Electronics > RF, Microwave, Ham Radio

Noisy Wallplug PSUs for the HF receiver

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vinlove:
I have a few 12V wallplug PSUs which plugs into the wall AC mains socket, and it gives out 12V DC.
When they are used for the other devices, they are perfect - powering them and making them work.

But when they are plugged into my Shortwave HF Receivers, they are the source of the hash noise in the receiver.
It is very high level of static noise they cause, so that the receivers are not able to hear the weak signals.

Are there known effective ways to clear this problem?  Obviously these wall plug DC PSUs are not the radio's original PSUs, but they are the cheaper OEM made or unknown makes.

geggi1:
Get a PSU with a transformer not a switcher and you are most likely good.

M0HZH:
You can experiment with choke ferrites on the power cable, but I'd recommend either a linear supply or at least a quality SMPS with proper filtering.

profdc9:
On the radio I designed, I included a filter for the input DC voltage, also to prevent radiation of the local oscillator on the power cable.

It consists of a conventional arrangement: two shunt capacitors and a common-mode choke between them.  The two shunt capacitors are tied to separate grounds on each side of the choke.

You could try something similar if you need to filter a noisy wallwart.

M0HZH:

--- Quote from: profdc9 on March 21, 2023, 03:05:53 am ---On the radio I designed, I included a filter for the input DC voltage, also to prevent radiation of the local oscillator on the power cable.

It consists of a conventional arrangement: two shunt capacitors and a common-mode choke between them.  The two shunt capacitors are tied to separate grounds on each side of the choke.

You could try something similar if you need to filter a noisy wallwart.

--- End quote ---

That is a good step, unfortunately it won't stop EMI radiated by the power cable from the switcher to the input of the radio, which then gets picked up by the radio's antenna. A second choke at the switcher's output could help.

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