What Causes Wildly Fluctuating Reception of DTV Broadcasts of Certain UHF Channels?
aruzinsky
broadcasts originate. I have big UHF and VHF antennas (designed for
roof installation) inside my attic, pointed toward the Loop. These
are combined in a device (I forget the name) connected to a coaxial
cable which runs to a Radio Shack UHF amplifier (for mast mounting)
that is about 10 ft. from a splitter to 3 digital tuners connected to
one analog TV. I receive channels
2 (CBS) (12 (RF Channel))
5 (NBC) (29)
7 (ABC) (7)
9 (WGN) (19)
11 (WTTW) (47)
13 (WOCK) (4)
20 (WYCC) (21)
23 (MeTV) (27)
26 (WCIU) (?)
32 (FOX) (31)
38 (ION) (43)
44 (WSNS) (45)
48 (MeToo) (?)
50 (WPWR) (51)
60 (WXFTDT) (50)
62 (WJYS) (36)
66 (WGBO) (38)
Channel 5 (NBC, RF Channel 29) gives me, by far, the worst reception
and it fluctuates like a random walk. Some weeks are fine but, at
other weeks, I mostly get "no signal," in which case, the signal
strength meter jumps erratically back and forth. This is on all three
of my tuners, although one tune is substantially better than the other
two. How I do I determine whether it is NBC's fault or mine?
Also, 13 (WOCK) (4), has perfect video but no sound. What's the deal
with that?
Albert Manfredi
Would be nice to know what device is "combining" the signal from each
antenna, however my immediate reaction from your description is that
maybe you're overloading the tuners in your three converter boxes
(receivers). I say this because if all the broadcasts do originate
from 9 miles away (is it line of sight?), are all in that one
location, and you have large antennas + the antenna amp, it sounds to
me like overload is a possibility.
To test this, it may be easiest to disconnect the antenna lead to one
of the receivers you're using, and replace that lead with the lead
from a simple UHF indoor antenna, then tune to Ch 5 (real Ch 29) and
select that receiver at your analog TV. Is it better now? Try also
WOCK.
If the signal were actually weak, you wouldn't see wildly fluctuating
signal strength indications in the boxes' signal monitor.
Did you try this setup before analog TV went off the air? If yes, how
was analog reception?
Bert
aruzinsky
>
> - Show quoted text -
Thank you for your input.
It will be awhile before I can perform your prescribed test because,
at this moment, my reception of channel 5 is perfect.
I guess most of the broadcast antennas are on the Willis (formerly
Sears) building and some are on the Hancock building.
Here are scans from the manual for my UHF amplifier:
http://www.general-cathexis.com/images/UhfAmplifier.png .
Apparently, it is no longer sold. I have been using this amplifier
for about 20 years and have always had wild fluctuations on analog 50,
which was typically weak and snowy. I always suspected that the
broadcast antenna of channel 50 was moving in the wind. Prior to June
12, DTV 7 was near RF 50 and gave me the same problems as DTV 5, but,
as you can see, DTV 7 is now back to RF 7. DTV 50 (RF 51) and DTV 60
(RF 50) give me great reception.
Wouldn't interference cause the signal meter to fluctuate? Could, RF
31 (Fox) be sporadically exceeding its bandwidth?
Albert Manfredi
> Wouldn't interference cause the signal meter to fluctuate? Could, RF
> 31 (Fox) be sporadically exceeding its bandwidth?- Hide quoted text -
Yes, that's possible, but that's part of the front end overload
problem. There are some frequencies that are particularly vulnerable
to interfering with the desired channel, such as N +/- 1 and N +/- 2.
There are also combinations of 3 channels that, when they exist, can
create particularly difficult conditions for many receivers on the
market.
The solution in most of these is to make sure that the intermodulation
products created inside the receiver are at least 15 dB lower than the
signal of the channel you're tuned to. You do this by attenuating the
incoming signal. Intermodulation products can be nasty, because they
accumulate the power of the offending channels, so they can soon
overpower your desired signal.
