Slightly OT: strange TV reception issue

G

Glenn Pure

Guest
Has anyone seen the following and know what the cause is...

One of my UHF TV channels (normal analog) has a reasonable but not
perfect picture. However, the sound is dreadful. It is distorted
although improves to "normal" every half minute or minute, then goes
crap again.

I'm puzzled why I can get an acceptable picture but lousy sound. I'd
expect signal deterioration (if that's what is happening) to bugger
the picture before the sound.

Note, that the sound is OK if I take the video output from my VCR
(picture is similar). Sound is only crap if I use the TV tuner.

This only affects one channel. All the rest, both UHF and VHF are
fine.

Cheers
Glenn
Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net
 
"Glenn Pure" <glenn*delete_this_for_reply*@evans-pure.net> wrote in message
news:fecsu016g2llo4rgdt4mopmk4un20n9v5m@4ax.com...
Has anyone seen the following and know what the cause is...

One of my UHF TV channels (normal analog) has a reasonable but not
perfect picture. However, the sound is dreadful. It is distorted
although improves to "normal" every half minute or minute, then goes
crap again.

I'm puzzled why I can get an acceptable picture but lousy sound. I'd
expect signal deterioration (if that's what is happening) to bugger
the picture before the sound.

Note, that the sound is OK if I take the video output from my VCR
(picture is similar). Sound is only crap if I use the TV tuner.

This only affects one channel. All the rest, both UHF and VHF are
fine.

Cheers
Glenn
Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net
Two possible main causes spring to mind. There may be others.

Selective fading, where parts of the signal, especially the carrier wave,
are almost completely missing. When demodulated ,such a signal can be
grossly distorted. This is more common with short wave reception, and AM
signals, and is highly random.

Multipath reception, a cousin of selective fading. In this mode the antenna
receives one or more versions of the same signal that have travelled
different distances. The direct signal will then be mixed with signals that
arrive later having been reflected or refracted, and some phase cancellation
occurs. As the various paths vary in strength, perhaps with
weather/temperature variation, so will the effect on the received signal. If
you ever see a ghosted picture on a TV, this is caused by multipath
reception.


It is also just possible that if you have a very poor antenna system, with
poor cable, and unconnected and/or unterminated spurs of co-axial cable,
that parts of the system act as stub filters at the exact frequency of the
channel that has poor sound. This can produce an effect similar to selective
fading, but is less random in the effects it produces.

Cures?

Swing antenna a few degrees either way.

New complete antenna system.

Borrow a digital set top box to see if you can use the existing system for
digital reception.

Buy new house.

Take up knitting and to heck with TV :<))


There may well be professional installers who can add a few ideas to the
above

Luck,

Bill.
 
"Bill Bailley" <JustMe@Home> wrote in message
news:41ee62d8$0$3872$afc38c87@news.optusnet.com.au...
"Glenn Pure" <glenn*delete_this_for_reply*@evans-pure.net> wrote in
message
news:fecsu016g2llo4rgdt4mopmk4un20n9v5m@4ax.com...
Has anyone seen the following and know what the cause is...

One of my UHF TV channels (normal analog) has a reasonable but not
perfect picture. However, the sound is dreadful. It is distorted
although improves to "normal" every half minute or minute, then goes
crap again.

I'm puzzled why I can get an acceptable picture but lousy sound. I'd
expect signal deterioration (if that's what is happening) to bugger
the picture before the sound.

Note, that the sound is OK if I take the video output from my VCR
(picture is similar). Sound is only crap if I use the TV tuner.

This only affects one channel. All the rest, both UHF and VHF are
fine.

Cheers
Glenn
Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net

Two possible main causes spring to mind. There may be others.

Selective fading, where parts of the signal, especially the carrier wave,
are almost completely missing. When demodulated ,such a signal can be
grossly distorted. This is more common with short wave reception, and AM
signals, and is highly random.

Multipath reception, a cousin of selective fading. In this mode the
antenna
receives one or more versions of the same signal that have travelled
different distances. The direct signal will then be mixed with signals
that
arrive later having been reflected or refracted, and some phase
cancellation
occurs. As the various paths vary in strength, perhaps with
weather/temperature variation, so will the effect on the received signal.
If
you ever see a ghosted picture on a TV, this is caused by multipath
reception.


It is also just possible that if you have a very poor antenna system, with
poor cable, and unconnected and/or unterminated spurs of co-axial cable,
that parts of the system act as stub filters at the exact frequency of the
channel that has poor sound. This can produce an effect similar to
selective
fading, but is less random in the effects it produces.

Cures?

Swing antenna a few degrees either way.

New complete antenna system.

Borrow a digital set top box to see if you can use the existing system for
digital reception.

Buy new house.

Take up knitting and to heck with TV :<))


There may well be professional installers who can add a few ideas to the
above

Luck,

Bill.

