CH48 interference on HDRFOX-T2 Boxes

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phit03

Member
I have a problem with the BBC MUX that is on CH48 on the Midhurst Transmitter on my HDRFOX-T2 boxes, usually at times of high pressure weather patterns with loss of signal for programs on that MUX.
I either lose the feed for programs on that MUX completely or get very poor signal strength (normally around 75% strength and 100% quality).
Newer boxes like the Humax FVP5000T and my network connected HDHomeRun boxes are not affected to the same degree.

I'm assuming that atmospheric propagation conditions at the times I lose the signal on the HDRFOX-T2 boxes are causing signals from adjacent transmitters or mobile phone masts to drown out the signal at the CH48 frequency and younger boxes have filters to mitigate this situation.

Anyone have any ideas as to what I could do to improve the situation? I've looked at the possibility of inserting an inline filter in the aerial feed but don't understand what frequencies I should be filtering and one that is supposed to fix this sort of problem says that it filters CH48 and upwards which I assume would cause complete loss of signal at that frequency.
 
Check the predictions of interference for your location at https://www.freeview.co.uk/corporate/detailed-transmitter-information
and post the two Served and Marginally served figures (% of locations in the 100m x 100m prediction square) for ch 48.

Define what you mean by other boxes "are not affected to the same degree."

Are all receivers fed from the same aerial (antenna) and if so how is the signal split and distributed?
If not, what is the differences in antennas and their locations?
 
phit03 said:
I've looked at the possibility of inserting an inline filter in the aerial feed
Click to expand...
You can't filter co-channel interference (obviously) caused by atmospherics (or any other cause). The only thing you can do is improve the directional rejection of unwanted signals, if that's even possible. It's not something your average bloke-on-horseback will know anything about.

FWIW, my channel 48 isn't very good, and nor is channel 47 on the wrong half of my distribution. I don't know why, as it used to be OK before the last aerial died.
 
Rodders53 said:
Check the predictions of interference for your location at https://www.freeview.co.uk/corporate/detailed-transmitter-information
and post the two Served and Marginally served figures (% of locations in the 100m x 100m prediction square) for ch 48.

Define what you mean by other boxes "are not affected to the same degree."

Are all receivers fed from the same aerial (antenna) and if so how is the signal split and distributed?
If not, what is the differences in antennas and their locations?
Click to expand...
As mentioned in the post, a Humax FVP5000T Freeview box and 4 network connected HDHomeRun boxes (plus an LG and Samsung TV) connected to the same aerial feed are not affected to the same degree (some pixellation but able to view the program) by interference during periods of "abnormal" tropospheric conditions leading me to wonder whether they have some form of extra filtering. In comparison, the HDRFOX-T2 boxes say that there is no signal on the CH48 programs most of the time during these conditions and when they do manage to decode the channel, typically show a single bar for signal strength and nothing for quality.
The aerial is in the loft and it's signal is split in the loft by a Labgear 4 port UHF distribution unit to 4 sockets in different rooms (part of the original house build). Only 2 of those sockets are used (front room and office). In the front room, the signal is further split by another Labgear 7 port distribution unit feeding an LG TV, 3 Humax HDRFOX-T2, 1 Humax FVP5000T and a passive splitter feeding the 4 HDHomerun network attached tuners. In the office the signal is split by another Labgear 7 port distribution unit feeding a Samsung TV and 4 Humax HDRFOX-T2. At times of "normal" atmospheric conditions all works well with no problems with programs on the CH 48 MUX on the HDRFOX-T2 boxes.
The Labgear distribution units claim to have 45db "typical 4G interference protection".
I have had an aerial engineer to check the aerial installation and using his sophicated (to me) handheld device he has measured the output and quality of the signal to all of the attached devices. It was on his advice that I changed the splitter feeding the HDHomerun devices from a Labgear active splitter to a passive splitter as these were being overdriven. All other devices had a good signal. I asked whether I should have the aerial moved outside to improve the signal (it was moved inside as it was shading some solar panels) and he thought it wasn't worth it.
I should also mention that we are (as the crow flies) half way between 2 transmitters (Midhurst and Heathfield), the Freeview website says that the Midhurst transmitter is best for our postcode and house number (BN6 9GB). We may also receive signals from the Crystal Palace and Rowridge transmitters during abnormal atmospheric conditions.
S & M figures are 95 and 100 for the Midhurst transmitter for our postcode and house number.
I will finally add that during these periods of poor CH48 reception, the BBC HD channels on CH36 are fine so I do have an alternative.
 
prpr said:
You can't filter co-channel interference (obviously) caused by atmospherics (or any other cause). The only thing you can do is improve the directional rejection of unwanted signals, if that's even possible. It's not something your average bloke-on-horseback will know anything about.

