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[quote author=”Diekgait”]Stelios, are you going to implement GPS for cariersync and maybe digitall mpx delay?
Dennis[/quote]
Hi Dennis,
Not for these 5 prototypes, but yes, there is plan for SFN support.
There will be a separate box (SFN Adapter) at each DDS exciter, plus one SFN Controller at the studio.
The concept is based on DVB-T standards and it is viable only with digital audio or D-MPX.[quote author=”sigmacom”][quote author=”Diekgait”]Stelios, are you going to implement GPS for cariersync and maybe digitall mpx delay?
Dennis[/quote]
Hi Dennis,
Not for these 5 prototypes, but yes, there is plan for SFN support.
There will be a separate box (SFN Adapter) at each DDS exciter, plus one SFN Controller at the studio.
The concept is based on DVB-T standards and it is viable only with digital audio or D-MPX.[/quote]
Sounds very interesting! Can you please explain the idea a bit more. Wil it be a combination of tcp-ip to connect the boxes and gps for sync?Greetings Dennis
[quote author=”Diekgait”]Sounds very interesting! Can you please explain the idea a bit more. Wil it be a combination of tcp-ip to connect the boxes and gps for sync?[/quote]
There must be phase, frequency and modulation syncronization of all RF carriers that constitute the SFN.
I need AES/EBU, no matter if it’s over IP or any other media! At the moment I don’t know if the boxes will have IP interface by default.
Synchronization will be based on GPS receivers and will follow the basic concept of ETSI TS 101 191 specs.
I am dying to describe in detail how it will work, but I don’t think it is wise to reveal this… 🙄[quote author=”sigmacom”][quote author=”Diekgait”]Sounds very interesting! Can you please explain the idea a bit more. Wil it be a combination of tcp-ip to connect the boxes and gps for sync?[/quote]
There must be phase, frequency and modulation syncronization of all RF carriers that constitute the SFN.
I need AES/EBU, no matter if it’s over IP or any other media! At the moment I don’t know if the boxes will have IP interface by default.
Synchronization will be based on GPS receivers and will follow the basic concept of ETSI TS 101 191 specs.
I am dying to describe in detail how it will work, but I don’t think it is wise to reveal this… 🙄[/quote]We’ll maybe a serial interface will do, because you can use a pc to feed the digitall mpx anyway. So that pc can control the box using rs232/usb as well. I hope Leif can find time to write the ip-stl software, this will be so damn interesting to fieldtest!
[quote author=”Diekgait”]We’ll maybe a serial interface will do, because you can use a pc to feed the digitall mpx anyway. So that pc can control the box using rs232/usb as well. I hope Leif can find time to write the ip-stl software, this will be so damn interesting to fieldtest![/quote]
Serial port, for what purpose? SFN synchonization? Not needed! 😀Okay… In a few words, the concept is:
Digital L/R audio or D-MPX in AES/EBU format, must be fed into the SFN controller. There, an integrated GPS receiver will provide internally a timestamp, which will be inserted into the original audio AES/EBU frames. Also, a system parameter "MaxNetworkDelay" will be injected periodically. This transforms the original AES/EBU frame into "SFN frame".At each DDS TX site, the received "SFN frame" from an IP or digital radio STL, is passed into the SFN adapter which also has an integrated GPS receiver.
Then, the frame timestamp and the "MaxNetworkDelay" parameter are extracted, and the original audio payload is buffered.
Now, the job of each SFN adapter (besides the reference clock generation for the phase synch of the DDS RF carrier) is to hold each audio frame in the buffer, until the most-distant member of the SFN has received the same frame. When this time comes, all the SFN members will modulate on air the same audio frame.The most important issue here, is the estimation of the maximum network delay. That is, the time that every audio frame needs to reach the most-distant TX site.
With a time-unstable transport media (like IP STL), the SFN operator may have to define a big value for "MaxNetworkDelay" parameter – like 2 or 3 seconds.
That means, if you say "Hi" on the microphone, you will hear it after 3 seconds on your radio receiver, even if there is a transmitter on the roof of the studio.