Of course, the better solution is to build better receivers.
Bert
sorry-spammers
Not likely, especially by two channels.
I suppose interference would cause the signal meter to fluctuate but I think interference to WMAQ from other stations at only nine miles is unlikely.
I think Bert is on the right track: you're overloading your receiver.
Consider an oversimplified example. Let's say you have an amplifier with a gain of 10. Put in 0.001 volt of signal and you get 0.01 volt out. Put
in 0.01 volt of signal and you get 0.1 volt. This amplifier is powered by a 9-volt battery.
Now, let's say you put in 1 volt of signal. The gain of 10 suggests you will get 10 volts of signal out -- but you can't, because the power supply is
only 9 volts.*
The relationship between the amplitudes of the various components of the signal is lost. This is a potentially critical problem with digital TV,
where there are eight discrete signal amplitudes possible. If the receiver can't tell the difference between #7 and #8 (because they're being
"smashed") you'll lose something like 12% of the data. The receiver can correct for some errors but 12% is probably not going to work.
Offhand I would suggest the quick thing to try is removing the amplifier.
For what it's worth, WLS (channel 7) has filed to move to RF 44.
--
Doug Smith W9WI
Pleasant View, TN EM66
* yes, I know, you can use various circuits to get 10 volts out of an amplifier powered by a 9-volt battery.....
aruzinsky
I removed the UHF amplifier and signal strengths generally improved.
I am not currently having problems with Ch. 5 (NBC) but it does have a
relatively low signal strength. If and when I have a loss of Ch. 5's
signal, I will update this post. Thank you again.
Albert Manfredi
> I removed the UHF amplifier and signal strengths generally improved.
> I am not currently having problems with Ch. 5 (NBC) but it does have a
> relatively low signal strength. If and when I have a loss of Ch. 5's
> signal, I will update this post. Thank you again.- Hide quoted text -
Excellent!
By the way, I agree with Doug that it's unlikely that the interference
would be caused by Ch 31 *exceeding its bandwidth*. Especially from 2
channels away.
But when the FCC tested a whole slew of receivers some time ago, maybe
a year ago or more, they did find that many receivers were prone to
problems if populated channels existed at +/- 1, +/- 2, and then +7 or
-6 (or maybe it was -7 and +6) from the desired channel. So, even
though you'd expect that selectivity would not be an issue when the
next channel over is several channel slots away, you might be
surprised. And as I mentioned before, combinations of other channels
can also conspire to create problems in a desired channel.
Receiver design, meaning cheap front ends, are the problem. But the
quick solution is always to attenuate the incoming antenna signal,
which is what you have done.
Bert
aruzinsky
I experienced some breakup on ch. 5 while watching the Ellen show. My
Magnavox converter box gives a signal strength readout on a 0 to 100
scale. Here are the relative signal strengths, (low-high), within an
approximate one minute interval.
2 (CBS) (12 (RF Channel)) (84-88 (signal strength))
5 (NBC) (29) (49-64)
7 (ABC) (7) (90-96)
9 (WGN) (19) (90-94)
11 (WTTW) (47) (80-90)
13 (WOCK) (4) (80-86)
20 (WYCC) (21) (76-80)
23 (MeTV) (27) (34-43)
26 (WCIU) (?) (30-40)
32 (FOX) (31) (70-72)
38 (ION) (43) (82-86)
44 (WSNS) (45) (84-88)
48 (MeToo) (?) (38-55)
50 (WPWR) (51) (90-96)
56 (WYIN) (?) (18-19)
60 (WXFTDT) (50) (61-64)
62 (WJYS) (36) (67-76)
66 (WGBO) (38) (90-98)
Interestingly, ch. 56 has a low but stable signal strength and does
not break up.
If channel 5 had a problem, how would they know it? The upper
management and news reporters probably use dish and cable services in
their personal lives. Same for upper management of advertisers. If
NBC knew that there was a problem, they would probably try to keep it
a secret from advertisers. Maybe, nothing would be done until the
problem manifests itself in Nielsen ratings.
