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Digital Radio?
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gamevision
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Joined: 30 Apr 2004
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Post Digital Radio? Reply with quote
Lately i have heard that Radio will soon be turning Digital, what does this mean? What new equipment will this involve? any idea about the cost?

Thanks and Regards

Andre`
(93.3 Central FM radio Station Manager)
www.centralfmradio.cjb.net

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Sun Dec 19, 2004 11:25 pm View user's profile Send private message Visit poster's website MSN Messenger
Sir Nigel
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It depends on a lot of things. Over in the US, they're working on adding digital "hash" in-between the frequencies for digital radio. Despite what some say, this does cause undesirable interference on other freqs. In Europe a different freq. range is being used for it, and they're ahead on progress.

A large problem seems to be everybody will need to upgrade to a new radio to get these broadcasts, so that means $$$s not everyone wants to spend. Plus broadcast range is not as great, if the station gets weak, you just lose it (of fall back to the analogue signal).

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Sun Dec 19, 2004 11:43 pm View user's profile Send private message Visit poster's website
Sir Nigel
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Although the page is old, it's still interesting, read:

http://www.digitaldisaster.org/

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Mon Dec 20, 2004 1:42 am View user's profile Send private message Visit poster's website
pcs
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This is not appropriate for small scale broadcasting, such as 1W
transmitters.

The reason is simply that there must be numerous users that are all
added to the multiplex. Will you be looking for 5 or 20 other people
who want to transmit with you?

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Mon Dec 20, 2004 10:18 am View user's profile Send private message Visit poster's website
Medus
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Post Reply with quote
pcs wrote:
This is not appropriate for small scale broadcasting, such as 1W
transmitters.

I agree, but for different reasons than that which you gave. As mentioned above digital has a signal threshold below which you just lose the broadcast entirely... so, yes, for a digital broadcast you need a stronger transmitter to achieve the same effective range and penetration. This is offset by the use of SFN's or (Single Frequency Networks) ... the idea being that 3 smaller transmitters operating on the same frequency (overlapped) can be spread around the target area to provide extended coverage and provide better penetration. It also gives greater fault tolerance.

This will actually be of benefit to the pirate too because it makes locating a given transmitter a little less straightforward (intentional multipath interference)... Then, once that transmitter is finaly placed out of action (a smaller loss than one large single transmitter) the others continue to broadcast content... essentially, you lose transmitters slower and it would be rare to be put 'off-the-air' entirely during an FCC/RA crackdown.

pcs wrote:
The reason is simply that there must be numerous users that are all
added to the multiplex. Will you be looking for 5 or 20 other people
who want to transmit with you?


I don't know how this works commercially. I am assuming though that he has various options:

1 - Buy space on an existing SFN... this will allow you to use their existing transmitter network with content delivery and maintenance taken care of. You provide the stream and they provide the distribution and transmission network and logistical support.

2 - Place a local digital station. Larger outlay but you can rent out your unused streams to other local content providers. I don't know how this works out in terms of costs and licencing... do you pay for dead channels? Probably - because you still take the same bandwidth.

3 - Form a partnership of local broadcasters and enter DAB together pooling the equipment costs between yourselves. If any space remains this can possibly be rented off in the future. You're asking these questions... it makes sense that other analogue stations are asking them too. Get together now and beat out some ideas for partnering-up on digital content delivery. Unless you're looking towards national coverage you may get a better deal as a local consortium with shared interests than individually letting space from the big boys.


Of these I'd say the first is the easiest and most likely. It probably won't be the cheapest but it will avoid a lot of pitfalls. I'd say the third option is certainly worth pursuing too.




And for unlicensed stations...?

Unused sub streams do not NEED to be utilised unless you are a professional station paying the license. There's nothing wrong with a pirate streaming two 192kbps streams as a full-quality stereo provider and leaving the other channels as dead air. Alternatively, the same pirate can stream the same station 6 times with different identifiers making it more likely for others to stumble across his channel ... or ... allow competing pirate stations to pool transmitter resources and both STL to the same transmitter pool. If the STL is microwave then the DAB Processor (The FPGA's and DSPs that build the broadband subcarrier) could be located at a covert groundstation which removes a lot of the risk.

Lets face it, digital could be GREAT news for pirates:

- Transmitters in SFN's are harder to locate (taken down less often)
- The option of sharing transmitter useage and thus dividing individual transmitter costs.
- Multiple smaller transmitters means FCC/RA takedowns don't put the station off-air

Heck, want transmitters at a sixth of the price? Buy one and lease channel useage to other pirates in your area. And, since its a sixth of the price why not buy more... spread them about the town broadcasting on the same overlapped frequency and when the FCC/RA *finally* manage to triangulate one out of the mess you're still '83% on-air' and each actual content provider loses just a sixth of the transmitter cost.


And what IS the transmitter cost?

People seem to think that digital is going to cost a fortune and thats not the case. The FM transmitter is still pretty basic. It is the processor that produces the multiplexed subchannel ensemble that costs the money - and that needn't be physically connected to the transmitter if my figuring of microwave STL bandwidth is correct.

Ultimately DAB is still basic traditional analogue circuitry on the RF side. As for the processing side a single FPGA chip can give you 4 stereo MPEG2 encoders running at 192kbps (The discrete digital streams) From there one requires the multiplexer with Forward Error Correction, Etc ... Essentially its not so expensive to build a DAB solution written in VHDL/Verilog and the effect is the same as having 'custom silicon'


Of course, the first developer that ships these to hobbyists (probably sometime after analogue dies-so some years yet) is bound to charge a small fortune but that doesn't mean that these will be expensive to produce - only that, in the absence of competition, some kit developer can charge whatever the heck they wish. I think the reason we haven't seen these yet is most developers right now are handy with a simple microcontroller such as a PIC or 8052 (which are way too slow for this application) - but mention coding up a 'custom silicon' solution as an FPGA core in VHDL/Verilog and they just blink.

Its gonna come though : )


-Medus
Sat Jul 29, 2006 5:23 pm View user's profile Send private message
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