Just Sharing This Switch Mode Power Supply Woes - New Aerial/Mast head amplifier.

jeallen01

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Just reading their repl

I tried loads of different type ferrites, it made no difference.
At around 200kHz, the beads would have to VERY big to have any effect (think PSU chokes), and, of course, the ferrites in them differ in terms of frequency response and most beads are intended for much higher frequencies.
Also (and I'm now getting a bit rusty at this, not having been involved in EMI suppression for over 3 yrs, so it could be the other way round!) if the coupling mode is Common, rather than Differential, Mode then they won't have much effect as the coupling path would also include the return path via a capactive external "virtual ground" link through the plastic case to whatever else is close to the unit.
 

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The PSU itself needs to shielded, it's not along the cables.

I have huge ferrites here as well :)
 
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Channel Hopper

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Try a car battery, see what noise remains.

Turn off everything else in the house to check , except the TV (and sky box)

Oh wait !
 

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RustySpoons

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Try a car battery, see what noise remains.

Turn off everything else in the house to check , except the TV (and sky box)

Oh wait !
:-rofl2:-rofl2:-rofl2

That's quite a theme here actually when I'm looking for QRM with the ham gear.
 

jeallen01

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The PSU itself needs to shielded, it's not along the cables.

I have huge ferrites here as well :)
So it would probably seem to be LF, with harmonics, radiated noise - as you say, that would need shielding, and/or on-board suppression around the primary switching oscillator chip (secondary side is probably less of an issue if the primary cct is fixed).
 

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So in the name of "Science" or is it curiosity? I opened it up and took some pictures.
There was a thin layer of some form of "potting" however that came out very easily.

Not much (If any) Primary side filtering, I.e. EMI/RFI X Capacitors etc.
Very simple SMPS design, I'm surprised they even through an opto-isolator in there.

Nothing on the AC side in terms of protection, no air gaps between the Live/Neutral for AC creepage nor between the primary and secondary.

And just love the way the F Type's are connected, that won't be 75ohm and not shielded as the centre connection is just flapping in the breeze, also "Screened" I don't think so...
20180910_221612.jpg
20180910_221621.jpg
20180910_221639.jpg

1536615571348.png
 
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Amazon might not accept the return if it rattles.
 

jeallen01

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@RustySpoons
Ref POST #49 - as you say, absolutely no Primary filtering or Screening - so most of the EMI is probably escaping via the mains cable = brilliant antenna!
Primary-Secondary Creepage and Clearance distances don't look bad, but can't say anything about what they are like inside the isolation Txfr.=
 

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Amazon might not accept the return if it rattles.
What if it hums?
@RustySpoons
Ref POST #49 - as you say, absolutely no Primary filtering or Screening - so most of the EMI is probably escaping via the mains cable = brilliant antenna!
Primary-Secondary Creepage and Clearance distances don't look bad, but can't say anything about what they are like inside the isolation Txfr.=
Im getting tempted to unwrap the Txfr and see how well its insulated...
 

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Nice looking PBC, but in no way is that screened as they mentioned.

The power supply should be in a seperate metal case and there should be a 3 wire connection to a grounded outlet....With the metal case grounded.

The RFI is going to go where it wants to.

Do you have an RF spectrum analyzer??? If so then hook it up and see whats coming out.
 

jeallen01

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What if it hums?

Im getting tempted to unwrap the Txfr and see how well its insulated...
Now back again!
Unwrapping txfr windings is often quite difficult because they are usually, or should be, resin/varnish impregnated - sometimes it is better to section the transformer with a fine-toothed saw to show the cross-section of the windings and core. Even then, and especially on a very small Txfr, you won't be easily able to see how many insulation wraps there are, and/or whether they extend sufficiently past the edges of the winding wires.

Anyway, the main issue ATM is the EMI - and that looks like a slam-dunk "failure" for constructional reasons.
 

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Now back again!
Unwrapping txfr windings is often quite difficult because they are usually, or should be, resin/varnish impregnated - sometimes it is better to section the transformer with a fine-toothed saw to show the cross-section of the windings and core. Even then, and especially on a very small Txfr, you won't be easily able to see how many insulation wraps there are, and/or whether they extend sufficiently past the edges of the winding wires.

Anyway, the main issue ATM is the EMI - and that looks like a slam-dunk "failure" for constructional reasons.
This looks like they just went for the cheaper option. Tape. Bet it's single layer too.
 

jeallen01

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This looks like they just went for the cheaper option. Tape. Bet it's single layer too.
That would be a slam-dunk on safety grounds as well.

If so, Antiference Ltd (or should we now call them "Interference UnLimited":-doh) are likely to be in deep sh1t when the authorities find out - not just in the UK but across the EU and then have to issue product recalls. See the EU RAPEX site here

Updated: Edited the "new name" after I thought of a "better" one!:-rofl2
 

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Here is the latest reply from Antiference:

"Thank you for your patience Dale while I gather this information for you.



I have attached copies of the certificates for this model of PSU.

You will notice that the original applicant details are on the certificate as this product is not an Antiference original design.

As you know this power supply is a low cost unit and the case is very small, it was originally conceived 8 years ago and more than half million pieces have been sold worldwide without any complaints from customers about electrical performances and/or safety. As mentioned we really have a very low returns rate. The CE certification was granted some years ago as per the attached certificates.

Regarding the EMI filter; it was decided not to include it because we reached acceptable ripple even without it and also this would increase the size of the case.

With regards to the screening, you will have noticed that when you opened up the unit, it has included an epoxy resin within the case. This acts as a suitable screen in conjunction with the metal plate on the front of the RF part. The original design featured a metal case around this section but after some testing with the full screen, there was some undesirable harmonics and resonances at some frequencies so the design was changed. The combination of the metal plate and epoxy resin avoids any resonance or interference.



If you have any further questions, please let me know.



Kind regards
Dan"
 

Attachments

  • LVD certificate MTI150106002CS.PDF
    220.1 KB · Views: 4
  • CE -PS12F.PDF
    222.2 KB · Views: 2

jeallen01

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Sounds like "corporate BS" to me - given what you experienced!

Primary Cct "Ripple" control = maybe, that says nothing about the effect of the lack of filtration on the mains lead conducted and radiated emissions ! :rolleyes:
Never known potting compound to have any screening function - except if it were to be loaded with enough metallic particles to absolutely "slam dunk" the Pri-Sec insulation!:eek:
 
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