FWIW, my channel 48 isn't very good, and nor is channel 47 on the wrong half of my distribution. I don't know why, as it used to be OK before the last aerial died.
Click to expand...
See my reply to Rodders53 for more info on my setup.

I freely admit my ignorance of signal reception but I seem to remember that you can have problems with harmonics from other frequencies causing interference.
However, thinking about about it, no amount of filtering will have any affect in that situation or will it?

Thanks for your reply.
 
Thought I might try this to see if it makes any difference:

Labgear 5G/LTE 700 Interferace Filter , with Coax flylead​


Part No: F5GA


£12.99

Low Band Pass Frequency: – 5-694MHz (VHF-UHF Ch48).
In-band Insertion Loss: – Typ. <1.0dB. High Band Stop Frequency: – 703-1000MHz (Ch50-69+SAT). Out-of-band Rejection: – Typ. >40dB.
In-band Return Loss: – Typ. <-15dB.
 
So 95% of the locations in the prediction square are Served to the less than 1% of time interference level. Less than 1% of time is still up to 3.65 days or 87.6 hours of interference though. Typically such interference lasts minutes to at most a few hours once or twice a day when the conditions are right for signal ducting to occur.

Looking at the full prediction for that postcode suggests that the other muxes have slightly poorer interference predictions. Also suggests that Heathfield is similar.

I don't know the source of interference on Midhurst, c48 in particular... but from the continent it would be getting in on the side lobes of the loft antenna as it points West (280 degrees).
Significant erp UK sites using 48 are Angus (10kW), Knock More (10), Selkirk (5), Carmel (10), Moel-y-Parc (10),
Emley Moor (174), Mendip (100), Redruth (10), Sandy Heath (170), Dover (40), and Whitehawk Hill (4).

I guess that the tuner-decoder-error correcting mechanisms in more modern kit has potentially improved over the -T2? It's also known that the -T2 is one of the more sensitive units out there so maybe it sees the interferers 'better'.

The UK transmitter network is designed around the use of external aerials at 10 metres above the ground. Lofts typically lose around 10dB cf being outside from the construction materials. Solar panels will block signals so I must assume the antenna points through a gable end rather than through the panels.

It is generally bad practice to cascade amplifiers like you are doing. (Added noise and non-linearities).
What are the model numbers of the loft 4-way and two 7 port jobs so I can see the specs.

Passive splitters lose 4dB (2 way) or 8dB (4 way). I'd prefer to see a passive split in the loft then the two 7-way used? Perhaps?

Don't waste money on the filter it will not help the problem if this is cci. It will introduce some loss (but it should be minimal).
If the issue was amplifier overload from mobile phone masts and handheld then it might prove useful.
 
Black Hole said:
Yes, you posted in the Foxsat forum.
Click to expand...
Rodders53 said:
So 95% of the locations in the prediction square are Served to the less than 1% of time interference level. Less than 1% of time is still up to 3.65 days or 87.6 hours of interference though. Typically such interference lasts minutes to at most a few hours once or twice a day when the conditions are right for signal ducting to occur.

Looking at the full prediction for that postcode suggests that the other muxes have slightly poorer interference predictions. Also suggests that Heathfield is similar.

I don't know the source of interference on Midhurst, c48 in particular... but from the continent it would be getting in on the side lobes of the loft antenna as it points West (280 degrees).
Significant erp UK sites using 48 are Angus (10kW), Knock More (10), Selkirk (5), Carmel (10), Moel-y-Parc (10),
Emley Moor (174), Mendip (100), Redruth (10), Sandy Heath (170), Dover (40), and Whitehawk Hill (4).

I guess that the tuner-decoder-error correcting mechanisms in more modern kit has potentially improved over the -T2? It's also known that the -T2 is one of the more sensitive units out there so maybe it sees the interferers 'better'.

