Masthead Amplifier testing

[naz1054]

Hopefully someone is able to help. I have brought a house and the previous owner used Virgin for his TV. I am not subscribed to any services so want to use Freeview. There is already a loft antenna with the following step:

Antenna > Masthead Amplifier > Split to two TV outlets.

The TV is downstairs and the cable from from the Amp runs down the house would have to be at least 7 meters run. The TV gets a signal but not a very good signal, so most channels are blocky, with radio stations mostly working well and a few low resolution channels like Dave ja Vu working well. Overall on auto scan it detects 50 channels. I got myself a TV signal tester and the results are as follows:

1. Reading with tester plugged in directly to antenna in the loft - 60DBuV
2. Reading after the amplifier - 60DBuV
3. Reading at TV - Nothing

The location is in a high reception area, 7 miles from a major transmitter that covers most the region. In reality even at the antenna the signal should be stronger however from what I have read it still should be ok. There is a 4g transmitter nearby and a 5g one however most channels should not overlap from what I have read. Although I did still put a 4g filter to see if that made any difference and it did not.

Interestingly enough, if you plug the tester into the cable that runs to the TV, that returns a 50DBuV reading aswell.

My question is the amplifier should boost the signal by 24Db if I understand correctly, however from the tester results it looks like it does nothing, is my understanding correct? I have already brought a new PSU which it is running. The Amp appears to be working fine from the lights that are on. What should be the next thing I should check?

 

[winston1]

Bypass the amp and connect one TV directly to the aerial. If that works try a 2 way splitter instead of the amp. Amps are often installed unnecessarily by unqualified people.

 

[naz1054]

Thanks Winston.

Forgot to mention that in the original post, did try that because I suspected the Amplifier could be at fault, however that made no different if not a bit worse. I have been in the loft again, tracing the cables. So turns out there are three outlets for the TV and the masthead is a variable amplifier.

So, I have gone around the outlets testing the the output, the results:
Upstairs bedrooms - tester shows 50DBuV
Downstairs both sockets shows nothing.

Went up again into the loft with the tester, started adjusting the Masthead with the tester attached, changing the gain did make a difference and got all the way upto 80DBuV. Went back down to the to outlet the TV is and tester still showed nothing however the TV reception had improved. The result was picked up about 60 channels in total, some BBC channels are no longer pixelated inc HD, however channels are still pixelating.

Its not quite all the channels yet, but not sure what the next steps would be. It appears the cable length is quite long, its hard to trace the cable, but it runs from the loft to the eaves and then down, but its not on the external wall, so its routed somewhere inside the house. Long story short I would say then length of the cable is around 10m and chased into the walls. The other runs from the splitter are on the outside. There appears to be a lot of cable loss or its running close to power cables.

Currently there is quite a basic aerial, I would say appropriate for the fact that the area overall is a strong reception. Would flipping to a high gain aerial make a difference.

 

[Lucid]

It sounds like your meter tells you about signal strength but doesn't tell you anything about signal quality. That's the more important part of the deal. It's possible to take a really crappy signal and amplify it to kingdom come but the results will still be garbage even though the strength is through the roof. Conversely, you could have quite a weak signal but it's really clean and get great reception.

There is a way you can get some information about the quality. Most TVs with a digital tuner have some built-in metering. It reports on strength and on quality. You'll generally find this in the TVs tuning menus. Have a look under Manual Tuning. The metering might be quite basic though, so you might have to make some allowances when you read it. You could also find that it's a little on the optimistic side.

Where a TV's metering comes in handy though is that it reports on each mux rather than the average of the whole signal. This helps paint the picture of which are the stronger and weaker muxes, and what the quality of each is like. The reason this is useful is that each mux has its own frequency, and because of the spread of frequencies, some muxes may be at points where the aerial's reception is strong whilst others are now at weaker points following the reshuffling to accommodate the sell-off of the upper frequencies of the RF band for 4G ad 5G.

