Topband: Polarity and Phase

[W0UN -- John Brosnahan]

At 06:09 AM 4/15/2004, john battin wrote:

>It requires  a time delay of about 1ms to take two 500hz. tones from being 
>in phase to being out of phase. I can see no way that adding 180 degrees 
>of feedline to one of the recievers input (added delay about 3us) will 
>cause a noticeable change of phase in the output of two recievers.
>John K9DX

John,

I think you are confusing time lag with phase shift here.  Phase relationships
are maintained through frequency conversions.

Rather than get into a mathematical discussion about it let me just
mention the old HP 8405 Vector Voltmeter.  This measures the relative
phase of two signals from about 1 MHz to 1000 MHz by down-converting
the two signals that you want to measure for their phase relationship
to an IF of 20 KHz.   The actual phase measurement is then made
at 20 Khz.

Whatever the phase relationship of the two signals is at their original
frequency is maintained after their down conversion.  Change one by
180 degrees at (say) 1 GHz by adding 4 inches of RG-58 (1/2 wave)
and you will see their 20 KHz signals change by 180 degrees.  Otherwise
the HP8405 would not function as a phase measuring device.

If phase relationships did NOT survive the frequency conversion
process the subtleties of music, such as the ambience of the hall,
would not survive being broadcast on the radio and the subsequent
down-conversions in the receivers.

73--John  W0UN

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