On Wed, 28 Apr 2004 13:06:59 -0500, Jeremy Salch
wrote:

Allan Butler wrote:

Maybe use some capacitors from the control wires to ground to short out
the
rf right to ground before it gets to the toroids. The toroids then won't
have so much rf to work with and they may not be as likely to saturate.

Be careful with the capacitors that you get transmitting style that can
handle a good amount of rf current.

I've heard of doing this before, with the capacitors, so would this be the
ceramic type? and how would i distinguish between "transmitting" style and
regular capacitors?

Hi Jeremy,

There should be no distinction between caps for this job - almost
anything will work as the control voltages are so low that even
dielectric breakdown is unlikely.

On the other hand, the package style may be more carefully considered.
The high end designs use what are called "feed-thru" button styles
that are designed for bulkhead connections with a pig-tail on either
side and the cap looks like a threaded stud with a collar. These are
specifically designed to decouple rf off of dc lines. They provide
the shortest lowest inductance path to ground (essentially zero lead
length).

These would be a must for UHF, but at HF you are just as well off with
simple, leaded Micas, Ceramics, Paper-oil, polystyrene, tantalum, or
any of a host of others. You don't really want massive capacitance
(which is to say perhaps tantalums and like are unnecessary overkill)
because 10,000pF is more than enough but 0.22mF works just as well.
If you assist the cap with a small choke (on the noisy side of the
current) you gain that much more isolation. Again, any value is
better than none (but it hardly begs 1H audio chokes).

73's
Richard Clark, KB7QHC