On 06/04/2014 05:22 AM, Tony Greene wrote:
About 50 years ago I ran into a Frequency Division Multiplexer that used a
redundant master frequency system. I beleive they combined the same frequency
for the master oscillator, but it was something like a special hybrid
combiner. I remember that they used a phase angle of 135 degrees - and then if
they lost one signal, the power went down by 3 db on the main pilot. Anybody
no any details on this type of system ?
What I am looking for is to have an input to a distribution amplifier where I
can connect and disconnect two different inputs and keep the output systems up
and running.
Two methods is being used as far as I know:
1) Phase microstepper to shift into phase. Quadrature phase
multiplication is one approach to achieve it.
2) PLL and then alternate which is the reference source. As you loose
the current reference, the oscillator in the PLL act in hold over until
the PLL has locked to the other reference.
This is being used in essentially all the telecom SSU like redundant
chassis.
Cheers,
Magnus
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