[OZAPRS] on pilot tones and freq references

Glen English VK1XX glenlist at pacificmedia.com.au
Mon Nov 20 16:17:58 AEDT 2017


most commercial broadcast stations 1970-2003 used external stereo
generators either in one box (AGC multiband limiter/ composite stereo
generator like ORBAN 8100 8200 or discrete units like CRL SG-800 , Aphex
etc . Traditionally, stations used composite stereo links, where the
stereo encoder was at the studio and the entire composite baseband 30Hz
to 53kHz (+SCA) was piped over the 850 MHz link..... Over time stations
have moved to discrete L and R microwave links in the city, or for long
throws in the bush , and moved the entire processing chain to the
transmitter (but still requiring an AGC unit at the studio)

Some transmitters offered internal stereo generators, usually cheap
Italian TX junk used by the cost sensitive community broadcast stations
and some rural commercial stations.....  but these were widely avoided
by tier 1s  until the advent of the full digital stereo exciter came
along from the AMerican manufacturers like BE and Harris and Nautel .
NEC actually offered stereo generators within their widely used FBN
10/20kW cream tube TXers , this stereo generator was usually avoided
because the composite audio chain was full of tantalums and this
resulted is rather poor IMD if the station ever bothered to wonder why
it sounded like it did.

I can go on...



:-) g



On 20/11/2017 3:55 PM, Matthew Cook wrote:
> Hmm...  The stereo pilot tones on all the generators I've worked on
> were typically derived from the same master LO that feeds the PLL i.e.
> 10MHz.  So once the master LO was locked then the whole station was
> locked, mind you I've not worked in commercial Broadcast since the
> late 90's so things may have changed.  I'll go and find out.
>
> 73
>
> Matthew
> VK5ZM
>
> On 20 November 2017 at 06:21, Glen English VK1XX
> <glenlist at pacificmedia.com.au <mailto:glenlist at pacificmedia.com.au>>
> wrote:
>
>     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>
>     <mailto: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>
>     <mailto: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>
>     >>         <mailto: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>
>     >>         <mailto: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>
>     >>>       
>      <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>
>     >>         <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://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>
>     >>         <mailto: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>
>     <mailto: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>
>     >>         <http://lists.aprs.net.au/mailman/listinfo/ozaprs
>     <http://lists.aprs.net.au/mailman/listinfo/ozaprs>>
>     >
>     >
>     >     --
>     >     Gavin Rogers mobile
>     >
>     >     _______________________________________________
>     >     OZAPRS mailing list
>     >     OZAPRS at aprs.net.au <mailto:OZAPRS at aprs.net.au>
>     <mailto: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>
>     >     <http://lists.aprs.net.au/mailman/listinfo/ozaprs
>     <http://lists.aprs.net.au/mailman/listinfo/ozaprs>>
>     >
>     >
>     >
>     >
>     > _______________________________________________
>     > 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>
>
>
>     _______________________________________________
>     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>
>
>
>
>
> _______________________________________________
> OZAPRS mailing list
> OZAPRS at aprs.net.au
> http://lists.aprs.net.au/mailman/listinfo/ozaprs




More information about the OZAPRS mailing list