Given that his sound and picture are okay if using the VCR as the tuner,
this is unlikely. Probably he has the RF output from the VCR tuned very
close to the channel being interfered with on his TV.

Ken
 
..


Given that his sound and picture are okay if using the VCR as the tuner,
this is unlikely. Probably he has the RF output from the VCR tuned very
close to the channel being interfered with on his TV.

Ken


Good point Ken. I didn't think of that one.

There is another mode that actually occurred to me, but I assume it is rare.

In this case, my channel nine vhf picture would start to slowly tear, taking
about 30 seconds to become un-watchable. After that there was a brief white
flash and the picture was normal again for perhaps a minute. Then the whole
process started again. To add to the mystery, the sound and all other
channels were unaffected and the condition only started to happen after nine
PM.

Because my antenna system was a long standing installation that had worked
perfectly for years, I was able to do a "Sherlock Holmes" while sitting in
my armchair, and come up with a viable theory that proved to be correct.

Got to rush!

More later.

Bill.
 
"Ken Taylor"

Given that his sound and picture are okay if using the VCR as the tuner,
this is unlikely. Probably he has the RF output from the VCR tuned very
close to the channel being interfered with on his TV.

** I'll put a few bucks on that one too - win or place.




............. Phil
 
Thanks for all the posts. I have tried the fine tuning. It doesn't
help. I'll look into the RF from the VCR, although I'm actually
connecting through the direct A/V outputs, I expect the VCR RF out is
still active.

Cheers
Glenn

pedro <pedro@nowhere.com> wrote:

Glenn Pure wrote:


Has anyone seen the following and know what the cause is...

One of my UHF TV channels (normal analog) has a reasonable but not
perfect picture. However, the sound is dreadful. It is distorted
although improves to "normal" every half minute or minute, then goes
crap again.

I'm puzzled why I can get an acceptable picture but lousy sound. I'd
expect signal deterioration (if that's what is happening) to bugger
the picture before the sound.

Note, that the sound is OK if I take the video output from my VCR
(picture is similar). Sound is only crap if I use the TV tuner.

This only affects one channel. All the rest, both UHF and VHF are
fine.

Cheers
Glenn
Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net



Have you tried to adjust the fine tuning manually?
Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net
 
On Thu, 20 Jan 2005 10:56:25 GMT, Glenn Pure
<glenn*delete_this_for_reply*@evans-pure.net> put finger to keyboard
and composed:

Thanks for all the posts. I have tried the fine tuning. It doesn't
help. I'll look into the RF from the VCR, although I'm actually
connecting through the direct A/V outputs, I expect the VCR RF out is
still active.

Cheers
Glenn
Do you still have this problem if you bypass the VCR by connecting
your TV directly to the wall socket?


pedro <pedro@nowhere.com> wrote:

Glenn Pure wrote:


Has anyone seen the following and know what the cause is...

One of my UHF TV channels (normal analog) has a reasonable but not
perfect picture. However, the sound is dreadful. It is distorted
although improves to "normal" every half minute or minute, then goes
crap again.

I'm puzzled why I can get an acceptable picture but lousy sound. I'd
expect signal deterioration (if that's what is happening) to bugger
the picture before the sound.

Note, that the sound is OK if I take the video output from my VCR
(picture is similar). Sound is only crap if I use the TV tuner.

This only affects one channel. All the rest, both UHF and VHF are
fine.

Cheers
Glenn
Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net



Have you tried to adjust the fine tuning manually?

Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net

- Franc Zabkar
--
Please remove one 's' from my address when replying by email.
 
Problem has disappeared (temporarily??). I can't do much checking just
now.

Glenn

Franc Zabkar <fzabkar@optussnet.com.au> wrote:

On Thu, 20 Jan 2005 10:56:25 GMT, Glenn Pure
glenn*delete_this_for_reply*@evans-pure.net> put finger to keyboard
and composed:

Thanks for all the posts. I have tried the fine tuning. It doesn't
help. I'll look into the RF from the VCR, although I'm actually
connecting through the direct A/V outputs, I expect the VCR RF out is
still active.

Cheers
Glenn

Do you still have this problem if you bypass the VCR by connecting
your TV directly to the wall socket?
Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net
 
Well, I tried changing output channel on the VCR. It made no
difference.

I have yet to try routing antenna straight into the TV (but this won't
be a fix).

Cheers
Glenn

Glenn Pure <glenn*delete_this_for_reply*@evans-pure.net> wrote:

Problem has disappeared (temporarily??). I can't do much checking just
now.

Glenn

Franc Zabkar <fzabkar@optussnet.com.au> wrote:

On Thu, 20 Jan 2005 10:56:25 GMT, Glenn Pure
glenn*delete_this_for_reply*@evans-pure.net> put finger to keyboard
and composed:

Thanks for all the posts. I have tried the fine tuning. It doesn't
help. I'll look into the RF from the VCR, although I'm actually
connecting through the direct A/V outputs, I expect the VCR RF out is
still active.

