Radio 3 interference

Posted by: rn on 24 February 2003

I have gone back to using an analogue tuner after a couple of years of using a DAB. All the channels are OK except Radio 3 which has now got a slight but noticable warble. All the other BBC stations are fine. I live in the south Bucks area. I suspect the FM aerial may have been moved when the DAB aerial was installed. Anybody got any other ideas?

Posted on: 24 February 2003 by paul99

rn,

Some questions:

By warble, do you mean a background noise that you hear during quiet passages or periods of silence?

Does it only happen in stereo?

Did your tuner always do this?

During the period that your tuner has not been in use has the number of local, or otherwise stations increased?

Have you tried tuning in accurately with AFC switched off?

Regards,

Paul.

Posted on: 25 February 2003 by rn

Thanks for the reply. Here are the answers

Some questions:

By warble, do you mean a background noise that you hear during quiet passages or periods of silence? Yes, like a fax machine working faint but very annoying.

Does it only happen in stereo? No.

Did your tuner always do this? No. I have tried another tuner and it does it as well.

During the period that your tuner has not been in use has the number of local, or otherwise stations increased? Sorry don't know.

Have you tried tuning in accurately with AFC switched off? Yes.

Any ideas?

Posted on: 25 February 2003 by paul99

rn,

The warbling sound you describe usually only occurs in stereo. This is because the width of the stereo baseband is 53kHz. To demodulate this baseband from the carrier means that more of the transmitted spectrum is used. The buffer between transmission channels is quite small and unless the receiver selectivity has a sharp cut-off some of the adjacent channel will be received. This leads to aliasing which is heard as the warbling you describe.

I have never heard of this occurring with mono, only 15kHz of the baseband is used and so any interference from adjacent channels is not responded to, usually.

It could be a tuner fault, but as two tuners do this it seems unlikely. Is there a strong signal in an immediately adjacent channel?

If the problem is really due to interference from other signals, then your original suggestion of positioning the antenna for the strongest Radio 3 signal may be the answer.

If it were an adjacent channel problem I would probably end up putting traps in the antenna cable, if I could be bothered. My tuner always used to warble in stereo, I solved the problem by relegating the FM tuner to the B-system and sticking with DAB.

Sorry - nothing clever to suggest.

Regards,

Paul.

Sorry,