Rigol DS4024 generates EMI on VHF FM radio

[Pedro4]

I bought a Rigol DS4024 in 2018 and am very happy with it. It came with a free upgrade to 350 MHz bandwidth which I didn't need but thought "what's not to like?". Over Christmas I've been repairing a friend's Hacker VHF FM radio (88 to 104 MHz FM only). I quickly discovered I had to leave the Rigol powered off or it produced sufficient EMI to dominate the radio audio whether tuned to a station or not, and whether connected to the Rigol or not. I fell back upon my old Hitachi 60 MHz CRT scope. That has a metal case and produced no audible EMI on the radio.

I'm just wondering is this par for the course if you have lots of digital electronics in a seemingly plastic case, or might I have a rogue DS4024?

[Slh]

I haven't tested it with a radio but my Rigol DSO1074 has a clear 100MHz ring, repeating at a few hundred kHz if you zoom in to the shortest time base and a few hundred mV.

Not something that's caused me issues yet but I was disappointed to find it.

[iMo]

Any equipment of that sort generates an EMI. It depends on the construction and resulting intensity of course. There are switching power supplies (it could be 2-4) inside the box, tons of digital electronics with pretty steep XXXps signal edges (thus it may generate a continual spectrum from Hz up to many GHz), etc.
Your FM radio could have a sub uV sensitivity so you get it all in.
What may help (except a good shielding) is using coaxes with BNC or SMA connectors (instead of the probes when talking the o'scope) and clap-on ferrite clamps cores put on the cables (best put it everywhere).
A single core adds up usually around 100ohm impedance around 100MHz, so you may judge how much common mode suppression you may get. With N cores you get N*100ohm.

[DaJMasta]

Interesting. Have you tested with a battery powered radio instead of a plugged in one?

I've got a DS4024 that I hadn't noticed issues with so I pulled out my SA, slapped on a 2 foot telescoping antenna, and swept through the FM bands and I don't really see a difference with it on or off.  It's a handheld unit and was on battery power, but perhaps there's conducted EMI that I'm not seeing because of that.

In any case, it's a product that had to go through the same EMI compliance testing as a lot of it, and it really sounds like yours would not pass in its current condition.  It's probably not worth the time, but it could be interesting to look at the power supply module, for example, to see if it had some failing caps or something that were dumping a lot more noise out than it ought to.

[Pedro4]

Thanks. But it still happens even if no probes connected to Rigol. I have tried the radio on battery power with same result. I think the FM signal is weak in my lab. I just found that if I touch the telescopic aerial (i.e. using my body as an antenna) the radio station strengthens and the Rigol noise reduces. I guess the plastic Rigol case is the weak point; does it have a conductive film or paint on the inside?

[TurboTom]

Inside the plastic housing, the DS4000 scopes are completely shielded in a substantial sheet metal enclosure. If any interference in the FM band is escaping, it's got to be conducted via the mains cord. From my experience, RFI countermeasures are pretty decent in Rigol's mature instruments, so my assumption would be some defective components within the RFI filtering circuitry. I may do some testing tomorrow...

Happy New Year everybody,

Thomas


Edit: See Connor Wolf's teardown video for reference