Changing your aerial for a higher-gain model may help, but it has to be the right reception profile to match the frequency distribution of your muxes as they sit now. Ordinary wideband high-gain aerials are becoming less relevant. They have their strongest reception at the upper end of the old ch21-68 range. A big chunk of that has been sold off. Once all the dust settles then the new range will be from RF channel 21 to 49 inclusive.

For most of us who need more gain, a group A or group B aerial will give the strongest signal. Groups C/D, E and wideband are now redundant. Group K will become the new wideband aerial once the Ch55 muxes disappear.

Once you have a better visualisation of what's happening with the various muxes then you can start to make some plans on how best to progress. You can also use the colours on the chart here to check against your current aerial. Older grouped aerials had red or yellow or green end caps on the boom. Old style Widebands still use black. Newer Group Ks will be grey.

You have signal in a bedroom, so if there's a TV in there then you can try with the signal metering on that one. Just bear in mind that some of the muxes are only available to TVs with a full HD tuner, so if you have gaps where you're expecting signals then this could be the reason.

Regarding the loss of signal for the ground floor, check the wiring on any plugs and RF wall sockets.

 

[Harry Bloomfield]

Are the coax cables run inside the house, or as many do, draped down the outside. Draped down the outside and flapping about with the wind, they frequently suffer damage, damage allows water ingress, which wrecks the cable inside. Coax is cheap, buy a roll and try bypassing sections you can get easy access to, also try bypassing the amplifier. LED's lit on an amplifier do not confirm it is working, only that it has power.

 

[ericmark]

We always said rubbish in means rubbish out, so no amplifier will help if bad aerial. However most masthead amplifiers need power up the coax to work, mothers house had a masthead amplifier and the problem was power to the amplifier, so TV guy would arrive with his box of tricks, and declare there was no fault with aerial system, since the amplifier was getting power from his tester.

While testing the power supply had been off, so on reconnecting TV was A1, as power supply cold. The LG TV had the option to send out power, with that turned on and no power supply the aerial seemed to work, but would not work the set bottom box, the amplifier was designed to take the signal from two aerials and combine them, from the days when English and Welsh TV had different programs, mother wanted Welsh, dad wanted English, so I think maybe the power required was more than the power supply could deliver?

Also had problems at home with a loft amplifier passing DC for the digi-eye to work, from days with original sky boxes. It seems some aerial face plates have braid breaks in them to stop the user getting a shock when high winds blow past the aerial, clearly it also stops supply to any device needing DC.

 

[naz1054]

Are the coax cables run inside the house, or as many do, draped down the outside. Draped down the outside and flapping about with the wind, they frequently suffer damage, damage allows water ingress, which wrecks the cable inside. Coax is cheap, buy a roll and try bypassing sections you can get easy access to, also try bypassing the amplifier. LED's lit on an amplifier do not confirm it is working, only that it has power.

While there is a cable running to the outside, the cable that I am interested is not exposed or damaged in the loft my checks. The issue is that it is chased in the wall inside the house, so the could possibly be damage inside the house I am not sure. I have bypassed the amplifier and nothing changes.

We always said rubbish in means rubbish out, so no amplifier will help if bad aerial. However most masthead amplifiers need power up the coax to work, mothers house had a masthead amplifier and the problem was power to the amplifier, so TV guy would arrive with his box of tricks, and declare there was no fault with aerial system, since the amplifier was getting power from his tester.

While testing the power supply had been off, so on reconnecting TV was A1, as power supply cold. The LG TV had the option to send out power, with that turned on and no power supply the aerial seemed to work, but would not work the set bottom box, the amplifier was designed to take the signal from two aerials and combine them, from the days when English and Welsh TV had different programs, mother wanted Welsh, dad wanted English, so I think maybe the power required was more than the power supply could deliver?

Also had problems at home with a loft amplifier passing DC for the digi-eye to work, from days with original sky boxes. It seems some aerial face plates have braid breaks in them to stop the user getting a shock when high winds blow past the aerial, clearly it also stops supply to any device needing DC.

While the aerial is not exactly new, there doesn't appear to be damage to it physically and the condition is not that bad. What are the visible signs that an aerial is no good any more.

