[time-nuts] Si570 question

[Neil Schroeder]

Jim-

Do you need to tune it?  The 571 is the VCXO - but if you're feeling
adventuresome you  could drive the 570 as an NCO (numerical) via its i2c
interface.

NS

On Tuesday, November 18, 2014, Jim Lux <jimlux at earthlink.net> wrote:

> On 11/18/14, 11:19 AM, Orin Eman wrote:
>
>> I have one of these: http://sdr-kits.net/PA0KLT_Description.html
>>
>> built with the CML output Si570 that goes to 1417 MHz (!)
>>
>> There is a schematic in the assembly manual that's linked to from that
>> page.  They use 100n and 1n capacitors in parallel on Vdd and 4K7 pullups
>> on SCL/SDA.  They have 100n DC blocks directly on the output pins.
>>
>> Into a 50 ohm load, the CML outputs produce about 4dBm as I recall.
>> Obviously, the CMOS output will be different.
>>
>> There is a review of a different Si570 kit on the Clifton Labs site:
>>
>> http://www.cliftonlaboratories.com/si570_kit_from_k5bcq.htm
>>
>> I got similar results comparing my kit against an HP 8640B.  The Si570
>> beats the 8640B close in just as shown on the Clifton Labs site.
>>
>> Some Softrock SDR radios also use the Si570.  They use a single 10n
>> capacitor on Vdd and 2K2 pullups...:
>>
>> http://www.wb5rvz.org/ensemble_rxtx/03_lo
>>
>> I have the Softrock Ensemble RXTX.  It works fine on RX, but unfortunately
>> I have not been able to get satisfactory image rejection on TX.  I suspect
>> the FST3253.
>>
>> So, it looks like decoupling isn't that critical - 10n or 100n||1n in
>> these
>> examples.  1K pullups on SDA/SCL seem to be overkill and anything
>> reasonable <= 4K7 should work.
>>
>> Orin.
>>
>>
>>  thanks... looks like it's time to stop analyzing and go find a piece of
> copper clad to stick this thing down on.  I see a lunchtime project coming
> up,
>
>
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