Damping resistor matching perfect value - series vs parallel

[cristiano.sar]

If we found the ideal damping resistor value with a damping tool and we could not find a resistor with that specific value in the market, is it better to put resistors in series or in parallel (with each other) to match the value?
For example, suppose my coil requires a damping resistor of 360R and I can't find a 360R resistor in the market, is it better to put 2x 160R in series or 2x 720R in parallel.
Thanks.

[Detectorist#1]

Hi cristiano.sar,
Take my opinion as joke - 2x160R=320R, not 360R. Also it is very hard to find 720R resistors (maybe impossible) with power of 1W or 2W. In all my PI designs, I use at least 2 or 3 serially connected resistors for damping pupose.

[cristiano.sar]

haha, sorry, I mean 2x 180R
Thank you

[Carl-NC]

It doesn't really matter, but I prefer parallel.I can then place a main resistor (in your example, maybe 390 ohms) and then add various parallel resistors and watch a live waveform as I try them out. In your example, maybe 4.7k is ideal. You can do the same thing with series (maybe a 330 ohm main resistor) and then try small series resistors (maybe 30 ohms), but every time the series R is removed to try another the waveform is trashed. Also, most people have a good selection of medium-high value resistors, not so much the very low values.

[Detectorist#1]

Hi Carl,
For PI detectors I prefer serial connection. The reason is the allowed peek voltage on metal oxide resistors (with lower noise than carbon resistors).
500V peek voltage for 1/4W
600V peek voltage for 1W
700V peek voltage for 2W
The new, modern power transistors - IGBT, SiC and MOS FET allow peek voltages up to 2000V and this give possibility to made PI MD with more TX power.