wrote:
..
Here, on page 23...

http://www.icomamerica.com/support/k...?Download=1265

...Icom shows four 0.15 uf capacitors in parallel acting as a DC
block / galvanic isolator in the RF ground circuit of an SSB system.
I assume the caps are in parallel to increase the voltage rating...?
Are these plain old ceramic caps, like an 'orange drop' - say 400 VDC?

Many Thanks.

The transmitter wants to pass 150 watts to an antenna via a 50 ohm
coaxial cable. Thats a feed current of about 1.7 amps (I^2.R = 150W)
The transmitter would prefer not to use any of those 150 watts on
heating up a capacitor or wire, so they specify an AC resistance much
less than 50 ohms for the antenna ground path at the lowest frequency of
interest.
Let's say at 3 MHz you want to use a DC blocker that looks like less
than 1% of 50 ohms.
1/100 X 50 ohms = 1 / (2.pi.f.C) so
C = 1 / (2.pi.3X10^6 X 0.5) = 0.1 microFarads or more.

On the face of it, just one cap would do it. But there are practical
issues. There is an inductance associated with each capacitor,
so the AC resistance of a single cap starts rising again at some
frequency. If you put four in parallel, then this inductance is divided
by four, while the capacitance is multiplied by four. Sometimes,
designers put a low value capacitor in parallel with the others, because
this has low series inductance at high frequencies...
They are in parallel, so the voltage rating stays the same.
That's the main reason for paralleling them - to keep the AC resistance
LOW at any frequency you might tune, no matter how high.
Ceramic caps are useful at high-frequency and they are durable - may be
variable with temperature - but that's not critical here.

Brian W
Refs: Electronics G.H Olsen. Butterworths
The Art of Electronics Horowitz & Hill Cambridge UP