TV OR NOT TV? – a Case Study
By Ian Jackson VK3BUF
Editor’s Note: Whilst this article relates to a television reception problem, the underlying issues and processes employed by Ian apply to amateur radio. The subject could just as easily have been an amateur radio receiver as opposed to a television. This is also an EXCELLENT example of how Ian applied the QRM Guru process end-to-end… from problem identification through to resolution. Every step is clearly demonstrated and can be applied in your own situation.
It’s August 2024. I visited my father a few days ago, and he advised his TV had stopped working. Sure enough, the digital TV had a No Signal message on every channel. A second TV in another room suffered the same symptom. This ruled out a fault on the TV itself as the problem had to be common to both sets. The antenna system was an obvious candidate.
The antenna is a common log-periodic with a masthead pre-amp and a splitter designed for digital TV. It was only a couple of years old and seemed to be in good condition. It was dark at the time, but a sturdy shake of the antenna pole did not resolve the problem, so an intermittent mechanical problem was unlikely. Likewise, a shake of leads and connectors between the TV and the wall connection introduced no telltale fluctuations. The DC supply which fed power up the antenna appeared intact and working. I resolved to return the next day and continue diagnostics in daylight.
The following morning I received a call to say that the problem had ‘fixed itself’ and nothing had to be done. Later that day I received another call. “It stopped working again.”
I planned to return with test gear and portable TV receiver to see what was going on. At that point I had a followup call with a pivotal observation: “When I turn on the lounge room lights, the stations all disappear, when I turn them off, everything works again.”
This shifted the focus of the problem from an antenna continuity issue to a QRM issue. Evidently one of the four LED down lights servicing the room had gone rogue and was generating extreme interference, wiping out both television sets.
I packed up some gear and returned to the house. My first step was to set up the spectrum analyser next to the TV and shift the TV antenna from the telly to the analyser. I started wide, selecting a receiver range from 1 MHz to 1 GHz. With the lights off, it looked like this:
All was normal. Not too much noise and a couple of commercial transmissions evident. Then I turned on the lounge room down lights and it looked like this:
This was a mess, with an obvious noise source disrupting a good part of the spectrum. These LED lamps had been in place for 6-7 years. It was probable that one or more of the filter capacitors in the lamp regulator had dried out and were no longer cleaning up the high-speed switching that was applied to the lamp elements. Two different size lamps were in use, but they were all under control of a common wall switch.
The next action was to visit Bunnings to purchase replacement LED lamps. I had previously assessed some of their lamps. They were inexpensive and all proved to be RF quiet. It was not worth trying to determine which lights had failed, but simply replace all of them.
The lamp replacement proceeded without difficulty. With the new lamps in place and activated, both television sets performed normally. A good outcome.
While this case did not directly relate to Amateur Radio, there are strong implications for us.
- Although none of his neighbours were Amateurs, conceivably they could have been. Had a prominent Amateur antenna been nearby and interference was being experienced, some residents would be fast to conclude that this was the cause. In such situations, the non-technical neighbour can’t be relied upon to behave rationally or systematically. The effects of the interference are very real for the people concerned.
- If the broadcast signal into the neighbour’s TV was strong enough to penetrate the interference caused by their own LED lamps, the lamps could still produce S9 noise on several HF bands over a large radius. The house owner could be unaware of the problem. Maybe their wifi runs somewhat slower, but they hadn’t noticed. The consequences for a sensitive HF receiver next door could be tragic and obliterate the enjoyment of an Amateur Radio installation.
These situations are relevant and more likely to occur as society embraces modern electronic appliances . More and more, the process of identifying interference sources has become part of the hobby of Amateur Radio. We cannot rely upon or expect the ACMA to dispatch field operatives to resolve these issues for us. (Editor’s note: It’s fair to say the ACMA are unlikely to assist Amateurs with interference unless they can illustrate they’ve conducted their own analysis and can provide supporting evidence of the noise source)
The website QRM.guru is a free resource dedicated to dealing with exactly these sorts of situations. It describes the process of identifying the origins of interference and lists the actions that can be taken to resolve these issues. Fundamentally, if there is radio noise, there must be a noise source. Once it has been identified, the goal should be resolution, rather than tolerance.
Readers are encouraged to visit the site and read up on some of the case studies.. For the shack wall, download a copy of the QRM tracking flowchart that helps those suffering QRM to correctly profile radio noise sources.
In this instance, the interference issue was resolved and that trashy, advert filled medium known as ‘free-to-air TV’ has now been restored to its former glory. The old lamps were disposed of as recyclable scrap metal.
If you haven’t already, visit QRM.guru and get informed on how to identify and minimise unwanted RF interference.