[time-nuts] Re. Interesting experiments with SDR

[Andre]

Hi all.

I found something intriguing, on at least some SDRs the 28.8MHz crystal is way off by about -2%

Reset mine using Island FM to fine tune, a simple reverse biased blue LED (6pF) to tweak the

centre frequency a bit and now my 1990 vintage Black Star counter and SDR agree correctly.


Actually found that blue LEDs make remarkably stable fixed capacitors, if you reverse bias them with a

moderate DC voltage a "useless" dim blue LED from a UPS makes a very good wide range varicap diode.


Does anyone have an idea how to verify my calibration(s)? Unfortunately I lack a Rb or Cs module

but can (barely) get MSF here with a loop antena if it is far enough away from lighting etc.

Have a few random parts including some MK484 ICs so should be able to make some sort of

MSF bodge which will be stable long enough to calibrate the system.


It seems that Island FM actually calibrate against GPS so this should be highly accurate.


-Andre