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Problem with OTA broadcasts

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Anonymous
May 10, 2005 5:59:29 PM

Archived from groups: alt.video.ptv.tivo (More info?)

I live in the Pittsburgh, PA area. Channel 2.1 is at 22 deg. from my house.
Channel 4.1 is at 104 deg. If I point my antenna to about 52 deg, I get
good signals on both and everything in between except for two channels. One
I know is down on power but the other, channel 11.1, is at 28 deg and claims
to have the same power output as 2.1. I called their egineering department
and they are at a loss as to why this might be happening. The engineer
lives in Washington, PA (I am almost exactly in the middle) and he says he
has to point his antenna exactly at the tower to receive it, as I do.

I am trying to get a compromise position so I can Tivo any HD channel
without having to worry about moving the antenna. Furthermore, since I have
a DirecTV Tivo, I can record two channels at once, but not if one is 11.1
and the other is 4.1. I have no idea what the problem might be. As far as
I know there are no obstructions that would affect 11.1 without affecting
2.1. Signal strength on 2.1 and 4.1 are both around 70-72 on my Tivo when
the antenna is pointed to 52 deg., but 11.1 drops down to about 20-30!

Does anybody have any idea what is going on or what I might be able to do
about it?

More about : problem ota broadcasts

Anonymous
May 10, 2005 11:14:39 PM

Archived from groups: alt.video.ptv.tivo (More info?)

In article <4280f682$1_2@news.nauticom.net>,
Robert B. Peirce <rbp@cooksonpeirce.com> wrote:

>I live in the Pittsburgh, PA area. Channel 2.1 is at 22 deg. from my house.
>Channel 4.1 is at 104 deg. If I point my antenna to about 52 deg, I get
>good signals on both and everything in between except for two channels. One
>I know is down on power but the other, channel 11.1, is at 28 deg and claims
>to have the same power output as 2.1. I called their egineering department
>and they are at a loss as to why this might be happening. The engineer
>lives in Washington, PA (I am almost exactly in the middle) and he says he
>has to point his antenna exactly at the tower to receive it, as I do.
>
>I am trying to get a compromise position so I can Tivo any HD channel
>without having to worry about moving the antenna. Furthermore, since I have
>a DirecTV Tivo, I can record two channels at once, but not if one is 11.1
>and the other is 4.1. I have no idea what the problem might be. As far as
>I know there are no obstructions that would affect 11.1 without affecting
>2.1. Signal strength on 2.1 and 4.1 are both around 70-72 on my Tivo when
>the antenna is pointed to 52 deg., but 11.1 drops down to about 20-30!
>
>Does anybody have any idea what is going on or what I might be able to do
>about it?

It could be one or more factors.

One factor is your antenna's actual gain pattern. If it's a high-gain
antenna (highly directional) it may very well have a steep "null" in
its sensitivity pattern, located some distance on either side of the
main lobe (i.e. the "forward" direction). It's possible that when
you're pointing at 52 degrees, the antenna has a null at 28 degrees,
and that this is dropping the signal power too much. You're trying to
pick up signals from transmitters scattered over an arc of almost 90
degrees... a pretty wide span.

It's also possible that you have multipath problems. If the signal
from 11.1 is arriving at your antenna via two different paths (e.g.
direct line-of-sight, and also via a reflection from a nearby hill or
tall building), the signals from the two paths will probably be out of
phase to some extent. The worst case is if the two paths result in
signals of near-equal strength, and a close-to-180-degree phase
difference. When this happens, the two signals tend to cancel each
other out, and the signal quality falls through the floor. You can
sometimes hear this effect when listening to a distant FM radio
station, if you're driving or if a plane flies overhead - there's a
characteristic comes-and-goes sound effect called "picket fencing"
caused by multipath reinforcement and cancellation.

So, what can you do about it?

If the problem is due to a null in your antenna pattern, one possible
cure is to use an antenna which is *less* directional. You'd want an
antenna whose primary "lobe" is broad enough to take in the signals
from all of the stations you're interested in. One measure of this is
the antenna's "half-power beam width"... if the antenna's HPBW is
fairly small there's a real risk that some of the stations will be
outside the main lobe. They may be picked up OK if they're in one of
the secondary lobes, but will not be picked up well if they happen to
fall inside a null.

