My colleague lent me his DIY version of 5uH CISPR-25 LISN to measure and compare its performance – unit in smaller housing with many inductors in series to form total 5uH inductance.
Output impedance measurement reveals CISPR-25 incompliance below 200kHz as well as earlier occurring incompliance above 30MHz. Due to its 1uF input capacitance it would be also impacted by power supply harness inductance issue as described in simulation project log.
Insertion losses measurement reveals true weakness of this design. Its response is rather unpredictable. Instead of flat response above 1MHz, there are many depression peaks. I don’t think the measurement could be calibrated reliably for this behavior. Complex PCB with many inductors, that are coupled, is definitely not a good idea if you consider this.
Channel isolation measurement on the other hand reveals how great idea is to have two separate units instead of one multi-channel. Low frequency cross-talk does not occur at all. Between 20 – 40MHz there is still a cross-talk above noise floor, which was not present on my unit. This could be caused by the same design issue as described in insertion losses measurement above.
Overall, without tuning insertion losses to be flatter above 1MHz I would consider this construction as not reliable.
kevarek
Discussions
Become a Hackaday.io Member
Create an account to leave a comment. Already have an account? Log In.