It sounds like your meter tells you about signal strength but doesn't tell you anything about signal quality. That's the more important part of the deal. It's possible to take a really crappy signal and amplify it to kingdom come but the results will still be garbage even though the strength is through the roof. Conversely, you could have quite a weak signal but it's really clean and get great reception.

There is a way you can get some information about the quality. Most TVs with a digital tuner have some built-in metering. It reports on strength and on quality. You'll generally find this in the TVs tuning menus. Have a look under Manual Tuning. The metering might be quite basic though, so you might have to make some allowances when you read it. You could also find that it's a little on the optimistic side.

Where a TV's metering comes in handy though is that it reports on each mux rather than the average of the whole signal. This helps paint the picture of which are the stronger and weaker muxes, and what the quality of each is like. The reason this is useful is that each mux has its own frequency, and because of the spread of frequencies, some muxes may be at points where the aerial's reception is strong whilst others are now at weaker points following the reshuffling to accommodate the sell-off of the upper frequencies of the RF band for 4G ad 5G.

Changing your aerial for a higher-gain model may help, but it has to be the right reception profile to match the frequency distribution of your muxes as they sit now. Ordinary wideband high-gain aerials are becoming less relevant. They have their strongest reception at the upper end of the old ch21-68 range. A big chunk of that has been sold off. Once all the dust settles then the new range will be from RF channel 21 to 49 inclusive.

For most of us who need more gain, a group A or group B aerial will give the strongest signal. Groups C/D, E and wideband are now redundant. Group K will become the new wideband aerial once the Ch55 muxes disappear.

View attachment 259754


Once you have a better visualisation of what's happening with the various muxes then you can start to make some plans on how best to progress. You can also use the colours on the chart here to check against your current aerial. Older grouped aerials had red or yellow or green end caps on the boom. Old style Widebands still use black. Newer Group Ks will be grey.

You have signal in a bedroom, so if there's a TV in there then you can try with the signal metering on that one. Just bear in mind that some of the muxes are only available to TVs with a full HD tuner, so if you have gaps where you're expecting signals then this could be the reason.

Regarding the loss of signal for the ground floor, check the wiring on any plugs and RF wall sockets.

The TV does have some info on Signal and Quality. Its a bit of a pain because you have to manually check all the bands, what it does show is that some bands to have a highers signal than others with varying ratios between strength and quality. Example is band 39 is getting 40% Signal and 20% Quality.

 

[Lucid]

The TV does have some info on Signal and Quality. Its a bit of a pain because you have to manually check all the bands, what it does show is that some bands to have a highers signal than others with varying ratios between strength and quality. Example is band 39 is getting 40% Signal and 20% Quality.

If you haven't already done so, start with the channel and mux list here Channel listings for Industry Professionals | Freeview to identify one channel from each of the muxes (BBCA, SDN etc). Bear in mind that some muxes broadcast in a way that can only be received by a HD tuner (DVB-T2).

Your mux on RF ch 39 shows marginal strength and lousy quality. That's going to be a problem to receive. 40% strength but 80-100% quality would give satisfactory reception in a lot of cases so long nothing else changed. There are several reasons for strength being higher than quality. The main one is that the signal is over-amplified. That could be because the signal itself is from a transmitter other than your local one.

For example, although I'm in the northwest (Winter Hill, Granada region) my low gain unamplified aerial picks up some Yorkshire TV transmissions from Emley Moor. Even though it's marginal, the signal direct off the aerial has higher quality than strength. If I was to apply a lot of amplification though then the situation would reverse. The electrical noise from the amp would change the signal to noise ratio and so reduce the quality even though the strength would increase. It would become a louder crappy signal rather than a quiet but acceptable one.

