OTA reception questions

Mark Atanovich

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Nov 24, 2003, 10:07:44 PM11/24/03

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Howdy,
I've just upgraded to a HD set top box and have installed an OTA antenna to
pull in local HD broadcasts and improve FM reception (roof mounted Channel
master 3016 connected via diplexer on satellite dish cable...total run from
OTA antenna to stb is something just short of 100') . Things work fairly
well, but I'm having difficulty bringing in the "blue" stations, as defined
by the info supplied at antennaweb.org. One blue station only registers 15
on the stb meter and the other two don't register at all. Questions:

1. How much stock should I put in the antennaweb recommendations? They
claim to take local terrain into account, but I'm somewhat skeptical (I'm in
the Scottsdale, Az area with Mummy Mt. between me and the broadcast towers).

2. Antennaweb recommends a preamp in addition to the medium directional
antenna; I have not yet installed the preamp. Will the preamp make a large
enough differerence that the stations that don't currently register at all
to give a stable, high quality picture?

3. I'm not interested in VHF signals and FM reception is just fine. Do UHF
preamps provide unity gain for non-UHF frequencies or filter them out? What
out UHF/VHF preamps with FM traps?

5. Should I ditch the 3016 and FM reception and go straight to something
hardcore like a Channel Master 4248? Any other "cult" favorites for those
in my situation?

Thanks in advance

Pamela

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Nov 25, 2003, 7:57:22 AM11/25/03

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Always get a better antenna before investing in a preamp

An10uh

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Nov 25, 2003, 1:09:32 PM11/25/03

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I have found that a diplexer significantly cuts UHF signals,
especially in the higher frequencies. My first experiment would be to
run a separate cable for the antenna if at all possible.

Jeff Rife

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Nov 25, 2003, 2:28:21 PM11/25/03

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An10uh (An1...@aol.com) wrote in alt.tv.tech.hdtv:

> I have found that a diplexer significantly cuts UHF signals,
> especially in the higher frequencies. My first experiment would be to
> run a separate cable for the antenna if at all possible.

Having tested the same cable with diplexers and without, I find that the
4dB or so loss isn't significant, even to channel 59 (which is higher
than OTA digital TV will be after the analog cutoff).

Web Williams

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Nov 25, 2003, 7:04:44 PM11/25/03

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I guess that depends on how much signal you have to begin with.
3dB loss is -HALF- your signal strength. So 4dB of loss is
greater than half... that's a lot to give up when you're doing
weak-signal work to start with.

-Web Williams in Myrtle Beach, SC

kay are four double-ewe emm at earth link dot net

In article <MPG.1a2d7764f...@news.nabs.net>, we...@nabs.net
says...

Jeff Rife

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Nov 25, 2003, 8:33:46 PM11/25/03

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Web Williams (so...@notgiven.net) wrote in alt.tv.tech.hdtv:

> I guess that depends on how much signal you have to begin with.
> 3dB loss is -HALF- your signal strength. So 4dB of loss is
> greater than half... that's a lot to give up when you're doing
> weak-signal work to start with.

Not really. Do you have two TVs? Do you want them both to display from
the same antenna? That's 3.5dB for the splitter.

Likewise, do you have a TV and a recording device, or maybe a 2-input
recording device/STB like the coming HD TiVo? You also take a 3.5dB loss
from that split.

From experience, if 3dB really make the difference between "watchable"
and "unwatchable", the picture will degenerate into "messed-up" far too
often for comfort.

I have a digital station that is "on the bubble" for being able to receive
it, yet even a 10dB reduction (through a variable attenuator) doesn't
change the signal. My good stations have nearly 30dB of spare signal
before they become a problem.

So, 4dB isn't really that much.

Mark Atanovich

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Nov 25, 2003, 11:14:38 PM11/25/03

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While were on the subject of signal strength, anybody know what the scale is
for the stb "meters"? Is is linear, log, or something in between? I've
purchased a preamp (Winegard 8275) and will report my results in a couple
days. Chances are that should solve my problems as I'm pretty sure the root
cause is attenuation over the long cable run and through the diplexers.

Mark

"Jeff Rife" <we...@nabs.net> wrote in message
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Jeff Rife

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Nov 26, 2003, 1:31:37 AM11/26/03

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Mark Atanovich (m.ata...@cox.net) wrote in alt.tv.tech.hdtv:

> While were on the subject of signal strength, anybody know what the scale is
> for the stb "meters"? Is is linear, log, or something in between?

