[opendtv] Re: 5th generation Test
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Wed, 16 Mar 2005 20:20:17 -0500
Manfredi, Albert E wrote:
>>How much extra are we talking about here?
>
>
> Well, since everyone was marveling at the low cost of
> the first gen Freeview boxes, and they were dual
> conversion designs, the cost cannot be prohibitive.
> However, it won't follow Moore's law, so the cost
> will not erode over time quite so fast.
Is this RF front end something that could be sold separately and stuck
on the antenna input of existing receivers?
- Tom
> Tom Barry wrote:
>
>
>>It sounds like "IM3 products" (whatever they are) and
>>good RF frontends are supposed to be known technology.
>
>
> IM3 is third order intermodulation distortion products.
> Created in receivers when multiple incoming carriers
> and the local oscillator beat together. Ideally, any
> such IM products would fall way outside the IF passband
> and be attenuated nicely. But with single conversion
> tuners, they are not all outside the passband.
>
> It appears that the low cost of single conversion
> tuners is enough of an incentive that manufacturers
> seem to jump at the chance of going that route. As we
> were informed a couple of weeks ago, even COFDM did
> this. As Al Limbert and others explained, if your
> RF amp up front is tuned to the channel you want and
> can reduce its gain in the presence of strong signals,
> the IM distortion can be greatly reduced, so single
> conversion tuners can work okay.
>
> With co-located transmitters, the problem might not be
> so acute. Because you will never see unwanted signals
> that are louder than the desired signal. But if the
> unwanted signal is louder than the wanted signal, then
> this can be a problem. The numbers we saw showed that
> a 3 dB increased level to the receiver, from unwanted
> signals, can cause up to 9 dB increase in this in-band
> IM3 distortion (IIRC). So, big deal. And a 3 dB
> increase into a receiver is not so hard to imagine if
> there are loud transmitters close by, even if your RF
> amp is tuned. The shoulders of the RF amp's passband
> won't be vertical. Dual conversion, i.e. where the
> receiver goes through two IF conversions, takes care
> of this nicely.
>
>
>>But if that's the case then maybe we (collectively,
>>not me) also know what it would cost to add them to a
>>box with an LG5 chip in it.
>>
>>How much extra are we talking about here?
>
>
> Well, since everyone was marveling at the low cost of
> the first gen Freeview boxes, and they were dual
> conversion designs, the cost cannot be prohibitive.
> However, it won't follow Moore's law, so the cost
> will not erode over time quite so fast.
>
> Bert
>
>
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