To make sense of what's going on then you could do with reading the S and Q values for each mux with the signal direct from the aerial. i.e. bypass the amp completely. This will show you whether or not the aerial is still a good match to the distribution of mux channels from your local transmitter. With the signal direct off the aerial there will be no electronic amplifier noise affecting it. Any noise then would be from interference from stuff such as noisy local power supplies that's picked up by inadequately shielded coax. I see this quite a lot i the run-up to Christmas. Folk get out the Christmas lights or buy some new and then find there's some loss of their Freeview reception. Often it's the wall wart type transformer with their switch-mode power supplies chucking out a load of RFI hash. It gets in to the RF signal chain through some cheap/crappy coax fly lead.

You have an older aerial installation with cable buried in-wall. That could have been from the analogue TV days where coax was only single shielded. The coax we use now for digital TV has to have two shields; a foil as well as the braid. Older stuff just has the braid and so it's a bit more vulnerable to noise.

Once you have a list with the muxes and their strength and quality results for each, and you've eliminated any red herrings from transmitters out of your local area, then you're in a position to judge if the aerial is still a good match. (At this stage there's no amp in the equation to muddy the results.) You say you're in a strong area for reception, and so if the aerial is still okay then I'd expect Quality to be high across the board (80-100%) and strength to be high (60%+) for the main muxes that run on high power services at your local transmitter. If you're not seeing this then try checking the state of the physical connection at the aerial (is it loose / corroded / wet?) and maybe try realigning the aerial. If still no good then it could be time to replace it.

If all was well then it's time to add the amplified splitter back in to the equation to see what that does to the signal. You said it's a very high power unit (26dB). That's a hell of a lot of power to throw at a signal for any reception area, but really unnecessary for a strong reception zone. It's before my time with aerials, but these sorts of power levels were common in the early days of digital TV (1990s) when DTV ran on a low power service so as not to interfere with analogue too much.

Analogue was more tolerant of a lot of amplification. DTV isn't. When analogue was switched off the transmitter power for DTV was boosted. Aerial systems that had huge amps in them started to show problems with DTV. The oversaturation of signal level causes the Quality to fall because it screws up the signal to noise ratio. Removing the amps no longer required often fixed the problem. A simple passive splitter became the better choice.

Your splitter power is variable. But even so, it's still chucking in a fixed amount of noise even when the adjuster is set to low.

Try what I've suggested. If you want, you can post the results here and one of us will take a look over. If you can also find the name of your local transmitter then that would help.

 

[naz1054]

If you haven't already done so, start with the channel and mux list here Channel listings for Industry Professionals | Freeview to identify one channel from each of the muxes (BBCA, SDN etc). Bear in mind that some muxes broadcast in a way that can only be received by a HD tuner (DVB-T2).

Your mux on RF ch 39 shows marginal strength and lousy quality. That's going to be a problem to receive. 40% strength but 80-100% quality would give satisfactory reception in a lot of cases so long nothing else changed. There are several reasons for strength being higher than quality. The main one is that the signal is over-amplified. That could be because the signal itself is from a transmitter other than your local one.

For example, although I'm in the northwest (Winter Hill, Granada region) my low gain unamplified aerial picks up some Yorkshire TV transmissions from Emley Moor. Even though it's marginal, the signal direct off the aerial has higher quality than strength. If I was to apply a lot of amplification though then the situation would reverse. The electrical noise from the amp would change the signal to noise ratio and so reduce the quality even though the strength would increase. It would become a louder crappy signal rather than a quiet but acceptable one.

To make sense of what's going on then you could do with reading the S and Q values for each mux with the signal direct from the aerial. i.e. bypass the amp completely. This will show you whether or not the aerial is still a good match to the distribution of mux channels from your local transmitter. With the signal direct off the aerial there will be no electronic amplifier noise affecting it. Any noise then would be from interference from stuff such as noisy local power supplies that's picked up by inadequately shielded coax. I see this quite a lot i the run-up to Christmas. Folk get out the Christmas lights or buy some new and then find there's some loss of their Freeview reception. Often it's the wall wart type transformer with their switch-mode power supplies chucking out a load of RFI hash. It gets in to the RF signal chain through some cheap/crappy coax fly lead.

