[time-nuts] NOT digest, I forget the subject not sure why the digest received Richard's reply and not me ? Oh well, never mind.

[Bruce Griffiths]

Stanley Reynolds wrote:
> http://www.unusualresearch.com/AppNotes/TimeNuts/OptDualMixer.pdf
>
>
>
> Fig 1 shows a phase shift of OSC 1 is this required ? Or is it just a indication of the difference in phase of the two OCS's ? Or is this a way to prevent injection lock ?
>
> Further on they say:
>
> "Interference may cause an undesired phase lock by an injection locking process between the measured oscillators. Fortunately these undesired phase locks can be easily detected. The more dangerous are near-false phase locks where the phase is only disturbed."
>
> Maybe that is the propose of the phase shifter on one of the two oscillators ?
>
> Stanley
>
> PS when I attached the pdf it bounced (> 128 KB) so this is a copy with no attachment just the link.
>
>   
Stanley

The purpose of the phase shifter is to approximately align the zero
crossings of the 2 bat frequency signals being compared.
This reduces the sensitivity to the phase noise of the offset oscillator.
It has little or no effect on injection locking.
Other measurement methods can be used that have high rejection of the
offset oscillator phase noise without requiring approximate alignment of
the zero crossings of the 2 beat frequency signals.

Some injection locking paths are:

1) from the RF port of one mixer to its LO port and thence to the LO
port of the other mixer to its Rf port.

2) from the RF port of either mixer to its LO port and hence to the LO
via its output buffer.

As depicted in the circuit diagrams this particular implementation has
significant coupling from the RF port of the mixer to the RF port of the
other mixer.

The coupling from the RF port of either mixer to the LO port will be
even higher.

The reverse isolation of the output amplifiers of both the OCXOs and the
offset oscillator will need to be very high to avoid injection locking.

The statement that injection locking can easily be detected is somewhat
glib and brushes over the detail.
Its not always easy to detect especially if you don't know what to look for.

Bruce