EMRFD Message Archive 6157
Message Date From Subject 6157 2011-04-20 15:12:42 dnorbury Ceramic capacitor values I hope this isn't too dumb of a question.
I bought some 220 pF ceramic disk capacitors and some were labeled '220' and some were labeled '221.' According to how I understand the labeling nomenclature, a value of '221' means 22 x 10 to the first power (which equals 10), or 22 x 10 = 220 pF. But '220' should mean 22 x 10 to the zero power (which equals 1), so '220' should be 22 x 1 = 22 pF.
But it would more sense for a 22 pF cap to just be labeled '22', of course. So there would no point in labeling a 22 pF capacitor '220.'
So, are capacitors labeled '220' as well as '221' both 220 pF? In the case of a '0' multiplier is the normal naming rule ignored?
6159 2011-04-21 00:36:23 Kerry Re: Ceramic capacitor values Not dumb at all; you highlight a common problem with capacitor markings.
Google "capacitor markings" or the like; you will step into a minefield. :)
The G-QRP Club has a good overview of capacitors; go to http://www.gqrp.com/sprat.htm and download the Guide to Capacitors.
I find that ceramics are the worst in this respect; they can be marked with the EIA markings (220, 221, 222 etc as you describe) or with the value which can be in pF or uF.
One of the batches of capacitors that you have may be "old stock" made prior to the adoption of the EIA system by that particular manufacturer.
There are other marking systems that might be occasionally encountered; sometimes they are not marked at all!
SMD ceramic capacitors are not marked; heaven help you if you mix them up. :)
A capacitance meter is indispensable if the experimenter is to make sense of all this; I have an AADE meter but there are others if you prefer.
The only shortcoming of the AADE meter is that it does not measure resistance; it would be nice to have C, L & R all available on the one instrument instead of having to reach for the multimeter.
But I am cavilling; other than that very mild criticism I have only praise for the AADE L/C meter.
6160 2011-04-21 03:55:35 Leon Heller Re: Ceramic capacitor values 6161 2011-04-21 04:09:58 Leon Heller Re: Ceramic capacitor values 6162 2011-04-21 10:35:31 Tim Re: Ceramic capacitor values I know that the fancy-pants digital reading RLC meters are all the rage these days. Some here have full-blown network analyzers.
But would it make sense to have some simple AC bridge circuits in the "next" EMRFD? Or is this something that's so well covered by nearly-century-old ARRL handbooks that it's superfluous today? I still build impromptu bridges, hook them up to a oscillator
6163 2011-04-21 18:07:49 Ashhar Farhan Re: Ceramic capacitor values There was an LC meter described in the measurements chapter, probably
towards the end pages. I am on the move, so I cannot recall it exactly
but I suspect it was Bill's design.
The best way of course is to simply add the unknown value to an
oscillator with a set of known lumped constant values, read off the
frequency and figure out the capacitance/inductance. The readings can
be far more accurate than usually needed.
For instance, I can usually eliminate trimmers in tuned circuits by
accurately setting the inductance in the test oscillator (as
recommended by the 'triad').
On 4/21/11, Tim <firstname.lastname@example.org> wrote:
> I know that the fancy-pants digital reading RLC meters are all the rage
> these days. Some here have full-blown network analyzers.
> But would it make sense to have some simple AC bridge circuits in the "next"
> EMRFD? Or is this something that's so well covered by nearly-century-old
> ARRL handbooks that it's superfluous today? I still build impromptu bridges,
> hook them up to a oscillator
6164 2011-04-22 06:32:23 Tim Re: Ceramic capacitor values That's why I still have a grid dip meter :-). In many senses it's far more valuable to know where the LC is resonant at, than the individual values for L and C.
Fig 7.24 shows Hartley and Colpitts test oscillators that are good for LC measurements at RF ranges. But what I was particularly impressed by (and very happy with my version) was the Fig 7.27 general purpose oscillator. The bandset/bandspread arrangement lets me hand-sweep crystals reliably and repeatedly at the 10 Hz level.
One easy add-on for the old handbook and Millen dip meters etc. is a cheap modern frequency counter.
I still like my old HP oscillator on the bench with an impromptu bridge for audio frequency range L and C comparisons, and I was surprised that it works so well with very small L's and C's too.