So testing via bypassing the amp completely gives the follow results:

Channel 39 - 25/25 Strength/Quality
Channel 40 - 40/0 Strength/Quality

The rest of the channels were basically 0 on quality and maybe 10% on strength

You have an older aerial installation with cable buried in-wall. That could have been from the analogue TV days where coax was only single shielded. The coax we use now for digital TV has to have two shields; a foil as well as the braid. Older stuff just has the braid and so it's a bit more vulnerable to noise.

Checking the cable it is indeed just the core, dielectric, braid and outer sheath, there is no foil to shield the signal.

Once you have a list with the muxes and their strength and quality results for each, and you've eliminated any red herrings from transmitters out of your local area, then you're in a position to judge if the aerial is still a good match. (At this stage there's no amp in the equation to muddy the results.) You say you're in a strong area for reception, and so if the aerial is still okay then I'd expect Quality to be high across the board (80-100%) and strength to be high (60%+) for the main muxes that run on high power services at your local transmitter. If you're not seeing this then try checking the state of the physical connection at the aerial (is it loose / corroded / wet?) and maybe try realigning the aerial. If still no good then it could be time to replace it.

If all was well then it's time to add the amplified splitter back in to the equation to see what that does to the signal. You said it's a very high power unit (26dB). That's a hell of a lot of power to throw at a signal for any reception area, but really unnecessary for a strong reception zone. It's before my time with aerials, but these sorts of power levels were common in the early days of digital TV (1990s) when DTV ran on a low power service so as not to interfere with analogue too much.

Analogue was more tolerant of a lot of amplification. DTV isn't. When analogue was switched off the transmitter power for DTV was boosted. Aerial systems that had huge amps in them started to show problems with DTV. The oversaturation of signal level causes the Quality to fall because it screws up the signal to noise ratio. Removing the amps no longer required often fixed the problem. A simple passive splitter became the better choice.

Your splitter power is variable. But even so, it's still chucking in a fixed amount of noise even when the adjuster is set to low.

Try what I've suggested. If you want, you can post the results here and one of us will take a look over. If you can also find the name of your local transmitter then that would help.

I dont think the results show the amp at fault here. The aerial has been replaced and the results that we have above are for the the new aerial. The replacement aerial was the Tri-boom Very High Gain TV Aerial. I will agree its not probably the best for the situation however based on the single metric of the Strength, the new aerial did not get a better strength then the old one.

I dont have a small TV that I could take up there to see directly from the aerial what situation is or even in the upstair bedroom where the signal is stronger at the socket, will see if friends/family have one that I could borrow.

My thoughts here is that the cable is fault here, its is both killing the strength of the signal and also picking up a lot of noise from somewhere, possibly because although we cannot see it, a screw or nail has gone into it or because the wall is shared with next door, they have something on the other side introducing lots of noise.

As for the transmitter, it is Sutton Coldfield.

 

[Harry Bloomfield]

I dont have a small TV that I could take up there to see directly from the aerial what situation is or even in the upstair bedroom where the signal is stronger at the socket, will see if friends/family have one that I could borrow.

A nail or screw will not be likely to affect both downleads.

My thoughts here is that the cable is fault here, its is both killing the strength of the signal and also picking up a lot of noise from somewhere, possibly because although we cannot see it, a screw or nail has gone into it or because the wall is shared with next door, they have something on the other side introducing lots of noise.

As I suggested earlier, get a roll of coax from an electrical or antenna wholesaler. You want CT100 or equivalent.

 

[Lucid]

Sutton Coldfield transmitter: Most of the TV muxes transmit at 200,000W. You're only 7 miles away. Unless there's some specific local difficulty such as you live at the bottom of a quarry or inside a huge Faraday cage then you should be able to put up a bit of wet string and get 10/10 signal and quality.

I live 4x the distance from a transmitter with only half the power. My TV aerial is one of the lowest gains its possible to have. I have enough signal that I can split 3 ways and still keep 10/10 Q and S. I even get solid reception of the 5,000W and 10,000W local transmitter muxes meant for city centre Mcr and Liverpool despite being about 20 miles outside of their target zones.

