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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