Albert Manfredi
It's likely that Channel 5 is being received with more ghost energy
than 56, so that the receiver occasionally drops the signal, when the
ghost is too much for it to be able to accommodate. Signal strength
meters vary greatly in how they work. For example, I have one box
whose signal strength meter freezes at 49 percent when it sees a
signal but cannot sync up to it due to ghost. If the signal improves
slightly, to where it's decodable, then the meter will start reading
credible values, fluctuating slightly as you'd expect, and so on.
Possibly, your Magnavox is fluctuating for the same reason on Channel
5, and is good with 56 because 56 is a very clean signal?
> If channel 5 had a problem, how would they know it?
I'm not a broadcaster, however TV stations monitor the output from
their transmitter. They won't know how good their signal might be in
every neighborhood, perhaps, but they should know whether their signal
suddenly goes bonkers.
> The upper
> management and news reporters probably use dish and cable services in
> their personal lives. Same for upper management of advertisers.
And the FCC commissioners too, is my bet.
Bert
sorry-spammers
> I experienced some breakup on ch. 5 while watching the Ellen show. My
> Magnavox converter box gives a signal strength readout on a 0 to 100
> scale. Here are the relative signal strengths, (low-high), within an
> approximate one minute interval.
>
> 2 (CBS) (12 (RF Channel)) (84-88 (signal strength))
> 5 (NBC) (29) (49-64)
> 23 (MeTV) (27) (34-43)
> 26 (WCIU) (?) (30-40)
> 48 (MeToo) (?) (38-55)
For what very little it's worth, all three of these stations are on RF channel 27 - they're three subchannels of the same transmitter. (MeToo does
have a permit for a digital operation on channel 46 but to my knowledge it's not yet operating)
> 56 (WYIN) (?) (18-19)
RF 17 from Lake County, Indiana.
aruzinsky
>
> - Show quoted text -
The signal meter behaviors are similar on all three of my tuners which
are:
Magnavox TB100MW9 converter box
Zenith DTT901 converter box
Toshiba D-R560KU DVD recorder
I suspect that there is some sort of time averaging in these meters
and that ch. 5 is fluctuating more than indicated within a period of
seconds. It also fluctuates greatly over a period of days and weeks.
Rain causes the signal strength to drop more than other stations.
I vaguely remember from one of my EE classes that the signal strength
isophotes from broadcast antennas (dipole I think) can be deeply
lobed . Do you know whether this is the case for typical UHF
broadcasts? If so, my receiving antenna might be located near the
side of a lobe and slight motion of the broadcast antenna in the wind
or expansion/contraction with temperature could cause large
fluctuations in my received signal strength. In such cases, many
people would have a similar problem with other stations. The obvious
solution would be to broadcast on two UHF frequencies or stay on VHF
like ch. 7.
I am certain of one thing. UHF is error fraught and the FCC has
instituted Murphy's law.
Albert Manfredi
> I vaguely remember from one of my EE classes that the signal strength
> isophotes from broadcast antennas (dipole I think) can be deeply
> lobed . Do you know whether this is the case for typical UHF
> broadcasts?
No reason to ask about "typical," since the FCC gives you the exact
transmit antenna pattern.
Go to this site:
http://www.fcc.gov/mb/video/tvq.html
and type in the call sign (WMAQ, I believe). Then scroll down and ask
for the "detailed output." Among other things, there's a link to the
polar plot of the antenna pattern.
Some are circular. The one for WMAQ is not. So you might be onto
something, depending where you are wrt the plot.
> If so, my receiving antenna might be located near the
> side of a lobe and slight motion of the broadcast antenna in the wind
> or expansion/contraction with temperature could cause large
> fluctuations in my received signal strength. In such cases, many
> people would have a similar problem with other stations. The obvious
> solution would be to broadcast on two UHF frequencies or stay on VHF
> like ch. 7.
>
> I am certain of one thing. UHF is error fraught and the FCC has
> instituted Murphy's law.
