Is there any known problem with the Freeview decoder in a BT Vision box that 
makes it need a stronger aerial signal than other Freeview decoders?

I was installing a BT Vision box for a customer last night and I noticed 
that most channels had very pixellated, blocky pictures with lots of JPEG 
artifacts around contrasty edges when decoded through the BT Vision box 
(connected by SCART to the TV) whereas the same channels viewed through the 
TV's built-in Freeview decoder were better - though still more blocky and 
artifacty than I'd have liked. The BT Vision box reported DTT signal 
strength of about 40% for most channels, although the signal quality was 
100%.

The incoming aerial goes into the BT Vision. The aerial output from that 
goes in a VCR and the aerial output of the VCR goes into the TV.

In article <1JCdnWhp7Mj6Z7zVnZ2dneKdnZydnZ2d@plusnet>, Mortimer 
 writes
>Is there any known problem with the Freeview decoder in a BT Vision box that
>makes it need a stronger aerial signal than other Freeview decoders?
>
>I was installing a BT Vision box for a customer last night and I noticed
>that most channels had very pixellated, blocky pictures with lots of JPEG
>artifacts around contrasty edges when decoded through the BT Vision box
>(connected by SCART to the TV) whereas the same channels viewed through the
>TV's built-in Freeview decoder were better - though still more blocky and
>artifacty than I'd have liked. The BT Vision box reported DTT signal
>strength of about 40% for most channels, although the signal quality was
>100%.
>
>The incoming aerial goes into the BT Vision. The aerial output from that
>goes in a VCR and the aerial output of the VCR goes into the TV.

One does wonder if something was double- or un- terminating the RF feed. 
Did you try them in a different order, and/or just the BT box on its own 
with a 75 Ohm terminator across the output?

Signal 'quality' of 100% doesn't tell you very much and is evidently 
misleading in this case...

Regards,

Simonm.

-- 
simonm|at|muircom|dot|demon|.|c|oh|dot|u|kay
SIMON MUIR, BRISTOL UK
EUROPEANS AGAINST THE EU                   http://www.eurofaq.freeuk.com/
GT250A'76  R80/RT'86  110CSW TDi'88  www.kc3ltd.co.uk/profile/eurofollie/

"Mortimer"  wrote in message 
news:1JCdnWhp7Mj6Z7zVnZ2dneKdnZydnZ2d@plusnet...
> Is there any known problem with the Freeview decoder in a BT Vision box 
> that makes it need a stronger aerial signal than other Freeview decoders?
>
> I was installing a BT Vision box for a customer last night and I noticed 
> that most channels had very pixellated, blocky pictures with lots of JPEG 
> artifacts around contrasty edges when decoded through the BT Vision box 
> (connected by SCART to the TV) whereas the same channels viewed through 
> the TV's built-in Freeview decoder were better - though still more blocky 
> and artifacty than I'd have liked. The BT Vision box reported DTT signal 
> strength of about 40% for most channels, although the signal quality was 
> 100%.
>
> The incoming aerial goes into the BT Vision. The aerial output from that 
> goes in a VCR and the aerial output of the VCR goes into the TV.

My neighbours have serious reception issues with their BT Vision. Their loft 
mounted aerial is a compromise and is waiting for me to replace it with an 
outside installation (which as they live in a chimneyless bungalow is 
waiting for me to obtain a 16' mast.) However they also have a Philips 
Freeview box which suffers only periodically. So the answer to your question 
is "possibly!"

"Doctor D"  wrote in message 
news:qpSdnR13J8LLkL_VnZ2dnUVZ8s6inZ2d@plusnet...
>
> "Mortimer"  wrote in message 
> news:1JCdnWhp7Mj6Z7zVnZ2dneKdnZydnZ2d@plusnet...
>> Is there any known problem with the Freeview decoder in a BT Vision box 
>> that makes it need a stronger aerial signal than other Freeview decoders?
>>
>> I was installing a BT Vision box for a customer last night and I noticed 
>> that most channels had very pixellated, blocky pictures with lots of JPEG 
>> artifacts around contrasty edges when decoded through the BT Vision box 
>> (connected by SCART to the TV) whereas the same channels viewed through 
>> the TV's built-in Freeview decoder were better - though still more blocky 
>> and artifacty than I'd have liked. The BT Vision box reported DTT signal 
>> strength of about 40% for most channels, although the signal quality was 
>> 100%.
>>
>> The incoming aerial goes into the BT Vision. The aerial output from that 
>> goes in a VCR and the aerial output of the VCR goes into the TV.
>
> My neighbours have serious reception issues with their BT Vision. Their 
> loft mounted aerial is a compromise and is waiting for me to replace it 
> with an outside installation (which as they live in a chimneyless bungalow 
> is waiting for me to obtain a 16' mast.) However they also have a Philips 
> Freeview box which suffers only periodically. So the answer to your 
> question is "possibly!"

