On 7/2/2015 6:08 PM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message
...
The mismatch you are counting on for a 50 ohm transmitter and a 75 ohm
feedline and 75 ohm antenna is in the tuned circuits/matching circuit in
the
transmitter. Whatever power comes out of the transmitter will make it to
the antenna minus the loss of the coax, but not additional loss due to
swr.
The power comming out of a 50 ohm transmitter will be less due to
mismatch,
but not because of swr of the antenna system which is 1:1.



Incorrect. The connection between the 50 ohm transmitter and the 75 ohm
coax is also part of the antenna system. The system starts at the
transmitter output (actually the output of the final stage - but since
this is converted to the 50 ohm standard, you can effectively consider
the output of the matching network to be the start of the antenna
system), not the coax.

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So with my Icom 746 with a built in tuner, where does the system start ?
Within a small range 3 or 4 to 1, the internal SWR meter will show a 1:1
match, an external SWR meter will show a differant SWR if there is a
mismatch. If I hook up a good 75 ohm load and 75 ohm coax I will have no
SWR by definition . A 50 ohm bridge will show 1.5:1 but the internal
tuner/bridge will show 1:1.

Which SWR meter is correct ?




A built in tuner is an entirely different story. The output from the
transmitter is not necessarily 50 homes at this point.

It's a shame they've dumbed down the exams so much that you don't need
to know anything to hold a ticket any more. Back when I got mine, even
the General Class was tougher than the Extra Class today - and it was
administered by the FCC, with no public question pool or cheat sheets.
You had to actually know something other than just memorizing a few answers.

And at the time, the Amateur Extra was harder than the First Class
Radiotelephone.

Nowadays, an 8-year-old can pass the Amateur Extra with virtually no
knowledge of math or electronics at all - just the ability to memorize a
few answers.

Learn something about electronics, AC power transfer and other theory.
Than maybe we can converse with a modicum of intelligence. As it is,
I'm tired of trying to teach an idiot who refuses to learn.

--
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Jerry, AI0K

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