VCR seems to block BBC1 & 2 signal

Col the Mol

Standard Member
Hi,

I am a bit lost and wonder if anyone could advise me.

I am trying to sort out my elderly father-in -law's TV which has been playing up since we all had to re-tune our Freeview boxes recently.

He did not have Freeview but his analogue signal seemed to become worse after the re-tune, so he bought himself a new Panasonic viera set with a built in digital tuner. He complained to me that he was still getting a poor picture on his new set on the original four channels, but the new channels were fine. When I checked he was getting the original four channels on analogue, so I got the set to search for digital channels, with the original loft aerial plugged direct into the set. All was then well as it found all the channels and everything was digital. However when you plugged the aerial in through the vcr, then BBC1 and BBC2 showed a no signal message on screen.

I consulted the man at Curry's who suggested that the signal may be too weak to run the VCR and TV, which sounded plausible to me. I bought a Labgear 27885LAB Megaboost Amplified Outdoor Aerial kits from Screwfix and fitted that, but it makes no difference. The green light is on the booster box and i'm reasonably confident that all the connections are OK. The aerial lead runs direct from the box on the mast to the PSU and the supplied lead runs from the box to the TV. If you connect the in and out aerial leads behind the VCR to by-pass it, then all stations are available on digital.

What do you think? Have I missed something or do I need some more kit?
 

JayCee

Distinguished Member
What do you think?

The analogue signals weren't affected by the recent Digital retune.
If the analogue channels on the TV are worse only when the VCR is switched on it's probably just the VCR modulator needing adjustment.
If they're poor with the VCR in standby it's probably a fault in the VCR.
 

Geofbob

Well-known Member
As I read your post, when the signal runs directly into the TV, all channels - on both analogue & digital - are OK; but when the signal runs through the VCR it is weak, even when boosted. (And apparently it always was weak, since you refer to 4 analogue channels, so presumably Channel 5 was always missing.) The "culprit" therefore definitely seems to be the VCR. As JayCee says, the retune itself is irrelevant, since it didn't affect analogue channels.
 

Gavtech

Administrator
...so I got the set to search for digital channels, with the original loft aerial plugged direct into the set. All was then well as it found all the channels and everything was digital. However when you plugged the aerial in through the vcr, then BBC1 and BBC2 showed a no signal message on screen.

I think the modulator channel setting will be the problem, as Jaycee says above. [ although only referencing the analogue channels]

This can also take out the digital channels.

If you know the transmitter, suitable modulator channel setting options can be provided.
 

Col the Mol

Standard Member
Thanks to you all for your input. I haven't a clue what is meant by the modulator channel settings, but the signal comes from Rowridge on the Isle of Wight. If someone can tell me what they should be I'll try and adjust them to suit.

Thanks again
 

Gavtech

Administrator
Thanks to you all for your input. I haven't a clue what is meant by the modulator channel settings, but the signal comes from Rowridge on the Isle of Wight. If someone can tell me what they should be I'll try and adjust them to suit.

Thanks again

The VCR intakes the normal channels on it's aerial and 'modulates' it's own output onto a channel resembling a conventional TV channel so that a TV can tune into it and see the VCR's output [ It was the old way of getting TV's to 'see' VCR's. Direct connection is much better]

Traditionally, the middle part of the waveband was the emptiest and so VCR's were usually shipped with their modulator outputs set to channel 36 which had the best chance of not causing interference.

That makes it a good candidate as being the cause of the problem here because the Multiplex that carries the BBC channels is on channel 34 from Rowridge, which, assuming the VCR is set at channel 36 is close enough to knock out the BBC Mux channel.

It may also be knocking out Mux C which is on channel 37 from Rowridge

[ You can see a list of what channels are on each Mux here.]

The objective here is to tune the VCR modulator away from any channels where it may cause interference with wanted channels

The full waveband goes from Channel 21 to 68.
All the wanted channels from Rowridge are in the top half of the waveband from channels 21 to 37, thus you need to tune the modulator up to anywhere beyond channel 40 to give a few good channel spacings away from any wanted channels.... but see the following.

For complex reasons, channels that are + or - 5 channels, or + or - 9 channels away form any wanted channel should also be avoided.

On this basis, anything setting at channel 47 or above should be satisfactory.


You may run into a snag here depending on the age of the VCR.
Very old VCR's could only vary their modulator setting by a few channels... perhaps + or - two channels either side of Channel 36... usually by a tuning slug on the modulator itself near to the aerial connections.

Later models moved to a wider but still limited range but still adjusted by tuning slug.

Later still, and tuning control was moved to software control and usually covered the entire band from 21 to 68.

You'll have to check the VCR manual to determine the type of adjustment and the range available.
 

Col the Mol

Standard Member
Thanks Gavtech,

I did as you suggested and all is now well. Changed the VCR to channel 47 after a bit of a struggle but I now know more than before!

Thanks again to you all.
 

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