[opendtv] Re: White paper from CEA
- From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 4 Nov 2005 09:07:52 -0500
You shouldn't use a wideband LNA. The preamp should be tuned also, easy to
do with electronic tuning, even at masthead.
Al
----- Original Message -----
From: "Richard Hollandsworth" <holl_ands@xxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Friday, November 04, 2005 2:55 AM
Subject: [opendtv] Re: White paper from CEA
> But an IF derived AGC only responds to on-channel and adjacent channel
signals.
>
> A typical RF Front End might have a 3 dB bandwidth that is not much more
than three channels wide. I've only seen a few claims re RF bandwith,
mostly in the 15-30 MHz range, depending on the operating frequency (Q less
than 40). Very few Tuner manufacturers include this (or overload) in their
posted spec sheets. [Probably because they are just too embarassed...]
>
> With only a single stage of L-C tuning and the relatively low Q of typical
varactors, I wouldn't expect very much suppression several channels away.
> These are the "other" signals that can drive a LNA into non-linearity,
preventing reception of weak signals.
> <holl_ands>
>
> ////////////////////////////////////////
> Allen Le Roy Limberg <allimberg@xxxxxxxxxxxx> wrote:
> An IF derived AGC control voltage is OK if it is a wideband IF amplifier
> driving the AGC detector. One that responds to Adjacent Channel
> Interference (ACI). A narrowband IF amplifier using a SAW filter will
drive
> the demodulator.
>
> Al Limberg
>
>
>
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