In a more time-accurate and fast transport media (like digital radio STL), the total delay could be reduced to a few hundreds of mS – or less.The serial port could be used to read the status of the SFN adaptar, to see how close it comes to running out of audio in case of a internetstream for example.
Using this together with Leif’s idea of streaming mpx at 128khz 12bit using Flac(Which will result in a bitrate somewhere between 1.1 and 1.3mbit) could make it able to use the internet to create a SFN! Make sure you add quite some memory to the SFN adaptar, so that it can create a large buffer.
And for the delay, 100ms is already to much to monitor of air. So if you can’t monitor of air, what’s the difference between 100ms and 3s? The listener won’t notice:)[quote author=”Diekgait”]The serial port could be used to read the status of the SFN adaptar, to see how close it comes to running out of audio in case of a internetstream for example.
Using this together with Leif’s idea of streaming mpx at 128khz 12bit using Flac(Which will result in a bitrate somewhere between 1.1 and 1.3mbit) could make it able to use the internet to create a SFN! Make sure you add quite some memory to the SFN adaptar, so that it can create a large buffer.
And for the delay, 100ms is already to much to monitor of air. So if you can’t monitor of air, what’s the difference between 100ms and 3s? The listener won’t notice:)[/quote]
Buffer size is not a big issue for me, but SFN over internet scares me a bit…
Anyway, it will be a very interesting experiment. 🙂Look at the center column of page 2 on this brochure. How does this design differ from previous incarnations of digital exciters?
http://www.broadcast.harris.com/media/digitcd-brochure_25-8385.pdf
Nautel has a direct to channel exciter: http://www.nautel.com/M50.aspx
I’m just curious.
From the Harris Brochure..
"A single stage upconverter mixes the output of the digital modulator with a synthesized local oscillator, producing the on-channel FM carrier".
Sigmacom’s DDS exciter does not create an intermediate frequency which is upconverted, it generates the required carrier frequency directly, so where the Harris TX will create the carrier/modulation at approx 5mhz, then upconvert it to say 100Mhz, the Sigmacom makes the carrier on 100mhz in the first place, no upconversion. This is a much better way to do it as mixing creates harmonics which need to be filtered, no mixing, no harmonics. Filtering will also distort the wanted signal.The Nautel brochure does seem to suggest this does direct carrier synthesis which is similar to the Sigmacom method but what Sigmacom’s unit offers, and the thing that has got all us BBP users excited is it’s ability to take an MPX signal digitally, either via optical or coaxial. No other exciter yet can do this.
Both the Harris and the Nautel can take in audio as L/R digitally (which would normally have gone through a processor) and then use an onboard stereo encoder and an outboard RDS coder to give the final MPX signal but this will be vastly inferior to the audio being processed, encoded into stereo AND having the RDS digitally injected by BBP, then the resulting MPX being inserted to the exciter digitally and this digital signal being directly modulated, digitally onto the direct to frequency carrier which itself is created, you guessed it, DIGITALLY…
Do not underestimate how big of a leap forward this is, this is as clean and as close to perfect an FM broadcast will ever get, and most likely there will never be a tuner good enough to fully exploit how good of a signal is being transmitted.[quote author=”sigmacom”]
Buffer size is not a big issue for me, but SFN over internet scares me a bit…
Anyway, it will be a very interesting experiment. 🙂[/quote]A very interesting experiment indeed, when I was discussing with Leif how we might like a Digital MPX STL to work (this seems like ages ago..), I did conceed the point that MPX over the internet might be a little optimistic but I’m certainly hoping to be able to use it over LAN and WLAN networks such as 5.8Ghz TCP/IP links. This now will be all the more of a sweet idea if an SFN will work over this too although I guess some extra functionality/compatability may have to be included in any future IP/STL to allow the extra SFN info to be passed.
Fun times ahead I can predict.I LooOoOOoOoooove this Fu@@@cking G@@@@d d@@@@am forum! 🙄 🙄
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Sound proccesing engineers , hardware engineers, software engineers !everyone is here and …predict the future of FM !
Keep up!
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