Cheers
Glenn

Do you still have this problem if you bypass the VCR by connecting
your TV directly to the wall socket?


Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net
Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net
 
"Glenn Pure" <glenn*delete_this_for_reply*@evans-pure.net> wrote in message
news:gsm9v0tgtgmcrm82obhlu2rbmvg26jhtiq@4ax.com...
Well, I tried changing output channel on the VCR. It made no
difference.

I have yet to try routing antenna straight into the TV (but this won't
be a fix).

Cheers
Glenn
I am sure that there are more than a few people still interested in your
problem.

It would be interesting to know if you have a masthead amplifier and/or a
distribution amplifier feeding extra locations around your house. Under
certain circumstances such a system may become intermittently unstable, and
produce a wide variety of baffling symptoms.

JustMe +2c
 
No masthead amplifier or splitters. The antenna plugs straight into
the VCR and then through to the TV. I replaced the antenna and cable
about a year ago and all has been gong fine until recently. All
connections look clean and some re-positioning of antenna has made a
small difference but not a complete fix.

Cheers
Glenn

"Bill Bailley" <JustMe@Home> wrote:

"Glenn Pure" <glenn*delete_this_for_reply*@evans-pure.net> wrote in message
news:gsm9v0tgtgmcrm82obhlu2rbmvg26jhtiq@4ax.com...
Well, I tried changing output channel on the VCR. It made no
difference.

I have yet to try routing antenna straight into the TV (but this won't
be a fix).

Cheers
Glenn


I am sure that there are more than a few people still interested in your
problem.

It would be interesting to know if you have a masthead amplifier and/or a
distribution amplifier feeding extra locations around your house. Under
certain circumstances such a system may become intermittently unstable, and
produce a wide variety of baffling symptoms.

JustMe +2c
Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net
 
"Glenn Pure" <glenn*delete_this_for_reply*@evans-pure.net> wrote in message
news:hdtev05srfee2fmug5a075c0m2rlco3fk2@4ax.com...
No masthead amplifier or splitters. The antenna plugs straight into
the VCR and then through to the TV. I replaced the antenna and cable
about a year ago and all has been gong fine until recently. All
connections look clean and some re-positioning of antenna has made a
small difference but not a complete fix.

Cheers
Glenn
Yet more interesting. With such a simple set-up there are only a few
possibilities. My money is now on possible DX co-channel interference
facilitated by tropospheric ducting, or perhaps poor RF image rejection by
your TV set.

If the problem just fades away with the changing season, the first
possibility is the most likely answer.

Go digital - the pictures will knock your socks off :<))

Bill.
 
The old TV failed late last year. The new one could be the problem. It
is nothing flash. I will go digital eventually -- thanks for the tips.

Cheers
Glenn

"Bill Bailley" <JustMe@Home> wrote:

"Glenn Pure" <glenn*delete_this_for_reply*@evans-pure.net> wrote in message
news:hdtev05srfee2fmug5a075c0m2rlco3fk2@4ax.com...
No masthead amplifier or splitters. The antenna plugs straight into
the VCR and then through to the TV. I replaced the antenna and cable
about a year ago and all has been gong fine until recently. All
connections look clean and some re-positioning of antenna has made a
small difference but not a complete fix.

Cheers
Glenn


Yet more interesting. With such a simple set-up there are only a few
possibilities. My money is now on possible DX co-channel interference
facilitated by tropospheric ducting, or perhaps poor RF image rejection by
your TV set.

If the problem just fades away with the changing season, the first
possibility is the most likely answer.

Go digital - the pictures will knock your socks off :<))

Bill.
Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net
 
Is there a 'Distant/Local' or similar switch near the RF output from the
VCR?

Ken

"Glenn Pure" <glenn*delete_this_for_reply*@evans-pure.net> wrote in message
news:aqdjv01kbmjt9lokf3ol3h3jk6it4eno41@4ax.com...
The old TV failed late last year. The new one could be the problem. It
is nothing flash. I will go digital eventually -- thanks for the tips.

Cheers
Glenn

"Bill Bailley" <JustMe@Home> wrote:


"Glenn Pure" <glenn*delete_this_for_reply*@evans-pure.net> wrote in
message
news:hdtev05srfee2fmug5a075c0m2rlco3fk2@4ax.com...
No masthead amplifier or splitters. The antenna plugs straight into
the VCR and then through to the TV. I replaced the antenna and cable
about a year ago and all has been gong fine until recently. All
connections look clean and some re-positioning of antenna has made a
small difference but not a complete fix.

Cheers
Glenn


Yet more interesting. With such a simple set-up there are only a few
possibilities. My money is now on possible DX co-channel interference
facilitated by tropospheric ducting, or perhaps poor RF image rejection
by
your TV set.

If the problem just fades away with the changing season, the first
possibility is the most likely answer.

Go digital - the pictures will knock your socks off :<))

Bill.


Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net
 

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