Hi Noy,
I know as much about this circuit as anybody
![Cheesy :D](https://www.eevblog.com/forum/Smileys/default/cheesy.gif)
THX, i'm new to these things. Still waiting for arrival of my SA/VNA.
I'm only working on DC <60V so do i need 2 devices for DC ?
Why is this design using 2 serial caps with instead of 1 in the other?
You mean cut out on "top" on the opposite side from the inductors? I thought it is for shielding because there is no additional case top like the tekbox approach.
Why 10db? I mean 3.61 is uncommon? Better 6db (2) or 20db (10) ? I don't understand why 10db is used in this designs.
Edit: Can answer myself. Forgot power db its 10 not 20 (Volt) for 10x..
The design shown in this post:
https://www.eevblog.com/forum/projects/5uh-lisn-for-spectrum-analyzer-emcemi-work/msg404662/#msg404662is my original design.
I gave the design to Linear Technology and they developed the DC2130A demo board that can be found here:
![](https://www.analog.com/en/design-center/evaluation-hardware-and-software/evaluation-boards-kits/dc2130a.html#eb-overview)
The Linear Technology design was copied and presented here:
https://github.com/LibreSolar/5uH-DC-LISNWhen Linear Technology made their version, they made three changes:
1) They increased the thickness of the traces on the inductor wiring:
![5uH LISN for Spectrum Analyzer EMC/EMI work](https://www.eevblog.com/forum/index.php?action=dlattach;topic=27952.0;attach=1109748;image)
![](https://www.eevblog.com/forum/projects/5uh-lisn-for-spectrum-analyzer-emcemi-work/?action=dlattach;attach=1109748;image)
This makes the RF performance worse.
This is addressed in their demo board manual. They suggest lifting the inductors off the board to minimize the capacitance to the ground plane.
Look at page 15 of this document:
https://www.analog.com/media/en/dsp-documentation/evaluation-kit-manuals/DC2130AF.PDF(I have since built a few versions of the my original LISN using a single-sided PCB, no ground plane, and they work even better.)
2) They added a 22uF 100V Electrolytic across the input. The useful part of the electrolytic is the ESR. It is providing damping. This can be analyzed like this:
![5uH LISN for Spectrum Analyzer EMC/EMI work](https://www.eevblog.com/forum/index.php?action=dlattach;topic=27952.0;attach=1109752;image)
![](https://www.eevblog.com/forum/projects/5uh-lisn-for-spectrum-analyzer-emcemi-work/?action=dlattach;attach=1109752;image)
These models look at the impedance of the LISN for different conditions on the input.
There is OPEN, SHORT and inductance. The inductance represents the wiring between the LISN and the power source.
![5uH LISN for Spectrum Analyzer EMC/EMI work](https://www.eevblog.com/forum/index.php?action=dlattach;topic=27952.0;attach=1109756;image)
![](https://www.eevblog.com/forum/projects/5uh-lisn-for-spectrum-analyzer-emcemi-work/?action=dlattach;attach=1109756;image)
The results show that if the wiring and the LISN is in the approximate range 0.1uH to 0.5uH the LISN doesn't meet the impedance specification.
If the 22uF capacitor, including 1 Ohm ESR, is added it does.
This is a good change.
3) Two capacitor in series.
This is done to as an extra safety measure to protect the spectrum analyzer input in the event that the capacitor fails short.
The change in effective capacitance from 0.1uF to 0.05uF has very little impact on the RF performance.
Since there already is the 9kHz HP filter, built into the LISN, there is little benefit to this change. It does not make the performance worse.
I consider this a neutral change, neither good or bad.
10dB
10dB is a very easy number to work with on a Spectrum analyzer, since they typically display amplitude on a log scale. On my spectrum analyzer, there is a setting for an external pre-amp. I set the pre-amp gain to -10dB. This corrects the display for the attenuation in the LISN.
Regards,
Jay_Diddy_B