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Old 24th Oct 2020, 8:07 am   #21
Diabolical Artificer
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Default Re: Diode switching noise on mains power supplies

"to be "diode induced" in the context of this thread, they would need to be repetitive at 50Hz or 100Hz" check, but still only 100mV P-P ish but higher than N/ripple but not audible.

What would be defined as problematic diode noise? More than 1v RMS & audible?

Andy.
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Old 24th Oct 2020, 9:14 am   #22
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Default Re: Diode switching noise on mains power supplies

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Originally Posted by Radio Wrangler View Post
In one of mankind's greatest ever goofs the levels of permitted radiated and conducted interference were set assuming there would only ever be one interferer at a time within range of a victim receiver. They completely failed to see the explosive growth of doodads.

Then pile on top making self-certification allowed and not having effective enforcement.

Oh, and did I mention the spread-spectrum loophole where SMPS and CPU clocks are FM'd deliberately so most of their power falls outside of the bandwidth of the measuring receiver called up in the standard?

What a mess!

David

David,

I think there has been a quiet agreement behind government scenes, across multiple countries, to write the HF bands off as obsolete junk. There are few users now in Europe that get any commercial benefit from them. And the Internet and satellites have taken over such uses of HF.

Evidence? Well I would cite the persistent attempts by the amateur community to defend HF bands from the interference you describe, with an equally persistent refusal by government to honour their legal responsibilities. It started with power line comms some 20 years ago. That was a minor prelude of course for what was to follow.


The second bit of evidence was making amateur licences free. I don't know the legalities, but its difficult for those getting a freebie to make serious complaints.

Richard
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Old 24th Oct 2020, 9:51 am   #23
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Default Re: Diode switching noise on mains power supplies

I watched the EMC regulations get formed and even designed the measuring receiver system for the German authorities who were the primary source of these standards. It was all evolutionary and the model was of an arcing thermostat in a heater, or sparking brushes in a vacuum cleaner in one apartment creating interference on a radio or TV in the next apartment. Levels were set based on how much interference was tolerable on a receiver tuned to a broadcast and within its planned service area, along with the typical spacing of one apartment from another as being the minimum separation between interferer and interfered.

There was no conspiracy here, there was just no vision of a future where a huge number of interferers, synchronised by the mains waveform would combine and fill the spectrum with noise.

Equipment manufacturers saw the required test methodologies and exploited the measurement bandwidth realising that they could get a pass by not reducing the amount of crap, but by spreading it around more. This was cheaper! A loophole happened to have been left - inadvertently, and all the manufacturers exploited it. Take a PC, any PC, even one of the posh full price Western brands and set it up as used. Now put it through the current EMC tests for either domestic or commercial (easier!) levels and it will fail. I have actually done this with a full, certified EMC facility, open air test site, screened rooms and all. It fails, just sitting there with a normal windows desktop showing on its monitor. So how do the PC makers get to stamp CE on their products?

Well, they claim that such static operation is not representative of 'real world use' and they write special programmes to exercise the machine in a more random sort of way. You guessed it! The ******s are cheating, the programmes are designed to spread the emissions so that at any moment only a fraction of their power fits into the specified bandwidth od the measuring receiver. And now the things pass... only just.

Just coincidentally it was the same firm wanting to use a PC in a large system and had to get the entire system EMC'd as was the firm who made the PC. As a consequence I got to talk to the people who did the EMC work on the PC and I got to get real answers. This might have been a world first.

So the rules have big holes, and many companies work hard to meet the word of the rules while totally neglecting their purpose.

There is no conspiracy against amateur radio's HF bands. We are simply being ignored, considered unimportant, and of no consequence. This is bad enough.

I've watched it through the period concerned, with access inside regulatory authorities, a manufacturer and a test house. I can say that there has been no conspiracy. All the damage has happened simply through human greed and laziness steering everyone in the same direction.

They were sufficient.

