[opendtv] Re: Latest S/N tests
- From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 28 Jan 2005 08:45:42 -0800
S.J. Birkill's following message is very much worth reading. I'm reposting
since the subject line used might cause one to pass it over.
----- Original Message -----
From: "S J Birkill" <sjb@xxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Friday, January 28, 2005 1:54 AM
Subject: [opendtv] Re: opendtv Digest V2 #24
>> From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
>> Subject: [opendtv] Re: Latest S/N test
>> Date: Thu, 27 Jan 2005 15:13:13 -0800
>>
> <...>
>>
>> Zarlink recently announced design of a single ended tuner
>> for Thompson that they say exceeds the ATSC's A74
>> recommendation. That is nothing exceptional given that it
>> is a marginal spec. I was advised last year that Zarlink, RMT,
>> and others, supply triple conversion receivers, with significantly
>> better specs than A74, to the European COFDM markets,
>> where they are serious about OTA performance.
>> See these web page.
>> http://products.zarlink.com/product_portlets/thomson_pnp.htm
>> http://www.rwt.com.uk
>>
>> Tthe Zarlink spec sheet doesn't give one a clue
>> about how their single conversion image rejection scheme
>> functions but I did note that the Noise Figure is a paltry 13db.
>> As I recall, the DVB-T spec. is 8db or less and a typical
>> DVB receiver is in the 5db range.
>
> RWT (correctly rwt.co.uk) designed the SetPal tuner which helped enable
> the
> UK DTT 'Freeview' market in 2002 with the first < GBP 100 STBs. SetPal-1
> used double conversion with Zarlink tuner chips, autonomous wide band RF
> AGC derived after a discrete LNA (overall NF 4dB) and a broad
> alignment-free tracking filter to reduce mixer IM loading, a 1220MHz 1st
> IF
> with AGC and a 36MHz final IF with AGC. Overall phase noise was in fact
> lower than with single-conversion designs because the 1270-2080 MHz
> upconversion VCO PLL could use a wide-band loop with 4MHz comparison
> frequency (for an 8MHz channel matrix). The downconverter needed to tune
> only a handful of 41.667 kHz steps, so a narrow loop could be used here.
>
> The later SetPal-2 uses the Zarlink image-rejection MOPLL in a
> single-conversion design with wide band RF AGC and alignment-free tracking
> filter. As will all consumer MOPLL devices an LNA is required for the
> required NF. SetPal-2 features in several current brands of STB, iDVCR,
> iDTV and DVR, including products which combine DAB radio.
>
> Conventional DTT tuners (i.e all the others, I believe) in the UK use
> single conversion with narrow tracking filters, derived from standard
> analog tradition, but with improved-phase-noise converter chips (Philips,
> Infineon) for digital. These, as with all consumer analog TV tuners
> worldwide, incorporate a simple tracking filter of nominally 12 to 15 MHz
> bandwidth, which is production-line tuned by bending coils or 'goalpost'
> wire loops until a response template is met. Inevitably tracking is
> sub-optimal, and in-channel slope, as well as NF, can be quite high, which
> limits ACI protection as well as sensitivity.
>
> SJB
>
>
>
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