[time-nuts] Re. Interesting experiments with SDR

paul swed paulswedb at gmail.com
Mon Apr 10 15:03:22 EDT 2017

Very interesting on the blue LED varicap. I'll have to see if I have one to
If a few it would be interesting to see if they track with V/C.
With respect to Island FM. The station is unclear to me but the easiest
thing to do is simply call them and ask what there reference is. You indeed
may have a great reference for free.
On FM even if calibrated to some reference I think you have to average the
signal to remove the modulation effects.

On Mon, Apr 10, 2017 at 2:00 AM, Andre <Andre at lanoe.net> wrote:

> 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
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