USB Modem Causes Radio Interference??

  CKT 13:03 26 Oct 05

I have just installed broadband using a USB Modem supplied by my ISP. Everything performs as advertised with an extremely stable connection at a good speed. However, I noticed very quickly that the modem transmits interference on MW radio frequencies - we listen to Radio 5 etc in other rooms in the house and all rooms have interference when the modem is on. If I take the power off the modem [unplug the usb with the computer still on] the interference disappears.

The modem is a BT Voyager 105

Before I talk to my ISP, I wonder if anyone has this make of modem and can confirm whether or not they get interference - in other words, do I have a fault in my particular modem or is the interefrence a characteristic of all BT Voyager 105s

  octal 13:15 26 Oct 05

You may some imbalance in you telephone line, it shouldn't radiate that badly. Having said that the frequency used for your BB is 30KHz and 1.1MHz considering if you are listening to the Brookmans Park Radio 5 Live transmitter which transmits on 908KHz it is within the passband of the BB.

I think its worth having a word with your ISP, whether they will understand I don't know. Do you have a friendly Radio Amateur near you? They are fully aware of these problems and might be able to talk to your ISP on your behalf.

  CKT 13:22 26 Oct 05

Many thanks - I have disconnected all my telephone device [3 others] so that only the modem is connected - still no change lots of MW interference. very Odd.

  octal 13:38 26 Oct 05

Have got a portable radio? If you have you might be able to confirm if the interference is either coming from the phone line or the computer. Tune the radio to a clear frequency around 700KHz and bring the radio close the the phone line and see if there as an increase in noise, if there isn't then try near the computer, the USB cable is a likely suspect. You will probably notice there is an increase in noise anyway because computers are notoriously noisy radio radiators anyway.

What you are looking for is a substantial increase in noise.

  CKT 18:36 29 Oct 05

Many thanks for your help. The portable radio trick suggests that it is the phone line. Even outside the house [on the opposite side to the modem] if I move the radio close to the external phone line [en-route to the BT Pole] the interference increases dramatically.

Radio 5 reception is notoriously bad in our area anyway and the interference is in a narrow band [500KHz - 1 Mhz] which just covers their frequencies! C'est la vie.

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