The UK transmitter network is designed around the use of external aerials at 10 metres above the ground. Lofts typically lose around 10dB cf being outside from the construction materials. Solar panels will block signals so I must assume the antenna points through a gable end rather than through the panels.

It is generally bad practice to cascade amplifiers like you are doing. (Added noise and non-linearities).
What are the model numbers of the loft 4-way and two 7 port jobs so I can see the specs.

Passive splitters lose 4dB (2 way) or 8dB (4 way). I'd prefer to see a passive split in the loft then the two 7-way used? Perhaps?

Don't waste money on the filter it will not help the problem if this is cci. It will introduce some loss (but it should be minimal).
If the issue was amplifier overload from mobile phone masts and handheld then it might prove useful.
Click to expand...
Yes, the problems seem to occur evenings and mornings.

I think the aerial is less than 10 metres above ground level but not much less (2 story building with the aerial close to the apex of the roof in the loft) and points through a single layer brick gable end (timber frame construction with a brick facing). No buildings at the west side of the house just open agricultural land for miles. There used to be a large Oak tree in the signal path but this has since died and has no leaves in spring/summer.

Don't know the make/model of the aerial, it was moved by the solar installers (who were aerial installers before taking on solar as well). Don't even know if they used the original aerial or fitted a new one.

The south facing roof has solar panels on it. Would this help shield the aerial from signals from the south? (Whitehawk Hill is probably the closest transmitter but there are parts of the South Downs between us and it so unlikely)

The Labgear part numbers for the 8 port (I got that wrong as well, they have 8 ports plus a full signal output) devices is LDA2081LR.
The Labgear part number for the 4 port device is LDA204LR. This was purchased to replace the original powered splitter (can't remember the make/model) which failed. I assumed the original was active as it had a mains power supply.
As I mentioned, the aerial engineer checked the signal levels at each device and only commented on the 4 HDRHomerun devices being overdriven (at this time the loft distribution was using the Labgear splitter).
It won't take much to replace the loft distribution device with a passive version. Do you have any recommendations regarding make/model?
Too late for the 5G filter as I've ordered it, it's not going to break the bank. Unlikely it will make any difference as we're rural so little chance of 5G infrastructure reaching here in my lifetime and there's a 4G filter on the Labgear devices.
I assume the best place to fit the 5G filter is between the aerial and the splitter in the loft.

Thanks for all your help, please don't spend too much time on this as I have a workround by using the BBC HD channels to record instead of SD.
 
Rodders53 said:
Passive splitters lose 4dB (2 way) or 8dB (4 way). I'd prefer to see a passive split in the loft then the two 7-way used? Perhaps?
Click to expand...
The best thing to do from an engineering point of view (barring putting the aerial outside) would be an amplified 2 way split in the loft and then use passive splitters everywhere else. That amplifies the signal at the point it is cleanest, and the gain of that should be chosen to be enough to offset the loss from the later passive splitters but not much more to avoid over driving.

There will be loss in your cables, both of signal strength and picked up interference. How much loss depends on the type of cable and the type of connectors. Ideally it should all be double screened, both the coax (CT100 etc style braid and foil screened) and the wall sockets. But if this was all installed by the builders it probably isn't to that standard and you will get pickup on the cables. Amplifying the signal before those cables mitigates that problem.
 
phit03 said:
The aerial is in the loft and it's signal is split in the loft by a Labgear 4 port UHF distribution unit to 4 sockets in different rooms (part of the original house build). Only 2 of those sockets are used (front room and office). In the front room, the signal is further split by another Labgear 7 port distribution unit feeding an LG TV, 3 Humax HDRFOX-T2, 1 Humax FVP5000T and a passive splitter feeding the 4 HDHomerun network attached tuners.
Click to expand...
OMG :frantic:
I asked whether I should have the aerial moved outside to improve the signal (it was moved inside as it was shading some solar panels) and he thought it wasn't worth it.
Click to expand...
Not an opinion I agree with (in the vast majority of cases). Putting it outside will give you more signal and more decode margin than putting it inside. You will also need less amplication which again gives you more decode margin, and it is this that you appear to be short of in certain conditions.
Shading solar panels? Really? Come on.
phit03 said:
I assume the best place to fit the 5G filter is between the aerial and the splitter in the loft.
Click to expand...
The golden rules: Start with the best signal you can get out of the air; filter before you amplify; amplify before you split; only use as much amplification as is necessary to overcome cable/splitting losses; use properly screened cables/connectors (i.e F type rather than Belling, and adapt as necessary at the receivers).
The south facing roof has solar panels on it. Would this help shield the aerial from signals from the south?
Click to expand...
No.
 
