Most used AWG range in RF coils, transformers, etc.

[VSV_electron]

I'm buying a bulk of enameled wires for my RF experiments (baluns, ununs, all imaginable kinds of coils/transformers you can think of) and they come in 100g coils so while 1.0 mm (AWG18) wire is about 12m long the 0.1 mm (AWG38) wire coil is over 1200 m long.

Having 0=zero experience in RF, let me ask you which of the AWG from my potential buying list below is worthless in RF (consider anything you you've ever heard of and personally used in your projects) and is likely to collect dust forever:

AWG18
AWG20
AWG24
AWG28-29 (0.3 mm)
AWG32
AWG38

Should I consider any other AWG sizes outside of the potential list above or in between of the gauges listed?

[tszaboo]

What frequency? What power?
I use 0402 thin film inductors for RF. A Ham radio guy will do something completely different.

[VSV_electron]

Suppose you want or aim to cover all the stuff in the W.Hayward's 'Experimental Methods in RF Design'. What wire gauges from the above list you would consider applicable? What is missing from the list? What gauges are worthless in the context of the book as a selected guide?

[fourfathom]

I expect that someone will correct me, but I've never had to use #18 or #38.  I work with low-power (10W and under) and in the 1-100 MHz range, mostly iron powder and ferrite toroid inductors, and the occasional ferrite transformer.  From time to time I use an air-core low-value inductor, this is probably #22 or #24 gauge.  #18 and larger are useful in higher-power inductors and transformers, usually baluns and the like.

On one typical project that covered 3.5 to 50 MHz, in the resonant filters I used #32, #30, #28, and #26, wound on T37-2 and T37-6 iron powder cores.

It's a trade-off among several factors: inductance, core size and saturation current (saturation not usually an issue at my power levels) -- these each affect the number of turns needed.  Then it's how many turns you can fit using a given gauge, and how much interwinding capacitance matters in the design.  Then use the largest wire gauge that lets you meet these requirements.  Mechanical also need to be considered:  Can the wire itself reliably secure the inductor, or do you need something in addition.

All of these affect your wire gauge choice.  You don't need to carry all the sizes, you can usually go one-size smaller.

VHF and up have additional complications.

[Bud]

VHF and up often have to use thicker gage for coils to be physically rigid, even in small power circuits.

[VSV_electron]

I expect that someone will correct me, but I've never had to use #18 or #38
...

Right now i'm looking at pages 86 and 87 of J.Carr's 'RF Components and Circuits'. On these pages the author describes the design of the RF push-pull transistor amplifiers and as a part of the design provides the details of winding the baluns with AWG #30 and #36.

[T3sl4co1l]

That's probably fine.  Keep in mind you can parallel two strands to get approx. 3 AWG's lower equivalent cross section, so one every 6 is reasonable (so, 18, 24, 30, 36?).  You might want very fine wire for litz, but you might be better off buying it straight up and as needed (https://www.ebay.com/str/elecmall is a source I've used, and there are many others) since it's a PITA to make, and won't be "served" (wrapped).

The coarser sizes are more for power and frequency; the use at high frequencies might be more for helical resonators or high-Q coils, and of course power amps (tuning or RFC); otherwise, just power, at lower frequencies probably in combination with ferrite or powder cores for SMPS use (where skin effect may or may not matter, depending on use: mainly that skin effect and core loss are deprioritized in deep CCM, but high ripple fraction or DCM, and transformer duty, benefit from finer stranding and lower core loss materials).

Which, for SMPS use, a selection of E, P, T or other core shapes might not be a bad idea.  But if you're doing mostly low level RF projects, just sticking to small toroids (in materials such as #2, #8, #43, etc.) and binocular cores might be more important.

Wirewrap wire in the 26-30AWG range might also be of interest.  Insulation is thicker than magnet wire (obviously), giving a diff pair impedance closer to 100Ω, and more isolation voltage which may be of interest for diverse application (isolated gate drive for example).  Or CAT5/etc. style cable, chopped up into pairs, a bit thicker (24AWG usually) but the insulation has nice low loss.

Tim

[fourfathom]

And some HF transformers use copper tubing for the transformer primaries.  So as you can see, it helps to have a wide range of wire sizes, and it doesn't always have to be enameled "magnet wire".  Fortunately these days it's fast, easy, and reasonably cheap to order any wire gauge, so don't stress over having gaps in your inventory.