Author Topic: EMI for beginners: DAB Radio  (Read 977 times)

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Offline NivagSwerdnaTopic starter

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EMI for beginners: DAB Radio
« on: January 10, 2020, 11:29:03 am »
I built myself a VFD clock... it has...

12V input

Voltage regulator (TPS5410) 12V -> 5V
Voltage regulator (TPS61175)12V -> 70V
Filament Supply (LM4871) 5V -> 5V AC
Multiplexed IV-18 VFD tube

My multiplexing is based around a 27kHz interrupt
27kHz across 9 digits... = 3000 ticks/digit gives 100 'frames' per digit per second for effects

It all works (although I do notice a certain amount of instability of brightness in the digits which I am investigating) but today I came across a big problem...

I have a DAB radio which just about locks to BBC Radio 4 which I leave burbling along in the background whilst I work but today I discovered that if I turn my VFD clock on... DAB drops out entirely... nothing!

The clock is not yet in a case... but I intended to use perspex so had not planned any shielding.

What should I do next?  Stop listening to DAB?

Thanks

 

Offline T3sl4co1l

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Re: EMI for beginners: DAB Radio
« Reply #1 on: January 10, 2020, 12:52:44 pm »
Yikes... that sounds hideous!

Did you use ground planes?

Tim
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Electronic design, from concept to prototype.
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Online PA0PBZ

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Re: EMI for beginners: DAB Radio
« Reply #2 on: January 10, 2020, 01:03:22 pm »
If your reception is already marginal than there's not much needed to stop it from working. First thing I'd say is trying to get a better reception by either moving the receiver to a better spot or hooking up an external antenna if that is possible. Of course you can also try to find the course of the interference but that will only work until you bring in another device and kill the reception again.

Do you have a spectrum analyzer? If so you could examine the clock with a (home-made) near field probe and see where the problem is. If you stop the multiplexer is the problem gone? How do you create the 5V AC, is there an oscillator involved that is a bit too enthusiastic? Switch it off and see what happens. Ferrite beeds can actually help to suppress unwanted radiation, try them on the 12V entry and make sure you have no wires longer than needed. Lastly, a picture would be nice!
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Offline NivagSwerdnaTopic starter

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Re: EMI for beginners: DAB Radio
« Reply #3 on: January 10, 2020, 01:29:02 pm »
If your reception is already marginal than there's not much needed to stop it from working.
Yeap DAB was barely working anyway; I have to wiggle the antenna to get a signal without distortion.
Unfortunately I don't have a spectrum analyser.  The design does have ground planes.   
I'm interested in what would be throwing the DAB off... isn't it up in the 200MHz range... miles away from the operating frequency of the clock.

 

Online PA0PBZ

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Re: EMI for beginners: DAB Radio
« Reply #4 on: January 10, 2020, 01:35:33 pm »
Yes it is around 200MHz but you only need one square wave in your clock to get there, we are talking uVolts. I'd enable part by part of the clock (or the power supply) and see where the problem is. You mentioned flickering, that could also point to something oscillating that shouldn't oscillate. Time to get one of those SDR sticks for $15 I'd say.
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