I have used the 8307 in several projects, and found it to be an extremely sensitive device.? To get a good noise floor you really should shield the? 8307 stage. I have etched my own double sided boards, or have had them made. If you wish I can send the gerber files for ones I hade made by oshpark.? The separate regulator also goes a long way to reducing any noise from the Arduino which can raise the noise floor. I found that good shielding and layout can lower the noise floor by almost 10 dB.? If you want I can post the Gerber files for a small board with regulator I hade made by OSH Park, files should be OK for most of the other board houses.
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DuWayne,? KV4QB
DuWayne Schmidlkofer