OT - period TV channels

[MdB]

A 6 way passive splitter will reduce the signal strength by a factor of 10 on each output compared to the input. This is the same as the signal strength you would get 50 miles from the transmitter (3.3 x 15miles) so I don't see this being a problem.

I would guess that any unused outputs should have a 75 ohm resistor across them but I could be wrong on that.

It is also possible that the piece of coax in question is of a length that creates resonance and the tv end is a null point.

I guess this is possible but with a 75 ohm source, cable and load, I would have thought this unlikely.

 

[Lime]

So would I but it is simple to check it.

If digital reception was good with the existing aerial prior to switchover it is quite likely to overload some tvs sometimes.
Dismissing possibilities on the basis of "not probable" may be why the coax problem(?) still exists.

 

[Flyfisher]

Yes, that's a fair point about overloading. Could Me! confirm when the problem actually started? It might be a clue if it coincided with the recent switchover.

Also, does the offending TV work correctly when connected to one of the other aerial wires?

 

[Lime]

It also depends on which transmitter is used.
In East anglia there are 3 main areas, Sandy Heath (main transmitter), Sudbury and Tacolneston.
There are several relay transmitters too.
The changeover is almost complete. Some MUX power changes will happen later this year when London switches over.
The various changeover times so far are listed halfway down in the pdf below:
http://www.digitaluk.co.uk/__data/assets/pdf_file/0019/33274/DG0065_3m_Anglia_3Mnth_1.pdf

 

[Flyfisher]

Me! said the aerial points toward the Tacolneston transmitter.

 

[Lime]

Me! said the aerial points toward the Tacolneston transmitter.

Then the relevant times are the 9th November and 23rd November 2011.

 

[Me!]

Thank you for the suggestions.
The length of coax that is causing the problem has worked fine for about 5 years with the old analogue signals, and it did sometimes work with digital before switchover but was always unreliable with digital. Some days it was fine, and others absolutely nothing, and I assumed that this was because of the low power digital signal being transmitted before the analogue switch-off. Since the full digital switchover, it did work fine for about a week or so, but then it died completely.
The thought of a standing wave node being just at the end of the cable got me thinking “that’s just my luck!”. The BBC frequency seems to be 745.8 MHz from Tacolneston which I believe works out to a wavelength of 40cm, so I’ve just tried cutting 10cm off the end of the coax but that didn’t change anything. I also then tried plugging a very thin, cheap and nasty aerial extension lead onto the end to try and attenuate the signal a bit in case it is too strong, but still no change.

Oh well, off to B&Q (in the snow!) to get some more coax!

 

[Me!]

I've fitted the new length of coax and it is working fine. All four TV sets have a perfect picture even when all on at the same time.
Even now I have removed the old bit, I still can't see anything wrong with it, but it is obviously faulty somehow!

Thank you again for all the help.

 

[Flyfisher]

Have you retried the old bit since removing it? It might have just been crushed or kinked when in situ, perhaps we'll never know. Good to hear that all is now working though.

 

[Me!]

That is an interesting idea from Flyfisher. So, I have just fitted a couple of plugs to the ends of the bit of coax I removed and then plugged it in as an extra extension lead between the new bit and the TV, ... and it works! So, I added more plugs and sockets to the other bits I chopped off either end of the old as part of the diagnostics, and connected the whole lot back together, ... and it still all works
Digital TV, flippin' black magic more like :evil:
Now, where's that old valve wireless I put in the loft? Do they still transmit the light programme?

 

[Penners]

Do they still transmit the light programme?

Yes, but only in black-and-white.

 

[Flyfisher]

I have just fitted a couple of plugs to the ends of the bit of coax I removed and then plugged it in as an extra extension lead between the new bit and the TV, ... and it works! So, I added more plugs and sockets to the other bits I chopped off either end of the old as part of the diagnostics, and connected the whole lot back together, ... and it still all works
Digital TV, flippin' black magic more like :evil:

Adding the old cable as an extension to the new cable is not quite an equivalent test because of the different overall length (thinking about the too-high-signal-strength possibility), but I know what you mean about digital black magic and I'd also be thinking that life's too short to worry too much about such things. The new cable is working, the old cable can go into the bin, job done.

The home service on a valve wireless sounds good though.

 

[Penners]

The home service on a valve wireless sounds good though.

In my distant youth I had a huge Bush valve radio with a walnut cabinet - it was the size of a moderate suitcase. It took ages to warm up, but had a wonderful sound quality and tone. I was addicted to Journey Into Space, PC 49, Riders of the Range and Dick Barton, Special Agent.

I think I'm sounding rather old, am I not? I wonder why.

 

[Lime]

I bought a copy of the series Journey into Space from an american website a couple of years ago.
I used to recall the programme from childhood with great excitement and affection.

The recordings now sound a bit different to my adult, worldly ear.
There is a lot of talking (obviously) but also a lot of fading in and out of scenes that sound clumsy and crude on my hifi system.
Far better to be young, listening to it crouched over a big warm radio with nothing to worry about except the weekend's homework and trying to hear over the loud crackles of interference (from mum's electric iron plugged into the light) while snatching the last vestige of my day before bedtime.

A spaceman with a very strong australian accent and another with the voice of Bootsie (from Bootsie and Snudge) come over strongly, somewhat marring the whole atmosphere.
Then there is the scene when they first get up into orbit around the Earth and the crew begin to relax before the journey to Mars.
To celebrate the successful launch they each light up a cigarette in the space ship!
I found that exceptionally funny but it lost the wonder the series once held for me.
It threw the series back to whence it came, a long time ago in my young life, which filled me with sadness.

Sometimes it is best to leave things in the past.