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Author Topic: 160m RFI from fixed telephone  (Read 1015 times)
M0KDX
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Posts: 6




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« on: January 29, 2004, 02:44:17 PM »

Gentlemen,
          Hope you can help. I have recently decided to operate on Topband but have an RFI problem i just cannot cure. My dial up modem connection causes the interference on 160m to rise by at least 3 S points.

I know its the modem and phone line because I can hear the dial up tones as I connect. Has anyone an idea how I may cure this problem. It only occurs on Topband and with the modem off the noise level drops considerably

Regards

Paul M0KDX
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KA5S
Member

Posts: 229




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« Reply #1 on: January 30, 2004, 05:53:46 AM »

Paul,

You might satisfactorily suppress such noise using the same filters meant to keep MW broadcastng out of telephones.

A home-made verson might use a ferrite toroid of about 9,000 permeability, magnet wire bifilar wound to about 2 mHy inductance, the self capacitance resonating it it where you need isolation. However, you have to be careful the insulation is enough to withstand the DC bias (I believe in EU that's up to 70 volts) and the 90 volts of so of LF AC used for ringing on top of that. And the wire must be heavy enough to not open on the occasional lightning transient.

It is just possible this noise indicates non-CE-approved equipment, since in EU the RF current on signal and peripheral lines, as well as power, is limited. It's just not limited at a very low level.

Cortland
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MW0KIK
Member

Posts: 22




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« Reply #2 on: April 12, 2004, 01:12:26 PM »

Paul,

I suffered something very similar with my modem.  Try winding the cables through some torroids.  This worked for me...

I have a digital satellite reciever that gives me s9 noise on topband and no matter what i try i cant get rid - hopefully this will not be the case with your modem..

good luck

leigh
mw0kik
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