5V Power Supply who output a "clean" 5V Power for SDR?

[Lord of nothing]

Hi
I ordered an USB Isolator who should work with my SDR. Sadly on <30Mhz my Power supply produce to much Noise. So Is there a 5V Powersupply on the European Market who filter, block,... or what ever every noise who could come via the Power Cable?
  Maybe some Lab Power Supply?
The USB Dongle dont draw that much power so for that nothing special is necessary.
The main part is no additional noise should get truth the Power cable.

[madires]

You could try an LC filter at the output of your PSU. Start with 10-33µH and 220-470µF. Or do you have a linear PSU with transformer?

[Lord of nothing]

Nope nothing.

[Gyro]

Ditch the DC-DC converter on the USB isolator. Then purchase an old transformer based wall wart with 9V output from ebay and add a 3 terminal 5V linear regulator.

This is the approach I took with my 16 bit Pico ADC216 scope and USB isolator with good results.

[Bud]

A USB rechargeable juice pack for cell phones.

[Lord of nothing]

So next week the Isolator should arrive here.

Then purchase an old transformer based wall wart with 9V output from ebay and add a 3 terminal 5V linear regulator.

How should I know if the use that? 

[Gyro]

They will almost certainly be second-hand, eg. from an old modem, cordless phone etc. Weight and volume are another clue. Another one is that mains input voltage and frequency will be specified over a small range, eg. 230VAC +/- 10% 50Hz, rather than, say, 100-240V. Lastly their may be a reference to the supply being thermally fused.

A couple of example UK listings:

https://www.ebay.co.uk/itm/9V-Mains-AC-DC-Plug-Power-Adapter-BS0900350-For-Electric-Keyboard-tested-used/392304456528
https://www.ebay.co.uk/itm/US-Robotics-SP3a-9V-1000mA-1A-AC-DC-Modem-Power-Supply-Mains-Adaptor-PSU-UK-Plug/372683226233

EDIT: Actually the second one is a 9V AC output, a very definite clue!

[ebastler]

Do you actually know that the noise is coming from the power supply?

Before you chase a used transformer-based power supply and tinker with adding a linear regulator, I think Bud's suggestion above is a great one, at least for testing: Use a USB power bank (rechargeable battery) to power your SDR and cofirm that the noise goes away.

[ogden]

Use a USB power bank (rechargeable battery) to power your SDR and cofirm that the noise goes away.

Unfortunately most USB power banks are no better than phone chargers/adapters - because they have switching boost (or buck) converter inside.

[ebastler]

Unfortunately most USB power banks are no better than phone chargers/adapters - because they have switching boost (or buck) converter inside.

Duh -- didn't think of that. 

The marvels of modern technology... Thanks for pointing that out!

[Lord of nothing]

Do you actually know that the noise is coming from the power supply?

When I disconnect the power supply from my Laptop most noise are gone.

[Wolfgang]

why no trivial linear PSU ? Heats your flat and keeps noise out. 

[mariush]

You could make your own linear power supply

Get a transformer that outputs 6...7.5v AC
Get a bridge rectifier or 4 diodes to convert the AC voltage to DC
Get a big capacitor to smooth the output
Get a linear regulator to regulate the voltage down to 5v

Here's transformers that would fit your needs, just get one that can provide the current you need : long link to transformers at tme.eu
bridge rectifier - any bridge rectifier would do, as long as it has the current rating
capacitor... 3300uF 16v should be enough, it's a common value used in atx power supplies so should be easy to find


example :

[Gyro]

Yes, you can absolutely do that too. Buying a second hand transformer based wall wart off ebay just saves you the hassle of the mains side and enclosure and is probably cheaper. Just add the 7805 and capacitors of your choice.

[Lord of nothing]

Hi
Today I received the Isolator. Sure I dont have a Power Supply yet.
Here 2 Screenshots.
1) with the Isolator: https://www.delock.de/produkte/S_62982/merkmale.html
2) with the USB Hub: https://www.delock.de/produkte/678_extern/63311/merkmale.html

Both are powered by the Latop (who is a Power Plug connected)

[The Soulman]

Do you actually know that the noise is coming from the power supply?

When I disconnect the power supply from my Laptop most noise are gone.

Does your laptop have a grounded plug? if so, is it connected to a properly grounded outlet?

[Lord of nothing]

Yes
And I guess Yes.

[madires]

Have you already tried to power your SDR via a different wall outlet (or different phase, or different room)? I had a similar issue with a SW receiver which was resolved by moving the receiver's linear PSU to another socket. I've tried a cap between the PSU's negative output and PE, also a direct connection to PE. Slight changes, but still no real improvement. My guess is that the noise was created by the PE current from computer and monitor SMPSUs (Y caps) powered via the same socket. Moving the receiver's PSU to another socket, not daisy-chained with the former one, without any SMPSUs worked wonders in my case. Solving noise problems can be quite time consuming, but also very educational.