High Definition TV

[John]

It is common knowledge that the best way, probably the only way, to
receive 1080pixels TV in North America is ODA.
I just installed a TV Antenna and I am pleasantly surprised at the
results. A signal that before would give a very noise picture,
digitally, will give an excellent picture.

But I have a problem. How does one orient the antenna for the best
signal. Before we would rotate the antenna for the strongest signal
but with digital signals the signal is on or isn't there. Rotating
the antenna and parking between the 2 "no signal" positions, is one
way but I would prefer to adjust it to the maximum signal.
There is probably an agc signal that can be tapped inside the rx but
that I would like to do after the warranty expires

Another puzzle I have is that I installed an antenna that is no more
than 40 x 50 cm with 6 elements and claims to have a minimum gain of
28 dB from 40 to 890 MHz.
Four of the directors are inside of plastic that may have inductors to
increase their electrical. The main dipole goes inside of a box that
include the electronics to rotate the assembly and may have an rf
amplifier.

Comments please.

John

 

[TTman]

snip

Another puzzle I have is that I installed an antenna that is no more
than 40 x 50 cm with 6 elements and claims to have a minimum gain of
28 dB from 40 to 890 MHz.
Four of the directors are inside of plastic that may have inductors to
increase their electrical. The main dipole goes inside of a box that
include the electronics to rotate the assembly and may have an rf
amplifier.

Comments please.

John

In the uK, most digital Rxs have built in signal strength displays- AGC, SNR
and BER.
Tho these are mainly for satellite....

 

[Kevin McMurtrie]

It is common knowledge that the best way, probably the only way, to
receive 1080pixels TV in North America is ODA.
I just installed a TV Antenna and I am pleasantly surprised at the
results. A signal that before would give a very noise picture,
digitally, will give an excellent picture.

But I have a problem. How does one orient the antenna for the best
signal. Before we would rotate the antenna for the strongest signal
but with digital signals the signal is on or isn't there. Rotating
the antenna and parking between the 2 "no signal" positions, is one
way but I would prefer to adjust it to the maximum signal.
There is probably an agc signal that can be tapped inside the rx but
that I would like to do after the warranty expires

Most TVs have a signal quality menu to help in programming the rotator.

Another puzzle I have is that I installed an antenna that is no more
than 40 x 50 cm with 6 elements and claims to have a minimum gain of
28 dB from 40 to 890 MHz.
Four of the directors are inside of plastic that may have inductors to
increase their electrical. The main dipole goes inside of a box that
include the electronics to rotate the assembly and may have an rf
amplifier.

There are plenty of fake TV antennas in stores and catalogs.

DTV frequencies vary by region so the type of antenna needed varies. If
you're lucky, the lower frequencies aren't used and the longest rods of
a yagi antenna aren't needed. If you're really lucky, it's all UHF so a
small bowtie array can be used.

Channels 2-6 are for short range TV in the SF/SJ Bay Area. Nothing
worthwhile has shown up there yet so I may change to a 7-69 channel
antenna when my wideband antenna wears out.

 

[Martin Brown]

snip

In the uK, most digital Rxs have built in signal strength displays- AGC, SNR
and BER.
Tho these are mainly for satellite....

Panasonic kit in the UK also allows signal level and quality display for
terrestrial DTV from the setup menu. The digital decode quality result
is a bit abrupt, but the signal level indicator is useful.

In the US it seems most of these features are disabled or undocumented.
Several vendors make aerial alignment aids that are little more than a
fancy diode rectifier and a moving coil meter, possibly with an audio
tone feedback that increases in pitch with higher signal levels. You
need one extra F connector cable to put the breakout box in line. That's
how I adjusted mine accurately onto the right satellite.

Regards,
Martin Brown

 

[John]

To my surprise I am getting Channel 3 and 5 that are about 50 miles
from my location and as you know are below FM frequencies.
To receive them with little noise it used to required an assembly of
2 five elements Yagies. Before they switched to digital and using the
same antenna I wouldn't even get the sync signals.

