[cma-l] DAB trials

[Tony Bailey]

I'm not so sure about that analysis, after all, the report implied that 
it was the SDR that was under-run at 5mW presumably because the output 
daughterboard was intended for AM/FM modulation?  Also, it was common 
IBA practice to run a several kilowatt bottle at a hundred watts or so, 
the excess input power being necessary to ensure class A linear 
operation.  The point being that the rf amp has to be linear, and it 
isn't, you can't just turn it down a bit.

Tony Bailey


On 09/03/15 22:41, tlr at gairloch.co.uk wrote:
> Pete: We know what software and modulator they will probbaly be using, 
> but one of the key features of Ofcom's proposals for low-cost DAB 
> broadcasting is avoiding the use of the conventional large and 
> expensive DAB mask filters (typically 6-cavity high power devices) on 
> th efinal output.
> This can be achieved by a combination of tactics, including a very 
> under-run driver stage (eg 100mW stage running at only 5mW) and 
> relatively underrun RF amplifiers (eg maybe using an amplifier 
> potentially capable of say 250-500W continuous carrier power to 
> produce a DAB signal of less than 100W), so that there are fewer 
> spectral regrowth components to be filtered. Plus with the whole kit 
> running at relatively low ERP anyway, the filtering is not as critical 
> as it would be for a high-power transmitter because the absolute level 
> of spurious products is low relative to neighbouring high-power 
> signals and aeronautical limits.
> Alex
>
> > On 09 March 2015 at 20:18 Pete <peter at engineeringradio.co.uk> wrote:
> >
> >
> > It's obvious what type of exciter they will be using if you have 
> been following them. It's obvious it will be SDR based. The amps may 
> be a different matter. I don't think it is clear what they would be 
> using. They would probably use filtering to the spec set out for DAB.
>
>
> _______________________________________________
>
> Reply - cma-l at commedia.org.uk
>
> The cma-l mailing list is a members' service provided by the Community Media Association - http://www.commedia.org.uk
> Twitter: http://twitter.com/community_media
> http://www.facebook.com/CommunityMediaAssociation
> Canstream Internet Radio & Video: http://www.canstream.co.uk/
> _______________________________________________
>
> Mailing list guidelines: http://www.commedia.org.uk/about/cma-email-lists/email-list-guidelines/
> _______________________________________________
>
> To unsubscribe or manage your CMA-L mailing list subscription please visit:
> http://mailman.commedia.org.uk/mailman/listinfo/cma-l


-- 
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/20150310/b174a9b1/attachment.html>