Electronics > RF, Microwave, Ham Radio

EMC equipment: Coupling-Decoupling Networks CDN DIY, EN 61000-4-6

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Just wanted to clarify, the RF in is connected to the USB shield (through the 100 \$\Omega\$ R), otherwise the cable is just wrapped through the cores?

I'm looking at the standard and your M2 diagram. Do the lines around the inductors imply something particular, like the shield and the lines are inductively coupled through the same iron core? Is that just another symbol for a common mode choke?

Your schematic is for CDN-S1 designed for shielded cables (like coax). For those cables, only the shield is coupled through the 100 Ohm resistor to the signal input (signal line will be coupled as well through signal-shield capacitance).

I think this design can be used for shielded usb cable (specially something like usb 3 with many data lines). For simple 4-wire usb 2.0 you could couple the signal through 400 Ohm resistor and 10nF cap for each wire. You can extend this approach for any number of signals. For 1 signal the coupling resistor should be 100 Ohm, for 2 signals 200 Ohm, for 3 signals 300 etc. You have to keep the parallel resistance of all the coupling resistors at 100 Ohm (together with 50 Ohm generator resistance they form the required 150 Ohm coupling resistance/impedance).

The lines around the inductors indicate coupled inductors (as you figured out). In fact, this is a single core that the cable is passed through (it doesn't have to be only 1 core but all the signal lines and shields are wrapped around all the ferries together/parallel). The inductor part is for decoupling the auxiliary equipment side (AE) from the device under test side (DUT). The standard requires maintaining 150 Ohm impedance from DUT side to ground (with signal input terminated with 50 Ohm) in the tested frequency range (150kHz to 80Mhz or 230MHz). This requirement has to be fulfilled for AE side shorted to ground (PE). See the graph in the first post. This is the reason for using multiple ferrites to keep the AE-DUT impedance high in the required frequency range. This is the hard part.


--- Quote from: piotekp90 on August 13, 2023, 04:44:05 pm ---Which resistor are you using?

--- End quote ---

I use "random" TO220 thick film resistors... so far, none of them had issues up to 230MHz...

--- Quote from: piotekp90 on August 13, 2023, 04:44:05 pm ---Did you build the CDN T8 RJ45?

--- End quote ---

I did a CDN T4 ... the problem is that you need to decouple common-mode and differential mode.

So you need the cores to get the CM-Impedance and then you need some additional inductors to get the signal decoupled from your interference.

These SMD CM-chokes for data-lines were ok for me... just be carefull with the current-rating.
3V test-level should be no issue, 10V, however, are tricky to find.

In the standard are suggested inductance-values... just stack some (tiny, small, large, huge) to get into the desired range. (IIRC, I used 3 different values).
Remember, if you use, these CM-chokes wrong, they get useful for diff-mode signals :)

--- Quote from: seuberte on September 11, 2023, 07:11:10 pm ---Any thoughts about open sourcing the designs?

--- End quote ---

Yes... I even considered kind of a building kit (ie. panels and cores; you'll need to print the plastic mount for the connectors, get some cable, and add your resistors,...)
So far no real demand... hence, the documentation postponed :)
This might be some chicken/egg problem, I guess...


As I wrote earlier, I made an amplifier to power the CDN  ;D It operates in the 100kHz - 230MHz range (and even 300MHz at lower power) and achieves 20W and even 35W for some frequencies. The distortion level is better than -18dBc. MRF101A/B transistors are used as output stages. The driver for these is a BLP15H9S100GZ fed from a GALI84+ preamplifier.

The gain is approximately 47dB +/- 1.5dB. Power consumption is 150W, 24V power supply.
What remained was to clean up the PCB, build in an attenuator to improve the S11 and protect against an overly high input signal, improve the bias of the transistors to drift less with temperature, add overcurrent protection.


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