Owen Smith said:
The best thing to do from an engineering point of view (barring putting the aerial outside) would be an amplified 2 way split in the loft and then use passive splitters everywhere else. That amplifies the signal at the point it is cleanest, and the gain of that should be chosen to be enough to offset the loss from the later passive splitters but not much more to avoid over driving.

There will be loss in your cables, both of signal strength and picked up interference. How much loss depends on the type of cable and the type of connectors. Ideally it should all be double screened, both the coax (CT100 etc style braid and foil screened) and the wall sockets. But if this was all installed by the builders it probably isn't to that standard and you will get pickup on the cables. Amplifying the signal before those cables mitigates that problem.
Click to expand...
Problem with this approach is that i would need a passive splitter or splitters to provide a UHF signal to 9 devices in one room and 5 devices in the other. Would the insertion losses caused by this amount of passive splitting be workable?
Also, would this would mean that I would need an active splitter in the loft with a variable amplification facility to cater for future changes i.e. addition/removal of downstream devices?
At the moment I have a solution that works 99% of the time with a workaround for the other 1% (or just always record programs from the BCC HD channels on CH36 all the time as I have plenty of disk space on the boxes and take my chances with any other channels that I might want to record from on the CH58 MUX).
 
phit03 said:
Problem with this approach is that i would need a passive splitter or splitters to provide a UHF signal to 9 devices in one room and 5 devices in the other. Would the insertion losses caused by this amount of passive splitting be workable?
Click to expand...
Yes, you'd just need to use enough amplification in the loft to be a bit more than the loss from the largest passive splitting. If that ended up too strong after the 5 way splitter (you might have to buy a 6 way) add an attenuator before that splitter.
phit03 said:
Also, would this would mean that I would need an active splitter in the loft with a variable amplification facility to cater for future changes i.e. addition/removal of downstream devices?
Click to expand...
Depends how many devices you think you're going to be adding / removing. If you go for something like two 12 way splitters that would provide plenty of room for expansion and then get a fixed gain amp in the loft to match. It's not what devices you have connected, it's the loss in the passive splitters and you can have split outputs unused.
phit03 said:
At the moment I have a solution that works 99% of the time with a workaround for the other 1% (or just always record programs from the BCC HD channels on CH36 all the time as I have plenty of disk space on the boxes and take my chances with any other channels that I might want to record from on the CH58 MUX).
Click to expand...
It's up to you, we're just trying to explain why your current solution is pretty dreadful from an engineering point of view. The golden rules from @prpr match what I'm saying. If you want to carry on as you are then fine, but you asked for advice and this is the advice.
 
Thanks everyone for your time invested in looking at my problem with failed recordings with programs on the CH58 MUX on the HDRFOX-T2 PVRs during periods of atmospheric ducting and providing your inputs.
It seems from your responses that the problem could be alleviated by making changes to my aerial (move to outside) and the signal distribution system (active splitter in loft and Passive splitters downstream).
I've learnt a lot about the correct way to go about designing a system for optimal signal reception and distribution.
I was really looking for a quick fix to the problem and it seems that there isn't one and I don't have the time or inclination to start again and set things up from the top down as it were.
I will live with what I have for now and change what I can to ameliorate the situation by recording BBC programs in HD rather than SD on the HDRFOX-T2 PVRs thus avoiding the troublesome CH58 MUX.
 
I think you mean CH48, there are no broadcasts on CH58 these days.

You should also consider your coax and faceplates, did the builders put cheap crappy "low loss" coax and unshielded faceplates in? You ideally want double screened foil and braid coax and screened or F type faceplates. This may be hard if it is buried in the walls.

Quick fixes for RF problems are few and far between.
 
Owen Smith said:
I think you mean CH48, there are no broadcasts on CH58 these days.

You should also consider your coax and faceplates, did the builders put cheap crappy "low loss" coax and unshielded faceplates in? You ideally want double screened foil and braid coax and screened or F type faceplates. This may be hard if it is buried in the walls.

Quick fixes for RF problems are few and far between.
Click to expand...
Yes, it should say CH48.
 
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