NPO capacitors are Class 1 capacitors which are more stable and designed for resonant circuits. You have a better chance of getting a capacitor of this type with a low RF ESR
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The disadvantage of the class 1 types is the size. For a certain size you may not be able to get the appropriate voltage rating.
Mike N2MS
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On 05/08/2021 9:36 AM jerry@... <jerry@...> wrote:
On 2021-05-08 05:49, n2msqrp wrote:
These capacitors have a X7R dielectric. I would look for capacitors
with a NPO dielectric
Does the temp coefficient matter? This isn't a VFO. I just looked it
up -
X7R is considered relatively temperature stable. I found a graph - the
capacitance peaks around 20C, and at 0C and 40C it will be down 1% to
2%.
For a lowpass filter, that should be just fine. I would worry more
about voltage rating, AC current rating, and ESR (Equivalent Series
Resistance).
