The best capacitors for RF decoupling are monolithic chip caps. They
have a slab of solid material such as tantalum nitrile to separate the
two poles of the cap, which are typically splattered-on leadless plates.
These are normally used in parallel or series with the signal path in
low-loss devices such as preamps, for high power use they are also
suitable, but examine their RF power handling (current and voltage)
characteristics carefully.
Proper RF decoupling is never associated with a single cap, that's why a
row of caps such as 4.7p, 47p, 470p, 4700p, 47000p, etc, are often used.
Each cap "bypasses" the particular freq of interest, all the more
important in a device such as a wideband amp where there could be a 17:1
(30 MHz/1.8 Mhz) frequency range.
For example, much has been said on this page regarding input and anode
tuning components and their values, but little on low impedance RF
bypassing of the intermediate stages, crucial on high frequency devices
such as the 4CX250 and 2C39. Maybe even on the 3-500, some tailored
bypassing may leak off the "big bang" before it becomes destructive...
Ian ZS6BTE
Hans Goldschmidt wrote:
>
> Very interesting. What capacitor would be the best then? Hej daa de Hans
> SM5KI
> ----------
> >
> >
> >Hans Goldschmidt wrote:
> >> ----------
> > The best broadband
> >> condenser should be a multilayer chip condenser that has no leads at all.
> >
> >This is not correct.
> >If the layers were "unrolled", the overall length could exceed that of a
> >ceramic disc or mica cap with leads clipped short, producing inductance.
> >Ian, ZS6BTE
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