Incoming President Requests DTV Cutover Delay

[WB4JFI]

A straight sensitivity test will not tell you much.  You really need to test
the boxes with a varying amount of multipath injected as well.  I saw many
times where there was PLENTY of signal, including at my old house in Falls
Church where I could SEE the towers, but the boxes would not decode.  A
spectrum analyzer showed serious peaks and dips across the 6MHz signal,
which was preventing the box from decoding.  Thanks 8VSB.

The newer boxes are a LOT better with multipath (especially post-main
signal), but this is still a major cause for failing to decode DTV.  Most
boxes are still not great with a pre-main-bang multipath, which is where you
are picking up mostly a reflection.

I'm sure there is a thorough study comparing the boxes, within the last
year.  I remember seeing a reference to it in my consulting.  Not sure where
it is anymore, but I will try to find it.

Also, remember that each site is different.  The DC stations are mostly in a
cluster in upper-NW, but if you want some of the outlying stations, that
could affect the type of antenna, etc.  Also, if you want to pick up
Baltimore, Salisbury, or MPT, that brings in the directionality as well.
And, if you have a large building (or more) nearby, that causes more
problems.

When Gannett was in Rosslyn, we used to pick up the DTV signals the best (at
least 4, 7, 9), by pointing the antenna at another Rosslyn building.  At
that time, 5 was very low-power, 20 was not on the air, and 26 was on a
small tower in Arlington.  Our offices were mostly on the wrong side of the
building, facing Arlington Cemetary and the Pentagon.

Terry


> -----Original Message-----
> From: tacos-bounces+wb4jfi=amrad.org at amrad.org
> [mailto:tacos-bounces+wb4jfi=amrad.org at amrad.org]On Behalf Of Frank
> Gentges
> Sent: Saturday, January 24, 2009 10:08 AM
> To: km4vj at amrad.org
> Cc: Tacos
> Subject: Re: Incoming President Requests DTV Cutover Delay
>
>
> Will,
>
> I did some of that testing.  We got several units from others and tested
> them with the same antenna and attenuator.  I then noted the attenuator
> setting for each unit.
>
> In the end, all units were very similar in sensitivity.  I did not find
> that one model that would be significantly better than the others.  With
> similar components available to all makers and the lack of a design
> flaw, this is pretty much what you would expect.
>
> I did notice some real differences in features related to decoding and
> displaying station menus.  All the units get the data but some choose to
> show a lot and some very little.
>
> Frank K0BRA
>
>
> Will Russell wrote:
> > Also, there is a question of the sensitivity of the converters (and the
> > receivers in the DTV receivers).  Assuming  there are standards
> it would
> > seem that the various designs would perform differently.
> > My recollection is that a member talked about testing these
> devices last
> > summer.  If that person reads this could he or she respond with whether
> > the tests covered the performance of the units and if so what data was
> > obtained?  Another possibility is that performance data is available on
> > line.  Any links?
> > Thanks.
> > Will Russell
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