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Old 8th Nov 2018, 10:37 am   #1
CambridgeWorks
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Default TV aerial amp and splitter works when switched off!

Several years ago I fitted a used Labgear MSE143 4 way amp in the airing cupboard when rewiring my aerial system to 4 rooms. About 3 years ago tv programmes started breaking up as they do with digital and weak signal. I bypassed the co-ax to the main tv, all ok.
In my workshop I replaced the main smoothing caps first ad they were old and been in a warm environment.
I then made a couple of bnc to belling lesds to crudely test with my 50 ohm spec tracking gen and analyser.
Output level was between +1.5 and +2 db on each port.
I refitted it and all was ok.
Fast forward to this week, it played up again. Seeing it had moved a bit under the shelf I unplugged and replugged all connections.
All ok again.
Yesterday, same low signal happened again first thing in the morning. I switchef it off at the mains. My wife shouted "thats better". I switched on and still ok. I switched off and the last 24 hours it has been off, the 2 main tvs (only ones in daily use) still work perfectly!
I will need to remove it and put on the bench to test again, but any ideas what is going on?
All I can think is the digital signal from Waltham is so great it doesn't need amplifying to split outputs and some instability occurs corrupting the signal causing the problem
But, I am not aware of the signal being so large here. Also, a fet, transistor or whatever is used would be quite an attenuator when unpowered?
Rob
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Old 8th Nov 2018, 10:58 am   #2
Boater Sam
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Default Re: Tv aerial amp and splitter works when switched off!

I had had many problems with TV aerial amps and powered splitters over the years.
Some amps are so slow that they fail to give any worthwhile results on the digital signal I find.
With the reasonable signal strength being available in most areas now, I have just a decent aerial ( long folded log periodic ) and no amp at all.
I have found that when we are in a really bad signal area, like Banbury, and being low down on the water, nothing will make any useful difference. Line of sight to the mast is still the best way.

Last edited by Boater Sam; 8th Nov 2018 at 10:59 am. Reason: add
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Old 8th Nov 2018, 10:59 am   #3
paulsherwin
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Default Re: Tv aerial amp and splitter works when switched off!

Well, if it's unpowered then it can't be amplifying, so it must be operating as a passive splitter. It sounds as if your signal strength is better than you thought.
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Old 8th Nov 2018, 11:17 am   #4
OscarFoxtrot
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Default Re: Tv aerial amp and splitter works when switched off!

I think some tellies or set top boxes can send a voltage up the co-ax to power masthead amps, so you don't need a separate power unit
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Old 8th Nov 2018, 11:34 am   #5
G6Tanuki
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Default Re: Tv aerial amp and splitter works when switched off!

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Originally Posted by OscarFoxtrot View Post
I think some tellies or set top boxes can send a voltage up the co-ax to power masthead amps, so you don't need a separate power unit
Yes, it's quite a common 'feature'. Is usually turn-on-and-offable in one of the configuration menus.
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Old 8th Nov 2018, 12:18 pm   #6
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Default Re: Tv aerial amp and splitter works when switched off!

Ok. Just had the amp on the bench, undisturbed and immediately it showed the small gain as when normal. A few seconds later the output dropped erratically by about about 25dB. I powered off and on and it showed the same fault. Then, after about 30 seconds resumed normal gain and would not fault with tapping, banging etc.
So, I concluded the signal level is way above what I thought and the amplifier was not needed, but a splitter was.
A quick experiment removing a couple of smd caps and fitting a short wire link resulted in a ripple loss of about 10 - 15dB worst case on any output and between 470 and 870Mhz.
So, crudely sorted my problem and saves 10p of electricity!
I only have tv, no boxes.
So, Paul, yes, I do have a very strong signal.
Btw, It is the splitter to 4 tv that is the requirement, not masthead amp.
Thanks all,
Rob
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Old 8th Nov 2018, 1:07 pm   #7
paulsherwin
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Default Re: Tv aerial amp and splitter works when switched off!

I used to have a preamp in the loft, but after the Freeview muxes had their power increased I started getting glitching on some boxes because they were overloading. This hadn't been a problem with analogue or low power Freeview. I removed the preamp and all was fine.
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Old 8th Nov 2018, 1:20 pm   #8
Welsh Anorak
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Default Re: Tv aerial amp and splitter works when switched off!

We get occasional calls from people moving into their new house and getting no signal. Remedy - find the amplifier in the loft or airing cupboard, and switch it on!
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Old 8th Nov 2018, 1:35 pm   #9
G6Tanuki
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Default Re: Tv aerial amp and splitter works when switched off!

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Originally Posted by Welsh Anorak View Post
We get occasional calls from people moving into their new house and getting no signal. Remedy - find the amplifier in the loft or airing cupboard, and switch it on!
Yes, though it's also quite common for people moving house to take the power-injector (that normally loiters behind the telly) with them when they move, thinking it's something they need at their new house.
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Old 9th Nov 2018, 9:38 pm   #10
MotorBikeLes
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Default Re: Tv aerial amp and splitter works when switched off!

This is very interesting. I managed to have no TV in the living room for over a year, but now one has been fitted by decree from above. She has one in the bedroom, watched for a while most nights, and periodically I received complaint of "Only BBC works properly", with breakup on Ch 4 etc. I have now seen this on the living room set, something that normally only happened when a dozen trail bikes come past the cottage. I have a bowtie looking across the Irish sea to the transmitter there (no local signals can be picked up) and that has always had a high gain masthead amp fitted. Is this signal breakup due to too much signal perhaps? I never knew signal strength had been increased. When we first got digital signals, still with analogue for a year or so, we had a fair signal from the get go, providing the the Irish Sea was "quiet". Must I try without the masthead amp, or maybe try a lower gain one instead?
Les.
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