Is there anything really worth watching on over-the-air TV, digital or
otherwise?

...Jim Thompson

Jim

The answer to that is that PBS (Public Broadcast Stations) have 2
channels on my area and each channel also transmits on 3 sub channels
for a total of 8 channels that normally have different programs or
have delayed broadcast.
The main channels are 1080 but the sub channels are 720 or 410. The
410 is normally used for old and classic programs, unavailable to the
staitions in HD.
The CBC in Canada are also doing a good job with the news but they are
schedule to go digital next year.

To my knowledge OTA is the only way we can get the sub channels.
PBS has by far the best programming because it is subsidized by the
government and the public. The commercials are limit to sponsors and
the programs include a daily retransmission news from the BBC and
believe me also from Algesiria.
Of coarse they must satisfy a large number of the population with
money and consequently include popular programming .

Just for this I think it is worth having an antenna

John

 

[John]

Panasonic kit in the UK also allows signal level and quality display for
terrestrial DTV from the setup menu. The digital decode quality result
is a bit abrupt, but the signal level indicator is useful.

In the US it seems most of these features are disabled or undocumented.
Several vendors make aerial alignment aids that are little more than a
fancy diode rectifier and a moving coil meter, possibly with an audio
tone feedback that increases in pitch with higher signal levels. You
need one extra F connector cable to put the breakout box in line. That's
how I adjusted mine accurately onto the right satellite.

Regards,
Martin Brown

The devices I have seen are for satellite adjustments that only
receive one or two channels. Absolutely essential .

For OTA we need a unit with a band pass filter that rejects all minus
one channel. Like a receiver.
I have 2 sat receivers and they have the function you describe.

My TV set is a 52" Sharp and I can't see any reference to help to
adjust the Antenna.
I may call Sharp and ask the question

Thanks

John

John

 

[John]

Are you in the US?
If so, visit the FCC (or other) web site.
Get the coordinates for the TV's main tower (some stations in larger
markets may have a 2nd transmitter as an emergency/spare/back-up at
different coordinates).
Get a map of the area.
Then, go get out your boy scout compass...

The rest is rather self-explanatory.

On the old days use to be easy, You just start by point the antenna on
the same direction as all the others and then adjust for maximum.
Today a TV antenna is a rarity.

I will follow your advise, thanks

John

 

[John]

On the old days use to be easy, You just start by point the antenna on
the same direction as all the others and then adjust for maximum.
Today a TV antenna is a rarity.

I will follow your advise, thanks

John

One more question:

I know that in order to maximize a power transfer the load impedance
must be equal to the source impedance and the transmission line but,
if I have un amplifier that uses a high impedance fet and is installed
at the main dipole of an antenna and the line is located after the fet
amplifier with unity gain, don't I gain 6 dB relative to a perfectly
matched system ???
Assuming zero loss for the line attenuation .

Must the dipole see the right impedance in order to perform as in
theory

I know that a fet exposed to that environment wouldn't last very long
but that is another problem
John

 

[Kevin McMurtrie]

Is there anything really worth watching on over-the-air TV, digital or
otherwise?

...Jim Thompson

I'd say it's worth the low cost of maintaining an antenna. There are a
few good hours a week to watch.

An interesting effect of DTV is that what used to be a scattered bunch
of low power analog signals with 1 to 10 mile transmitters is now 480i
streams sharing channels on 15 to 60 mile transmitters.

 

[Jeff Johnson]

It is common knowledge that the best way, probably the only way, to
receive 1080pixels TV in North America is ODA.
I just installed a TV Antenna and I am pleasantly surprised at the
results. A signal that before would give a very noise picture,
digitally, will give an excellent picture.

