Sourcing silver plated wire / high Q inductors in 20 - 100nH range - Page 1
Forum section: electronics / rf-microwave

author: rf-fil
author_rank: Regular Contributor
timestamp: February 11, 2025, 07:26:35 am
content: This is for a 144MHz and 423MHz LNAs - hoping to add some filtering ahead of the LNA without much loss. Coilcraft tops out around Q = 250 for these kind of tiny inductors.Can I get higher Q than ~250?Is there a source for proper silver-plated wires for RF?

author: radiolistener
author_rank: Super Contributor
timestamp: February 11, 2025, 10:18:17 am
content: Quote from: rf-fil on February 11, 2025, 07:26:35 amI think it will be better to use pure silver wires. The reason is that silver plated layer can be easy damaged during soldering or winding. This is what exactly happens with Chinese silver plated wires. So I recommend to use pure silver wires to avoid such issues.

author: David Hess
author_rank: Super Contributor
timestamp: February 11, 2025, 01:04:23 pm
content: Quote from: rf-fil on February 11, 2025, 07:26:35 amSure, 2 meter to 440 MHz helical cavity filters are practical. They do require piston trimmers to maintain high Q.QuoteAnd they do not require silver to achieve high Qs, although I use silver plated wire wrap wire for coupling links.

author: JohnG
author_rank: Frequent Contributor
timestamp: February 11, 2025, 02:16:11 pm
content: Be aware that silver does not buy you much. The conductivity is 5% to 7% better, but the skin depth is thinner due to the higher conductivity, so you get something like 2-5 % improvement. That assumes that the plating is a few skin depths thick. If not, the electrical benefit is even less. For uncoated copper, silver plating does have the benefit of improved corrosion resistance since the tarnish that typically forms is self-passivating to a certain extent.If the inductors are already designed to maximize Q, then your only real option is to go bigger.John

author: radiolistener
author_rank: Super Contributor
timestamp: February 11, 2025, 03:44:47 pm
content: Quote from: JohnG on February 11, 2025, 02:16:11 pmThis small difference is important, because it is multiplied in LC circuit due to Q factor. For high Q factor even small difference gives very significant effect.

author: JohnG
author_rank: Frequent Contributor
timestamp: February 11, 2025, 06:14:58 pm
content: Thanks, I did not know that it would make that much difference. It's been a long time since I looked at signal level LC filters.

author: coppercone2
author_rank: Super Contributor
timestamp: February 11, 2025, 10:28:45 pm
content: I don't really see the problem with using solid silver wire on a custom made inductorthe only problem is, where do you get enameled silver wire ?The cost of making the inductor is going to beat out the materials by a long shot, unless its a massive inductor. This is VHF, not VLF, so the inductor is small, especially because its a LNA inductor not a power inductor.Can you simply thin down varnish and dip+ dry a strand of silver wire to make it? It won't be very longOr does it require something exotic like a PVD coating for thin enamel wire?

author: David Hess
author_rank: Super Contributor
timestamp: February 11, 2025, 10:56:16 pm
content: Quote from: JohnG on February 11, 2025, 02:16:11 pmWhen I was designing and building helical resonators, silver plating obviously helped, but for prototypes increasing the cavity size by 10% gave the same improvement as silver plating.QuoteI seem to recall inductor Q is maximum when the length is twice the diameter.Quote from: coppercone2 on February 11, 2025, 10:28:45 pmSilver plated wire wrap wire with Kynar insulation is readily available. Is there any reason not to use it?Or is wire larger than 30 gauge required?

author: radiolistener
author_rank: Super Contributor
timestamp: February 12, 2025, 04:23:24 am
content: Quote from: coppercone2 on February 11, 2025, 10:28:45 pmWhat is the reason to have enameled layer around silver wire? It can affect inductance and Q factor, because enamel material has different wave propagation speed than air and has siginficantly higher loss. For a thin layer the difference may be small but what is the reason to have it?Quote from: David Hess on February 11, 2025, 10:56:16 pmAs I read old-school RF manufacturers recommendations, they recommended equal length and diameter in order to achieve the maximum Q-factor.

