[opendtv] Re: opendtv Digest V2 #24
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 28 Jan 2005 17:04:37 -0500
S J Birkill wrote:
> 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.
> ...
> 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,
Ah well, at least it's common practice. Still no excuse
if you're trying to establish a name for yourself as a
premier DTT tuner company, though.
If Mark Schubin had better luck with the LG 5th gen
than with the Linx, assuming the Linx was tested there
as was hinted, then I wonder if this single vs dual
conversion wasn't the main difference.
In the Linx tests conducted in Chicago by Linx
themselves, as I recall, every single failure was in
sites and frequency bands where there was a strong
adjacent NTSC channel. Analog adjacent channels would
be particularly problematic, because of their stronger
carrier and stronger peak signal power. This implies
less than ideal IM distortion specs could be an issue.
I would think that in NYC, strong adjacent NTSC would
be the a common occurrence. Otherwise, the obvious
difference between the Linx and LG specs would be a
slightly lower echo tolerance for Linx (+/- 38 usec
for Linx, +/- 50 usec for LG 5th gen).
Bert
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