I have tested several genuine Apple 5w compact plug top power supplies, they hav a switching frequency of around 100KHz (dependent upon load), and the noise spurs tend to be relatively low on frequencies greater than 500kHz.
This plot shows the RF noise measured on the DC output of the supply from 0Hz to 1MHz.
The yellow trace is an Apple 5w charger running with a 1A load.
The purple trace is a linear power supply using a LT1083 5A LDO regulator.
The cyan trace is the ambient noise level with the power supply turned off.
Cheap Chinese chargers can easily produce 15 to 20dB more noise at around 1MHz.
Obviously, this is not the whole story. Earth loops and radiated emissions are other mechanisms by which power supply noise can cause interference. But this at lest give some indication of typical performance.
Hi, Martin. How did you take the measurements? I am most interested in LT1083. My linear power supply has 3 LT1083 pieces. There are also L7812 and L7805 and the like. But I used good LC filters for the output voltage. Should I be worried that this noise is spreading into the airwaves?
An easy test is to terminate the KiWi RF input with a 50 ohm load, and see if the noise floor rises with the power supply you wish to test.
If it does, then the supply is really noisy, and it will be very evident if the setup shown below is used.
The diodes protect the Spectrum Analyser from excessive voltage spikes, and the transformer helps to eliminate possible ground loops.
In practice, earth loops and radiated emissions are still likely to be the most significant factors,
So if it only seems noisy when the antenna or coax is connected, then the test setup that I detailed earlier in this thread, is more suitable to help identify the common mode noise contribution.
I performed some measurements on the cheap Chinese filter boards mentioned earlier in this thread. I tried the 50V 4A version which had 22uH inductors and 470uF capacitors fitted.
The differential mode rejection is pretty good, but the common mode rejection is poor, and somewhat disappointing.
One of the boards had a damaged inductor, so I swapped both for 470uH 1A inductors of the same size and style.
This improved the common mode rejection on the LF bands, but made the overall performance worse on the HF bands.
Comments
I think you may have a fake.
I have tested several genuine Apple 5w compact plug top power supplies, they hav a switching frequency of around 100KHz (dependent upon load), and the noise spurs tend to be relatively low on frequencies greater than 500kHz.
This plot shows the RF noise measured on the DC output of the supply from 0Hz to 1MHz.
The yellow trace is an Apple 5w charger running with a 1A load.
The purple trace is a linear power supply using a LT1083 5A LDO regulator.
The cyan trace is the ambient noise level with the power supply turned off.
Cheap Chinese chargers can easily produce 15 to 20dB more noise at around 1MHz.
Obviously, this is not the whole story. Earth loops and radiated emissions are other mechanisms by which power supply noise can cause interference. But this at lest give some indication of typical performance.
Regards,
Martin
Hi, Martin. How did you take the measurements? I am most interested in LT1083. My linear power supply has 3 LT1083 pieces. There are also L7812 and L7805 and the like. But I used good LC filters for the output voltage. Should I be worried that this noise is spreading into the airwaves?
An easy test is to terminate the KiWi RF input with a 50 ohm load, and see if the noise floor rises with the power supply you wish to test.
If it does, then the supply is really noisy, and it will be very evident if the setup shown below is used.
The diodes protect the Spectrum Analyser from excessive voltage spikes, and the transformer helps to eliminate possible ground loops.
In practice, earth loops and radiated emissions are still likely to be the most significant factors,
So if it only seems noisy when the antenna or coax is connected, then the test setup that I detailed earlier in this thread, is more suitable to help identify the common mode noise contribution.
Regards,
Martin
@W4BF maybe read this : https://forum.digikey.com/t/a-17-bench-supply-worth-it-ps-1502dd/13143
But many use the same name/code (PS-1502DD)
I performed some measurements on the cheap Chinese filter boards mentioned earlier in this thread. I tried the 50V 4A version which had 22uH inductors and 470uF capacitors fitted.
The differential mode rejection is pretty good, but the common mode rejection is poor, and somewhat disappointing.
One of the boards had a damaged inductor, so I swapped both for 470uH 1A inductors of the same size and style.
This improved the common mode rejection on the LF bands, but made the overall performance worse on the HF bands.
Regards,
Martin