I've recommended that my customer gets his aerial checked: the cable is a 
very thin coax, rather than the normal type which is about twice as thick 
(so there may be more attenution) and the plug on the end was loose on the 
cable: I tried removing it and making sure there was a kink in the end of 
the solid core so it made good contact with the tip of the plug, and made 
sure the braid made good contact with the strain-relief insert and hence 
with the body of the plug; I also checked for stray wires from the braid 
shorting to the tip. All of this gave me a slight improvement, but new 
low-loss cable, a wide-band aerial, correctly aligned, and maybe a masthead 
amplifier may improve things. Certainly www.wolfbane.co.uk is recommending 
"Amplified extra hi-gain".

>> My neighbours have serious reception issues with their BT Vision. Their 
>> loft mounted aerial is a compromise and is waiting for me to replace it 
>> with an outside installation (which as they live in a chimneyless 
>> bungalow is waiting for me to obtain a 16' mast.) However they also have 
>> a Philips Freeview box which suffers only periodically. So the answer to 
>> your question is "possibly!"
>
> I've recommended that my customer gets his aerial checked: the cable is a 
> very thin coax, rather than the normal type which is about twice as thick 
> (so there may be more attenution) and the plug on the end was loose on the 
> cable: I tried removing it and making sure there was a kink in the end of 
> the solid core so it made good contact with the tip of the plug, and made 
> sure the braid made good contact with the strain-relief insert and hence 
> with the body of the plug; I also checked for stray wires from the braid 
> shorting to the tip. All of this gave me a slight improvement, but new 
> low-loss cable, a wide-band aerial, correctly aligned, and maybe a 
> masthead amplifier may improve things. Certainly www.wolfbane.co.uk is 
> recommending "Amplified extra hi-gain".


Wolfane usually recommends that.
This website http://www.digitaluk.co.uk/ is better though you should tick 
the aerial trade box for more information.

The cable is of paramount importance, and is sounds as though that one is 
decidedly dodgy! Some people solder the plug for better results.

A wideband aerial may make matters worse. It has less gain than a grouped 
aerial, so only use one if your transmitter requires it.
Likewise an amplifier. Use one if required but go easy on the gain, and make 
sure it's a well screened unit.

For my neighbour, I have an unused Antiference TC18E (Sutton Coldfield) 
ready to go up with Webro WF100 cable and a Labgear variable gain screened 
masthead amplifier. All it needs is the wretched 16' mast, which are like 
hens teeth to get delivered to the door!

Doctor D wrote:
> 
> Wolfane usually recommends that.
> This website http://www.digitaluk.co.uk/ is better though you should 
> tick the aerial trade box for more information.

That one suggests Oxford might be a possibility for me, despite 
Watlington Hill (755 ft) being on the line-of-sight path to my house.

And no hints on aerial, beyond the group...

Andy

Andy Champ wrote:
> Doctor D wrote:
> 
>>
>> Wolfane usually recommends that.
>> This website http://www.digitaluk.co.uk/ is better though you should 
>> tick the aerial trade box for more information.
> 
> 
> That one suggests Oxford might be a possibility for me, despite 
> Watlington Hill (755 ft) being on the line-of-sight path to my house.
> 
> And no hints on aerial, beyond the group...
> 
> Andy

Try here to see what is in the way.

http://www.megalithia.com/elect/terrain.html

Mike

"Andy Champ"  wrote in message 
news:3_adncRu_aYAzL7VRVnytQA@eclipse.net.uk...
> Doctor D wrote:
>>
>> Wolfane usually recommends that.
>> This website http://www.digitaluk.co.uk/ is better though you should tick 
>> the aerial trade box for more information.
>
> That one suggests Oxford might be a possibility for me, despite Watlington 
> Hill (755 ft) being on the line-of-sight path to my house.
>
> And no hints on aerial, beyond the group...
>
> Andy

It certainly won't give any advice on the type of aerial required.
By ticking the aerial trade box you've indicated that you're tooled up with 
an analyzer, know how to use it :-) and will pick and install the correct 
aerial.

For several postcodes I've tried it seems fairly accurate - if a little 
pessimistic.