Wire impedance with DB9 output?

Question

Arduino

Guys, a stupid question: to connect two devices via a CAN network, you need to use a wire with two 120 Ohm terminators, it looks something like this .
So, does a regular null modem cable already have an impedance of 120 ohms? Or does it need to be soldered on the sides?
the cable is about the same , there is no multimeter at hand.

Answer 1

You need to solder on the sides, a regular null modem cable has a resistance of the order of fractions of an ohm (it's just a copper cable and two connectors).

Answer 2

There is the wave impedance of the cable, and there is the resistance of the terminators. In order to avoid signal re-reflections, they must match. Therefore, resistance at the ends is needed.

Answer 3

If we are talking about a regular null-modem wire for COM ports, then usually there are no resistors there.
And, in my opinion, the resistors should not be in the cable, but in the devices themselves, as close as possible to the CAN controllers.

Answer 4

Considering that the null-modem cable has a maximum length of 15 meters, you can generally not bother with the wave impedance of the cable, but it is advisable, of course, to twist two wires into a twisted pair. However, a null-modem cable will also work at low speeds. It is better to put one resistance in the device that is the master, the second in the extreme, farthest sensor from it (SLAVE).