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Entry Level SDR recommendations

 

If the amplifier is genuinely running in class A (which I doubt) it should not generate any RFI.
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It is difficult to tell from the video if the interference varies in unison with the audio, but the Spectrum Analyser plots suggest a single switching frequency and harmonics, which to me suggests a power supply issue.
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I believe the noise is most likely being introduced from the USB port, or whatever is powering the amplifier, so personally I would concentrate on that rather than the amplifier, as I think you have tried just about every usual technique of RFI suppression on the PCB itself.
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I'd suggest trying a screened PSU cable, with good decoupling of the supply cores at each end, and a decent bond to ground at the PC end.
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Regards,
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Martin
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On Sun, Feb 23, 2025 at 05:17 PM, enriqueeeeee2001 wrote:

Trust speakers, it has a class A amplifier and radiates a lot s of RFI
 

I agree with Simon, and he raises a valid point that you can use smaller diameter cables, but sometimes things like moulded USB connectors prevent their use, and you have to resort to larger cores.
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Regards,
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Martin
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On Sun, Feb 23, 2025 at 06:47 PM, Simon wrote:

However you do NOT need to use ft240/(31/43) cores.. Ft240 is the size of core. As your cable is not rg213 ie thick, one can use cheaper smaller diameter cores..just as long as one can get the required turns though and are of same spec. Ie type 31/43 etc.
 

Maybe is the power supply causing this problem. I have tried to feed with a well filtered external USB adptor but the problem persit. I forgot also I purchased a USB isolator but not results at all . I have several 31-43 mix toroids and big 43 ferrite clamps.? As I said before the cable is not too long I will purchase extra cables in order to wind the toroids.

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