Re: QRPoMeter


Todd Carney <carneytf@...>
 

Just a bit more on these two caps. The one from your junque box (and on the left in your picture) is probably a MLCC (Multi-layer ceramic capacitor). The one on the right in the photo is a "legacy"-type ceramic disk (most likely single layer). Other factors the same, MLCCs are smaller than single-layer caps.

Another important factor with ceramic caps (all caps, really) are the characteristics of the dielectric--the non-conducting material between the "plates" (layers) that form the capacitor. An important characteristic for RF work is the temperature coefficient ("TC"--change in value per degree of temp change) of the dielectric. Whether or not this is important depends on the function of the cap in the circuit. If the cap is being used for RF coupling or bypassing, drift in value due to temperature change is far less important (often totally inconsequential) than a capacitor used in RF frequency-determining parts of an oscillator or filter. Caps with X5R or X7R (the most common general-purpose types) are generally used for coupling and bypassing and for that purpose are made in the higher end of the range of values (for ceramic caps, anyway).

Your 0.001uF cap (and most caps spec'ed in uF) is an example. Caps valued in picofarads (pF)--especially in small values--are usually used in frequency-determining parts of a circuit and their TCs can be critical. For ceramic caps, the NP0 (negative-positive zero) types are far-more stable than the more common X5R and X7R types.

For a really thorough and well-illustrated (but still accessible) article on ceramic capacitors, see https://en.wikipedia.org/wiki/Ceramic_capacitor. It's really quite fascinating (but I'm a nerd, so . . . )

K7TFC_sig.JPG



On Sat, Oct 19, 2019 at 7:12 PM Aaron Scott via Groups.Io <k5atg=yahoo.com@groups.io> wrote:
I'm building the QRPometer kit and I ran into a minor problem. My kit did not have the C3 capacitor. The C3 cap has a value of 0.001 and has the number 102 stamped on it. In my junk box, I found some caps that have the same value and the 102 stamped on it but it is a little different than the ones that come in the kits.
 
The capacitor on the left is the 102 capacitor that I had in stock. The one on the right is an example of the caps that came in the kit. So I'm wondering if it would be ok for me to use the cap that I found since it has the exact values as the one that is missing in the kit. 
Thank you
'72 
Aaron K5ATG

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