I think we're having a terminology problem here.  Strictly speaking, a
"bridge" in physics is a collection of resistors or, for "impedance
bridges", resistors, inductors and capacitors, connected in such a way
that the electronic system has certain properties.  For example, the
Wheatstone Bridge that I mentioned yesterday or the day before is a bunch
of resistors wired in such a way that if a galvanometer is wired into the
circuit in a certain way, one can vary one of the resistors so that no
current flows thru the galvanometer.  In the case of a meter reader using
a Wheatstone bridge, the galvanometer is replaced by a resistor and
something which periodically interrupts the circuit in series with an
amplifier or headphones across the resistor so that one adjusts the
variable resistor for no sound.  When this condition obtains, the
potentiometer has a known, predictable resistance so can be used to read
the meter.

Similarly, an antenna noise bridge is a series of components which, when
adjusted so that no current obtains in a certain circuit path, the values
of the components can be predicted and thus the impedance of a certain
component (in this case, the ATU) can be known.

Usually these days, the device used to peak your transceiver's power
output is not a bridge in the sense above but is rather a
voltage-controlled oscillator as I mentiond the other day with a
diode/resistor combination to rectify the RF as the voltage source.

In any event, the output of the transceiver/transmitter goes to the unit
you use to peak the transceiver/transmitter's output; this goes to the
noise bridge which then goes to the ATU which then goes to the antenna

Mike Freeman < K 7 U I J >
"All men tend to become that which they oppose." - Laurence van der Post

On Fri, 22 Nov 2002, Michael Ryan wrote:

> That takes care of one bridge.  What about the second one which is used to
> tune up the transceiver it self? This one picks off some RF current for the
> purpose of dipping  plates and loading.
>
> Michael
>