P style=3D"MARGIN: 6pt 0in"><SPAN=20
style=3D"COLOR: blue; FONT-FAMILY: Arial; mso-bidi-font-size: =
10.0pt"><SPAN=20
class=3D370460100-08122001><FONT color=3D#000000 size=3D2>I also noticed =
that both the=20
ground and input leads must be disconnected to eliminate the RFI. =
If=20
either wire is left connected, the RFI is present. I tried a clip =
lead=20
between the doorbell module ground wire and the intercom chassis - no=20
effect.</FONT></SPAN></SPAN></P>
<P style=3D"MARGIN: 6pt 0in"><SPAN=20
style=3D"COLOR: blue; FONT-FAMILY: Arial; mso-bidi-font-size: =
10.0pt"><SPAN=20
class=3D370460100-08122001><FONT color=3D#000000=20
size=3D2></FONT></SPAN></SPAN> </P>
<P style=3D"MARGIN: 6pt 0in"><SPAN=20
style=3D"COLOR: blue; FONT-FAMILY: Arial; mso-bidi-font-size: =
10.0pt"><SPAN=20
class=3D370460100-08122001><FONT color=3D#000000 size=3D2>I have hope in =
that it=20
appears that the RF is not coming in through the speakers. I have =
isolated=20
it down to two wire. This should be =
simple.</FONT></SPAN></SPAN></P>
<P style=3D"MARGIN: 6pt 0in"><SPAN=20
style=3D"COLOR: blue; FONT-FAMILY: Arial; mso-bidi-font-size: =
10.0pt"><SPAN=20
class=3D370460100-08122001><FONT color=3D#000000=20
size=3D2></FONT></SPAN></SPAN> </P>
<P style=3D"MARGIN: 6pt 0in"><SPAN=20
style=3D"COLOR: blue; FONT-FAMILY: Arial; mso-bidi-font-size: =
10.0pt"><SPAN=20
class=3D370460100-08122001><FONT color=3D#000000 size=3D2>Can anybody=20
help?</FONT></SPAN></SPAN></P>
<P style=3D"MARGIN: 6pt 0in"><SPAN=20
style=3D"COLOR: blue; FONT-FAMILY: Arial; mso-bidi-font-size: =
10.0pt"><SPAN=20
class=3D370460100-08122001><FONT color=3D#000000=20
size=3D2></FONT></SPAN></SPAN> </P>
<P style=3D"MARGIN: 6pt 0in"><SPAN=20
style=3D"COLOR: blue; FONT-FAMILY: Arial; mso-bidi-font-size: =
10.0pt"><SPAN=20
class=3D370460100-08122001><FONT color=3D#000000=20
size=3D2>Thanks,</FONT></SPAN></SPAN></P>
<P style=3D"MARGIN: 6pt 0in"><SPAN=20
style=3D"COLOR: blue; FONT-FAMILY: Arial; mso-bidi-font-size: =
10.0pt"><SPAN=20
class=3D370460100-08122001><FONT color=3D#000000 size=3D2>Tim=20
K8XS</FONT></SPAN></SPAN></P></DIV></BODY></HTML>
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