David (Conspiracy theories debunked while-U-wait)
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Old 24th Oct 2020, 11:46 am   #24
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Default Re: Diode switching noise on mains power supplies

Im my experience, a suitably (over-)rated 0.01uf ceramic disc, (i.e. 1KV upwards) across each diode deals with the noise effectively.
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Old 24th Oct 2020, 12:28 pm   #25
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Default Re: Diode switching noise on mains power supplies

"There is no conspiracy against amateur radio's HF bands. We are simply being ignored, considered unimportant, and of no consequence. This is bad enough"

David,

Agreed there is no conspiracy. The government doesn't need to do such things. All they have to do is ignore laws that turn out to be inconvenient, particularly when ignoring those laws means that some people can make loads of money, and hopefully pay more taxes on their profits. And as you say amateurs are regarded as unimportant and can be safely ignored politically.

Thats what I think has resulted in the HF bands becoming a dumping ground for devices that barely meet the regs, do not meet the regs or can only meet by ruses such as the spread spectrum one you cite.

Clearing up the polluted HF bands now, with all the LEDs , SMPS, etc would be rather like attempting to get all the microplastics out of the sea!

Richard
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Old 24th Oct 2020, 12:48 pm   #26
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Default Re: Diode switching noise on mains power supplies

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Im my experience, a suitably (over-)rated 0.01uf ceramic disc, (i.e. 1KV upwards) across each diode deals with the noise effectively.
As it happens, that was the starting point of this thread, since I had precisely that in place in my particular diode bridge - and they definitely did not work!

And this thread has shown very elegantly, and helpfully that there are far better solutions - namely a) use fast switching diodes (i.e. UF4007 rather than 1N4007), and b) fit a R-C snubber, not across any of the diodes, but across the transformer secondary. See previous answers for the details.


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Old 24th Oct 2020, 1:53 pm   #27
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Default Re: Diode switching noise on mains power supplies

The high voltage end of the 1N400x series can be used successfully as PIN diodes, switching and carrying 100W of RF, though their junction C limits the isolation in the off direction unless you apply lots of volts of reverse bias.

They can also be successful as low-ish value varactor diodes.

What they aren't fit for is power rectification.

Rather ironic, really.

David
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Old 24th Oct 2020, 7:20 pm   #28
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Default Re: Diode switching noise on mains power supplies

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Originally Posted by Radio Wrangler View Post
The high voltage end of the 1N400x series can be used successfully as PIN diodes, switching and carrying 100W of RF, though their junction C limits the isolation in the off direction unless you apply lots of volts of reverse bias.

They can also be successful as low-ish value varactor diodes.
Indeed: here I'm currently working on a voltage-tuned 5.0-5.2MHz oscillator using four 1N5407 diodes as the tuning elements.

They provide Varicap™, function, sure - but I've got 50 of the things here and it's a right-royal PITA to find four of the things from a from-the-same-bandolier batch-of-50 that will 'play' linearly in a 2x2 opposed-pair.

[I've got the lot into an Excel™ spreadsheet which shows - in a simple 2-plane voltage-vs-capacitance model; that's simple. Next comes the 3-plane model which introduces temperature-variations! Am I mad to be doing this?]
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Old 24th Oct 2020, 10:58 pm   #29
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Default Re: Diode switching noise on mains power supplies

Yes.
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Old 24th Oct 2020, 11:36 pm   #30
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Default Re: Diode switching noise on mains power supplies

Semiconductor modelling software, SPICE and its variants may have semiconductors represented by their physical dimensions and doping parameters at the core of their simulations, but PIN and SRD diodes can't be modelled because SPICE lacks a carrier lifetime parameter. So the PIN diode behaviour is missing, as is the sudden pulse of SRD action.

So though you can model rectifier/smoothing/transformer circuits and mains filters, the RFI pulses are left as a surprise for when you actually build one.

THere is some work on modelling carrier lifetime, but it doesn't seem to have entered the mainstream.

David
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