The first thing I'd suggest doing, is some measurement. Set your
system to 11.1, then gradually rotate the antenna from 0 degrees to
110 degrees in 10-degree increments, and write down the signal
strength. Plot it on a chart.

If the signal strength on 11.1 falls gradually and smoothly whenever
you point the antenna away from the transmitter, then the antenna's
gain pattern is probably OK.

On the other hand, if you the signal strength drop off very sharply as
you begin to rotate away from the 28-degree heading, and then "bounce
back up", it indicates that the gain pattern is fairly sharp and has
one or more "nulls" in the forward quadrant. In this case, you may
need to buy an antenna having a somewhat lower forward gain, and a
broader main lobe.

Now, if the problem is multipath, you may need a different solution.
Multipath cancellations are very sensitive to the antenna location -
moving the antenna a few feet will change the signal-path lengths and
can turn a cancellation into a reinforcement, or vice versa. If
you're losing signal due to multipath cancellation, you may be able to
fix it by simply relocating the antenna mount by a few feet. This is
difficult to predict, and some amount of experimentation may be
required.

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Anonymous
May 11, 2005 3:30:42 AM

Archived from groups: alt.video.ptv.tivo (More info?)

In article <118220vsbijcicf@corp.supernews.com>,
dplatt@radagast.org (Dave Platt) wrote:

Wow! Thanks for all the info. I'll giv e it a try to see what I can
find.

--
Robert B. Peirce, Venetia, PA 724-941-6883
bob AT peirce-family.com [Mac]
rbp AT cooksonpeirce.com [Office]
Related resources
Anonymous
May 11, 2005 3:57:22 AM

Archived from groups: alt.video.ptv.tivo (More info?)

> In article <118220vsbijcicf@corp.supernews.com>,
> dplatt@radagast.org (Dave Platt) wrote:
>
> Wow! Thanks for all the info. I'll give it a try to see what I can
> find.

Okay. I tested 11.1, First the good news. It is working tonight. It
is possible there was a transmitter problem yesterday. At any rate,
here are my readings:

Degrees Signal [0-100]
0 82
7.5 87
15 89
22.5 90 The tower is supposed to be at 28. My rotor may be off.
30 88
37.5 81
45 71
52.5 68
60 & + Fluctuating from 40 down to 4 at 75 degrees

This looks pretty good. Last night 2.1 and 4.1 were reading around 71
at 52 degrees. 68 is almost as good, but it falls off real quick beyond
that point.

Now the next problem is how can you count on these readings being there
when you are trying to record?? In other words, if I set my antenna at
52, which seems pretty good, but the power is down at the point when I
am trying to record, I am not going to get the signal!

The safe thing is to record the SD signal off the dish, but that kind of
defeats the purpose of having HD.

--
Robert B. Peirce, Venetia, PA 724-941-6883
bob AT peirce-family.com [Mac]
rbp AT cooksonpeirce.com [Office]
Anonymous
May 11, 2005 4:35:51 AM

Archived from groups: alt.video.ptv.tivo (More info?)

In article <bob-92D13F.19572810052005@news.verizon.net>,
Robert Peirce <bob@peirce-family.com.invalid> wrote:

>Okay. I tested 11.1, First the good news. It is working tonight. It
>is possible there was a transmitter problem yesterday. At any rate,
>here are my readings:
>
>Degrees Signal [0-100]
>0 82
>7.5 87
>15 89
>22.5 90 The tower is supposed to be at 28. My rotor may be off.
>30 88
>37.5 81

That looks like a fairly symmetrical pattern, centered somewhere
around 18. Wouldn't surprise me if your rotor/aim is off by about ten
degrees.

Hmmm... a thought... when you're figuring directions, are you
remembering to compensate for the difference between true north and
magnetic (or compass) north? Here on the left coast, a compass needle
points around 15 degrees east of true north. The correction is
certainly different where you live. If you're figuring directions to
the transmitter on the basis of true bearings (from a map) but are
setting your rotor position based on a compass bearing, and you aren't
correcting for the difference between magnetic and true north, then
that's the likeliest cause of an error!