But I have a problem. How does one orient the antenna for the best
signal. Before we would rotate the antenna for the strongest signal
but with digital signals the signal is on or isn't there. Rotating
the antenna and parking between the 2 "no signal" positions, is one
way but I would prefer to adjust it to the maximum signal.
There is probably an agc signal that can be tapped inside the rx but
that I would like to do after the warranty expires

Another puzzle I have is that I installed an antenna that is no more
than 40 x 50 cm with 6 elements and claims to have a minimum gain of
28 dB from 40 to 890 MHz.
Four of the directors are inside of plastic that may have inductors to
increase their electrical. The main dipole goes inside of a box that
include the electronics to rotate the assembly and may have an rf
amplifier.

Don't worry about it. If your picture quality is good and your not getting
"loss of signal" type of errors(no picture at all) then your fine. You can
be almost 100% sure that the quality is exactly the same as was sent.
Digital is digital and there are great encoding schemes used that have great
noise immunity and signal recovery. While I don't know much about DTV I
imagine that it works much much better than analog.

With analog any noise on the signal in the appropriate band at the
appropriate time would show up on the picture. This is not the case with
digital as it is 1's and 0's(encoded in an analog signal but generally
easily recoverable). It takes a lot of noise/low signal strenght to change a
1 into a 0 and vice versa. Of course if this happens one can generally tell
if they use crc's, hashes, checksums, etc and even recover from such errors.
This is virtually impossible to do with analog signals.

If you are getting good picture quality then be reasonably assure that it is
the best picture quality excluding the TV itself. If you are getting blank
screens intermittedly then your SNR is low. This could be do to antenna
orientation or various other possibilities.

 

[Kevin McMurtrie]

Don't worry about it. If your picture quality is good and your not getting
"loss of signal" type of errors(no picture at all) then your fine. You can
be almost 100% sure that the quality is exactly the same as was sent.
Digital is digital and there are great encoding schemes used that have great
noise immunity and signal recovery. While I don't know much about DTV I
imagine that it works much much better than analog.

With analog any noise on the signal in the appropriate band at the
appropriate time would show up on the picture. This is not the case with
digital as it is 1's and 0's(encoded in an analog signal but generally
easily recoverable). It takes a lot of noise/low signal strenght to change a
1 into a 0 and vice versa. Of course if this happens one can generally tell
if they use crc's, hashes, checksums, etc and even recover from such errors.
This is virtually impossible to do with analog signals.

If you are getting good picture quality then be reasonably assure that it is
the best picture quality excluding the TV itself. If you are getting blank
screens intermittedly then your SNR is low. This could be do to antenna
orientation or various other possibilities.

Early decoders were all-or-nothing because they couldn't re-synch the
stream after an error. Modern decoders will show lagging or garbled
blocks in moving images when the signal is weak.

 

[John]

Don't worry about it. If your picture quality is good and your not getting
"loss of signal" type of errors(no picture at all) then your fine. You can
be almost 100% sure that the quality is exactly the same as was sent.
Digital is digital and there are great encoding schemes used that have great
noise immunity and signal recovery. While I don't know much about DTV I
imagine that it works much much better than analog.

With analog any noise on the signal in the appropriate band at the
appropriate time would show up on the picture. This is not the case with
digital as it is 1's and 0's(encoded in an analog signal but generally
easily recoverable). It takes a lot of noise/low signal strenght to change a
1 into a 0 and vice versa. Of course if this happens one can generally tell
if they use crc's, hashes, checksums, etc and even recover from such errors.
This is virtually impossible to do with analog signals.

If you are getting good picture quality then be reasonably assure that it is
the best picture quality excluding the TV itself. If you are getting blank
screens intermittedly then your SNR is low. This could be do to antenna
orientation or various other possibilities.

Excellent information from all of you.

My sincere thanks to all

John

 

[JosephKK]

Hello John,

Gain issue
Probably there is an amplifier inside (that is fed directly from your
receiver/set top box). So an overall gain figure is given (without any
noise specification very likely). Making a 28 dBi antenna for these
frequencies will be very large.


Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me

And because of the physiccs very directional.