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Extreme EMI / RFI from U-DIO8 when "standing by" 3 years 4 weeks ago #50537

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Long story I'll try to dither down. Mastering engineer by trade. Also an amateur radio operator involved in "nets" (on air "meetings" concerning everything from everyday BS to emergency operations). Otherwise, a surprisingly "non-technical" guy, which is why I'm here.

Long story short part: I have a U-DIO8 that's putting out ridiculous amounts of RFI / EMI -- This happens during (Windows 10) boot, stops when the "logon sound" happens, comes back again until the unit is active again (playing audio). I'm still in the experimental phase here, but I thought I'd throw out what I know so far.

More details part: I found the issue "accidentally" while tuning to a particular repeater on 146.76 MHz. That repeater (a 100+ watt Motorola Quantar) is around 35 miles away and in line-of-sight from my position. Always a strong signal. The radiation from the D-DIO8 is strong enough to "full-quiet" that signal. That basically means that the radio is hearing a signal - although completely silent - that squelches the signal from that repeater 100%.

Beginning the investigation: I noticed that somewhat frequently (no pun intended), that repeater (or so I thought) was Tx'ing 100% of the time while I was listening. They're not made for that sort of duty cycle, so I contacted the group that manages that repeater and they told me - Nope, it's in normal use right now and people are talking about (blah, blah, storm damage and what not). So, I figured it must be a local source or something atmospheric. Looked at APRS and tropospheric ducting reports, solar activity, beacons - Nothing.

So, SDR (Software Defined Radio). Plugged in, loaded up and just in time to find out something about this mystery signal - and it disappeared. Didn't think much of that till the next time, when it again disappeared as soon as I loaded the program. Then it hit me that it must be coming from the SDR dongle. After a little experimentation, that was quickly discounted but certainly traced to that particular computer. Loaded SDR into a laptop, connected a dipole antenna and the plan was to start unplugging things until that signal stopped.

First thing was the U-DIO8. One-shot, one kill, signal gone. Repeated the whole thing a few times to get a handle on what was going on (the boot, the stand-by, the return of the signal until something calls on that interface, etc.).

So that's where I'm at. There are other peaks - there was one in the 136MHz range, a few more that were suspect. I just don't have the time to track them all.



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Extreme EMI / RFI from U-DIO8 when "standing by" 3 years 3 weeks ago #50576

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This one is indeed quite odd.. I wonder if it's a wiring issue on the DB25 cable.. It would sound like maybe a grounding issue as we can't reproduce it here.. Can you please start a tech support ticket with our team? support.minidsp.com

They can organize a replacement cable.

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