> > > Not according to my Bird 43 operating manual. If you have one,
see
> section
> > > 3-36 on p. 19. Also see the notes in section 3-37 on p. 20.
> >
> > But you left off the most important part of what I said here. Try
this
> sometime
> > with a 1/2 wave length of line. Take a piece of 75 ohm cable and
terminate
> it
> > with a 50 ohm load. Put your watt meter on it and you will see a
perfect
> match.
> > No reflected power. Forget about what the bird manual says. The
meter will
> see a
> > perfect flat 50 ohms. Also try it with other impedance lines as I
> mentioned
> > here. You will get the same results.
>
> Granted. It is a principle of transmission line theory that the
impedance
> is identical on either side of a half-wavelength. I believe the
point in
> the Bird manual is that we are not always dealing with 1/2-wave
lines in our
> measurements. Most of our measurements in this hobby are conducted
on line
> of unknown length.
>
> >
> > It doesn't matter what the characteristic impedance of the line
is. What
> > matters is what the meter sees. I can take a 1/2 wavelength
> > line that has a characteristic impedance of 100 ohms or 400 ohms
or 900
> > ohms. If I put a 50 ohm load on the end of that line and the
> > other end connected to the watt meter the meter will see 50 ohms
with no
> > reflected power. Impedance transformation.
>
> Fine. See above.
>
> > Yes and the reason that I mentioned it is that you earlier stated
that the
> > reflected power coming from the antenna was re- reflected by the
matching
> > network in a tube radio but in a solid state radio there was no
matching
> > network. My point being that if you claim that the reflected power
gets
> re-
> > reflected by a matching network in a tube radio why would it not
also be
> re-
> > reflected by the matching network in the solid state radio.
>
> Because the source impedance remains relatively constant at 50-ohms
with
> solid-state, broadband transmitters. Re-reflection requires a
conjugate
> (reactance cancellation) of the antenna + feedline. The solid-state
> transmitter has no way of achieving this without an external
mechanism.
> This can be satisfied with a transmatch, auto-tuner....and yes,
changing the
> feedline length to tune the antenna + line as a complete "system" as
you
> previously stated. However, without that mechanism in place, any
reflected
> power caused by the load-to-feedline mismatch is absorbed in the
> transmitter.
>
> > Well ok if you don't like a shorted line how about an open line
with
> infinite
> > resistance.
>
> Heh...I'm not the one who doesn't like your shorted line
hypothetical. We
> started with open lines and you moved to shorted lines. Let's stick
to one
> point at a time. Please explain why a zero-resistance short on an
> automobile battery would produce no power?
>
> > Well you don't tune the antenna with the transmission line that is
an old
> > misunderstood tale.
>
> Not quite. The antenna *system* which includes the line + antenna
can be
> tuned by changing the length of feedline.
>
> > What I am saying is that by the proper types of feed line lengths
to the
> > transmitter you can make the transmitter see 50 ohms with no
reflected
> power but
> > yet the feed line has reflected power on it. And we know that it
will have
> > reflected power on it because it's impedance does not match the
antenna.
>
> But you haven't expained why this works. The answer is that by
changing the
> line length, the system reactance is cancelled and the antenna +
feedline is
> now at resonance, even when the line-to-antenna is mismatched. This
is the
> essence of conjugate matching. The transceiver sees only the
resultant
> resistive component.
>
> > > If what you state is true (no load, therefore no power) and the
fact
> that my
> > > Bird 43 measured 100-watts forward and reflected into an
unterminated
> line,
> > > my transmitter shouldn't be drawing 20-amps at 13.8 volts. One
more
> > > time....where else can the power be dissipated?????
> >
> > What happens if you disconnect the feed line completely from the
> transmitter.
> > What happens if you hook the bird watt meter directly to the
output
> terminal of
> > your transmitter with just a double male connector (no cable
length. Then
> don't
> > hook any line at all on the other side of the meter. What will it
read?
>
> The exact same reading: 100-watts forward and 100-watts reflected.
No
> surprise there. I tried it again this morning. Mt transceiver is
still
> drawing 20-amps at 13.8 VDC with or without a feedline connected to
the
> radio. Where is the power being dissipated? By now, you know the
answer.
>
> -Paul, W9AC
>
What I want to know is why do you keep turning on your transmitter
without an antenna?
---
Ron
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