[time-nuts] 10MHz Square to Sine Wave Conversion

Bob Camp kb8tq at n1k.org
Fri Jul 17 13:26:50 EDT 2015


Hi

If you attach a filter with a shunt capacitor (capacitor to ground) at it’s input to the output of a logic gate,
that gate will pull far more current than it would without a shunt capacitor being present. You can try to
minimize this with a series resistor, but that’s only a partial fix. 

Bob

> On Jul 17, 2015, at 5:49 AM, timeok at timeok.it wrote:
> 
> 
> 
> It is the simplest solution because you have not to tune the  notch filter but you have -20dB on 2nd harmonic and -40dB for the third instead -50dB (min for both) if you made a low-pass with notch filters.
> 
> Luciano
> 
> 
> 
> 
> On Fri 17/07/15 05:10 , D W <watsondaniel3 at gmail.com> wrote:
> 
>> Hi,
>> 
>> A while back I ordered an item of equipment from a very excellent eBay
>> seller, johnkw40. He may be a member of the list, I'm not sure. He included
>> a schematic for a low pass filter circuit to filter a 10 MHz square wave to
>> a sine wave.
>> 
>> A quick analysis shows that it is a 5th order chebyshev filter with a
>> cutoff frequency of about 14MHz. You could do better, but this filter can
>> be built with only five standard value passives, which is quite convenient.
>> 
>> I made a little SMT version of it and ordered the boards on OshPark. It
>> seems to work pretty well. The circuit schematic and a screen shot of the
>> response is attached. Any comments from the list on how that looks would be
>> welcome.
>> 
>> Dan
>> 
>>> On Jul 16, 2015, at 10:49 AM, skipp Isaham via time-nuts  wrote:
>>> 
>>> re: 10MHz Square to Sine Wave Conversion
>>> 
>>> The GPSDO I recently acquired outputs a 10 MHz square wave. I'd like
>>> to convert it to a sine wave and I am looking for suggestions and info
>> re
>>> any reasonable pre-made circuits and/or boards. No sense reinventing the
>>> wheel if I can avoid it.
>>> 
>>> Otherwise I will start Sent from my iPhone
>>> 
>>> Thank you in advance for your replies.
>>> 
>>> Regards,
>>> 
>>> skipp
>>> 
>>> skipp025 at yahoo dot com
>>> 
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