TV Signal Amplification

petetobin

Standard Member
We have a bathroom tv which until yesterday was working well using a USB powered tv amplifier sited under the bath. I share an aerial with the flat downstairs and they were complaining about their signal so they got an aerial guy up on the roof and discovered that the aerial pole had corroded and detached from the wall. He installed a completely new pole, aerial and splitter and their signal is now amazing. I now get pixelation on certain channels without the amp but with the amp attached the signal on all the channels is much worse/unusable. i can only assume that the reason the amp makes the sreveption worse is that it is over boosting the signal. The amplifier is 20db and doesn’t have a built in attenuator. Would it be worth trying an attenuator before the amp to see if I can find a happy balance? I think the underlying problem may be the quality of my cable run but it is a massive house so replacing it is non-trivial. The problem is not the amp, I have tested it and it works fine. Without the amp I get SS and SQ of 100 on BBC but an SQ of 20ish on ITV and C4.
 

petetobin

Standard Member
Thanks, I have ordered an attenuator from Amazon and will give it a go tomorrow. It never occurred to me that it could be the problem but it’s the only logical explanation of what’s happening. I can’t see how the splitter can be powered as there is no power up there and the boys downstairs have a Youview box which probably has a better tuner than my Waterproof TV.
 

Rodders53

Distinguished Member
Location (approx) to estimate signal strength available.
What style of aerial has been installed? (to estimate it's gain).
A 2-way passive split is -4dB loss.
Receivers need 45-65 dB input in the ideal range (+/- a bit more depending on sensitivity etc.,. )
So with the first two I can guesstimate if overload could be possible in a passive split situation. (It's possible but rare).

Masthead amplifiers have indoor power units, check if there is one in your neighbour's (or in a shared loft space etc.,.)

I'm guessing there's more than this waterproof TV in your dwelling... so how many outlets and how are they fed (passive or amplified splitter)?
 

petetobin

Standard Member
Thanks for your help. I fixed the problem today by installing 10db of attenuation in front of the 20db amplifier. I must have a very sensitive "goldilocks" tuner as with no amplification I was getting low signal pixelation and with 20db amplification I was getting high signal pixelation. Installing the attenuator has now got me to 100 for SS and SQ on all channels (measured using the tv) and no pixelation.

By the way, the tv was installed professionally and the transformer is tucked away in a watertight box away from the main danger of water ingress. Luckily I had the foresight to leave the 5V USB port exposed which I used to power the Amp.
 

petetobin

Standard Member
Location (approx) to estimate signal strength available.
What style of aerial has been installed? (to estimate it's gain).
A 2-way passive split is -4dB loss.
Receivers need 45-65 dB input in the ideal range (+/- a bit more depending on sensitivity etc.,. )
So with the first two I can guesstimate if overload could be possible in a passive split situation. (It's possible but rare).

Masthead amplifiers have indoor power units, check if there is one in your neighbour's (or in a shared loft space etc.,.)

I'm guessing there's more than this waterproof TV in your dwelling... so how many outlets and how are they fed (passive or amplified splitter)?
Turns out that with the previous damaged aerial and the 20db amplifier, I able to hit the sweet spot for the tuner. When the aerial was damaged, although my picture still worked, it stopped for the guys downstairs. They repaired the aerial improving the signal enough for them to get a good signal but too much for my tuner which was then in a place where the signal was too weak without the amp and too strong with it, hence the need for the attenuation.

The one data point I did get from the installer was that my signal was weaker than the flat downstairs which I guess must be down to the age of my cabling. I am pretty sure he said 50db which is at the low end of your range.

I am not that far away from the transmitter (5 miles or so) but I live on Hove Seafront which is in a dip so I don't have line of sight. That, plus the unpowered splitter, my poor tuner, the long 30m cable run and the quality of the cable obviously are at the route of the problem but we have multiple tv aerials and satellite points so that aerial only serves the bathroom and the flat downstairs.

@Rodders53 the one thing I don't fully understand is why the signal is great without the Amp from one MUX and really poor from another. The result is that BBC was great but ITV and C4 were pixelating without the Amp. Assuming the transmission power is the same (which should be 4kW), I can only think it is an alignment issue or the effect of the environment between me and the transmitter, Is that right? Both MUXs are DTG-3 (Mode 3), the only difference is the frequency. Could the cable quality cause that?
 

Rodders53

Distinguished Member
Hove, Brighton.

Could be reception form the Rowridge I-oW transmitter, or the nearer Whitehawk Hill transmitter.

TV may be finding and tuning the other first with poorer results? (Auto tuning on older sets often starts at 21 and goes up... if a good enough mux is found that can be stored rather than the wanted better version at a higher frequency. Manual tuning is the fix for that.)

Aerial gain isn't often 'flat' so may collect more on one frequency cf the other
ATV aerial gain tests : all the gain curves - A.T.V. Poles, Brackets, Clamps & Aerials
So, potentially one above and the other below the digital cliff-edge of reception.

BBC SD = 48 WHH, 24 ROW
ITV SD = 35 WHH, 27 ROW

BBC local news is from Tunbridge Wells (BBC SouthEast) ex WHH, but from Southampton (BBC South) ex ROW so that might also help identify things?
Similar arrangements for ITV Meridian news.
 

Clem_Dye

Distinguished Member
I just don’t trust combinations like that! An electric kettle is one thing, but standing under an electric shower, if it develops a fault which might result in electrocution, doesn’t sit right with me. Strange perhaps, but that’s just how my brain is wired.
 

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