VHF would normally SEEM like a good idea. Although some of the
stations that moved back to VHF, especially the ones that did so up
and down the East coast, were cut in power so drastically that they
became impossible or difficult to receive for many that had no trouble
before, when they were in UHF.
Some examples are rather extreme. High VHF "full power" stations
transmitting at 5 or 9 KW ERP, for example. Think about it. A TV
station transmitting at power levels that are even low for FM
stations. With 36X as much RF bandwidth as FM tarnsmitters have to
worry about.
Bert
aruzinsky
Thanks. I didn't know about that site. Do I assume correctly that 0
degrees is North? That would put me near the relative minimum of
0.662 at 260 deg. but that is not nearly enough to explain the
variation in my received signal strength. I was imagining hundreds of
lobes with near zero in between them and this would have to be
calculated analytically rather than measured.
Albert Manfredi
> Thanks. I didn't know about that site. Do I assume correctly that 0
> degrees is North?
Yes.
> That would put me near the relative minimum of
> 0.662 at 260 deg. but that is not nearly enough to explain the
> variation in my received signal strength. I was imagining hundreds of
> lobes with near zero in between them and this would have to be
> calculated analytically rather than measured.
I have to believe that the fluctuations are caused by dynamically
ghost, maybe static or dynamic, right at the edge of what the
receivers can handle. I've only noticed the wild fluctuations in these
cases. Just before the so-called digital cliff.
If you do get a chance at some point, might be interesting to try the
simple indoor UHF antenna. Just to see if these wild fluctuations
persist on Ch 29. Try different antenna locations and azimuths,
hopefully close to a window facing in the right direction. This would
be a lot easier than trying to reorient your big antennas, I would
think. If the fluctuations stop, you'll know that the problem is not
with the transmitter site.
Bert
sorry-spammers
> Thanks. I didn't know about that site. Do I assume correctly that 0
> degrees is North? That would put me near the relative minimum of
> 0.662 at 260 deg. but that is not nearly enough to explain the
> variation in my received signal strength. I was imagining hundreds of
> lobes with near zero in between them and this would have to be
> calculated analytically rather than measured.
I would suggest you may well have such lobes on your *receiving* antenna.
=======================
VHF stations have had a lot of trouble with digital. The reason Bert cites is one of them: stations have been assigned fairly low powers. WLS was
assigned 4.75kw on channel VHF 7. It's not working very well for them; they've applied to move to UHF channel 44 with 473kw. I think a contributing
factor is that a lot of viewers wanted small indoor antennas, and vendors were happy to provide them, even though those antennas perform VERY poorly
on VHF channels. Also, there seems to be some evidence that digital-into-digital interference on the same channel is more troublesome than
analog-into-digital -- so co-channel assignment situations that worked before June 12th may not now. (but again at 9 miles I doubt interference is
*your* problem.)
=======================
Yes, the call letters on channel 5 are WMAQ.
aruzinsky
wrote:
But that would not explain short time fluctuations of signal strengths
for certain frequencies. My antenna is indoors in the attic and
cannot normally move within a period less than a second because it is
suspended from the ceiling on strings. Furthermore, I had been
plagued with similar fluctuations in signal strength on analog ch. 50
for decades. Bad reception of analog ch. 50 was the only reason that
I bought a UHF amplifier and large UHF antenna. Little did they help.
However, next time ch. 5 breaks up, I will manually move my uhf
antenna several degrees and see what happens.
Albert Manfredi
> But that would not explain short time fluctuations of signal strengths
> for certain frequencies. My antenna is indoors in the attic and
> cannot normally move within a period less than a second because it is
> suspended from the ceiling on strings. Furthermore, I had been
> plagued with similar fluctuations in signal strength on analog ch. 50
> for decades. Bad reception of analog ch. 50 was the only reason that
> I bought a UHF amplifier and large UHF antenna. Little did they help.
That sort of effect I would attribute to an echo that interferes with
the main signal in certain, maybe even weather-related conditions. If
the phase of the echo is right, it will cancel the main signal. If the
amplitude varies slightly in time, even if the phase does not vary in
time, you would end up with a fluctuating signal.
