On Sat, 16 Jan 1999 11:47:53 -0500 Carl Clawson
<CarlClawson@compuserve.com> writes:
>
>Do you have any handy rules of thumb to estimate RF capabilities of
>components? For instance, disk ceramic capacitors, various mica types,
>trimmer caps, etc. Can you judge by their size how much RF current
>they can
>take?
Start by reading thru old ARRLHandbooks, QST's etc; that will give you a
pretty good idea of what is used where, how and why.
Look at various commercial ham amps and notice the case size of the
silver micas in the input networks and the size of the compression
trimmers and toroids. Any quality amp does not use disc ceramic in the RF
path at much over 500W.
Are there other components for which you have favorite rules of
>thumb
>about voltage/current/frequency limits -- chokes,
Determining size of wire, a simple L meter and a GDO work wonders .
ferrite cores,
Not for tuned circuits. For input networks the T68 and T80 series
powerded iron are the common choices up to 200W.
>switches,
Grab a catalog from Newark, etc. They give ratings for most common
ceramic switches at sizes below RSC offerings. There are standard switch
sizes that have not changed in 50+ years, only the company names. For old
Centralab check out the Electroswitch web page. For instance the old 2500
and JV-9000 series are now D-7 and E-4 respectively. Those are/were
used in 90+ % of commercial ham amps.
For RF use measure the contact to contact and contact to ground spacing;
consult ARRL Handbook for DC breakdown rating. Subtract about 30% for
RF....RF does not like sharp edges or corners.
>relays, etc?
Start with the Newark catalog again. Similar size units change names but
ratings pretty much hold forever. Look again what is used in commercial
amps.
>
>Regarding silver mica caps, I note that Cornell-Dubilier's web page
>states
>that less than 0.05% of applied volt-amps are dissipated as heat.
The standard 500V SM can handle a 100W exciter with ease, go up one case
size for the 200W rigs. Mouser carries a nice selection.
73 Carl KM1H
>That's an
>example of the kind of thing I'm thinking of (although I would rather
>they
>had posted complete data sheets). With this, I can estimate how hard I
>can
>drive a given package without overheating it.
>
>Safe and non-destructive (at least to the test equipment) test methods
>are
>interesting, too.
>
>Thanks!
>-- Carl WS7L
>
>--
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>
>
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