[cma-l] DAB trials

[Tony Bailey]

Just in case anyone hasn't had enough of this topic, I found a useful 
document on the subject of Coded Orthogonal Frequency Division 
Multiplexing as used for DAB - see link below.  Just to further clarify 
(or possibly not!) the situation with DAB transmitters, the rated 
average power output (as e.g. heating up a dummy aerial load) may be 
only 10% of the peak power output. So a 100 watt (average) rated unit 
needs to be capable of handling transient peaks equivalent to 900-1000 
watts.

https://tech.ebu.ch/docs/techreview/trev_278-stott.pdf

Tony Bailey




On 10/03/15 16:36, Two Lochs Radio wrote:
> Yes, the multiplex signal itself is one size fits all. The 'couple 
> of stations' does refer to economic factors rather than technical. For 
> 10 stations each with a budget of (say) £1m sharing a 10kW transmitter 
> the cost equation is a bit different from from a couple of stations 
> each with, say, £30,000 budget buying a 100W transmitter.
> The old first-principles way of measuring the average rms power of any 
> arbitrary signal is to feed it into a resistive load and measure how 
> much heat it generates. But more usually nowadays, spectrum analyzers, 
> which are needed anyway for commissioning a broadcast transmitter, can 
> easily measure the total rms power of a signal at an instant or 
> averaged over time. Often there is an add-on pack for spectrum 
> analyzers that contains extra bits (such as a directional coupler/SWR 
> bridge and extra software) that calculates the various radio-related 
> parameters such as power, spectral occupancy, out-of-band harmonics etc.
> And for all I know the digital signal processors in the SDR can 
> also calculate  the average total power at the same time as they are 
> doing all the amazing on the fly maths to create the signal in the 
> first place - just a little bit more arithmetic for them to do on the 
> side!
> Alex
>
>     ----- Original Message -----
>     *From:* Tony Bailey <mailto:ravensound at pilgrimsound.co.uk>
>     *To:* tlr at gairloch.co.uk <mailto:tlr at gairloch.co.uk>
>     *Sent:* Tuesday, March 10, 2015 3:45 PM
>     *Subject:* Re: [cma-l] DAB trials
>
>     Thanks,
>
>     Arising from that (without boring the readers!) I was under the
>     impression that the mpex carrier was one lump, i. e. independent
>     of the number of programme feeds, so presumably the "couple of
>     stations" is an economic rather than technical factor?  How do you
>     arrive at an average power figure for 1500 parallel carriers any
>     of which could presumably be zero or 100%?
>
>     Tony
>


-- 
Local Reports at http://www.ravensound.pilgrimsound.co.uk

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.commedia.org.uk/pipermail/cma-l/attachments/20150311/9b08a80b/attachment.html>