Noise free 5V Power Supply? - Page 1
Forum section: electronics / beginners

author: Lord of nothing
author_rank: Super Contributor
timestamp: May 22, 2017, 12:47:50 pm
content: HiI looking for an Noise Free Power Supply for me Pi2 to receive some Radio Amateur Radio Stuff.I try different well known Brands for Cellphone/ Laptop Power Supply out and the noise level is higher than when I put the SDR Dongle on my Pc.So can someone Recommend an Power Supply who is available in Europe and give 5V to my Pis?Maybe there is some who is power efficient to keep my bill low.THX

author: VEGETA
author_rank: Super Contributor
timestamp: May 22, 2017, 12:52:52 pm
content: I think Pi comes with it's own power supply, why not using it? I don't know if it is switching or linear.Switching ones cause noise but linear ones are clean... just get a 7805 regulator and it is ok. It outputs around 1.5A so I think this is enough.You need to give it voltage first then it outputs 5v regulated... so maybe a 9v charger could do it.

author: bktemp
author_rank: Super Contributor
timestamp: May 22, 2017, 12:54:18 pm
content: Did you try using a power supply with a linear regulator instead of a SMPS? It will be less efficient, but should have a much lower noise than any SMPS.Are you sure the noise is from the power supply and not generated by the Pi itself? I have read somewhere, it does generate quite some noise.You could also try connection the Pi to ground. A PC is typically connected to ground since it uses a metal case, but most 5V power supplies are not.

author: madires
author_rank: Super Contributor
timestamp: May 22, 2017, 01:15:29 pm
content: An additional simple LC filter might help also.

author: The Soulman
author_rank: Super Contributor
timestamp: May 22, 2017, 01:35:30 pm
content: Tell us a bit more about your setup, I also suspect the lack of ground is causing the noise.

author: Kjelt
author_rank: Super Contributor
timestamp: May 22, 2017, 01:41:00 pm
content: The audio people are using linear powersupplies followed by Jung regulators ( $ $ $ $ $ ) see picture.If I am not mistaken the PI uCs are 3,3 or perhaps even 1,8V uCs so they have onboard regulation. It makes no sense only changing the external supply and leaving cheap smps regulators onboard.Better solder them off and build a nice external linear supply that provides all required voltages.If you say receive "Radio Amateur Radio Stuff" what do you exactly mean, does the pi need to decode an analog signal or are you feeding it a demodulated digital signal ?

author: Lord of nothing
author_rank: Super Contributor
timestamp: May 22, 2017, 01:44:07 pm
content: Quoteits the same crap like the other one.QuoteI dont know... The are the "cheap" USB one you get everywhere.QuoteRemote Power Bar -> USB Charger -> Pi2 -> DVB-T Dongle -> Antenna Signal Splitter -> Antenna on the RooftopOn the Signal Splitter is my Pc via another DVB-T Dongle. Then the Pc run the noisefloor is low. When the Pi is powered up the noise floor increase dramatically.QuoteMaybe the cheap USB Charger have no Ground.A friend of mine who also operate a lot of Pi the told me that he never have any problems. In my case I see it on the SDR Software on my Pc.

author: brabus
author_rank: Frequent Contributor
timestamp: May 22, 2017, 01:47:55 pm
content: I bet the problem comes from the earthing, not from the PSU itself.If the usage is not continuous, I would suggest batteries.

author: stj
author_rank: Super Contributor
timestamp: May 22, 2017, 02:27:53 pm
content: try with a battery & 78s05 regulator.just to make sure the noise is not from the Pi itself.

author: cdev
author_rank: Super Contributor
timestamp: May 22, 2017, 02:47:46 pm
content: Try a bunch of ferrite split beads first. That works wonders. Also make sure your antenna is appropriate for whatever your application is.Is an rtlsdr dongle involved? Also what frequencies, HF or VHF/UHF?

author: CJay
author_rank: Super Contributor
timestamp: May 22, 2017, 02:51:56 pm
content: Quote from: Lord of nothing on May 22, 2017, 12:47:50 pmSadly, my experience of the pi was that it's very noisy no matter what PSU you use, an SDR dongle on the PC next to my Pi immediately showed lots of spikes and broadband noise when I powered up the Pi and it made no difference which PSU I used.You're going to need to put it in a box and take some RFI/EMC measures to quiet it down.

author: cdev
author_rank: Super Contributor
timestamp: May 22, 2017, 03:00:46 pm
content: Perhaps you should try adding an additional Pi filter on the input?Two capacitors and a beefy choke.

author: Lord of nothing
author_rank: Super Contributor
timestamp: May 22, 2017, 03:11:10 pm
content: QuoteI will use RTL TCP (or how the call it) to digitalis the Signal and send it over LAN to an Virtuall PC where GNU Radio will run. The Pi are directly under the Roof who get extreme hot and cold. Thankfully I cold get the Server to the basement.QuoteYes my Pc is decode the Signal 24/7 without problems.QuoteSureQuoteVHF (now)QuotePi or Dongle? The Pi is in an Metal Case.QuoteWhere?Sorry I have a little knowledge about Electronics.

author: cdev
author_rank: Super Contributor
timestamp: May 22, 2017, 05:33:31 pm
content: Are you trying to use it with a TV antenna or CATV system? Thats not good unless your goal is watching TV. (sounds like it isnt) I would google for an antenna appropriate to whatever you want to receive most.Here, I did it for you,this Planar Disk Antenna is easy to make and works well, It catches a lot of wind if outdoors, should be indoors...You can build a collinear antenna for ADSB that looks a lot like a groundplane that also works passably well for VHF/UHF. (not the coax type, the vertical ground plane type)If you want to listen to ham radio, build a two band j-pole that can work really well for the two most popular ham bands. If you want to receive everything within a certain range build the above planar disk (the diameter of the disks will determine the lower limit of the antenna) or if you want to put it outdoors, try a biconical or discone antenna..The key thing for mobile services especially is that the antenna be vertical. TV antennas are horizontal.A splitter will also reduce the signals a lot. (at least 6 db) Try to avoid using one if you can. A splitter is only needed if you need to run two receivers off of a single antenna..If all the signals you want to listen to are in one direction only, consider building a directional antenna of some kind. Your antenna is the most important thing - Use the right antenna and you're virtually guaranteed success, because those dongles for the money they cost ($10 or less) are quite good for what they do. For the money. But the key to success is your antenna.Also you have to reduce the amount of noise that gets to them. Almost everybody who gets them goes through the same process of initially not receiving much, because of noise.You need a bit of thought to eliminate the RFI.Start with USB extensions and ferrites.Once you do that the signals will magically appear out of the noise..Use an adequate power supply in terms of current. You may want to use a powered hub if your Pi is one of the older ones that cannot power more than a single external device reliably.Put some ferrite split beads on the USB extension cable. At least two but preferably four or six or more. Two or three at each end. If your antenna is connected to the dongle by a length of coax (don't use the supplied antennas) put some split beads on that too, again several at each end if possible. In that context it may act like a balun to decouple the antenna from the feedline.Simply putting your antenna a bit away from the dongle can improve the noise situation a lot (assuming you are using a decent antenna which is attached with decent coax, not the one it comes with) You dont want the antenna right there because the dongles contain a DC-DC converter that itself puts out noise. I would invest in a bunch of ferrite split beads in a variety of sizes..If the above doesnt work, did you try a battery on your Pi?? That will tell you right there if the noise issue is in the power supply or something else.