>
>On Wed, 10 Sep 1997 08:45:27 +0000 w8jitom@postoffice.worldnet.att.net
>writes:
>.
>>> * RF-ground the cold end of the GTR with a triple-bypass using
>>roughly 100pF, 1000pF and 0.02uF. Use minimal lead lengths. This method
assures
>>> acceptable bypassing at 160m to10m AND the lower half of the VHF range.
>>
>>73, Tom W8JI
>...................................
Tom Rauch,, W8JI did not write the above. I did.
>One cautionary note:
>
>When paralleling multiple by-pass capacitors, it is a good idea to
>sweep the frequency response of the combination before applying
>power.
>
>I once tried this approach for a broadband J-FET follower circuit and
>found that the large capacitor became inductive in the band of interest.
>There was a high frequency PARALLEL RESONANCE formed by the
>inductive reactance of the large capacitor and the capacitance of the
>smaller capacitor. (These were for radial leaded low voltage ceramic
>caps.)
>
>In other words, two unequal value capacitors can actually form a
>parallel resonant circuit at a frequency above the series resonance
>of the larger capacitor. BE CAREFUL when paralleling unequal
>capacitor values.
>
>de Tom N4KG
Good point, Tom. That's why it takes at least three unequal capacitors
to make a widely effective bypass.
Rich---
R. L. Measures, 805-386-3734, AG6K
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|