receive CH23 but not 26??

Hi

Was chatting last night to a friend who has installed a PVR for his
parents. All was going well except no CH5 (&c) and he was stuck. I
checked out the info for Waltham and Mux A is on ch 26, so I assumed he
needed a wideband aerial and was spouting off explanations until he
explained that they'd just had a new aerial professionally fitted and it
was a Televes wideband.

So I headed round with my old Pioneer box (not used any more) just to
make sure it wasn't a fault with the PVR and, sure enough, ch26 is next
to no signal.

To top it off, all the other muxes (including ch23) are clear as day, no
picture breakup at all, with the signal level around 25% and green in
the crude Pioneer diagnostic menu.

I'm a bit confused: surely if 23 arrives clearly he should be able to
get 26? They're both transmitted at 4kW from Waltham.

Now my knowledge of aerials is a bit flakey - is there some way you
could mess up the install of an aerial to make this happen?
Unfortunately I couldn't tell which type of cable was used but I'd
assume that equal attenuation of 23 and 26 would occur if substandard
cable was involved?

To be clear, there's definitely nothing on the line to deliberately
attenuate ch26, you can follow the cable down the wall straight into a
wall socket, and all other equipment has been removed from the chain
(just to make sure).

Finally, it's a bungalow so the aerial's lower than it should be (it's
not on a mast) but again, surely that would cause problems for all muxes
if it did for any of them?

Thanks

Geoff

In article ,
Geoff Winkless ] wrote:
Hi

Was chatting last night to a friend who has installed a PVR for his
parents. All was going well except no CH5 (&c) and he was stuck. I
checked out the info for Waltham and Mux A is on ch 26, so I assumed he
needed a wideband aerial and was spouting off explanations until he
explained that they'd just had a new aerial professionally fitted and it
was a Televes wideband.

So I headed round with my old Pioneer box (not used any more) just to
make sure it wasn't a fault with the PVR and, sure enough, ch26 is next
to no signal.

[Snip]

two possible causes that immediately come to mind:

1. A severe bend in the cable giving rise to reflections. This is at a
point where the wavelength of ch26 means that a cancellation happens on
that channel only.

2. The impedance of the tuner is not 75 ohms at ch26. again leading to
reflections and cancellation.

No 2 can be 'cured' either by fitting an attenuator to the input to the
tuner (giving a more constant impedance) or by adding a few more feet to
the downlead and thus change the length.

No 1 is a "by inspection" job.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

charles wrote:
In article ,
Geoff Winkless ] wrote:
Hi

Was chatting last night to a friend who has installed a PVR for his
parents. All was going well except no CH5 (&c) and he was stuck. I
checked out the info for Waltham and Mux A is on ch 26, so I assumed
he needed a wideband aerial and was spouting off explanations until
he explained that they'd just had a new aerial professionally fitted
and it was a Televes wideband.

So I headed round with my old Pioneer box (not used any more) just to
make sure it wasn't a fault with the PVR and, sure enough, ch26 is
next to no signal.

[Snip]

two possible causes that immediately come to mind:

1. A severe bend in the cable giving rise to reflections. This is
at a point where the wavelength of ch26 means that a cancellation
happens on that channel only.

2. The impedance of the tuner is not 75 ohms at ch26. again leading
to reflections and cancellation.

No 2 can be 'cured' either by fitting an attenuator to the input to
the tuner (giving a more constant impedance) or by adding a few more
feet to the downlead and thus change the length.

No 1 is a "by inspection" job.

I've found Belling Lee type wall plates and plugs, especially if used in
conjunction with cheap moulded fly leads, can cause some strange and
mysterious faults. Well worth the few minutes spent checking them out by
substituting the whole lot with a decent quality length of lead, preferably
connected using 'F'connectors.

Geoff Winkless wrote:

I'm a bit confused: surely if 23 arrives clearly he should be able to
get 26? They're both transmitted at 4kW from Waltham.

Don't assume that all six muxes are transmitted omni-directionally
though. There are some transmitters were one or more muxes are
restricted in some directions, to avoid causing interference somewhere
else.

