> 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 ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.