[opendtv] Re: Transition report

I should have been more specific; the required isolation is from objects
that can impact RF energy transmission.
Antenna test ranges are often located on terrain such as wide river bluffs
where the antenna is on one bluff and an RF source on the other bluff, with
free space in between. Both supporting structures are generally constructed
completely of wood. The supporting structure for the antenna under test can
both rotate and tilt the antenna. There are also near field ranges but I'm
unfamiliar with their operation.

My concern is that testing the pattern and frequency characteristics of an
operational tower mounted antenna could be difficult.



-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx
[mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Dale Kelly
Sent: Wednesday, June 17, 2009 4:47 PM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: Transition report


Often called a "free space: measurement IIRC. As you say, it's the only way
to do such a measurement and is difficult to do. The receiver system must be
isolated from any other structures.

-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx
[mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Doug McDonald
Sent: Wednesday, June 17, 2009 12:38 PM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: Transition report


John Shutt wrote:
> Indeed, the ATSC exciter does have an adaptive equalization routine, but
> the sample point is taken at the output of the mask filter, not from a
> probe at the top of the tower sampling the output of the antenna.
>


Thus at low VHF, that could be a big big problem if the antenna were
not certified by the manufacturer for DTV.  If I were a low DTV
station, I would test the signal with a non-resonant receive
antenna high in the air well away from the antenna (i.e. in the main lobe)
on a spectrum analyzer.

Doug


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