EEVblog Electronics Community Forum
Electronics => RF, Microwave, Ham Radio => Topic started by: coppercone2 on November 29, 2024, 10:19:20 am
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I read a little bit about this, it seems to be done for some VHF supression networks.The idea is to wind a coil with nichrome.
Nichrome is common because its for heater use. But it made me wonder, because it might not be getting very hot, there are more options.
I know of kanthal, nichrome. I guess you can use any variety of wire, common might be solder, stainless steel, bronze, brass, aluminum. Might be a little difficult to terminate but its achievable. And you can use braids of those types, for what reason I don't know, but you can wind it I think. Zinc too.
It seems interesting that you can choose a wire to tailor a inductor.
What other options are there? Carbon fiber maybe, but I assume it might be unstable.
Has anyone seen any intentional weirdness like this in use with electronics before? You CAN get enameled nichrome for a off the shelf wire
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soft tungsten wire is high resistance too, titanium.
nichrome is highest along with maganese and mercury. Liquid metal stuff is uniquely interesting because it seems possible to make a high power one, with a poorly conductive liquid metal, that is water cooled through some big ferrites. I wonder what would use that sort of technology.
Fluid cooled liquid metal lossy air core inductor.
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Having spent most of my working life in the VHF/UHF radio field, I have not come across inductors that used deliberately lossy wire. Indeed you generally want the opposite, silver plated inductors are common.
In cases where you need to reduce the Q of an inductor, a common practice is to use a resistor in parallel with it. Where you need to safely deal with excess power, resistive attenuators are used, or tuned circuits to “dump” harmonics/image frequencies into a resistive load.
SJ
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I have seen pictures of professional ones they seem to exist sometimes but it seems specific for some tubes
also it says its a big argument with two experts going at each other throat about it. Nichrome ribbon is used too.
its for when your resistor method is not enough
it looks like the debate makes people fucking rage like crazy too :-DD , because there seems to be compelling evidence that they do work for some amplifiers where resistors would not etc
example
https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1988/10/page36/index.html (https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1988/10/page36/index.html)
I think of it a different way, in a simple bode plot it shows you have a LC low pass filter that has a bump at some frequency range before the down slope, and you need to add R to reduce it, it seems that winding the inductor out of nichrome might make it work OK with less parts. I am not sure how much resistance you can get from it but it seems like a plausible technique even for something as simple as a LC filter for a analog input? And I was thinking for like a big thin wire choke that needs resistance anyway, if you wind it from nichrome, its physically stronger, you won't tear a tiny wire so easily. That might take some stress out of winding a inductor
It should be 10 times harder to rip during winding compared to copper... for fine wire, that really takes the edge off
or even a relay, half the time it has a big current limit resistor anyway :-// . So long it can take a bit of extra heat, it seems your not losing anything from making it that way, since the wire is pretty non magnetic. maybe it would do something funky with iron wire.
I guess the only thing is, the tempco of the inductor, compared to the tempco of a copper inductor with the resistance in a resistor. i guess you would need manganin inductors in some cases.
It seems its approximately 60 or more times resistive then copper.
Looking at some RLC circuits that I think use reasonable components (i.e. ceramic cap + coil) in a simulator, it seems compared to a expected DCR of a coil, you need like at least 20 times more resistance then the measured DCR to get rid of the 'hump' on a dB scale. So actually using a nichrome inductor does get rid of it in some of my exploratory calculations.
a inductor between 0.1 to 1 ohm seems reasonable for a TH or SMT component (chip or axial, not a power converter inductor).
It at least seems plausible that using enamel nichrome wire to wind small inductors might be OK for prototyping to greatly reduce the problem of copper breaking...? The tensile strength should let you be rough with it. I am curious how it would compare on a VNA. Especially for something like a torroid with alot of turns of fine wire. That can make you fucking crazy if it rips, it already feels like your a seamstress with copper.
For simulation, it might help look at step response too.
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So the ideal idea would be to get a .. critically dampened? LC filter without the R for whatever, by using the best alloy.
(https://ars.els-cdn.com/content/image/3-s2.0-B9780124058668000024-f02-14-9780124058668.jpg)
Unfortunately it has no business with op amps, since its for inductors. I don't think it will help any filter then low pass? High, band pass/stop don't really have this problem with the L needing R.
Can it maybe get a more ideal frequency response if the R and L are combined like that? Kind of nice if you can avoid using a composite or ceramic resistor.
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I read a little bit about this, it seems to be done for some VHF supression networks.The idea is to wind a coil with nichrome.
Old tube radios often used inductors wound with a usual copper wire on a resistor.
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Well I doubt I will run across any unstable VHF power tube amps, but the dampened LC filter seems like a reasonable idea.
The biggest downside seems to be the tempco, with copper its 3900ppm/c, nichrome about 700, brass 1500 ppm or so.
However, the tempco of a carbon comp, that people say is a good choice, while carbon comp is probobly at least 1000ppm or way more and unstable. So it can get you similar or better performance to a CC resistor in terms of tempco of the DCR, especially in the 'aging' part.
A rugged Metox resistor is something between 250-600 ppm. So it can be similar or better to nichrome coils.
However, if you use manganin, even without the tempering and stuff, I bet it will be within 10-100ppm/c, so it brings it on the level of a standard metal film resistor (or possibly a better one) and beats out carbon film pretty well. And if its high power, you might have trouble getting metal film resistor to handle watts . it kind of looks like slim pickings
And in terms of a mixed RLC circuit, lets say you do standard copper inductor and a low tempco commercial resistor. You still have a substantial investment of total DCR into copper. For a generic simulation, you want like 5 times more resistance from the LC circuit, but this still means that between 20% to 5% (if you need high DCR) of your resistance is ugly 3900ppm copper.
So I think this might have some uses, even in precise applications, even with simple materials.
I don't know what electronics problem can be solved with this, but there at least seems to be... a narrow window of opportunities to utilize a strange non copper inductor.
I wonder if this will ever come in handy. Only problem is that I don't want to buy weird enameled wire for this experiment. :-DD
And I guess in most cases you won't get a perfect match to the element, unless you make custom alloy wires to meet the circuit needs. but it would still reduce your R requirement, usually smaller value resistors might be better. It would sure be alot of work to knock off some R's. I think I saw such a inductor in a romulan cloak generator.