[OZAPRS] on pilot tones and freq references

Mon Nov 20 15:05:08 AEDT 2017

I use ABC Classic, long pauses with no modulation (other than the stereo
pilot) so you can have a nice, clean GPS-disciplined carrier.

cheers
Carlos

Le lundi 20 novembre 2017, Glen English VK1XX <glenlist at pacificmedia.com.au>
a écrit :
> In general, I would say >95%, the 19kHz pilot tones of a FM radio
> station are free running, derived from a nothing special crystal. Don't
> expect better than +/- 50 ppm.
>
> From 1970 to ~ 1992 stereo generators were analog type , xtal derived
> +/- 100ppm, but usually within +/- 1Hz (+/- 52 ppm)
>
> When digital signal processing based audio processing began to appear,
> the 19kHz pilot was being derived from the sample rate clock. This is
> usually better than at least +/-25ppm.
>
> In the 2000s there has been a gradual move in the very most advanced and
> newest cap city stations to fully integrated audio chains from digital
> consoles to digital modulation FM transmitters, with the audio processor
> being fed by AES/EBU, however there is still an asynchronous sample rate
> converter and the 19kHz clock is likely to be still supplied by a +/-
> 25ppm oscillator.
> In some cases the FM modulator/transmitter is locked to a GPS, however
> this is generally asynchronous with respect to the input sample rate
> (and hence 19kHz pilot) because of the restrictions on SR in the
modulator.
>
> There is no required accuracy for 19 kHz pilot to function, as receivers
> have a VCO in their FM demodulator that gets locked to the incoming
> 19kHz tone, and used to demodulate the DSB 38kHz stereo signal (which is
> AM- being DSB).
>
> There are no easy good off air sigs. If you can demodulate (despread)
> the CDMA signal of 3.84Mcps this is probably the best source.
>
> But that's if you want Hz, but most people with their radio probably are
> just happen with 100Hz at 100 MHz, which is 1ppm. You can get that with
> a half decent off the shelf reasonably aged TCXO or OCXO.
>
> The DVBT  (digital TV) signals that are in single frequency networks are
> locked to the GPS, if you can figure out how to demod those, they will
> be excellent.
>
> The GPS locked ham beacons are an excellent option.
>
> -Glen.
>
> On 19/11/2017 10:39 PM, Matthew Cook wrote:
>> Gavin,
>>
>> You can go and find the stereo pilot tones in your commercial FM radio
>> station those are GPS locked rubidium.   We're lucky here in VK5 that
>> our VHF/UHF beacons are GPS locked, so I typically go and use these to
>> zero in RTL-SDR's to a few hertz... you might find the ones in Perth
>> are of a similar nature, never hurts to ask.
>>
>> 73
>>
>> Matthew
>> VK5ZM
>>
>> On 19 November 2017 at 14:56, Gavin Rogers
>> <grogers at vk6hgr.echidna.id.au <mailto:grogers at vk6hgr.echidna.id.au>>
>> wrote:
>>
>>     Maybe different in other states, but in Perth the only carrier
>>     with GSM still is Vodadone, and their coverage isn't good enough
>>     where I am to get a good calibration.
>>
>>
>>
>>     On 19 November 2017 11:21:49 am AWST, Peter VK2MPJ
>>     <vk2mpj at yahoo.com.au <mailto:vk2mpj at yahoo.com.au>> wrote:
>>
>>         I’m curious why you say that using kal and a GSM signal is not
>>         possible anymore?
>>         I did this locally just last weekend…
>>
>>         2MPJ
>>
>>
>>>         On 19 Nov 2017, at 12:42 pm, Gavin Rogers
>>>         <grogers at vk6hgr.echidna.id.au
>>>         <mailto:grogers at vk6hgr.echidna.id.au>> wrote:
>>>
>>>         On 19/11/2017 9:30 AM, vk4tec at tech-software.net
>>>         <mailto:vk4tec at tech-software.net> wrote:
>>>>
>>>>         Or, as i've mentioned before, just link to the existing
>>>>         Direwolf SDR+APRS guide, which covers off setting up an
>>>>         igate pretty
>>>>         well:
https://github.com/wb2osz/direwolf/blob/master/doc/Raspberry-Pi-SDR-IGate.pdf
>>>>         <
https://github.com/wb2osz/direwolf/blob/master/doc/Raspberry-Pi-SDR-IGate.pdf
>
>>>
>>>         In this guide, there's a link to a script that will tune to a
>>>         NOAA frequency and re-calibrate an SDR TV stick
>>>         ( https://github.com/khaytsus/direwolf-init
>>>         <https://github.com/khaytsus/direwolf-init> )
>>>
>>>         What would be a good high-stability signal source here in VK
>>>         for the calibration? I used to use the kal program to
>>>         calibrate against GSM transmitters, but that's not possible
>>>         any more. I'd think the trunking control channel for an
>>>         emergency services' channel would be stable, strong and
>>>         always on? Or DAB+ transmitter, or..?
>>>
>>>
>>>         73
>>>         Gavin.
>>>
>>>
>>>         --
>>>
>>>               Gavin Rogers                     |  Amateur radio station
VK6HGR
>>>             http://www.livingwaters.com/good
>>>         <http://www.livingwaters.com/good>   |
http://vk6hgr.ampr.org/
>>>                        MSN/Skype/Email: grogers at vk6hgr.echidna.id.au
>>>         <mailto:grogers at vk6hgr.echidna.id.au>
>>>         _______________________________________________
>>>         OZAPRS mailing list
>>>         OZAPRS at aprs.net.au <mailto:OZAPRS at aprs.net.au>
>>>         http://lists.aprs.net.au/mailman/listinfo/ozaprs
>>>         <http://lists.aprs.net.au/mailman/listinfo/ozaprs>
>>
>>
>>     --
>>     Gavin Rogers mobile
>>
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