Unfortunately the broadcasters choose not to publish radiation template
in the public domain, however the data should be reflected in
Freeview's (pessimistic) postcode checker. What does that say for his
postcode ?

Mark Carver wrote:

Geoff Winkless wrote:

I'm a bit confused: surely if 23 arrives clearly he should be able to
get 26? They're both transmitted at 4kW from Waltham.

Don't assume that all six muxes are transmitted omni-directionally
though. There are some transmitters were one or more muxes are
restricted in some directions, to avoid causing interference somewhere
else.

Unfortunately the broadcasters choose not to publish radiation template
in the public domain, however the data should be reflected in
Freeview's (pessimistic) postcode checker. What does that say for his
postcode ?

DTG site says:

Muxes received: ALL
Compass bearing: 55°
Distance: 35 kilometres
Aerial group: W Horizontal
Location: Grid Ref SK809233
Aerial elevation: 411 metres

The Freeview site says it's all fine and dandy: "Great news, your home
can see the whole family of Freeview channels."

http://www.wolfbane.com/cgi-bin/tvd.exe says a wideband extra-high gain
aerial is required but I get the feeling that's based mainly on the
distance. There's certainly no mention that any of the channels are less
attainable than others.

The terrain checker at megalithia.com gives an output which looks
reasonable - the aerial is at the top of a fairly large hill (120m AOD),
and there's no obstructions in line-of-sight.

I've recommended they get the aerial contractor back in and give it to
them to fix: it was fitted with the understanding that it would be used
for freeview and it clearly doesn't do the job. I'd have liked to have
able to tell them why though

Cheers to you and Charles & Ivan too for all the suggestions.

Geoff

In article ,
Geoff Winkless ] wrote:
Mark Carver wrote:

Geoff Winkless wrote:

I'm a bit confused: surely if 23 arrives clearly he should be able to
get 26? They're both transmitted at 4kW from Waltham.

Don't assume that all six muxes are transmitted omni-directionally
though. There are some transmitters were one or more muxes are
restricted in some directions, to avoid causing interference somewhere
else.

Unfortunately the broadcasters choose not to publish radiation template
in the public domain, however the data should be reflected in
Freeview's (pessimistic) postcode checker. What does that say for his
postcode ?

DTG site says:

Muxes received: ALL
Compass bearing: 55°
Distance: 35 kilometres
Aerial group: W Horizontal
Location: Grid Ref SK809233
Aerial elevation: 411 metres

The Freeview site says it's all fine and dandy: "Great news, your home
can see the whole family of Freeview channels."

http://www.wolfbane.com/cgi-bin/tvd.exe says a wideband extra-high gain
aerial is required but I get the feeling that's based mainly on the
distance. There's certainly no mention that any of the channels are less
attainable than others.

Wolfbane seems to say that no matter where you are. We are 7km and line of
sight to Beacon Hill and it says the same for us.
We get good digital reception most of the time on a loft mounted 2 element
caravan aerial put up as a temporary measure about 10 years ago.

The terrain checker at megalithia.com gives an output which looks
reasonable - the aerial is at the top of a fairly large hill (120m AOD),
and there's no obstructions in line-of-sight.

I've recommended they get the aerial contractor back in and give it to
them to fix: it was fitted with the understanding that it would be used
for freeview and it clearly doesn't do the job. I'd have liked to have
able to tell them why though

Cheers to you and Charles & Ivan too for all the suggestions.

Geoff

--
Peter Gillett :
Totnes : South Devon

Geoff Winkless wrote:

I've recommended they get the aerial contractor back in and give it to
them to fix: it was fitted with the understanding that it would be used
for freeview and it clearly doesn't do the job. I'd have liked to have
able to tell them why though

For what it's worth, the contractor came back and (quote) "wiggled the
aerial a bit" (technical term, I assume they mean he realigned it
slightly) and it now all works. I've no idea why that meant 23 was ok
but 26 wasn't but I no longer care

Thanks for all suggestions.

Geoff