I can't say whether it is linear or logarithmic, but basically, they just
measure the number of times the FEC (forward error correction) needs to be
used. "Never" == 100% and "all of it" == 0%.

Mark Atanovich

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Nov 26, 2003, 8:06:57 AM11/26/03

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Interesting, so there's no real correlation to signal strength. You could
have an extremely strong signal, but if the signal to noise ratio is to
high, it would register nothing, right?

"Jeff Rife" <we...@nabs.net> wrote in message

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bearman

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Nov 26, 2003, 10:42:48 AM11/26/03

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I think that when you're dealing with voltages (as in received signal
strength), 6dB is half. So 4dB is less than half.
When you're dealing with power ratios, 3dB is half (or twice, depending).

Bearman

"Web Williams" <so...@notgiven.net> wrote in message
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Jeff Rife

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Nov 26, 2003, 12:46:45 PM11/26/03

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Mark Atanovich (m.ata...@cox.net) wrote in alt.tv.tech.hdtv:

> Interesting, so there's no real correlation to signal strength. You could
> have an extremely strong signal, but if the signal to noise ratio is to
> high, it would register nothing, right?

I think you meant "signal to noise ratio is too low". If so, then you are
correct.

There is a very professional installer of antenna systems around here,
and he has measured actual levels of one channel with a dB-based meter and
found it to be *much* higher than another channel, yet it registers lower
on everybody's STB signal strength meter. We suspect it might be that
there is less FEC in the stream, or else some error in the stream that causes
FEC to be used a lot.

Web Williams

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Nov 26, 2003, 1:08:38 PM11/26/03

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Another problem I have seen is antennas that are mounted
near large bodies of metal. To see an example, look at an
analog signal on a TV with an outdoor antenna near a water
tower. You get severe ghosting unless the antenna is
adjusted "just so". This is caused by the reflected signal
arriving at the receiver at a slightly different time than
the desired signal. Sometimes it manifests as "ghosting".
Digital signals can suffer from signal degradation in a
similar manner- but the picture doesn't "ghost". What happens
is the secondary arriving signal cancels out part of the
desired signal, creating a poor S/N ratio and causing
reception difficulties. We found this problem at an installation
where the antenna was attic mounted near metal ductwork. Moving
the antenna outdoors and mounting it on a mast solved the
problem. Just consider that any large piece of metal near the
antenna (even a water tower within a block or so) could cause
reception problems due to the reflected signal cancelling out
the desired one. (You also may have noticed on an analog signal
what happened when an airplane flew over....same principle.)

-Web

w

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Nov 27, 2003, 1:20:58 AM11/27/03

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One important thing that I found was to get information about the DTV
broadcast Stations. I've discovered that some are at full power, some at
half and some are at the FCC minimum.
I found that I could pull in a station that was 90 miles away, but had a
slight problem pulling one in that was only 30 miles away due to it
broadcasting a low power signal.
r/ ww

L Alpert

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Nov 27, 2003, 1:15:32 PM11/27/03

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w wrote:
> One important thing that I found was to get information about the DTV
> broadcast Stations. I've discovered that some are at full power, some
> at half and some are at the FCC minimum.
> I found that I could pull in a station that was 90 miles away, but
> had a slight problem pulling one in that was only 30 miles away due
> to it broadcasting a low power signal.
> r/ ww
>

It can also be your type of antenna and it's orientation.

Sal M. Onella

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Nov 29, 2003, 1:02:06 AM11/29/03

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"bearman" <no...@home.com> wrote in message
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>
> I think that when you're dealing with voltages (as in received signal
> strength), 6dB is half. So 4dB is less than half.
> When you're dealing with power ratios, 3dB is half (or twice, depending).
>
> Bearman

Yes

Jeff Rife

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Dec 2, 2003, 12:36:22 PM12/2/03

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kryppy (kryppy@.) wrote in alt.tv.tech.hdtv:
> Get rid of the diplexor and make a home run from the antenna to the
> tuner. The difference will amaze you.

Not likely.

A correctly installed diplexer pair will cost you about the same amount of
signal as a single splitter. If you can't afford to split your antenna feed,
then your signals are already so dicey that some other solution will be
needed anyway.

Mark Atanovich

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Dec 5, 2003, 6:51:47 PM12/5/03

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I verified this myself. Running a direct feed to the STB did nothing to
improve things....

"Jeff Rife" <we...@nabs.net> wrote in message

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