Ever been stopped at a traffic signal in the car, and have the FM
radio signal you're tuned to become very bad? Then you inch up a bit
and the signal gets much better? There are interections close to where
I live where I can always predict reception problems of my favorite
station. But other stations are fine.
Back in analog TV days, I noticed that reception of some TV channels
would be very ghosty in dry conditions and much cleaner when the
ground got a good soaking. And that some stations looked better than
others even if they shared the same broadcast tower.
My guess is that you're seeing the digital equivalent of these
annoying RF effects.
Bert
aruzinsky
I don't think so because apparently ch 5 (WMAQ) (NBC) and ch 32 (WFLD)
(FOX) have nearly the same wavelength (0.53 , 0.52 meters) and are
apparently broadcast from the same antenna mast with only 33 meters
vertical distance between them. Any fluctuating constructive/
destructive ghost interference would involve movement of an
interfering object of, at least, half a wavelength, ~ 0.25 meters, and
would apply to both ch 5 and ch 32 simultaneously (although
constructive and destructive interference could be opposite in each).
I rarely have a problem with ch 32.
Please check my calculations from this data:
-----------------------------------------------------------------------------------------------------------
Licensee: NBC TELEMUNDO LICENSE CO.
Service Designation: DT Digital television station
Channel: 29 560 - 566 MHz Licensed
File No.: BLCDT-20010531ACY Facility ID number: 47905
CDBS Application ID No.: 570247
41° 52' 44.00" N Latitude Site in Canadian Border
Zone
87° 38' 10.00" W Longitude (NAD 27)
Polarization: Horizontal (H) Effective Radiated Power (ERP): 350.
kW ERP Antenna Height Above Average Terrain: 508. meters HAAT --
Calculate HAAT Antenna Height Above Mean Sea Level: 688. meters
AMSL Antenna Height Above Ground Level: 507. meters AGL TV
Zone: 1 Frequency Offset: Directional Antenna ID
No.: 31269 Pattern Rotation: 0.00
Antenna Make: DIE Antenna Model: TFU-12GBH-R 06
-----------------------------------------------------------------------------------------------------------
Licensee: FOX TELEVISION STATIONS, INC.
Service Designation: DT Digital television station
Channel: 31 572 - 578 MHz Licensed
File No.: BLCDT-20050606ABF Facility ID number: 22211
CDBS Application ID No.: 1067076
41° 52' 44.00" N Latitude Site in Canadian Border
Zone
87° 38' 10.00" W Longitude (NAD 27)
Polarization: Elliptical (H > V) Effective Radiated Power (ERP):
690. kW ERP Antenna Height Above Average Terrain: 475. meters HAAT
-- Calculate HAAT Antenna Height Above Mean Sea Level: 655. meters
AMSL Antenna Height Above Ground Level: 474. meters AGL TV
Zone: 1 Frequency Offset: Directional Antenna ID
No.: 65621 Pattern Rotation: 0.00
Antenna Make: AND Antenna Model: ATW14H3H-ETC2-31H
-----------------------------------------------------------------------------------------------------------
aruzinsky
> Licensee: NBC TELEMUNDO LICENSE CO.
> Service Designation: DT Digital television station
>
> Channel: 29 560 - 566 MHz Licensed
> File No.: BLCDT-20010531ACY Facility ID number: 47905
> CDBS Application ID No.: 570247
>
> 41° 52' 44.00" N Latitude Site in Canadian Border
> Zone
> 87° 38' 10.00" W Longitude (NAD 27)
>
> Polarization: Horizontal (H) Effective Radiated Power (ERP): 350.
> kW ERP Antenna Height Above Average Terrain: 508. meters HAAT --
> Calculate HAAT Antenna Height Above Mean Sea Level: 688. meters
> AMSL Antenna Height Above Ground Level: 507. meters AGL TV
> Zone: 1 Frequency Offset: Directional Antenna ID
> No.: 31269 Pattern Rotation: 0.00
> Antenna Make: DIE Antenna Model: TFU-12GBH-R 06
> Licensee: FOX TELEVISION STATIONS, INC.
