** A parasitic suppressor's design is a compromise that hinges on the
dissipative capability of R-sup.
To wit: If R-sup burns out at 29MHz, VHF oscillation becomes
substantially more possible. However, if R-sup has very low-R to reduce
its dissipation, VHF-Q increases, VHF ringing-V increases, and
oscillation becomes more probable. ["Calculating Power Dissipation in
Parasitic-Suppressor Resistors", March, 1989 *QST*]
> Here is a point I've never seen discussed , anywhere, and I've often
>wondered about it !!
** such has been discussed on AMPS. The key hurdle is understanding
parallel/series-equivalent circuits. (p.7 in the aforementioned *QST*
article)
> what reason is there for a specific value of resistor in a
>parasitic suppressor. ?? I have seen 50 ohms, 100 ohms, and two 50 ohms in
>parallel..
** lLowest VHF-Q is generally achived when XL = R - Provided R-sup can
withstand the dissipative burden @29MHz.
>! Is there a valid reason for using any particular value ?? over
>the years it seems that 50 ohms was the usual value, but today I found in
>the amp I'm working on , a 100 ohm, two watt unit.
** As a rule of thumb, if R-sup burns up (@29MHz), VHF-Q was too low.
If R-sup runs warm, VHF-Q is too high and an oscillation may be nigh. If
R-sup runs hot as hell, but does not burn out, VHF-Q was just about right
to dampen the invisible bell.
cheerz, Carl
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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