cool dc/dc things

I seem to recall your testing one like that, and finding that it was pretty ratty—the VHF switching happening in irregular bursts with lots of low frequency components.

Cheers

Phil Hobbs Feast of St Stephen the Protomartyr

Yes, some of these things "regulate" bang-bang in bursts. That's not good for efficiency either.

I'll have to try some more, on eval boards I guess. The classic potted converters work but are big and expensive and noisy.

I have a cool circuit idea but it needs 5 volts to switch a high-side GaN fet and I want small size and low jitter.

Had to look that up:

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

You remember Goog King Wenceslas?

So what? What's the advantage of a high switching frequency beyond a small transformer and how bad's the spurious RF output?

Small is good. Higher frequencies are better because they’re easier to filter out. Better still would be if it ran continuously, because then it would be nearly trivial to keep switching junk out of sensitive circuits.

Cheers

Phil Hobbs

Small and cheap are good. Especially small.

And I can lowpass filter 64 MHz easier than 100 KHz.

ICs, especially TI ICs, are taking over formerly discete, big, expensive functions. Micromirrors, BAW, magnetics, GaN. Fun stuff.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

That's a given. But the RF background noise from switching power supplies is giving radio amateurs a *major* headache these days. It's the radio equivalent of the recent phenomenon of light pollution. You might take creditable trouble over your filtering, but I can tell you there are plenty of manufacturers elsewhere whose wares are injecting all sorts of horrible s*it into the RF landscape. If there's a ham trying to pull through a delicate signal from a distant station at

-130dBm, all that crud becomes a serious problem and no one, it seems, is taking it sufficiently seriously.

The TI chips are spread-spectrum and designed to pass EMI specs.

Are kids getting into ham radio these days?

I was never interested.

You

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

I don't believe so. I sometimes attend ham rallies looking for anything you can't get from likes of Mouser and Digikey, like EHT transformers, tubes and moving coil meters for instance. When computers became widely available to the consumer market in the early

Surprising how many pro RF guys are *still* active hams who build stuff. I can't imagine having a hobby the same as my day job. They must be really obsessed!

Exactly. The same noise power spread out over even more frequencies so as to meet a spec but with no intention of minimising the hash.

Nowadays the gateway seems to be CB or PMR. Then they gradually realise that getting a licence will enable them to use other wavebands for longer distances - or join in contests - or experiment with different ideas ...whatever they find most interesting. One of our local clubs makes a point of welcoming CBers and assisting them to pass the Foundation exam.

A couple of us 'oldies' are learning CW - one because she has friends all over the World and finds CW is a more reliable way of contacting them (back to the topic of QRM). I'm not entirely sure why I'm doing it but I feel it could be useful one day - and it's good to keep learning new things. (It also makes for much simpler home-brew transmitters.)

Mo is a speech therapist and has worked with stroke survivors who can't talk or write but can communicate in morse code.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

There have always been noisy switching power supplies. There have also been some relatively quiet ones.

When I put together EMI's second phased array ultrasound scanner as clinical trials machine I made it lot lighter than the original (and the twenty pre-prodcution prototypes) by buying a quiet 5V switching power supply for the logic (and there was a lot of logic).

My 1996 paper on a millidegree thermostat used a switching drive for the Peltier junctions, which would have been a bad idea if I hadn't gone a lot of trouble to minimise the low frequency content of the switched currents, and a lot more to minimise the area within which the switched currents circulated. At one point somebody got worried that it hadn't been filtered out well enough and swapped in the much bulkier linear current drive we'd used early in development, but didn't see any difference at all.

Ralph Morrisons's "Grounding and Shielding Techniques in Instrumentation" deserves a lot of the credit. I'd read the first 1967 edition as a graduate student - it's reference 94 in my Ph.D. thesis - and I always had a copy around throughout my professional career, though the copy on my bookshelf is the 1998 4th edition.

Some people do, but nowhere near enough.

TI isn't a good choice if you want carefully designed ICs - they want the smallest, cheapest part they can sell in volume.

Analog Device and Linear Technology (until they were bought by Analog Devices) were more interested in higher performance parts that they could sell at higher prices.