>45 71
>52.5 68
>60 & + Fluctuating from 40 down to 4 at 75 degrees

The falloff once you get past 37.5, and the sharp degradation beyond
60, suggests to me that you've got a pretty deep null at an angle of
about 50 degrees either side of your center.

Without knowing what the calibration numbers mean in decibels, it's
impossible to figure out the formal "half-power beam width", but it
looks to me as if you start losing signal pretty badly once you've
turned more than 30 degrees away from the transmitter.

That's not terribly good news, in your situation. If you've got a
good-signal lobe that's about 60 degrees wide, and you're trying to
capture signals from transmitters spread over a 90-degree arc, you're
going to end up with some stations which aren't in the effective part
of the main lobe.

If channel 11.1 is giving you the best signal when the antenna's
pointed at around 20, and if you're trying to receive it properly with
the antenna pointed at 52, then it's probably just about to fall off
of the side of the lobe, and is probably well below its optimal
strength.

>This looks pretty good. Last night 2.1 and 4.1 were reading around 71
>at 52 degrees. 68 is almost as good, but it falls off real quick beyond
>that point.
>
>Now the next problem is how can you count on these readings being there
>when you are trying to record?? In other words, if I set my antenna at
>52, which seems pretty good, but the power is down at the point when I
>am trying to record, I am not going to get the signal!

Yup. That does seem to have been a problem here in the SF Bay area.
The local stations' ATSC signals are coming out of different
transmitters and different antennas, much of the time, and are often
not operating at ideal power levels. There have also been some
reliability problems. I've heard people report days when most of the
digital locals were unavailable, when (e.g.) there was work going on
at the Sutro Towers site in San Francisco.

Not much one can do about transmitter-side problems, I'm afraid. One
hopes that things will get better as time progresses.

Now, as to your reception problems. I suspect that at least part of
it is that your antenna does seem to have a narrower horizontal
pattern (main lobe / beam) than is ideal for your situation, since you
need to receive signals from a fairly wide horizontal arc. The
solution is to have less horizontal directivity. This will cost you
some amount of signal strength in the forward direction (i.e. stations
at which you point the antenna directly will seem to have weaker
signals) but will increase the effective strength of the stations
which are off to the side.

You may be able to compensate for this by having more *vertical*
directivity. This would be done by using an antenna which has more
elements stacked one above another.

UHF-band SD/HD antennas are often of the "bow-tie and reflector"
design... one, two, or four bow-tie-shaped wire dipoles, mounted a few
inches in front of a wire-grid reflector screen.

Placing the elements side by side, horizontally, increases the
horizontal gain and narrows the beam in the horizontal direction.

Placing them above one another has no effect on the horizontal
pattern, but compresses the pattern vertically.

So, if you're interested in picking up the UHF-band channels, a good
antenna for you to use would probably be one which has several bow-tie
elements mounted one above another, in a single vertical line. This
antenna would have a broad, but shallow main lobe (i.e. not very
directional in the horizontal direction, but quite directional towards
the horizon).

For VHF-band, you'll probably just need a standard log-periodic
antenna, as these don't have a lot of gain on either axis.

Another, more expensive option would be to have two separate antennas,
covering two different portions of the horizon, and then combine their
signals somehow. Tricky and not all that easy to design and engineer,
except for some special cases such as "one channel on antenna A, all
others on antenna B."

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Anonymous
May 11, 2005 4:35:52 AM

Archived from groups: alt.video.ptv.tivo (More info?)

Dave Platt (dplatt@radagast.org) wrote in alt.video.ptv.tivo:
> In article <bob-92D13F.19572810052005@news.verizon.net>,
> Robert Peirce <bob@peirce-family.com.invalid> wrote:
>
> >Okay. I tested 11.1, First the good news. It is working tonight. It
> >is possible there was a transmitter problem yesterday. At any rate,
> >here are my readings:
> >
> >Degrees Signal [0-100]
> >0 82
> >7.5 87
> >15 89
> >22.5 90 The tower is supposed to be at 28. My rotor may be off..
> >30 88
> >37.5 81
>
> That looks like a fairly symmetrical pattern, centered somewhere
> around 18. Wouldn't surprise me if your rotor/aim is off by about ten
> degrees.