> Service Designation: DT Digital television station
>
> Channel: 31 572 - 578 MHz Licensed
> File No.: BLCDT-20050606ABF Facility ID number: 22211
> CDBS Application ID No.: 1067076
>
> 41° 52' 44.00" N Latitude Site in Canadian Border
> Zone
> 87° 38' 10.00" W Longitude (NAD 27)
>
> Polarization: Elliptical (H > V) Effective Radiated Power (ERP):
> 690. kW ERP Antenna Height Above Average Terrain: 475. meters HAAT
> -- Calculate HAAT Antenna Height Above Mean Sea Level: 655. meters
> AMSL Antenna Height Above Ground Level: 474. meters AGL TV
> Zone: 1 Frequency Offset: Directional Antenna ID
> No.: 65621 Pattern Rotation: 0.00
> Antenna Make: AND Antenna Model: ATW14H3H-ETC2-31H
>
> - Show quoted text -
CORRECTION:
Movement of a reflective object one quarter wavelength, 0.125 meters
(5 inches) for ch 5 or ch 32, along the line of sight, would change
the reflected signal phase 180 degrees.
Albert Manfredi
> I don't think so because apparently ch 5 (WMAQ) (NBC) and ch 32 (WFLD)
> (FOX) have nearly the same wavelength (0.53 , 0.52 meters) and are
> apparently broadcast from the same antenna mast with only 33 meters
> vertical distance between them. Any fluctuating constructive/
> destructive ghost interference would involve movement of an
> interfering object of, at least, half a wavelength, ~ 0.25 meters, and
> would apply to both ch 5 and ch 32 simultaneously (although
> constructive and destructive interference could be opposite in each).
> I rarely have a problem with ch 32.
There are four differences between those two channels. The first two
probably would not account for indoor reception differences in your
particular case, although one never knows:
1. WMAQ is transmitted at substantially lower power. Which would bring
it closer to the digital cliff if there were other problems, such as
ghost, for the receiver to cope with. But you are only 9 miles away
and have a large antenna, so that's unlikely your problem.
2. The antenna height could potentially make a difference, although
that seems unlikely too. But you never know. Some particularly
reflective surface somewhere along the propagation path could be more
of a problem for WMAQ.
3. The ellyptical polarization of Ch 31 can definitely help indoor
reception or reception inside a city, where you would expect
reflections from buildings to mess with the polarization of the
transmitted signal. Matter of fact, many of the digital VHF stations
that have been having problems after 12 June have ordered circularly
polarized transmit antennas, I've read. Is your receive antenna
strictly horizontally polarized?
4. The transmit antenna patterns are way different. WFLD transmits
almost no power to the East. This could have a major impact on the
ghost energy you see as close in as you are, I would think.
I wouldn't be surprised if reception of those two stations is
different.
Bert
> Please check my calculations from this data:
> -----------------------------------------------------------------------------------------------------------
> Licensee: NBC TELEMUNDO LICENSE CO.
> Service Designation: DT Digital television station
>
> Channel: 29 560 - 566 MHz Licensed
> File No.: BLCDT-20010531ACY Facility ID number: 47905
> CDBS Application ID No.: 570247
>
> 41° 52' 44.00" N Latitude Site in Canadian Border
> Zone
> 87° 38' 10.00" W Longitude (NAD 27)
>
> Polarization: Horizontal (H) Effective Radiated Power (ERP): 350.
> kW ERP Antenna Height Above Average Terrain: 508. meters HAAT --
> Calculate HAAT Antenna Height Above Mean Sea Level: 688. meters
> AMSL Antenna Height Above Ground Level: 507. meters AGL TV
> Zone: 1 Frequency Offset: Directional Antenna ID
> No.: 31269 Pattern Rotation: 0.00
> Antenna Make: DIE Antenna Model: TFU-12GBH-R 06
> -----------------------------------------------------------------------------------------------------------
aruzinsky
>
> - Show quoted text -
1 and 4 are good points. Together they seem to suggest that I am
getting at least 4X more signal power from rf ch 31 than rf ch 29. Is
the signal power proportional to the square of the plotted "field
strength"?
