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While working on a circuit design the other day, I happened across a datasheet for a high-frequency resistor that specifically mentions that it uses a "non-nichrome resistive element". In fact, searching that specific phrase turns up a lot of datasheets from Anaren/TTM that put it as a headline feature.

But why would they so proudly advertise that they aren't using nichrome as the resistive element in these parts? What properties of nichrome are undesirable?

Hearth
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  • https://electronics.stackexchange.com/questions/460740/why-are-there-no-nichrome-resistor-pastes This claims it is related to permitivitty which seems relevant for your listed component (RF frequencies). You can self-post this as an answer if you want because this is not my own info. – DKNguyen Apr 05 '23 at 14:55
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    @DKNguyen The fact that it's hard to use nichrome in a thick film process doesn't seem to be relevant to the end user, just to the manufacturer. However, the answer to that question does mention "nichrome's permittivity is poor", which could be an answer to this question, with an explanation of what permittivity means in a fair conductor like nichrome--I have some idea, but a better understanding might help here. I've never worked with anything this high frequency before. – Hearth Apr 05 '23 at 15:01
  • Sometimes, the marketing people decide they need to sell a weakness and, if the resistor has a sh1tty tempco then, appearing to proudly boast that their component doesn't use Nichrome might just tip the balance on a few extra sales. It's basically saying go check the tempco. – Andy aka Apr 05 '23 at 15:58
  • For RF, I think NiCr could have quite a bit of magnetic losses. The web says it is non-magnetic, but that is usually a DC and room temperature statement.. – tobalt Apr 05 '23 at 16:03

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Unless the resistor is to be used solely as a heater, the temperature coefficient is important. Nichrome has a pretty good tempco - only an order of magnitude worse than manganin, which is close to the pinnacle of performance in terms of alloy wire tempco.

So, perhaps they mean that they used wire with better tempco than nichrome?

Kuba hasn't forgotten Monica
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  • There's no wire involved; the datasheet I linked, at least, says it's a thick film resistor. If it was the tempco, I would expect that it would call out low-tempco instead of just saying it's not nichrome, but it is a possibility. Especially for something rated to 45 watts, I think tempco would be a relevant parameter... which is why it's odd the datasheet doesn't specify one. Nor does it even specify a resistance tolerance, which is just bizarre. Perhaps that's normal for RF stuff, though. – Hearth Apr 05 '23 at 15:05
  • For something rated to 45W, tempco would be *especially important*, because the thing heats up so much you don't want the resistance to drift and affect the performance of the RF circuit, e.g. if the resistor is a part of a pad or a load. But I don't think they actually made a particularly stable resistor here. Most thick films are pretty low on the scale in terms of tempco and overall stability. I don't think there's anything special about their product being "non-nichrome". Perhaps they meant it doesn't use nichrome *wire*? – Kuba hasn't forgotten Monica Apr 05 '23 at 18:57