Challenge: 1 MHz FSK shock test on amplifier output – What would your scope show?

[DonH56]

You are right. For audio not necessary. I worked with audio devices now around for 50 years and did not need a radio frequency spectrum analyzer. But since I work also on radio and transmitters I bought used second hand hp ones for 250 and 400 EURO which work still very good. Actual new ones from asia manufacturers price is around 1000 € when not specialized. The real professional brands are much more expensive.

There are a number of reasonably priced 1-3 GHz spectrum analyzers now, though still expensive for a casual hobbyist. When I was a tech and designing my own stuff decades ago I had a used HP 1 GHz (I think) spectrum analyzer for general troubleshooting and to check for oscillations just as @pma does. I don't have any equipment beyond a cheap DMM now, plus a Digilent rig I have barely touched. One of the drawbacks of retiring is that I lost access to the millions of dollars of fancy test equipment, though most of it did not reach down to the audio band.

 

[fpitas]

There are a number of reasonably priced 1-3 GHz spectrum analyzers now, though still expensive for a casual hobbyist. When I was a tech and designing my own stuff decades ago I had a used HP 1 GHz (I think) spectrum analyzer for general troubleshooting and to check for oscillations just as @pma does. I don't have any equipment beyond a cheap DMM now, plus a Digilent rig I have barely touched. One of the drawbacks of retiring is that I lost access to the millions of dollars of fancy test equipment, though most of it did not reach down to the audio band.

Yeah, when I bought my Mini 300 I dragged it into the lab and set it up to test it. I'll miss that kind of thing if I ever retire.

 

[DonH56]

Yeah, when I bought my Mini 300 I dragged it into the lab and set it up to test it. I'll miss that kind of thing if I ever retire.

What was vexing was e.g. hauling in an audio component, hooking it up to our fancy 110 GHz network analyzer for a few tests, then realizing the lower frequency limit was 50 MHz. Stoopid Don Trick.

 

[sam_adams]

Don't you guys see it?

It's right there. In the middle of the picture.

 

[egellings]

True, although there are some reasonable options these days that use a PC as display etc. I think pma is just saying it's a good check if you have a new design.

True, but I think that there are few or no DIY audio hobbyists designing in the gigahertz region.

 

[fpitas]

True, but I think that there are few or no DIY audio hobbyists designing in the gigahertz region.

Some common transistors, especially MOSFETs, can and will take off oscillating at UHF frequencies.

The most insidious is when there are RF oscillation bursts (so-called parasitics) occurring at places along the device output swing.

 

[egellings]

Some common transistors, especially MOSFETs, can and will take off oscillating at UHF frequencies.

The most insidious is when there are RF oscillation bursts (so-called parasitics) occurring at places along the device output swing.

True.

 

[DonH56]

Some common transistors, especially MOSFETs, can and will take off oscillating at UHF frequencies.

The most insidious is when there are RF oscillation bursts (so-called parasitics) occurring at places along the device output swing.

BJT emitters get inductive as well and can behave badly...

 

[fpitas]

BJT emitters get inductive as well and can behave badly...

Yes indeed.