You bastard!

Setting up an urban minimalistic station: Part 3

By the time I got home, it was already quite late. But I couldn’t wait to power up my SunSDR for the first time. The burning question was THE most important question of all: how many signals – if any – are protruding through the noise ceiling?

Yes, the urban noise ceiling, not the countryside noise floor.

Before that, the shack had to be massively decluttered. Finding that a ground wire was still attached to a brass bus at the back of my operating table, was a rather pleasant surprise.

Thirty minutes later, the radio was finally on.

And there it was: the dreadful screen of Death!

The entire spectrum polluted with massive s9+20dB buzzers, spaced 9KHz apart. Not just on 20m but on any band from 40m to 10m.

This was a massive kick in the bum. Actually, the band was so useless that I literally felt physical pain. Urban DXing means putting up with high background noise, antenna restrictions and running low power, but this was simply so bad that I had no desire to neither transmit nor receive. Worst of all, the interference was not just overwhelmingly powerful but stubbornly constant. And yes, right on FT8 frequency too.

After ten minutes, I somehow recomposed myself and started looking for a culprit.

Everyone and everything was a suspect: the neighbours plasma TV, street lighting, solar inverters, switch mode power supplies in the shack, wall warts, internet modems and routers, computer screens, USB cables. I was going crazy: at one point I’ve even suspected the SDR radio itself! Disconnecting individual devices, shifting them around, adding ferrites to cables made no difference at all.

To get my mind off of my receiving problem, I decided to transmit. To my surprise, running 60W, the very first FT8 call was answered by BG5CCB from Ningbo City, east coast of China. A few minutes later, an Argentinean was in the log as well, followed by a Norwegian and a couple of Japanese. Clearly I was loud enough to generate a steady stream of callers, and miraculously, despite all the interference, the SunSDR and JTDX were managing to pull those signals out of RF mud.

The decision was made to wait until all neighbours turn their TVs off and go to bed. Unfortunately, the nasty interference was still there. I went to bed disappointed. “Wait until tomorrow morning, it could be the street lights” – said wife. “Some problems have no solution” – I replied.

With the first ray of sunshine, I strolled down to the shack. The interference was still there, laughing at me.

It was a time for drastic measures: shutting completely the power supply to the house. After all, before knocking on neighbours doors, I had to be absolutely certain that problem is not on my side. Luckily the SDR was powered by battery and run on a laptop.

XYL was happy to assist. “Watch for these lines. I am turning the power off, then back on; see if there is any change”.

“They’ve completely disappeared!” exclaimed the wife.

And so they did! Even with the power restored, the interference was gone. The band came to life, with many more signals showing on FT8 screen.

And then, a couple of minutes later, the interference was back on, with the same strength: neatly spaced buzzing spikes, everywhere.

Yet at that point I knew that it is just a matter of minutes before I’ll find the bastard and kill it once and for all.

It was in my house, hiding in plain sight, probably just meters away from the shack. The table has turned, my way.

To be absolutely sure: one more power on/off. Identical results. Clearly, we are dealing with an appliance which does not kick to life immediately after power up, but a few minutes later. A bloody fridge!

“Which one out of the two?” – she asked.

“This one!”

“How do you know?”

The door label was dead giveaway.

“DIGITAL INVERTER Technology!”

She quickly googled it.

“Digital Inverter Compressors: Unlike conventional compressors, digital inverter compressors do not abruptly start and stop. This ensures consistent, uniform cooling, as well as less energy consumption. Less Start & Stop also means reduced noise and less wear/tear of internal components, elongating compressor life.”

Urban DXing – killing nasty domestic RF polluters, one fridge at a time.

Quickly, as 20m band was dying off, I snatched a Spanish station and a couple more Japanese. We are in business baby!