That would make sense. The magnetic deviation in the Pittsburgh area is
about 9°. I would guess he is pointing his antenna using true north, and
the "supposed to be" number comes from a website that uses magnetic north.

--
Jeff Rife | "I'm reading a great John Grisham novel...it's
| about a young Southern lawyer who fights an
| evil corporate giant."
| -- Dick Solomon, "3rd Rock from the Sun"
Anonymous
May 11, 2005 2:23:21 PM

Archived from groups: alt.video.ptv.tivo (More info?)

"Robert Peirce" <bob@peirce-family.com.invalid> wrote in message
news:bob-92D13F.19572810052005@news.verizon.net...
> > In article <118220vsbijcicf@corp.supernews.com>,
> > dplatt@radagast.org (Dave Platt) wrote:
> >
> > Wow! Thanks for all the info. I'll give it a try to see what I can
> > find.
>
> Okay. I tested 11.1, First the good news. It is working tonight. It
> is possible there was a transmitter problem yesterday. At any rate,
> here are my readings:
>
> Degrees Signal [0-100]
> 0 82
> 7.5 87
> 15 89
> 22.5 90 The tower is supposed to be at 28. My rotor may be off.
> 30 88
> 37.5 81
> 45 71
> 52.5 68
> 60 & + Fluctuating from 40 down to 4 at 75 degrees
>
> This looks pretty good. Last night 2.1 and 4.1 were reading around 71
> at 52 degrees. 68 is almost as good, but it falls off real quick beyond
> that point.
>
> Now the next problem is how can you count on these readings being there
> when you are trying to record?? In other words, if I set my antenna at
> 52, which seems pretty good, but the power is down at the point when I
> am trying to record, I am not going to get the signal!
>
> The safe thing is to record the SD signal off the dish, but that kind of
> defeats the purpose of having HD.

I think 11.1 has a problem with its transmitter. I have a call in to them
to find out.

Last night I was getting good signal strength, comparable to 2.1 and 4.1.
This morning it was in single digits at 52 degrees. It should have been
close to 70. This basically means I can't count on them for a good HD
signal. I will have to check the current state before doing a recording
which eliminates using Season Pass unless I set it up for channel 11.

They told me they are doubling their power on 5/25, which probably means a
new transmitter, or at least some kind of work on the present one. It may
become more reliable after that.
Anonymous
May 12, 2005 11:52:25 PM

Archived from groups: alt.video.ptv.tivo (More info?)

In article <MPG.1ceb3cbede61afa4989d2e@news.nabs.net>,
Jeff Rife <wevsr@nabs.net> wrote:

> Dave Platt (dplatt@radagast.org) wrote in alt.video.ptv.tivo:
> > In article <bob-92D13F.19572810052005@news.verizon.net>,
> > Robert Peirce <bob@peirce-family.com.invalid> wrote:
> >
> > >Okay. I tested 11.1, First the good news. It is working tonight. It
> > >is possible there was a transmitter problem yesterday. At any rate,
> > >here are my readings:
> > >
> > >Degrees Signal [0-100]
> > >0 82
> > >7.5 87
> > >15 89
> > >22.5 90 The tower is supposed to be at 28. My rotor may be off.
> > >30 88
> > >37.5 81
> >
> > That looks like a fairly symmetrical pattern, centered somewhere
> > around 18. Wouldn't surprise me if your rotor/aim is off by about ten
> > degrees.
>
> That would make sense. The magnetic deviation in the Pittsburgh area is
> about 9°. I would guess he is pointing his antenna using true north, and
> the "supposed to be" number comes from a website that uses magnetic north.

Actually, probably the other way around. I am pointing with a compass
to magnetic north. I am getting my directions and distances from
AntennaWeb and they may be true directions. However, I guessed I would
want to be about mid-way between 22 and 104, which would be about 63,
and 63-9=52. Very interesting.

