Hi, I'm doing some EMI measurements on the AMP7 right now.
Now I'm in no way familiar with the procedures that are normally used to do this kind of stuff so if you want to know something in particular or have any hints or guidelines please tell me...
I am using a Rhode&Schwarz FS300 spectrum analizer with a 9cm long antenna connected to the input. (I know the formula is roughly (300/f)/4 times 0,8 should give the length of the antenna in meters, but I think this length should pick up EMI well enough if there is any) I have set the center frequency as 800Khz and the band I'm measuring in reaches from 9Khz to 1,6Mhz.
I have tested the amp at idle and with 1Khz tone connected. At idle I get some readings (800Khz) when I place the antenna real close (within 15cm of the board) The board is not shielded at all, just playing openly on my desk. When I move the antenna outside the 15cm radius the signal disappears almost instantly...
Have a look:
The amp: (with IRFP4228 and all parts chosen by me, the stock version will be somewhat different)
Pretty close up (aprox 20cm from the amp, you can see the speaker cable right under the antenna. We may conclude that the output filter works)
With the antenna poking right into the amp: (1cm away from the toroids, here we can see a clear 800Khz peak)
With the 1Khz tone at 10cm distance:
At 12cm running at idle:
I hope you guys find it interesting [^]
Next up is THD measurements...
------X-max. can be several meters on any driver, too bad it can be done only once...------