Nothing gets ruled out as far as video causing RFI--anything in the mix from the video card to the monitor itself generates RFI, and yes, the screen contents can affect where the RFI appears on the spectrum.
Bad RFI from Computer?
- Thread starter LunaEros
- Start date
- Status
The Cyberpower UPS is probably rated for 800 VA.
Convert VA to AMPS and then Watts and you will see UPS units rated in VA don't come close to the wattage rating that your plugged in equipment may need.
From your description, it sounds like the Cyberpower UPS is shutting down because it knows it's already exceeding the load it can supply.
It sounds like your total load may be right on the Cyberpower's max continuous load. Some UPS units also include the current used by loads plugged into the surge only outlets. That's usually done to protect small or less than ideal wire sizes inside the unit and if often included in the total load to meet the safety ratings of whomever your regulatory agency is.
In the old days, real UPS units were rated in Watts until you got into the large industrial units for server buildings or 3 phase units.
When everything started being made in China, Watts was replaced with VA as a marketing ploy as most consumers don't pay attention nor have a clue of the difference.
LunaEros
Member
That sounds plausible. But it doesn't account for when I only had a couple small wall warts plugged in and it still did it. Come to think of it I also had it plugged in for about a week with nothing in it's outlets and it shut off on it's own after about 5 days.
LunaEros
Member
Ok, back to square one. I pulled all the RTLs and rehooked everything up and it seems to affect all 3 of them. I did take the antenna exension cable that came with the first kit and wrapped each end around large ferrite snap core beads 6-7 times and made an air coil out of what was left between the ends and put it between the preamp and the RTL and it seems to queit it down a fair amount though it is still loud enough to be bothersome. I also found that if I substitute the Mobius with my Tram discone I instead get something more akin to a really faint high pitched whine instead of a buzz which I'm not even sure the whine is even RFI. There must be some way or some cheap device that can kill all this RFI buzz.
TomLine
Member
Do the usb sticks go directly into the computer or over an extension cable? I want to try using a long usb cable; which I could also choke, just to see. The small saw tooth looks like something a switching power supply can make if it's not filtered good. The underlying wave the teeth ride on look like FM broadcast. If you use an FM filter, the saw teeth may still be there.
LunaEros
Member
Yes, they're on a powered hub. Unfortunately the only cable I had to use is quite long too. I do have ferrite bead cores around each end of them though. And it uses one of those switching wall-wart supplies. The cable for that is rather short though.
And I also have both an FM Notch filter and AM band reject filter from RTL-SDR.Blog. It's their brand of them.
The preamp I'm using is Nooelec's HF through 150MHz wideband barbone LNA. It's shielded but not in a case.
I only really get the buzzwhen it's on the Mobius loop and only when the preamp is inline. Otherwise it's pretty much normal.
I'm wondering if there's some wide range RFI filter I can get for cheap. Or maybe I just have to get a large toroid and loop the antenna coax through it 20-30 times.
I wish you could make the lower bands sound like FM broadcast as in full quieting.
Chronic
Member
- Joined
- Nov 7, 2004
- Messages
- 574
- Reaction score
- 233
A Harmonic of the refresh rate of the monitor ?
I have an older Dell flat screen monitor. It was still pretty new when I discovered the RFI it produced.
When video was displayed on that monitor, it wiped out the 2 meter ham band.
It's funny as its noise started almost precisely at 144 MHz and ended abruptly at 148.250 MHz. It was almost like the thing was made to wipe out the 2 meter band.
It's RFI signal was also strong. It would full quiet any two meter radio even if they were mounted 30 feet away. I quickly learned the RFI was coming in through a rooftop 2 meter antenna which was much further than 30 feet away. Go outdoors with a portable and the monitor's noise started dropping off really fast around a 150 foot distance or so.
I tried changing the refresh rate as well as what type of signal was used. (HDMI vs DVI) for example. No change. Also tried different non-optimal video image sizes but still no help. The only thing that helped was when I'd let it go into power savings mode or powered it off!
I was about ready to trash the thing when I decided to make a crude RF probe and sniff it.
The hot spot for the RFI was coming off a large high voltage lytic capacitor mounted on its switching power supply board.
I swapped that cap with one that had a higher capacitance but the same voltage rating. It barely fit due to being a tad bit fatter in diameter but I managed to get the shields cover closed without forcing anything.
The new cap cured the problem and a sweep using a signal analyzer confirmed the different cap didn't just shift the RFI to a different range.
I was amazed that simple attempt to solve the problem actually worked! I still use that monitor daily to this day.
I forget whose name was printed on the LCD panel and the boards but it was made by someone else and only branded as a Dell monitor outside the housing on the model number sticker.
I tested the cap I'd removed with an ESR tester and it passed all tests. Who knows, did the extra capacitance offer better filtering? I don't really know. All I cared about was stopping the bad noise and replacing that one capacitor did exactly that. Even though the voltage rating was the same between the capacitors, I really expected fireworks when I plugged it in and turned it on! I think they were rated for 450 VDC.
I still don't fully trust the thing and only have it powered on when I'm sitting here using the monitor. I never leave it powered on unattended.
I changed that cap probably six or more years ago now and its never arched or popped or anything so It's probably safe but I just can't trust it for some reason!
Last edited:
Omega-TI
Ω
I've been reading this thread with interest as I also have a minor RFI situation and believe getting a little space between the PC and the dongle could be of help, but mainly because I want to tidy up all the damn cables. So, what length is best? Five feet, ten feet, fifteen? At some point all that cabling could become an antenna in it's own right, defeating the purpose, right?
Ubbe
Member
The USB cables that I own that do not have any RFI chokes on them will all start to emit RFI as soon as I connect them to the computers USB connector. It doesn't happen to any of my USB cables that has a RFI choke at both ends. Those cables cost more so are probably of better general quality using better shielding. Then the length of the cable doesn't matter for RFI but will have an impact on data speed and read/write errors. But it's probably no problem when using USB1 and USB2 speeds and "normal" lengths.
/Ubbe
/Ubbe
TomLine
Member
As SDR evoles, would be nice to have a "RFI Certified" label on various computer products. Not holding my breath.
- Status
