On Sun, 20 Jul 2003 22:10:26 GMT, Dilon Earl
wrote:
If you have three Watts reflected, it came from the transmitter and in
fact never left it, it simply turned to heat. The meter is indicating
a condition, not forcing it. A fever thermometer in your mouth will
tell you that you have a temperature in excess of the surrounding
environment (a clear mismatch except for rare summer days) and yet the
thermometer is not responsible for your fever (Thoreau once offered
that we were more comfortable before the thermometer's invention).

Ok, if it never left the transmitter, why or would there be a loss in
the feedline due to high reflected power?

The 3W you measured was/is at the transmitter end of that feedline, it
could have been 30W at the load, but the feedline burnt up 27W as it
came back (it also burnt up the same proportion of that power going
forward). One of the truisms of measuring SWR is that a lossy line
will make the worst of load reflections look better.

In a sense you could say that a lossy line is cooling your
transmitter. Think of it as a remote heat sink. ;-)

SWR can be thought of as being derived from an equivalent lumped load
attached directly at the antenna jack (it is) or as from the long
system variable extended across space and storing energy (it is). You
should judge the character of an answer as needing to respond to BOTH
views in proportion to actual circumstances. Neither is independently
correct to the exclusion of the other (and this is why some discussion
devolves into pulses).


You can use a circulator to heat a dummy load if you wish, or you
could use a tuner to reflect that power back to the antenna. You may
well wonder why a circulator was offered in the first place.
Rhetorical gamesmanship is the answer which has nothing to do with
offering any real solution to you.

I didn't see where a circulator had anything to do with my original
question. My SB-401 doesn't have one.

Nobody uses one. I would hedge that call with saying they are found
in "some" repeater installations, but only if the designer has the
sheckles (or savvy) to rummage one up.


Well, perhaps too much explanation, you can certainly survey the other
postings for their entertainment value in the form of cut-and-paste
theory or equipment operator myths.

73's
Richard Clark, KB7QHC

Thanks for taking the time to answer my questions. Its too bad a
newbie with a few simple questions can't ask them and get answers to
them. 99% of the answers made no sense to me. But I guess if they
did, There wouldn't be reason for me to ask my simple questions?

Hi Dilon,

Sometimes that is because they expect you to reference Google's
archives of yesterday's posts. The problem there is that same archive
is full of the same baloney offered to the last one they expected to
reference the archives. Others will sometimes offer a significant
search term that leads to a lengthy treatment quickly - the remainder
don't have a clue and insist on proving it the hard way.

Finding real, actual data, experience, or theory is as rare here as it
is anywhere when the price is nothing and the cost is high. Through
"lurking" (reading, but rarely jumping into the game) over an
extended period, you get to read personalities and observe personal
weaknesses. If you looked back up the chain of responses and side
threads, you should observe some correlations to answers offered in
good faith (even if they were less than eloquent, a bit off the mark,
or lost themselves).

Rarely is one blown off for simply being a newbie, but if anyone
marched in here saying "I don't know how this works, but I can prove
it ain't the way everyone says" - expect fried critic for dinner.

By-the-by. I noticed you referred to tube equipment along the way, or
simply took up a ride with strangers (dangerous habit). Tubes exhibit
the same problems with heat as transistors do. As this topic is
hardly closed (if you lurk or participate, you will see your same
question offered again); you should observe how denials emerge where a
tube is somehow immune.

The proper expression would be tubes are somewhat immune and in fact
are far more survivable than some transistor sets facing the same
mismatches. Tubes also have a vastly larger surface area (of the
plate) and thermal mass which offers much more resilience (the small
junction meltdown happens faster) and they glow cherry red to prove
it, as red as any carbon resistor flickering the guts of your rig with
surplus calories. You can recognize these veiled offerings of proof
of there being no way a transmitter suffers from reflected power in
that they talk about everything but the obvious inferno. Having that
larger surface area or mass also presents a problem though. It also
comes with a larger distance from any way to sink the heat except
through IR radiation and very little heat conduction (a lot is left up
to forced convection). In this sense, the Thermal Resistance is huge,
and the consequent failure is found in plates that melt or grids that
sag through heat expansion to the point that they short out to other
internal elements. My buddy's amp got so hot that the solder
connections to the socket pins of the tube (not the socket connector
it plugged into) dripped to the chassis pan and opened the filament
path.

If you read the dialog across enough time, you will observe that such
discussion is avoided so that any particular scribbler does not leave
a trail of admission to a fine point of Thevenin's theorem.... I will
leave such mysteries of the inner circle to other threads. ;-)

This last is probably more your problem of obtaining a straight answer
than any other source.

73's
Richard Clark, KB7QHC