[time-nuts] Austron 2010B (disciplined OCXO) square wave conversion

Charles Steinmetz csteinmetz at yandex.com
Sat Aug 6 17:19:18 EDT 2016

Ruslan wrote:

> Only later did I realize that for some bizarre reason,
> all of the outputs are square wave, not sinusoidal!
> I'd rather use something prebuilt than building my
> own converter

A simple Tee network lowpass filter will do the job -- see the attached 
schematic (NOTE: this circuit is designed for 10MHz -- you would need to 
scale it for 5MHz and 1MHz).  If the input is from 5v CMOS logic (0v 
low, 5v high) that will put out at least +/- 30mA and you use a 56 ohm 
input resistor, the circuit will deliver a sine wave output of ~1v RMS 
(= +13dBm) into a 50 ohm load, which is a common output level for 
frequency references.

Mini-Circuits sells a 5MHz LP filter with BNC connectors (BLP-5+), but 
it does not include the input resistor or the DC blocking capacitor 
shown in the attached schematic -- so you would need to add those 
yourself (again, I'm assuming that the Austron output is a DC-coupled, 
0-to-5v square wave).  Mini-Circuits does not list a 1MHz filter, and 
their 1.9MHz filter is not suitable because it wouldn't provide 
sufficient attenuation of the 3rd harmonic (3MHz).

You would put the filter between the Austron output and the 50 ohm input 
of a distribution amplifier.

Best regards,


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