[time-nuts] what is acceptable harmonic content & level for a 10Mhz standard?

Richard (Rick) Karlquist richard at karlquist.com
Tue Jan 26 17:16:02 EST 2016



On 1/26/2016 11:52 AM, walter shawlee 2 wrote:
> I have been working on a compact portable 10Mhz bench standard
> using both an FE FE5680A Rb oscillator and an Oscilloquartz ovenized

It is important for a 10 MHz source to launch a pure sine wave
and also to have an accurate 50 ohm impedance at 10 MHz and its
harmonics.  This is because a sine wave is the only waveform
having the property that it is immune from distortion due to
reflections from poorly matched loads.  IE, sine wave with
multipath resolves again to a sine wave.  It is important to
have a broadband 50 ohm output impedance to absorb reflections
from loads, especially load-generated harmonics.  You didn't
ask, but you also want a lot of reverse isolation to avoid
pulling the OCXO.  All of these were addressed in the design
of the output section of the 5071A cesium standard.  It was
really quite non-trivial.  Specifically, the harmonics are
down over 80 dB.

Rick Karlquist N6RK



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