Re: MH101: More cap questions

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From: John J. McDonough (wb8rcr@arrl.net)
Date: Sun May 13 2001 - 13:52:16 CDT


John

Those sure look like monolithics.

Quite often designers will use a polystyrene cap in a VFO. The reason is
that a PS cap has the opposite temperature coefficient to the inductor.
Usually the PS will be in parallel to an NPO or even a monolithic to get the
right balance in temperature coefficients. This can be pretty tedious
business, getting it right. One rig I saw, maybe the OHR-100, had about a
half dozen caps in parallel of different types in an attempt to make the
coefficients work out right.

72/73 de WB8RCR http://members.home.com/wb8rcr/index.htm
didileydadidah QRP-L #1446 Code Warriors #35

----- Original Message -----
From: "John Wagner" <john@neknetwork.com>
To: "Low Power Amateur Radio Discussion" <qrp-l@Lehigh.EDU>
Sent: Sunday, May 13, 2001 1:52 PM
Subject: MH101: More cap questions

> I was lucky enough to remember that a QRP Homebrewer I previously read
> had an article about capacitors by Paul Harden, NA5N. This is the
> Winter, 2000 edition of that journal.
>
> In that article, Paul states that the difference between Ceramic and NPO
> Ceramics are that the NPO's have a stable temperature coefficient. He
> says that non-NPO caps should be avoided in frequency determining
> circuits (like VFO's).
>
> In the VFO that I'm building for the MH101 project, I *think* I may have
> used two non-NPO caps for C4 and C8 in the VFO. I'm finding it difficult
> to ID what type these caps are. From the descriptions in Paul's article,
> they appear to be either Monolithic Ceramic Caps or Polyester Film caps.
> In the picture at: http://www.qsl.net/kb1ens/sw30/1231_004.jpg - they
> are the two yellow capacitors on the board. They are marked 121 CIE and
> 332 AIJ. Using the tables on pg 62 and 63 of the article, I can't find
> anything about the CIE or AIJ markings on these caps.
>
> Can someone kindly ID these caps for me?
>
> More importantly, are they OK to use in the VFO of the radio? I'm at the
> point now where they can be easily replaced.
>
> Thanks es 73,
>
> John, KB1ENS
> --
> John Wagner - john@neknetwork.com
> Web page: http://www.neknetwork.com
>


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