[mythtv-users] Understanding HD Antennas ( was HDHomeRun and jumpy video)
meatwad.get.the.honeys at gmail.com
Sat Sep 15 01:41:47 UTC 2007
Brian Wood wrote:
> Jon Boehm wrote:
>> I'm having HD antenna problems myself right now. My signal strength is
>> fine but I have unstable signal to noise ratio. :-( I have an
>> HDHomerun, which I love, with a Antennas Direct DB4 in the attic.
>> The antenna is directly attached to tuner0 of the hdhomerun with no
>> Antennaweb said that I needed a Small Multi-direction Antenna. Since I
>> was going to be mounting it in an attic I up sized to a Medium
>> Multi-directional antenna. I wonder if my noise problems are due to the
>> Muli-directional antenna? Any idea where I would go looking for the
>> noise problem? I have one of those DC offset amplifiers. I'm going to
>> give it a try this weekend.
> If you have sufficient signal strength but unusable signal the problem
> *might* be reflections, but it could be interfering signal(s), either
> on-frequency or even off-frequency if the signal is of sufficient
> strength to create mixer garbage in the HDHR.
> Sometimes *reducing* the input level to the tuner (with an attenuator)
> will actually make things better. You'd need a signal level meter or the
> like to really know what's going on.
> Does the signal look OK going directly into a TV set? (assuming you have
> one capable of ATSC)? Do you have any neighbors getting good or bad ATSC
That's where digital throws antenna installation a curve. You could
spend the whole day in the attic adjusting the antenna with the ATSC
tuner in the set.
I take a tiny little five-inch TV into the attic or atop the roof (bring
a jacket to shield the sunlight), tune in some known analog stations
with the TV's tuner to get a feel for what problems I might be dealing
with; signal strength (low/high), multipath, noise, etc... An analog
picture gives me a realtime view of these types of problems.
Mostly, you want to see how noise-free you can get the antenna before
you even try an amplifier. If you must, you can try a high-gain
low-noise preamp like Channelmaster's Spartan 3 lineup or Winegard's
excellent preamps. This is important because, unlike cable which
typically delivers a very strong, relatively noise-free signal to a
home, the output of a UHF/VHF antenna is typically very weak and highly
susceptible to noise. Preamps (as opposed to distribution amplifiers)
are designed to address antennas with fringe reception characteristics.
A high rear-rejection helps greatly.
Have some 3, 6 and even a 9dB attenuator on-hand (they screw inline
between an F connector and jack). If your signal is
almost-strong-enough-but-not-quite off the antenna, knock it down before
amplifying (if necessary) and if your amplifier is still too hot for the
number of tuners and wiring configuration, attenuate after the amp.
Use an analog station known to receive well at that location and
experiment until you can pull in as many analog stations up and down the
Old school works wonders some times. And remember to cap off all unused
splitter ports with a 75 ohm terminator.
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