[time-nuts] RFTG-m-RB

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Jan 19 20:46:53 EST 2008


The best phase noise and phase shift stability will be achieved by not
using a bandpass filter to extract the 10MHz signal, but by using a low
pass filter with low phase shift at 10MHz to eliminate the higher
harmonics, supplemented with high Q series tuned traps at the
fundamental (5MHz) and 5th harmonic etc to shunt these undesired
harmonics to ground. The high Q series tuned traps will have low phase shift and associated phase shift tempco at 10MHz.

This works best when either a common gate or common
base bipolar transistor is used to amplify the output (as in the Wenzel
application note) before driving the filters.

Whilst using a bandpass filter is the obvious solution it will have a
large group delay and phase shift tempco which will increase the phase
shift instability due to temperature changes.

Bruce




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