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

[Magnus Danielson]

Bob,

I intended nothing aiming for "perfect".
My initial proposal was actually for a 1 pole low-pass and then a block 
at 30 MHz for third overtone, but I never put that in mail-form.

Cheers,
Magnus

On 07/17/2015 02:57 PM, Bob Camp wrote:
> Hi
>
> But your 3 pole will not be as good as my 5 pole. My 5 pole will not be as good as the next poster’s
> 13 pole. My 5 added traps will not do as much as the next poster’s 13 traps.
>
> What *will* happen as all of these parts are added:
>
> 1) It becomes a real mess to properly lay out and align
> 2) Even with good equipment, you will need ever more accurate parts to implement it
> 3) The sensitivity of the result to minor parts variation will keep going up. (I get -180 dbc here and “only” -120 dbc 1% away).
> 4) The odds of anybody actually building one go down probably as the square of the number of parts involved.
>
> The simple filter topology posted earlier by Charles is indeed quite adequate. You can get -60 dbc harmonics without
> going very crazy on the design. Part values can either be calculated from formulas that have existed for > 80 years
> or you can play with simulation.
>
> Bob
>
>> On Jul 17, 2015, at 4:07 AM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
>>
>> I was thinking along these lines.
>> Cooking up a 3-pole filter in the form of a Pi-filter should be a good start, and then add traps for third and possibly fifth overtones that will not get much damping initially can be done if you need it pretty clean.
>>
>> Cheers,
>> Magnus
>>
>> On 07/17/2015 04:07 AM, Graham / KE9H wrote:
>>> All you need is a 10 MHz low pass filter.
>>>
>>> How far down do you need the harmonics/spurious to be?
>>>
>>> If 40 dB suppression of the 2nd and 3rd harmonics is adequate,
>>> (you can't see the distortion with the eye on an oscilloscope)
>>> you can make your own for about $2 in parts, not including a PC board or
>>> housing.
>>>
>>> Feel free to copy the low pass filter (L1, C9, C10) from here:
>>> http://openhpsdr.org/wiki/index.php?title=EXCALIBUR
>>>
>>> Or for about $35, you could get the same performance from an inline BNC
>>> filter from Minicircuits.
>>>
>>> http://www.minicircuits.com/pdfs/BLP-10.7+.pdf
>>>
>>> If you need more harmonic suppression, buy two and put them in series.
>>>
>>> --- Graham
>>>
>>> ==
>>>
>>>
>>>
>>> --- Graham
>>>
>>> ==
>>>
>>>
>>>
>>> On Thu, Jul 16, 2015 at 12:49 PM, skipp Isaham via time-nuts <
>>> time-nuts at febo.com> 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 from scratch and make a new wheel....
>>>>
>>>> Thank you in advance for your replies.
>>>>
>>>> Regards,
>>>>
>>>> skipp
>>>>
>>>> skipp025 at yahoo dot com
>>>>
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