"Is your receive antenna strictly horizontally polarized?"
I don't know how the antenna works except there are reflectors. Here
is a picture:
http://www.general-cathexis.com/images/antenna.jpg
Note that only two pair of elements are connected to the output lead.
I don't know what that herring bone pattern in front is supposed to
do, but it certainly occupies a lot of space.
The line of sight is about two feet left of this view of Willis
(Sears) Tower from the window which is 5 ft in front of the antenna.
http://www.general-cathexis.com/images/SearsTower1.jpg
http://www.general-cathexis.com/images/SearsTower2.jpg (You can see
the tower in the center through the tree branches.)
Actually, when I took these pictures, I realized the metal lattice of
the window was in the way and moved the UHF antenna more to the left.
Albert Manfredi
> 1 and 4 are good points. Together they seem to suggest that I am
> getting at least 4X more signal power from rf ch 31 than rf ch 29. Is
> the signal power proportional to the square of the plotted "field
> strength"?
Should be. The plots are "relative field strength" plots, which I'm
assuming refers to the E field strength. And power density is
proportional to the square of the E field strength.
Pdensity = E^2 / 120*pi, where E is given as V/m
> "Is your receive antenna strictly horizontally polarized?"
>
> I don't know how the antenna works except there are reflectors. Here
> is a picture:http://www.general-cathexis.com/images/antenna.jpg
> Note that only two pair of elements are connected to the output lead.
> I don't know what that herring bone pattern in front is supposed to
> do, but it certainly occupies a lot of space.
Nice pictures. Yes, they are horizontally polarized. The downleads
connect to a dipole element, often a folded dipole. The elements in
front of that dipole, i.e. toward the transmit antenna, are called
directors. The more of them there are, the tighter the main lobe of
the antenna becomes. They make the antenna more directional, to
achieve more gain, at the price of missing out on signals that might
come from other azimuths. The elements behind the dipole are called
reflectors. So all of these additional elements have the task of
channeling more of the RF energy to the dipole element (and the
downlead) than a simple dipole would be able to grab out of the ether
by itself.
> The line of sight is about two feet left of this view of Willis
> (Sears) Tower from the window which is 5 ft in front of the antenna.http://www.general-cathexis.com/images/SearsTower1.jpghttp://www.general-cathexis.com/images/SearsTower2.jpg(You can see
> the tower in the center through the tree branches.)
>
> Actually, when I took these pictures, I realized the metal lattice of
> the window was in the way and moved the UHF antenna more to the left.
Looks to me like the obstacles visible in the pictures are close
enough that they would mostly affect your signal strength, as opposed
to creating the sort of ghost that digital receivers would have
trouble with.
Bert
aruzinsky
> > the tower in the center through the tree branches.)
>
> > Actually, when I took these pictures, I realized the metal lattice of
> > the window was in the way and moved the UHF antenna more to the left.
>
> Looks to me like the obstacles visible in the pictures are close
> enough that they would mostly affect your signal strength, as opposed
> to creating the sort of ghost that digital receivers would have
> trouble with.
>
> Bert
Thanks Bert. I will try to point my UHF antenna better and raise it
higher. The other channels, principally ch 11, are broadcast from the
Handcock building which is about 1 mile behind the Willis Tower.
An argument could be made that NBC owned WMAQ is wasting half its 350
kW by broadcasting over Lake Michigan and is therefore anti-green.
Maybe, I should complain to the FCC for letting WMAQ drive an ether
polluting clunker. Also, I note that NBC owned WSNS is broadcasting
467 kW of Spanish programming. Broadcasting more watts in Spanish
than English seems a bit unpatriotic to me.
aruzinsky
receiving antenna toward the transmission antenna was apparently the
solution.