author: coppercone2
author_rank: Super Contributor
timestamp: February 12, 2025, 04:36:45 am
content: well it might tarnish and it looks bootlegI just thought it might be a pain in the ass to figure out exactly how thin to make it for a thin wire. I suppose actually the best method would just be to experimentally make a mixture, its not that much work for a tiny coil, if you over thin it, you waste like a table spoon. Every single air coil inductor I ever saw has been varnished, including the cheap ones without a bobin.I wonder if that UV cure PCB silk screen would be good, since it is supposed to be used on metal. I wonder how to thin that down. Then it should be as good as a PCB traceIf you are really going for high Q, I assume tarnish might screw with it, if you actually care that there is a silver layer on top.I wonder if it works OK on silverLike you got a excellent surface finish drawn wire (that ends up polished), why would you let that tarnish? For something hermetically sealed OK but thats alot of work compared to just painting it with something

author: radiolistener
author_rank: Super Contributor
timestamp: February 12, 2025, 08:33:12 am
content: Quote from: coppercone2 on February 12, 2025, 04:36:45 amIt's RF properties unstable and very depends on exact instance, so it's even hard to predict its properties for mass production. This is why RF transmission lines on PCB are not covered with silk screen in order to avoid bad SWR and higher loss. It uses uncovered copper on PCB for RF signal path wires.Using a thin layer of varnish does really help protect against oxidation and corrosion, but it also affects RF performance. So you need to decide what is more important.However, I have seen quite old high-Q old-school coils with a layer of silver. They did not have varnish and looked almost like new, despite several decades of age. If stored without an aggressive environment, this should not lead to serious problems with oxidation.

author: coppercone2
author_rank: Super Contributor
timestamp: February 12, 2025, 02:20:36 pm
content: keep in mind unless you know the plating thickness, if you don't protect it, it could just eat up ALL the silver. Old stuff was heavy handed with plating thicknessesI never heard that issue being considered outside of microwave circuits, this is a lower frequency, but you can be right.I wonder if polystyrene coating is corrosion resistant, because that one is easy to thin as much as you want.It really depends where you are I think, some people will never have a problem with corrosion and others might think your insane

author: mawyatt
author_rank: Super Contributor
timestamp: February 12, 2025, 02:41:54 pm
content: Quote from: radiolistener on February 12, 2025, 08:33:12 amWhen the conductor is covered with a solder mask insulator this adds additional loss as the RF signal penetrates the top insulator as well as the PCB below.Same reason in the old Helical resonators were solid uninsulated wire (usually silver plated). Only air between the Helix and side walls and distributed Helix capacitance used to resonate with the Helix Inductance and only a small "Trimmer" Capacitor required to tune to the exact frequency over a small range. Any wire insulator coating on the Helix (or interior walls) would have the RF penetrate such and thus experience an additional loss, small but in high "Q" networks every little loss matters!!Best

author: mawyatt
author_rank: Super Contributor
timestamp: February 12, 2025, 02:55:01 pm
content: This Silver plating brings back old memories of having anImpactImpatt Diode Oscillator imbedded in a waveguide. The oscillator waveguide section was getting hot so the tech decided to conduct the heat to the next section of waveguide and a heat sink with thermal paste. Back then thermal paste was BeO in a silicone gel and is highly abrasive. Some of the paste got smeared across the waveguide and the tech attempted to clean it off with Kim Wipes which just created more mess, so kept scrubbing until the Silver plating had wiped offNot a good day, as that was not a cheap MW OscillatorBest

author: artag
author_rank: Super Contributor
timestamp: February 12, 2025, 03:10:09 pm
content: Anti-tarnish coating is a thin varnish often applied to silver. No idea of it's thickness or properties but I imagine it's tough enough to survive mild abrasion if it's needed for insulation.

author: G0HZU
author_rank: Super Contributor
timestamp: February 13, 2025, 12:01:01 am
content: If you actually want some real numbers for a 100nH inductor at 145 MHz using a classic air cored solenoid, then consider the example design below.This is designed on some old software of mine that predicts the inductance and Q of air cored solenoids.It predicts that a 4 turn solenoid of 1cm diameter and about 1.1cm length will have a Q of about 400 at 145 MHz if 1mm diameter tinned copper wire is used.This represents something with realistic dimensions for use in an LNA if hand wound parts are allowed.If you need something physically smaller than this then the Q will obviously be lower. Also, if you place it very near any shields or screen walls then the Q will also be reduced.It is possible to get a higher Q than 400 at 145 MHz (for a 100nH solenoid) if you don't mind something physically bigger than the example below or if you use thicker diameter wire.

author: rf-fil
author_rank: Regular Contributor
timestamp: February 13, 2025, 11:26:25 pm
content: Thanks for the info. I've now found this tool -https://coil32.net/download-coil64-for-windows.html. It lets you choose the material and see what the Q would be. When I put Coilcraft inductor dimensions in, the estimated Q comes out about the same as in the datasheets - so the tool looks pretty accurate. And, yes - making the coil diameter larger and using thicker wire increases the Q a lot. Switching to silver only increases the Q by a small percentage, so I'd say, in my case, silver is not worth the hassle.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: February 15, 2025, 06:37:53 pm
content: Do people use Litz wire with RF inductors for higher Q?

author: coppercone2
author_rank: Super Contributor
timestamp: February 15, 2025, 06:43:44 pm
content: I don't think it goes past maybe 2MHz with litz.He is in VHF and UHF