Ofcom trace interference to a lightbulb

[J D 8]

Sounds like the transmitter visit was fun Geoff. We had for many years in a rented part of a shed on the farm a Ship to Shore radio repeater. There was a distinct smell from the valve radio.

A friend who is a radio ham has a Spark generator radio, like the sort on the Titanic . He found it at the local dump in very good condition complete in its lovely wooden case's! Say's he would like to fire it up but dare not as he thinks it would drown out most signals for miles around. Cheers John.

[Kevin Wilson]

Posted by Geoff S on 24/09/2020 14:56:36:

(snip)....... I think eventually houses will be wired with a 12 dc circuit for lighting with a central ac to dc regulator/rectifier and much simpler (and probably cheaper) LED bulbs with greatly extended life.

Geoff

Geoff, I work at a UK satellite TV broadcaster and wiring the buildings for DC was under passing consideration a few years back. One of my buildings is a large broadband hub and we have many DC systems at 50volt, a data centre standard evolved from GPO so I am told. Typical loading of a DC system is around 1000Amps. And that is the rub with LV DC. Low volts = big currents = big cables.
China and India are leading the way with MV DC transmission lines (yes, 1million volts) now possible by high efficiency HV semiconductor converters. hopefully they are built to a higher standard than the SMPS in domestic LED lamps.

[Peter Christy]

Many decades ago, I worked at the Holme Moss TV transmitter, just outside Huddersfield. This was a 405-line VHF transmitter (Geoff will know what I'm talking about!). I was told that it was the original Alexander Palace transmitter, famous for bending the German navigation beams during the war, while it was still at AP.

It looked like something out of H.G.Wells! Lots of brass, ebony and ivory, a "dynamotor" (3-phase electric motor turning a generator) to produce the current for the filaments in the valves, and a 3-phase mercury vapour rectifier, nicknamed "The Mekon" (again, older readers will get the reference!).

The actual circuitry was pretty basic, but the scale of it was enormous! Old hands used to measure the SWR by sliding their hands along the co-ax feeders (looked like sewage pipes!) feeling for "hot spots". Quite often, a day or two later, their hands would be peeling from RF burns!

I was on duty in the control room one day when the transmitter suddenly shut down! I hit the big red "Alarm" button to summon everyone to the front and started powering up the standby transmitter. Unbeknownst to me, someone was in the modulator section of the standby transmitter (a room the size of a small garden shed!) and was quite surprised when relays started pulling in all around him! Luckily it was all heavily interlocked, so he was in no danger, but it sure made him jump!

In the control room, circuit diagrams were pulled from their pigeon holes - a bit like legislation in the Houses of Parliament - and the various parchment scrolls studied.

"I reckon its R34", pronounced one of the senior engineers, "Have we got one in stores?". Receiving an answer in the affirmative, said engineer vanished into the transmitter hall, and into the bowels of the transmitter itself. Much banging and cursing later, he reappeared with a 3 ft long charred carbon rod. This had been "R34"!

"Told you so!", was all he said!

--

Pete

[Geoff S]

Posted by Kevin Wilson on 25/09/2020 17:49:11:

Posted by Geoff S on 24/09/2020 14:56:36:

(snip)....... I think eventually houses will be wired with a 12 dc circuit for lighting with a central ac to dc regulator/rectifier and much simpler (and probably cheaper) LED bulbs with greatly extended life.

Geoff

Geoff, I work at a UK satellite TV broadcaster and wiring the buildings for DC was under passing consideration a few years back. One of my buildings is a large broadband hub and we have many DC systems at 50volt, a data centre standard evolved from GPO so I am told. Typical loading of a DC system is around 1000Amps. And that is the rub with LV DC. Low volts = big currents = big cables.
China and India are leading the way with MV DC transmission lines (yes, 1million volts) now possible by high efficiency HV semiconductor converters. hopefully they are built to a higher standard than the SMPS in domestic LED lamps.

Of course that's true if you need real power for heating etc (one reason I think our 240v mains supply is superior to the US 110v - though we had a 110 v supply at work which was rarely used). However I would think the current involved in LED lighting would be quite modest and any extra copper conductor cost would be offset by the lower energy requirements of pure LED lighting (as opposed to the current LED bulbs which need 240v ac to a low voltage dc converter in each one with the potential for EMI). In your case the energy requiremnts may well justify high voltage/low current supplies but that probably wouldn't be the case in a domestic setting.

I admit I haven't done either the maths or any research but it seems worth consideration. Vehicle lighting is also becoming more LED based. When I edited a national cycle club magazine (Tandem Club Journal) back in the late 80s I was given some LED rear lights to review (red LEDs being really the only ones generally available then) and they were brilliant both literally and figuratively. The main advantage was their reliability and low weight. The so-called Never Ready cycle lamps were notorious for intertmittent operation LED cycle lighting is now so good that motorists complain about their being too bright whereas back in the 80s the complaint was of cyclists having no lights at all.

Geoff

[Chris Walby]

So was the lamp at fault.... or more likely what was passing through it?

Was it just acting as an aerial? There are plenty of candidates that produce higher frequencies than 50Hz or any of the harmonics associated with that fundamental frequency or switch mode power supplies operating at higher switching frequencies where their harmonic frequency aligns with the equipment effected operating frequency?