[Amps] Re: [Amps] Bird® 43 Manual

[Gary Schafer]

Tom Rauch wrote:

> > Hi Gary.
> > That is not the case .
> > The Bird 43 picks up current directionally. With a standing wave on
> > the line , current is washing back and forth through the line. It
> > still picks up signals directionally. --- Ron
>
> The Bird 43 element, like every other directional coupler device that
> measures forward and reflected power at one single point in a
> transmission line (rather than points separated by an appreciable
> fraction of a wavelength) samples both line current and line voltage.
>
> The null is cause by line voltage and current being in a
> predetermined ratio, and out-of-phase. When you reverse the
> element, the phase of the voltage sample always remains the
> same. Only the phase of the current sample inverts.
>
> The voltage and current are directly summed at the operating
> frequency, and the resulting voltage is detected and fed to the
> meter.
>
> The meter responds to both voltage and current, and that is why
> even if you totally do not terminate a meter it still registers
> correctly, with an infinite SWR and the correct apparent power.
>
> I can not think of any way to make a non-transmission line type of
> directional coupler that does otherwise.
>
> Of course there are accuracy limits caused by limitations in
> components, but this is a much better system with far fewer flaws
> than people here seem to think.
>
> 73, Tom W8JI
> W8JI@contesting.com

Tom,

Are you saying that because the bird meter measures both voltage and
current that it will read right no matter what the line impedance is that
it is connected to? This of course subtracting reflected from forward
readings.

How does this happen when there is no line connected to the output of the
watt meter and no current can flow? When you reverse the element you are
only reversing the current pickup phase. If that is true then in the case
of no line connected and no current the only thing that there is to
measure is voltage which the meter does not discriminate against
direction.

73
Gary   K4FMX