Solution to possible mobile phone tower interference in older radio system

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Prudle

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#318888 1-Mar-2025 22:03

Hello mobile comms and RF specialists,

A quick question from someone who knows little about the tech of RF comms and interference on radios.

Short story - friend's classic JVC mini system worked very well sitting in her apartment in Grey Lynn.

Then a mobile phone tower was built over the road and 30 metres down the street, so around 40 m distant, give or take.

Ever since, the mini system is outputting the classic interference pip pip pip-pitty pip noise through the speakers. I've tested with a pair of speakers from another more modern minisystem that doesn't have interference issues so seems to point the main unit being the issue.

The interference occurs also when it plays a CD (tested by playing with volume to 0) - so all you hear are the pips.

So my question - does anyone have if any practical remedy to cure this (a filter or something that might be inserted into a specific part of the circuit board.... or....)

it's a classic system with strong sentimental value. Shame to relegate it to just a shelf monument.

Any help appreciated

Tinkerisk

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#3349127 2-Mar-2025 03:53

The problem is quite wide-ranging. I would first add a filter to the mains supply, then make the speaker cables as short as possible and insert a ferrite core in ONE wire at each speaker. That's what you can do without any internal building work. Why? To ensure that induced RF radiation does not reach the unshielded interior via these paths. This may or may not be sufficient.

However, if such a high level of RF radiation enters the flat or house, you should also have it checked whether the transmission power regulations for the mobile mast have been complied with - this seems to be quite a lot of radiation in your case. That would be a first step.

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SATTV

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#3349146 2-Mar-2025 08:54

Tinkerisk:

However, if such a high level of RF radiation enters the flat or house, you should also have it checked whether the transmission power regulations for the mobile mast have been complied with - this seems to be quite a lot of radiation in your case. That would be a first step.

That site is only a few months old, I work not far from there, it will be within spec I am sure, these towers are low power by design as they are used for infill not distance.

Also they ( One at least ) are pulling sites off buildings and on to council land like this as it is easier access for maintenance.

As for the problem, can the stereo be moved from the current location to the furthest away from the tower to see if the sound is reduced or eliminated.

Another thing to try is put some tin foil directly between the radio and mast to see if if reduces the interferance.

Here are the licence details, there are six bands licenced, I dont know if they are using them all.

I know enough to be dangerous

Goosey

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#3349147 2-Mar-2025 08:56

I wonder what the “RSM” (radio spectrum management), office would have to say / suggest?

in this day and age, why is something so far away having an effect on a simple audio circuit?

MaxineN

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#3349153 2-Mar-2025 09:45

@SATTV

Can guarantee all would be used. Yep, solution would be the move it away further and/or possibly open it up and see if there's any shielding at all.

>Ever since, the mini system is outputting the classic interference pip pip pip-pitty pip noise through the speakers.

Sure it's not a nearby cellphone? Anything environmental in the house or even maybe next door?

Pointing fingers at a newly built tower is a bit fast to a conclusion.

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richms

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#3349203 2-Mar-2025 13:30

Ferrites on the speaker cables, disconnect any AM antennas from it (unless you use AM) and failing that opening it up and going liberal with copper tape and conductive paint on the inside of the plastic case are the 3 things that helped in a similar case of RFI, but it was from wifi APs and the 5Ghz really seemed to get into a cheap amplifier. It was for announcements so replacing it was a lot harder, and it had much longer speaker cables connected than a baby stereo system would have.

Richard rich.ms

Prudle

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#3349270 2-Mar-2025 20:42

MaxineN:

@SATTV

Can guarantee all would be used. Yep, solution would be the move it away further and/or possibly open it up and see if there's any shielding at all.

>Ever since, the mini system is outputting the classic interference pip pip pip-pitty pip noise through the speakers.

Sure it's not a nearby cellphone? Anything environmental in the house or even maybe next door?

Pointing fingers at a newly built tower is a bit fast to a conclusion.

That's a fair comment, but the timing for the new tower did seem to match.

The system is within an apartment block so definitely possible it's a new internal device the apartment, but friend had the same mobile devices before interference started and afterwards.

I'll open it up next weekend and see if there's any shielding in it and get some ferrites for the cables in.

Thanks everyone for your suggestions.

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richms

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#3349271 2-Mar-2025 20:46

Prudle:

That's a fair comment, but the timing for the new tower did seem to match.

The system is within an apartment block so definitely possible it's a new internal device the apartment, but friend had the same mobile devices before interference started and afterwards.

And the person on the other side of the paper-thin wall that you probably have the stereo system up against hasn't put a 5g router or anything there?

Richard rich.ms

RunningMan

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#3349274 2-Mar-2025 21:10

Prudle:[snip] but friend had the same mobile devices before interference started and afterwards.

Potentially that device could be using a different band though with the new cell site though, so perhaps turning it off or moving it to test may help.