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I am working on an SDR composed system that is plugged into a Raspberry Pi board powered by a 5V DC Power bank. The SDR is configured to measure a signal around 400 MHz.

The noise floor measured by the SDR seem to be affected by the power bank noise (compared to a setting with a lab power generator) which is causing lower SNR ratios in the SDR.

Is there any recommendation on how to get rid of the power bank interference ? Beside filtering the power bank output signal, is there any recommendation on 5V 3A DC power banks that can provide less noisy signal on multiple output channels ?

Thanks for any help.

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  • $\begingroup$ Recommendations for specific products, such as DC power banks, is outside the scope of this group. Because (a) we would spend our lives doing it, and this is a group about circuit design, and (b) the market changes so quickly that answers become obsolete. $\endgroup$
    – TimWescott
    Dec 28, 2022 at 16:07
  • $\begingroup$ Considering DC power banks without context may be outside the scope of this group. However, the main interest of the question is related to the quality of the signal thus signal processing considerations. $\endgroup$
    – M.FAKHFAKH
    Dec 29, 2022 at 13:13

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I can't give you a recommendation for a specific power bank, but I can give you a couple of general observations and recommendations:

First, if you're building a sensitive receiver, there is almost no chance that a consumer product will give you satisfaction. If you do find one, there's little chance that the next one you buy -- even of the same part number and everything -- will give you satisfaction. This is because consumer products aren't built that way.

Second, if you did find something that was actually specified for what you needed, it'd be some super-specialized industrial, medical, or military thing and the cost would be astronomical.

I think you're down to isolating the power bank from your radio yourself. How you need to achieve this will take some experimentation, but it starts with putting filters on the power inputs to your receiver, and if you have a really noisy supply and a really sensitive receiver, it ends with you putting the power bank(s) inside of your own RF-tight metal enclosure with the AC and DC connections carefully filtered.

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  • $\begingroup$ Hi Tim, Thank your for your reply. It makes sens and goes in line with what we were experimenting until now. We tried ferrite for the noise suppression and a faraday cage around the powerbank. Unfortunately, with consumer electronics that was still not enough as EMI was still strong. I guess that confirms the approach of designing the power bank according to the required performance. $\endgroup$
    – M.FAKHFAKH
    Dec 29, 2022 at 13:18
  • $\begingroup$ They're kind of a specialty item, but you can get pass-through capacitors and pass-through EMI filters. These are basically filters that are designed to be poked through a Faraday cage, hopefully shorting out any conducted emissions to the inside of the cage, while letting the low-frequency stuff that you want out. Spendy, but not as spendy as a purpose-designed power bank. $\endgroup$
    – TimWescott
    Dec 29, 2022 at 18:12
  • $\begingroup$ I'm sorry -- I said pass-through. At least in American technical English, the correct term is "feed through". If you're doing a web search (for sites in the US) you'll get more hits with "feed through". I have no clue if it's the same in Commonwealth technical English. $\endgroup$
    – TimWescott
    Dec 29, 2022 at 20:34
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This is really an answer (and question) that would be better migrated to the electronics stack-exchange site but will offer my perspective.

If your "DC portable power source" is running off of batteries, this would be particularly clean as long as your feeds are designed to minimize common-mode noise pick-up. The approach is to use batteries together with a linear regulator that itself has low 1/f noise (down to offsets you would particularly care about which depends on your modulation). If you are indeed using batteries, and a linear regulator, and shielded supply cables, this would not at all be challenging to minimize/eliminate power supply noise. This is the common technique used to isolate noise pick-up from AC supply sources and switch supply solutions (switch over to a battery/linear and see if the noise is gone).

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