The transmitters at 22 and 104 come in great, and 28 comes in great
sometimes, so I think the problem is with the station rather than my
antenna. My antenna may not be ideal, but it is okay.

--
Robert B. Peirce, Venetia, PA 724-941-6883
bob AT peirce-family.com [Mac]
rbp AT cooksonpeirce.com [Office]
Anonymous
May 12, 2005 11:52:26 PM

Archived from groups: alt.video.ptv.tivo (More info?)

Robert Peirce (bob@peirce-family.com.invalid) wrote in alt.video.ptv.tivo:
> > That would make sense. The magnetic deviation in the Pittsburgh area is
> > about 9°. I would guess he is pointing his antenna using true north, and
> > the "supposed to be" number comes from a website that uses magnetic north.
>
> Actually, probably the other way around. I am pointing with a compass
> to magnetic north.

If so, then that's not the issue.

Pointing at 22.5 magnetic is the same as 13.6 true, in the Pittsburgh area.

> I am getting my directions and distances from
> AntennaWeb and they may be true directions. However, I guessed I would
> want to be about mid-way between 22 and 104, which would be about 63,
> and 63-9=52.

First, 63 - 9 = 54. :) 

Second, 52 magnetic is 43 true.

A quick check shows that the bearing from your house (BTW, you live in
Canonsburg according to the USPS) to the KDKA (channel 25, virtual 2)
digital tower is 22.0° magnetic, or 13.1° true.

The WTAE (channel 51, virtual 4) digital tower is 103.2° magnetic, or 94.4°
true.

WPXI (channel 48, virtual 11) is at 27.9 magnetic, 19.0 true.

My advice would be to use two very directional antennas and combine them
With one pointing at 25°M and one pointing at 105°M, you shouldn't have any
problems with multipath.

|> I have no idea what the problem might be. As far as
|> I know there are no obstructions that would affect 11.1 without affecting
|> 2.1. Signal strength on 2.1 and 4.1 are both around 70-72 on my Tivo when
|> the antenna is pointed to 52 deg., but 11.1 drops down to about 20-30!

With KDKA on physical channel 25 (which reminds me, never use virtual
channel numbers when trying to diagnose these problems) at 1000kW and
WPXI on channel 48 at 501kW, that might be all the difference needed to
expose this problem. WTAE is also at 1000kW.

The only other thing I can think of is the low power channel 47 that is
in the same direction as WPXI. It shouldn't affect it, but it might.

--
Jeff Rife | "Damn it, I miss the sound of her voice. I tried
| putting silverware down the disposal, but it
| wasn't the same."
|
| -- Ned Dorsey, "Ned and Stacey"
Anonymous
May 13, 2005 5:53:28 PM

Archived from groups: alt.video.ptv.tivo (More info?)

In article <MPG.1ced948a5865b4d989d34@news.nabs.net>,
Jeff Rife <wevsr@nabs.net> wrote:
> WPXI (channel 48, virtual 11) is at 27.9 magnetic, 19.0 true.
>

I was investigating this further last night and found I could get good
signal strength over more than 90 degrees from 25/2-1 (22), 38/13-2
(40), 43/53-1 (25), 50/40-1 (28) and 51/4-1 (104), but 48/11-1 (28) only
comes in over a 45 degree range. 42/22-1 is also limited but it is low
on power.

It would appear that WPXI (48/11-1) is beaming their signal much more
than other channels, or at least that is the way it is seen by my
antenna and receiver. If WPXI had a little more spread, I could point
my antenna to about 45 degrees and get everything. As it is, there is
no overlap for 48/11-1 and 51/4-1 most of the time.

BTW, I actually live in Peters Township, just over the border from
Allegheny County. The chief engineer at WPXI lives in Washington, PA
and told me he has to point his antenna directly at the tower but gets a
good signal when he does so. On my HR10-250, all the major channels
peak at around 90% on my signal strength meter when the antenna is
pointed at the tower, and I can get excellent results at 70 or higher.

--
Robert B. Peirce, Venetia, PA 724-941-6883
bob AT peirce-family.com [Mac]
rbp AT cooksonpeirce.com [Office]
!