[time-nuts] FE 5680A "new version" - Filtering the 10 MHz
ed breya
eb at telight.com
Tue Nov 15 16:21:39 UTC 2011
You can add a crystal filter using a common 10 MHz crystal in series
with a low noise, high impedance amplifier. Terminate the input side
with about 50 ohms, and set the Q of the filter with the load
impedance. Since you're only worried about harmonics, the Q can be
fairly low, making the exact crystal characteristics (frequency
precision especially) less important. Extra components can be added
for more sophistication and compensation for parasitics (especially
parallel Co), if needed. More stages will make it even cleaner, but
the amplifier noises will add up. If there is enough signal power
available in the original output, you can leave out the amplifier and
use an impedance matching transformer instead, avoiding the amplifier noise.
Ed
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