Sunday, August 30, 2020

Local interference pattern emerging

 The terrible RF interference I see here right across HF looks like this:

But for three weekends in a row it goes off at 2:35pm local time on Sunday and the band looks pretty good for a suburban block. It comes back on again at 35 minutes after midnight. So, exactly 6 hours of peace a week.

What kind of appliance would be on all week except for Sunday afternoons?

The fundamental frequency, where it's strongest, seems to be at 421kHz where it's stronger than the local ABC Radio National transmitter here.

Another interesting pattern is that every 60 seconds, with good accuracy, the noise shifts slightly and then back. There is one example on the waterfall here.

Tecsun PL-365 on Longwave

Now that I've found the base frequency it seemed that I could locate it with a radio that receives longwave. I have a Tecsun PL-365 but it didn't seem to offer longwave even though it's listed as a feature. It turns out that longwave is disabled by default and frustratingly the manual's instructions for enabling it aren't quite right. 

The procedure that works for me is:
  • Turn the radio off.
  • Press the DEL (9/10k) button until it displays 9kHz (it switches between 10 and 9)
  • Press the MW key until it displays "150-" (it alternates between 522)
  • Turn the radio on, press MW and it will tune from 150kHz
As you can imagine, I've been walking around the neighborhood trying to find the source but it's very difficult to track down, perhaps due to the long wavelength.

Noise gone!

The broad spectrum noise I've been writing about ceased on Tuesday and hasn't come back. It's been three days now. Obviously it's possible that it could return but my theory is that it was some sort of battery charger that was being used by workers doing renovations next door.

I've just had a decent contact on 40m SSB with Kevin, VK2KB, who is in Sydney 677km from me. We have been running WSPR to figure out the best times to talk.


Unknown said...

Hi Marxy,

Just like here @ VK1XP, very noticeable on the 20m band with definite switch on/off during the day. Looks like an 8KHz harmonic rate, perhaps a switch mode power supply, perhaps some of those cheap LED down lights with their poorly designed power supplies.

I will be interested to see what others think might be the source.


Peter VK1XP

Struan said...

Pool filter pump? It definitely wouldn't need to be on that long..