A Tri-boom is a very hi-gain aerial for a wideband type. I have to be honest and say that it's probably the last choice I would make for somewhere 7 miles from a 200,000W per mux transmitter. I wonder if that'spart of the problem; too much signal as opposed to too little. It can have a very similar effect.

Your partially shielded coax cables might be adding to the problem by acting like aerials too, and so throwing more signal at the TVs downstairs.

It's all a bit of guesswork though when the site is unseen. If I was there I would put my meter on the direct aerial feed and read off the S and Q for each mux, then try some troubleshooting procedures such as attenuating the signal. I would also make some new connections from the loft to the ground floor TV points and replace any unshielded coax sockets with shielded ones. Coax fly leads would be replaced too. Webro WF100 cable all the way through.

 

[Harry Bloomfield]

It's all a bit of guesswork though when the site is unseen. If I was there I would put my meter on the direct aerial feed and read off the S and Q for each mux, then try some troubleshooting procedures such as attenuating the signal. I would also make some new connections from the loft to the ground floor TV points and replace any unshielded coax sockets with shielded ones.

The OP said 'Example is band 39 is getting 40% Signal and 20% Quality.' - from his TV's built in meter, which seems to suggest a too weak signal.

 

[HERTS P&D]

I love it when the diyers argue with the Pro's.



Andy

 

[Lucid]

The OP said 'Example is band 39 is getting 40% Signal and 20% Quality.' - from his TV's built in meter, which seems to suggest a too weak signal.

TBH it's all a bit of a mess and somewhat contradictory. There might be factors that haven't yet been mentioned or not even recognised that are throwing a spanner in the works. For example, since the start of this thread (I think) the aerial has been changed. The OP is doing their best with limited tools so we just have to wait to see what unfolds from the measurements direct off the aerial once it's possible to get a TV close enough to take some readings.

 

[naz1054]

Sutton Coldfield transmitter: Most of the TV muxes transmit at 200,000W. You're only 7 miles away. Unless there's some specific local difficulty such as you live at the bottom of a quarry or inside a huge Faraday cage then you should be able to put up a bit of wet string and get 10/10 signal and quality.

Funny you should say that.

So I managed to borrow a small, a bit old Freeview TV. Took it to the bedroom where the signal strength meter was showing 50DBuV. BBC one was already tuned, but the rather basic signal test on the TV suggest a very poor quality(it does not have numerical representation) and around 50% signal strength.

So next thing was to head up with the TV and do the tests from the aerial itself and after the amp. The results on the TV from both of them was 100%/100% on both signal and quality.

Just to give you context, on my first visit upto the loft for this issues, the leads for the cables were already plugged in, one was heading towards the back of the house into the eaves and the other towards the bedroom towards to the front of the house, and you could see the cables.

So the next thing I went to do is try and trace the cable for the bedroom by lifting a lot of the insulation. With the ceiling boards exposed, there appeared to be three coax cables coming up from the landing wrapped up with tape, not terminated, just there, something I know electricians do when customers ask for cabling in for sockets/switches for the future. The house has been re-wired in the last few years so I thought, maybe had the previous owner asked for the new cables to be put in but never used them because he always had virgin media. Anyway I had extra F Type connectors so I went ahead to put them on. The cable structure was sheath, plastic, braid, foil, foam dielectric and core. At this point I think I realised the other 3 cables in the amplifier were not connected to anything. Anyway they were long enough to reach the current Amp(not that they need that.) Dropped the gain and plugged all three in. Went downstairs, did a signal test and guess what 100/100 for both.

So in the end it means those cables on the amp were never connected to any of the sockets and it was this wrapped cables under the insulation and plaster was where the signal was coming from, and the only reason why they did pick something up is because the strength of the signal. The cables go from the loft, down the wall and then through the joists into all the rooms.

I can only guess that the old and new cable were crossing over at some point as to why turning the amp made any difference.

So in the end the damage is:

1. Hi-Gain aerial which was not required
2. Signal Meter, one for the toolbox
3. New PSU - not needed
4. F Type Connector only thing actually needed