Single channel interference??

[TonyS82]

Evening all hoping for some help with our annoying freeview tv issues.
Basically i have intermittant (more often than not its bad) issues with loss of signal for all tv channels on UHF Channel 26/514mhz. All other channels are perfect which im struggling to solve.
Our setup is quite basic:
DMX10A-F group A antenna pointing at crystal palace transmitter.
10m Webro WF100 drop cable run from antenna, down and under floorboards to a proamp24r distribution amplifier through a PROLTE5G700 5g filter currently feeding a single tv in the living room. The filter is new hoping it might have been 5g interference but no luck there.
Monitoring the tv signal info i can see the signal strength fluctuating between 70 to 75%. All other channels are over 85%.
Im thinking it might be time to add a masthead amplifier but don't want to just throw money at it without knowing if it will help and whether I'd need to upgrade anything else at the same time.

Any suggestions welcome.
Thanks
Tony

 

[Lucid]

Signal strength isn't the be-all and end-all of TV reception. Anything over 60% is normally more than enough. You need to have a look at signal quality. 80% or more is a reasonable rule of thumb, though TVs do have a habit of overestimating both strength and quality.

Check out the quality level and also whether it fluctuates. Compare it to your other channels.

Incidentally, 5G interference should be above 700MHz.

 

[TonyS82]

Hi lucid, on my samsung tv i have 2 measurements, signal strength and bit error rate.
On all the good channels I'm getting no bit errors, on the poor channels its fluctuating between 0 and 2.

 

[Lucid]

Have you had a look at the coverage checker for your area? There's one that gives more useful info, here: https://www.freeview.co.uk/corporate/detailed-transmitter-information

Pop in your postcode and house number. Once the info comes up then scroll down. At the head of the list you'll get the most likely transmitters. Then scroll further down for a rough guide to the signal levels in your area. The key to the chart tells you whether signal level is strong, variable or poor.

Take a screen grab and post the results back here.

Windows key + Shift + S, then click and drag to draw a marquee around the thing you want to grab. Open a reply and then CTRL + V to paste the image.

Other thought. Have you tried with the signal direct from the aerial rather than through the amplified splitter?


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It could be that you have a dent or sharp bend in the cable that is acting like a notch filter. That means it hobbles a certain frequency but not others. However, before going to the trouble of lifting boards and getting ladders out it's sensible to rule out other potential causes.

 

[TonyS82]

Hi lucid. Good signal strength and crystal palace is the recommended transmitter.

UPDATE
If the amplifier is removed i get nothing at all. Zero signal and maximum bit error rating on all tv channels

I've had another look at the aerial and it appears to be very slightly off horizontal, don't know if that could cause any issues?

 

[Lucid]

If you get nothing without the amplified splitter then you can't be in a good signal area. That, or something else is going on. Have you got trees or buildings in the direction the aerial is pointing? Is it in a loft and pointing through the gable ends of some adjacent houses?

You said you have a group A aerial, so that should give tou the strongest possible CP signal for your location. The predictor can only give general guidance, but even so, I would expect some kind of reception with the signal direct into the TV.

I thought you might have understood about getting a screen grab for the CP signal predictor. It's below the one you got. You have to scroll down. Keep going. A bit more. That's really the one we need to ssee. it has the individual muxes. Can you show us that?

 

[TonyS82]

Sorry im using my phone to get the screenshots so space is limited. More info attached.

the aerial is mounted on a 4 foot pole on top of the chimney stack. House is a bungalow, located at top of a large hill but there is a large wooded area behind us where the aerial is directed.

 

[Lucid]

With those sort of field strength numbers I am really surprised that you get no signal without the additional amplification that the powered splitter provides. The exception would be if the trees are right at the end of the garden or towering over your house.

I also think that there may be some damage to the aerial cable or some issue with one or more connections in the system.

There may also be an undisclosed issue that would be apparent if I or another professional installer saw the system first hand, but we're missing it because it's not in your descriptions. The aerial isn't pointing at the relay, is it? It is actually pointing at the CP transmitter, right?

In situations like this I would suggest going back to basics or getting in a local installer who can meter the system and check the aerial alignment.

If you want to try to troubleshoot this yourself then start with the plugs and cables. Use a multimeter on continuity setting. Disconnect the plugs at either end of each cable run. There should be infinite resistance (no tone) between the centre pin and shield. If there's just a single filament of braid wire bridging to the pin then you'll get tone or a resistance showing.

Check for damage to the aerial socket on the TV. I have seen it before where the centre connector was missing from the aerial socket. The signal still worked but at a massively reduced level. This is because at RF frequencies there's something called capacitive coupling. When the conductors are close enough but not touching the signal appears to bridge the broken connection.

Your objective should be to get a signal direct from the aerial with no additional amplification in the chain. Once you have that then you can put the splitter back in if needed.

 

[TonyS82]

The exception would be if the trees are right at the end of the garden or towering over your house.

Affirmative on both those

The aerial is pointing at the main transmitter. I double checked the compass bearing and it also matches my neighbours which is next to it.

When we bought the house it had the same model aerial with a masthead amplifier but it got damaged during a loft extension. The cables and amplifier were buried in the ceiling by the previous owner. Prior to the work there was no signal on the tv if the power was switched off to the old amplifier so i suspect it is likely the trees with another years growth.

I'll check all the connections again to be safe.

Thanks for your help

 

[TonyS82]

Hi Lucid, thank you for your help so far, I wanted to update you after the last few weekends messing around. Sorry its a long one.
Using a labgear signal meter ive realigned the aerial maybe a few degrees to achieve a stable 60db signal. Before the adjustment it was indicating an unstable 50/60 db signal.
Ive tested all my cables and all come back good.
The main tv is still having intermittant signal loss issues with channel 26 on frequency 514mhz. Without the amplifier there is no signal at all on this channel but other channels appear to be ok.
I wondered if my 14 year old samsung was the issue so i got our 2nd smaller tv out of storage and hooked it up. Its another samsung maybe 8 years old. This tv doesnt seem to have the issue to the same extent. Even when monitoring the signal on it it says 20% signal, lots of bit error but still happily plays away with little noticeable picture loss.
It seems maybe the tuner in the tv is the issue?
I'm wondering if a masthead amplifier and passive splitter might help the main tv reception Rather then the distribution amplifier i have?
I'd rather not have to buy a new tv unless its really necessary