"Power Leakage" on Remote Fed TV Booster

[Paul-man]

I have a Labgear remote powered distribution box which I've had about 4 years. However, I am already on to my 3rd PSU and that one I believe is on it's way out.

My set up is as follows:
1 TV aerial mounted on side of house externally (upgraded since buying amplifier) we are in a poor signal area due to trees blocking route to Crystal Palace transmitter) in to labgear box.

1 FM Radio loft mounted and connected to UHF port.

1 cable from labgear box to PSU (and back!)
1 fly from PSU to set-top box (YouView)
1 fly from YouView to TV, with the RF Port through enabled on YouView Box

1 cable from labgear to bedroom (PF100), into You view box
1 fly lead from youview box to TV (as above)

1 older cable from labgear to radio unit in lounge.

I phoned labgear technical to ask why I was losing so many PSUs. They told me that I must have a "leak" on my system that was causing it to leak power. He advised me to check everything for loose connections etc.

I asked if the buzzing would stop if I fixed it - he said he thought it might!

So I stripped everything out, so it was just the TV aerial, down to the PSU and nothing connected to TV. Still buzzing! I'm pretty sure all the connections on that were good. I have used screw on F-connectors throughout the installation.

Does the labgear guy's explanation sound reasonable? (I dont know what causes transformers to go buzzy!) or is he trying to palm off the problem due to an unreliable product?

How can I go about looking for leaks? Any kind of tester?

 

[winston1]

Although nothing to do with your problem the FM aerial should be connected to the VHF port not UHF.

What do you mean by "1 cable from labgear box to PSU (and back!)"? In particular I'm puzzled by (and back). There should be one cable only.

Everything else looks OK. Where is the power supply? It needs to be ventilated not say in loft insulation.

The only 'leak' can be in cable between power supply and amplifier so I thing he is woffling. Transformers buzz due to loose laminations or cheap transformers.

 

[Paul-man]

There is only 1 cable, but it is obviously taking the UHF/VHF signal from the amp to the PSU and the power from the PSU to the amp!

The radio is probably connected to the VHF (and TV in UHF) - I'm not at home so couldn't check, but presumably it'd not work at all otherwise.

I have always mounted the PSU to the wall. It is behind a TV unit and the outside of the wall gets warm (South Facing), but it is a cavity wall, so I wouldn't have thought it would cause it to overheat.

Could lightning be a factor?

Could bare wire hanging out from connector be a problem? (ie if I after screwing on the F-Connector, there was still excess? I have now trimmed this back, but wondered if it could be a source of the problem

 

[Sam Gangee]

So I stripped everything out, so it was just the TV aerial, down to the PSU and nothing connected to TV. Still buzzing!

No surprises there. Most aerials are effectively a short-circuit for DC so DO NOT connect an aerial to a PSU.

Labgear was taken over by Philex. It sounds as if you were speaking to a Philex salesman. Definitely not an engineer.

Labgear used to be quite high quality but, since Philex took over, it wouldn't surprise me if they have found ways to "reduce the cost of production".

Triax/Wolsey tends to be more reliable. This is what I'd recommend:-
http://www.satcure.co.uk/accs/page11c.htm#dab

 

[Paul-man]

Thanks guys for your help.

I didn't actually mean that I connected the aerial to the PSU - I had the aerial into the amp and the downlead from the amp to the PSU connected and nothing else- hoping the buzzing would stop! Wishful thinking. It does go quietly occasionally.

Just a quick one - is it safe to have it plugged in whilst buzzing / while we go out? I'm away and Mrs at home with littlun and we're all worrying if it is safe.

 

[Sam Gangee]

Nobody can guess "is it safe?"

How's your insurance?

Make sure that it's correctly screwed to a wall that is made from bricks or concrete, with nothing flammable nearby.

 

[Paul-man]

Rgarding the link posted - I presume you are referring to this PSU?

C46367 PSU


Will this be compatible with the amplifier I already have, or will I need to replace that too?

 

[Sam Gangee]

I have no idea. I linked to the Triax amplifier.

 

[Paul-man]

Sorry- read masthead and moved on down!

 

[Sam Gangee]

It's a professional aerial amplifier. It can be mounted in the loft but the nearer to the aerial the better.

 

[Paul-man]

Thanks.

So I could move it (the amplifier) to the other side of the loft (5m away) where the aerial comes in, but it would mean that some of my existing downleads would have to be joined and extended, so there is a trade off - which scenario is going to make it most reliable? (some of the leads provided aren't in use at the moment- just been provided for future use.
About to extend and run some additional wires so makes sense to get it right this time!

 

[Sam Gangee]

It makes no sense to amplify the noise picked up by/generated by 5 metres of cable. That's not to say it will harm to try it but why put an amplifier in a non-ideal position? The whole purpose of a signal amplifier is to boost the "clean" signal before it deteriorates in the cable.

Properly made joints will have negligible effect on the signal.
http://www.satcure.co.uk/tech/extend_cable.htm

 

[winston1]

Just a quick one - is it safe to have it plugged in whilst buzzing / while we go out? I'm away and Mrs at home with littlun and we're all worrying if it is safe.

Transformers often buzz. Ever walked passed an electricity sub station?

 

[winston1]

It's a professional aerial amplifier. It can be mounted in the loft but the nearer to the aerial the better.

It is a distribution amplifier not a mast head type for weak signals. Although nearer the aerial the better in theory with a distribution amplifier it probably won't make any difference as the signal 'should' be good at the input.

 

[Sam Gangee]

The one I linked to is definitely a low-noise (2.5dB*) "masthead" amplifier. A distribution amplifier generally has a noise figure of 3.5dB or worse because, as you say, it's designed for a stronger signal that is coming from, say, a Sky Digibox RF output. I wouldn't connect an aerial directly to a distribution amplifier unless the signal is definitely known to be high enough.

*A broadband amplifier (UHF + VHF) will always have a worse noise figure (e.g. 2.5dB) than a narrowband (UHF only) amp (e.g. 2dB).

With few exceptions**, a transformer that didn't buzz originally is definitely faulty if it buzzes subsequently. However, a pulse transformer in a Switch Mode PSU won't make any audible noise at all unless there's a fault.

**The exception is where a cheap & nasty transformer has been assembled with laminations that have come loose. If this happens, I wouldn't trust it anyway. It's converting more of the energy into sound and heat, which means its efficiency has gone down.

In many cases, use of the wrong equipment - or connecting it in the wrong place - will make no discernible difference. You'll find nothing wrong with the picture or sound. The problems won't be observed until something deteriorates - for example, the attenuation of the cable outdoors increases with age.

Doing it right will give you a better margin.