Hey folks

I am experiencing a loud buzz type interference on all my valve radios pretty much right across the AM band. Ive used a couple of battery radios and shut my electricity down at the box and its still there. Interestingly the buzzing occurs during the day but usually fine in the morning and night. but thats not always. Any ideas what could be doing this next door? I live in a 9-townhouse unit complex. what could it be?

Thanks guys

As its all of them that rather rules out them. This is where the oscilloscope is handy as you can pinch the wave form off of a valve radio and that will confirm it is buzz from something generating square waves, perhaps at 50Hz. You should be able to see it with the CRO if its riding on the mains on the transformer secondary and perhaps "B". Make sure the Oscilloscope can handle the voltage. Some modern test equipment can't.

If you shut the power off that should shut it up. However, if its a solar panel inverter and the sun rises, or it activates, off it will go and not shut up perhaps between 06:00 and 18:00 hrs. It should give the loudest buzz to transistor radio close to it.

Unfortunately, these days there is a plethora of potential sources of RFI around the home ranging from LED lights and battery chargers to solar inverters and even provider-supplied smart meters.

RFI can enter your house via the air or the mains, or both.

Having apparently eliminated your own townhouse by dropping the power, then the next logical step would be to do the same for the others, although I'm not suggesting doing that without the cooperation of the other occupants. How neighbourly are they? Often a fairly high level of cooperation on their behalf, and some diplomacy on your behalf, is required.

Are you 100% sure it's coming from next door? Perhaps start by walking up and down the townhouses with a portable radio noting where the RFI seems to be strongest. At best that may target a particular TH; at worst the signal will be strong everywhere.

If willing, and while using a portable radio to monitor, then after explaining your mission, I suggest that you ask each occupant of a suspected TH to briefly switch off the mains. If the RFI ceases then you have found the source TH. In that case the next usual step is to drop each circuit via the associated breaker/fuse and whittle the area of the house down. If a particular circuit is found, then it's a case of scanning that area for a likely suspect.

MPPT Solar panel regulators are VERY Prone to generating RFI which is very hard to suppress as the MPPT action impacts the feeder cabling to the Inverter and the solar panels themselves become quite good antennas .
The feeder cable usually being twin tends to cancel much of it out along the feeder run but some does escape as I have found at our Community Radio Station.
Our Off Air receiver is on the same rack that the solar regulator is mounted on and despite screened antenna cabling and antenna well away from the solar array as the regulator output ramps up as the sunlight gets stronger any output over about 25A going into our backup batteries the RF Hash on top of our FM receiver output increases dramatically.
A toroid with the + & - leads from the solar array each going through one with a few turns on each HAS reduced the hash considerably proving that it IS radiation from the solar panel cabling getting in.

Have heard of similar cases where each solar panel has a micro inverter and AM reception is nigh on impossible when the sun is shining brightly and output is the greatest.
FM band so much affected but its still there on the FM band.
So as STC & Marc have suggested its going to be a process of elimination with the co-operation of your neighbours very much needed.

Once you find the source you then have to work out how to reduce of stop it...then the fun begins !!!

I ran a cable up to the back fence and installed a "long wire" antenna there, out of the noise.

One way to be sure of the locality of the source is take a radio to work and plug it in there. If there's no buzz, you'll have confirmed that none of your radios have issues.

I have the cheaper than cable Wireless NBN. As far as AM goes to calibrate a radio you have to shut it off as its like a symphony orchestra.

Many years ago we did have RFI regulations.

Marc

Along those lines, one thing I found out many years ago is that just because the more expensive inverters (the type one would take camping) puts out a pure sinewave doesn't mean it'll play a valve radio without a rather loud mains hum - no matter how big the filters are. There went my chance to take a radio camping.

We have an issue where our garage and car remotes become deaf when the sun is shining.
We have to wave the remote directly under the garage controller when this happens.
Likewise the car remote has to be held very close to the car for it to respond.
If it's overcast or during night time hours everything works fine.
I imagine it's a cheap Chinese solar inverter in our vicinity causing it but no one is owning up to it.
We have only recently installed solar but the issue has been going on for years so I know it's not ours.
Infuriating.

A very good report and observation Irext.

What you have described is a classical radio jamming device, where a great salad of high power multi frequency radio transmissions are
broadcast simultaneously.

Very effective in overwhelming tuned receivers' AGC, effectively making them 'deaf'.
Extremely successful against radio controlled bombs, drones, etc.

And on a personal level, a serendipitous report for me, because the last few months my car has become impossible to unlock when I'm home
but OK elsewhere, and yep, new solar inverters popping up all around me. Problem solved, and here I was thinking my car was possessed.

There is a very useful (hence common) dual buck regulator chip from TI that has an internally fixed operating frequency of 630kHz.

Perfect for jamming ABC Newsradio in Sydney!