[time-nuts] Re. Interesting experiments with SDR

Adrian Godwin artgodwin at gmail.com
Mon Apr 10 15:38:37 EDT 2017

Assuming you're in the channel islands, you should be able to pick up BBC
radio 4 long wave on 198kHz, if your SDR can handle frequencies that low.
It's referenced to a rubidium standard and checked by NPL.

It can also be used to discipline a reference, or compared with some other
local standard such as your frequency counter.



On Mon, Apr 10, 2017 at 7:00 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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