Irritating tone on AM reception

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garyasta

75 posts

Master Geek

#93730 28-Nov-2011 14:15

I live in a remote bush situation. There are no power lines or telephone lines for at least a km (as the crow flies) each way.

I have a solar powered battery storage system. There is no cellphone reception.

We should be in a no-noise radio reception area. However, our house radio and the car radio have this irritating mono-tone that is present on the AM band, not the FM.

I have tried the reception with our 240v inverter switched off and using the radio batteries only. This means that all electrical appliances are not functioning. We still get the tone. There is a second-long break in the tone every half minute or so.

Has anyone got any ideas as to what this tone might be?

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#550987 28-Nov-2011 14:25

Broadcast AM signals can travel a *long* way due to their low frequency, and AM is the worst performing modulation scheme for interference. It's quite possible that the thing that's interfering with you is something nowhere near you. Any neighbours you can check with or take your equipment to try out?

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wellygary

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#550989 28-Nov-2011 14:26

What equipment are you using to trickle charge the batteries with? Have you tried powering off the inverter at night when presumably the trickle charger is not running?, that should totally confirm/rule out if the interference is caused by your PV setup

Does the AM reception ( when battery powered) reduce when you move away from the building which houses the Charger/Inverter/ Other appliances?

garyasta

75 posts

Master Geek

#550993 28-Nov-2011 14:42

Thanks for the responses.

A little more info - we live in a hilly area and the nearest neighbours don't have any heavy machinery that is likely to be operating. The homes are the standard residential type.

Our batteries are normally charged during the day using PV solar panels, so there is no charging during the evening after dark.

The battery supply feeds the inverter which converts 24v DC to 240v AC. So with the inverter off and the sun not in attendance, there should be no local interference being generated.

cyril7

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#550997 28-Nov-2011 14:54

Does the interference come and go during various times of the day?

Cyril

John2010

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Ultimate Geek

#550999 28-Nov-2011 14:56

garyasta:

...The battery supply feeds the inverter which converts 24v DC to 240v AC. So with the inverter off and the sun not in attendance, there should be no local interference being generated.

One assumes that at least the charge regulator (assuming there is one) between the panels and the batteries is still energised from the battery side though. There is also the possibility of a blocking diode failure which allows the panels to be reverse biased in darkness. To do a full isolation test you need to disconnect everything at the battery terminals themselves.

Do your neighbours have the same problem - if not then the source is likely to be originating on your own property.

What is the nature of the "noise" and when you say it goes off periodically is that right off or does its nature change

Dunnersfella

4086 posts

Uber Geek

#551006 28-Nov-2011 15:05

It has to be said...
But the irritating drone will no doubt be Newstalk ZB.
Try switching stations?

garyasta

75 posts

Master Geek

#551060 28-Nov-2011 16:04

I'll use a torch to see things by later tonight (my wife will go berserk when I switch the TV off) when I pull the fuses from the battery banks to see if that has any difference.

The tone is a monotone and the break is only for about a second.

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oxnsox

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#551077 28-Nov-2011 16:51

What Voltage is your radio running on??
(You've got a 24V DC system but does the radio run on 24V or is there another DC/DC converter [24-6??] in there somewhere)

Is your inverter an inverter/charger?
(Noisy devices that are never really off)

Do you get the same 'noise' on say your vehicle radio, tuned to the same station?
(It will be running off a totally different and independent power source)

garyasta

75 posts

Master Geek

#551088 28-Nov-2011 17:05

the car radio obviously has it's own battery and the house radio has either 240v AC stepped down by a standard 7.5v DC plug-in, or the internal radio batteries are used. Both supplies result in the tone.

The main house battery banks are charged using an MPPT controller from the PV panels. The inverter is a separate unit. Incidentally, the tone was there when we were using a different type of controller.

There is a separate charger that is connected to a diesel generator that is only used when the PV panels haven't done their job.

The tone is present on all AM frequencies, in the house, or in the car.

I'll see what happens tonight.

SaltyNZ

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#551089 28-Nov-2011 17:07

Dunnersfella: It has to be said...
But the irritating drone will no doubt be Newstalk ZB.
Try switching stations?

And I was so proud of myself for resisting that comment!

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wellygary

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#551095 28-Nov-2011 17:19

garyasta:
The main house battery banks are charged using an MPPT controller from the PV panels.

A quick google seems to indicate that MPPTs can be sources of radio interference, - but let us know what you isolation testing comes up with tonight,

oxnsox

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#551109 28-Nov-2011 17:32

My guess, if you're getting it across a number of devices on different power sources, is that it is due to the low signal levels where you are. And as Salty has said it's a (byproduct) function of the AM demodulation process, that you don't usually get with good signal levels. (Probably low level intermod products).

Is there any AM station you can listen to during the day that doesn't have the issue?

Also disconnecting the PV cells is one thing but are you isolating (disconnecting both inputs and outputs) the MPPT? (You may not be using them but they wil still be operating at some level if they have power getting to them)

garyasta

75 posts

Master Geek

#551304 29-Nov-2011 09:53

Yesterday I pulled the fuses from the power control panel, isolating the batteries and switched off the inverter. This meant that there were no power supplies and nothing running. We still had the tone.

We do live in a bit of a poor signal area and the analogue radio that I have been using over the past few days, is a little hard to tune, so I'll wait for a couple of days till I get a new digital radio and check a few stations then. Up until a few days ago I was using a Sangean digital until it had a problem, hence the replacement. The Sangean manifested the tone as well.

John2010

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Ultimate Geek

#551315 29-Nov-2011 10:04

Is the tone continuous over the whole AM broadcast band, over just some of it or just when you tune close in around a station?

garyasta

75 posts

Master Geek

#551463 29-Nov-2011 14:15

As I have mentioned, reception is poor here and the tone appears all over the AM band. The stronger signals are less affected with the tone audible but not intrusive. The weaker stations, and this includes Radio NZ national, have a stronger tone.

It is only noticeable when the station is tuned in fully. The background noise obscures it when the station is out of tune.

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