[opendtv] Re: Tired of the Silver Sensor?
- From: S J Birkill <sjb@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sat, 20 May 2006 12:26:06 +0100
The Spectrum antenna is still (broadband PIFA and all) just a quarter-wave
monopole, so it can only obtain a one-dimensional view of the 3D EM
standing-wave field in the vicinity of an indoor TV set. I'd guess its
fundamental horizontal radiation pattern would be an asymmetrical figure-8
rather than the approximate cardioid of the SS, so its ability to reject a
troublesome reflection would be restricted to manual rotation by the user,
pointing one of two sharp and frequency-dependent nulls toward the offender.
The advantage of an active antenna (which I assume this is, though I can't
see where it says so) is in optimized broadband matching between antenna
element and LNA, and in achieving a lower noise figure than the TV tuner's
own input. The former can be disadvantageous where strong out-of-band
transmissions cause blocking -- the ideal active antenna would be
channel-tuned automatically from the TV, providing some rejection. The
latter is worthwhile only because TV tuners in general have very poor noise
performance (7dB NF is still classed as good!)
Even if future DTT were UHF only, this type of thing, neat though it is,
wouldn't be the answer to the indoor-antenna woes of DTT. What's needed is
a set of n dynamically-tuned PIFA active antenna elements built into the
screen surround, working into an n-channel diversity tuner/demod. Now I
wonder who's developing that, and for whom... :)
SJB
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