Dave - I blew a cap on 40M this morning so I've got to open up the Titan
again...might as well upgrade some of the other caps in there as well.
Please e-mail me the info you offered...thanks!
Tom K2TA
tom@k2ta.com
----- Original Message -----
From: "Dave Bowker" <dbowker@mail.sjv.net>
To: <tentec@contesting.com>
Sent: Saturday, March 15, 2003 10:35 PM
Subject: [TenTec] Omni VI & Titan tuning repeatability
The major cause of the Titan I power output and tuning drift problem is due
to dielectric heating of the plate circuit DC blocking capacitors. Ten Tec
uses two 0.001 uF/6 kV disc ceramic capacitors with a Z5U dielectric
characteristic in parallel (C6 and C7) for this application.
Type Z5U disc ceramic capacitors exhibit poor RF current and temperature
performance (especially at the lower frequencies), and a very small change
in temperature due to dielectric heating causes a significant change in
capacitance, varying as much as +20% between the temperature range of
+20C to +35C (capacitance can actually vary as much as 45% over the
temperature range of +10C to +35C). Such a change affects the Titan I tank
circuit tuning capacitor (C26/C14) setting significantly as the temperature
of the blocking capacitor changes with operating time.
Replacing the two disc ceramics with 0.001/5kV Type 858 doorknob capacitors
having an X5V dielectric characteristic and rated for RF current handling
applications eliminates the drift problem.
I'll be happy to email temp. vs dielectric curves for the subject caps, mod
instructions, and photos to anyone requesting.
73, Dave, K1FK
Fort Kent, ME
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