Empathy List Archives

A

Andre

Mon, Apr 10, 2017 6:00 AM

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

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

PS

paul swed

Mon, Apr 10, 2017 7:03 PM

Andre
Very interesting on the blue LED varicap. I'll have to see if I have one to
test.
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.
Regards
Paul
WB8TSL

On Mon, Apr 10, 2017 at 2:00 AM, Andre Andre@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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Andre Very interesting on the blue LED varicap. I'll have to see if I have one to test. 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. Regards Paul WB8TSL On Mon, Apr 10, 2017 at 2:00 AM, Andre <Andre@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 > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. >

AG

Adrian Godwin

Mon, Apr 10, 2017 7:38 PM

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.

http://www.qsl.net/pa2ohh/07freqstd.htm

http://www.npl.co.uk/science-technology/time-frequency/products-and-services/time/time-and-frequency-bulletins-for-msf-droitwich-and-gps-off-air-signals

On Mon, Apr 10, 2017 at 7:00 AM, Andre Andre@lanoe.net wrote: