Hi Necks,

Does anyone know of a good design tool which will calculate the width/length of PCB tracks that can form inductors? I can find several online, but some don't seem to take account of the PCB relative permeability (or must make assumptions about it that can't be changed) and some have two different equations (a 'stripline' and a 'microstrip') which don't agree with each other...

Otherwise I guess it's resorting to the old fashioned winding wire around a former.

Rev

Generally, I've found that the tools for FR4 tend to be reasonably accurate for most types of board. You're not going to be able to get coils as accurate as conventional wound ones. Etched coils are ostensibly an attractive option, but at VHF they tend to be quite big, they radiate, and they can be microphonic (bang the box and you'll hear it on air!).

I have a Dutch 15W exciter here that works very differently when it's assembled into its metal box. The capacitive (and inductive) coupling between the etched output coils and the box change the output match impedance and spoil the lowpass characteristic of the filter. I can see why they went back to the conventional wound type!

Thanks Albert.

My design requires a ~50nH inductor which is around 3T on a relatively small former. If I use the Saturn PCB tools, for a 0.5mm wide track, this suggests a track length of 7.5cm which seems quite long. If I go for a planar inductor (spiral) then you have the problem of the additional link from the centre of the 'coil'. Maybe I'll stick to winding coils - at least that way you can tweak them!

Rev

i get one If you use PCB FR4 From JLCPCB valu is 5x5mm is 1pF
1pF 24,926 mm2 4,993 mm

Google “appcad” and download and use that, it will calculate all your stripline and microstrip pcb traces. Also if you’re going to etch inductors onto your pcb, try to use Rogers board material if you can instead of the usual FR4 as it’s got less loss.

FR4 is just fine up to 400W... but can handle 500+ in optimal conditions.