Dave Platt wrote:
The "treated carefully" is good advice - understanding the limitations
of the equipment is critical (and not specific to MFJ products!).

There are a number of stories going around, concerning people who have
managed to damage MFJ antenna tuners - typically, by burning up the
inductor (sometimes melting the form on which it's wound). In each
case I've read, the tuner in question has been a "T" configuration
(the commonest). One of the gotchas of a "T" tuner is that it can
appear to "match" an extremely nasty load (e.g. a short circuit) down
to a low SWR, while what's actually happening is that you're
"matching" the tuner's own internal losses. You can end up with
nearly 100% of your transmitter output being dissipated in the coil...
and this tends to let the magic smoke out, after a couple of minutes.

The other problem is that they are rated with numbers people don't really
understand. When MFJ says it is a "300 Watt" tuner, that's maximum possible
rating.

Like VA (volt-amps) which is used for transformers, and UPS's, it's much
higher than what you would actually use it for. For low frequency ratings,
you derate by the square root of 2 over 2 (.707) but I expect that's only
good at 50Hz or 60Hz, at RF, it's close to one third.

Geoff.


--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
New word I coined 12/13/09, "Sub-Wikipedia" adj, describing knowledge or
understanding, as in he has a sub-wikipedia understanding of the situation.
i.e possessing less facts or information than can be found in the Wikipedia.