How to make small inductors like 10-20nH? - Page 1
Forum section: electronics / rf-microwave

author: LM21
author_rank: Regular Contributor
timestamp: October 06, 2024, 07:24:58 pm
content: I have a several old VHF power transistors, and nice SimNec/SimSmith curves to match them. Then I noticed that making small inductances is not easy. I have large ARCO trimmers too, they are definitely not SMD. Modern PCB should handle grounding better than in 1978.There are formulas or net calculators for small loops. But I cant make a loops with a accurate enough diameter.In an old Motorola RF databook (from1978) they talk about airlines. That is, a strip over a ground plane. They could work. And they can be fine tuned easily, by lifting or lowering the strip. But they give only estimates and quesses of their inductance/length.I don't think it it is possible to make small enough real coils. That is coils with several turns.I think these airlines are the best way to do it. But how to calculate/get the dimensions?Perhapshttps://emclab.mst.edu/resources/tools/inductance-calculator/trace-over-ground/Edit:I tried that calculator. Its results are not good. No normal strip has an inductance of 6nH per metre it gave.Any comments?Modern RF powerfets are better and easier to use of course.

author: shabaz
author_rank: Frequent Contributor
timestamp: October 06, 2024, 08:10:31 pm
content: Hi,You can buy ready-made inductors if desired. Otherwise, it's absolutely possible to create inductors with a few turns (I usually use the smooth end of a drill bit for winding). However for easier repeatability, there are plastic-ish toroids (e.g. Amidon Type 0), they are pink. You'll find you can wind several turns on some of them, for low tens of nH inductance.Probably Coil64 software allows you to pick type 0.

author: langwadt
author_rank: Super Contributor
timestamp: October 06, 2024, 08:19:34 pm
content: https://dk.farnell.com/en-DK/coilcraft/0806sq-16nglb/inductor-15-7nh-2-4-4ghz-rf-smd/dp/2286597

author: LM21
author_rank: Regular Contributor
timestamp: October 06, 2024, 08:35:12 pm
content: Yes. A small inductor and a large transistor together feels a little odd, but at least at input a small SMD part should do. Then there are lead inductances. Everything has some.

author: coppercone2
author_rank: Super Contributor
timestamp: October 07, 2024, 08:37:24 pm
content: precise diameter plastic pins and drizzle with super glueor metal formers, but you need to make sure your wire is right. If you get semi hard etc wire, then it might change diameter, then you need to make a spring winding table to do adjustments and predictions.you want to get a gauge pin set, by 0.001 or smaller, and not use drill bits, that is just how you cut your hand

author: shabaz
author_rank: Frequent Contributor
timestamp: October 07, 2024, 09:14:28 pm
content: Quote from: coppercone2 on October 07, 2024, 08:37:24 pmOr, you could use your head. Do people have to teach you on this forum how to do everything?You could clamp it in a vise, or wrap the sharp end in tissue-paper.Using semi-hard wire that you refer to, sounds like a corner-case that you might have contrived just to be argumentative.

author: coppercone2
author_rank: Super Contributor
timestamp: October 07, 2024, 09:38:06 pm
content: I don't know why your angry that I said you can buy a cheap kit of pins to make basically anything you want with professional results instead of building it half assed like you broke into your dads tool closet at nightDid you ever even try to make a functioning RF circuit that needs small inductors?For those that actually want nice repeatable resultshttps://www.amazon.com/Accusize-Tools-0-011-0-060-Steel/dp/B00JOLCSF6?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&psc=1&smid=A27F0FNA6WTMGTand you can actually put them in a pin vise without trying to clamp on a spiral flute like a idiotWinding spirals is at least a.. several thousand year old machinists skill that has been perfected to a pretty exacting science.And that's not even the 'right' way. If I wanted to make someone do it right I would make them get a spring winding jig, I gave you the easy prototype way, since if you get the right materials you are working with ductile copper, the results will be half assed if you try to use this way to make a mechanical spring.

author: TimFox
author_rank: Super Contributor
timestamp: October 07, 2024, 09:59:20 pm
content: Threaded rod stock is readily available in acetal plastic.Better would be polystyrene, which has low dielectric loss and glues easily; seems hard to find, maybe hobby store?Threaded rod will control diameter and pitch.

author: tggzzz
author_rank: Super Contributor
timestamp: October 07, 2024, 10:40:55 pm
content: 10nH? 15mm of straight wire would be sufficient.Or choose a commercial parthttps://www.findchips.com/search/10nH

author: stretchyman
author_rank: Regular Contributor
timestamp: November 05, 2024, 06:59:21 pm
content: Stub tuning?

author: LM21
author_rank: Regular Contributor
timestamp: November 05, 2024, 08:15:01 pm
content: I think I'll use a copper strip over ground plane. They are easy to fine tune.This has a formula included.https://spok.ca/index.php/resources/tools/106-traceindcalcThere are plenty of others.My VHF power transistor is large, so copper strip is not too large.