EMRFD Message Archive 2905

Message Date From Subject
2905 2009-04-10 10:23:52 w2ads Which capacitor technology to use?
Many of the designs in EMRFD use .1u (or similar) caps
all over the place for both bypass and decoupling functions.
I am not sure which capacitor technology is appropriate: I.e.
ceramic, monolithic, mylar, poly, tantalum, etc. Same question
for RF coupling functions. (I assume silver micas are appropriate
for fixed resonant uses).

I am interested primarily in designs in the HF range,
but information for different applications and frequency ranges
would be very much appreciated.

Can someone spell this out for me? Thanks.

-Al, W2ADS
2906 2009-04-10 11:22:28 WA0ITP Re: Which capacitor technology to use?
GA Al,

Paul Harden's Data Book has an excellent table in the capacitor section which
spells out the useage of different types of caps.

-----------------------------
I love this radio stuff !
72, 73 Terry, WAØITP
www.wa0itp.com
www.4sqrp.com
http://www.wa0itp.com/ozarkcon2009branson.html
www.qrpspots.com



----- Original Message -----
2913 2009-04-11 09:36:15 Tony Fishpool Re: Which capacitor technology to use?
Paul allowed the GQRP club to make that section of his book into a data
sheet.

See http://www.gqrp.com/na5n.pdf

Kind regards
Tony G4WIF
www.gqrp.com

-----Original Message-----

GA Al,

Paul Harden's Data Book has an excellent table in the capacitor section
which
spells out the useage of different types of caps.

-----------------------------
I love this radio stuff !
72, 73 Terry, WAØITP
2930 2009-04-15 07:08:57 w2ads Re: Which capacitor technology to use?
Thanks for the responses so far.

To get down to brass tacks, as an example, consider
the W7EL amplifier in EMRFD on page 2.36, figure 2.97.
There are three 0.1u caps; two decouple the 12V supply (say c1, c2),
and the third (say c3) couples the RF output.
Suggestions for appropriate capacitor types (and part numbers)
for c1, c2, and c3? And your reasons?

On the same page, in figure 2.99, there are several 0.01u caps,
some used for bypass, some for coupling RF interstage.
Again, part type suggestions and reasons for the choice, anyone?

Not to put too fine a point on it, but going from general
considerations that we are all aware of (Q, dielectric strength,
voltage dependency, frequency dependency, etc.)
to the actual selection of parts is part of the
design process too. Of course, I'm assuming homebrew style
construction, not surface mount or industrial mass production
choices which may be different.

Thanks again for your thoughts
2933 2009-04-15 19:35:02 Harold Smith Re: Which capacitor technology to use?
For those kinds of applications -- general RF coupling and bypassing -- I
generally use ceramic disc or monolythic caps. Basically, I use whatever I
can get cheaply. Make sure they have a large enough voltage rating, and
will physically fit your space. (I almost always build ugly style, so size
isn't a big consideration.)

I use C0G (NP0) caps in VFOs and tuned circuits, where a precise and stable
value is called for, and electrolytics in audio circuits where ceramics
aren't available in large enough values. I use box-shaped mylar caps in
audio filters, because they are more stable than 'lytics, and available in
larger values than ceramics. Also, some ceramics are piezoelectric, and can
cause noise in audio circuits.

I have a drawer full of cheap, surplus .001, .01 and .1 uF ceramic disks,
bought mostly at fleamarkets or as add-ons when I mail order from surplus
houses, and use them like popcorn. Caps can be somewhat expensive if bought
new, prime and in small quantities, but they are much cheaper surplus, and I
have always had good luck with them.

Remember, part of the fun of homebrewing is maiking something from what is
available. Don't get too worked up about getting exactly the perfect part.
If you have something that will work, at least try it.

Good luck with whatever you're trying

de KE6TI, Harold



2935 2009-04-16 12:57:19 timshoppa Re: Which capacitor technology to use?