ARQ B multiplex reception strange behaviour

RetroRocker

Standard Member
Hi, I am 5 miles from Tacolneston (East of England) full Freeview transmitter. Almost line of site, barring a few trees. Loft aerial which is a Vision 10-28L log periodic type, (high gain definitely not needed). Signal is split in loft, feeding 2 TVs. Most multiplexes, excellent signal both in quality and strength, as you might expect, until you get to ARQ B.

This only really became apparent when I decided I'd like to watch the GB News (236) channel but I also have managed to correlate it to other channels eg. HGTV (43) and the common factor is ARQ B mux.

I can receive GB News with often 100% quality and 50 - 90% strength in the mornings. Late afternoon/evenings give often 0% quality and 0 - 10% strength... it really does fluctuate that much. Other Muxs receptions don't do this.

I can only think it's external interference between transmitter (currently no faults known) and aerial at specific frequency... 4G maybe ? (we don't have 5G around here) or maybe too much signal ?

Really would appreciate thoughts on this topic, many thanks.
 

A1944

Well-known Member
I don't know how realistic it is, but it is often mentioned that HDMI cables can radiate interference which can take out a single Mux. Do you perhaps have something using HDMI which is switched off in the morning, but on in the evening?
 

Rodders53

Distinguished Member
ArqB is freq ch 39, the lowest freq from TAC, so no likelihood of interference from mobile phone transmitters or anything else much as it is in the middle of the uhf tv band (21 to 48 inclusive, plus 55 temp com7). Especially as no amplifiers are in use.

Hdmis are a known problem and it's always worth fettling all cables and connectors as the majority of reception issues can be caused by dodgy connections!

Variable signal levels suggests multipath reflected signals to me... Reflections off trees, water, etc.,. causing frequency dependent cancellation and/or reinforcement, aka standing waves.
Loft spaces are renowned for that.
So the aerial may need repositioning to give more stable consistent reception? Higher/lower, crab fore/aft and left/right in a cube of space with 1 metre sides is something to try.

Also worth a check with aerial direct to TV as splitter loses 4dB?

Edit: The log 28 you have claims 8.5dB gain ref a dipole which isn't at all insignificant, but roof material attenuation plus splitter losses makes tuner overload probably unlikely?
A report of all 6/7/8 muxes strength/quality on the set might be worthwhile?
Perhaps, even, checking with another receiver on the same outlet?
 
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RetroRocker

Standard Member
I don't know how realistic it is, but it is often mentioned that HDMI cables can radiate interference which can take out a single Mux. Do you perhaps have something using HDMI which is switched off in the morning, but on in the evening?
Hdmis are a known problem and it's always worth fettling all cables and connectors as the majority of reception issues can be caused by dodgy connections!
Thank you very much for these replies, genuinely helpful & appreciated. I set about testing the installation with various peripherals selected on/off where these are connected to the TV via HDMI. It was pretty conclusive with the Blu-ray/DVD player. I had a run of about 10 inches where aerial & HDMI cable for this device were paralleling each other. Isolating/rerouting the aerial cable has now made channels on the ARQ B mux very much more stable. I can achieve 50 - 60% quality & signal strength now, peripherals on or off. Typically though I achieve 100% quality and 95% strength with the muxs which contain the channels such as BBC SD & HD, so PSB 1 to 3 and also ARQ A and ARQ C are high level quality & strength. ARQ B as mentioned, is now genuinely usable but this mux does still sit below all others in terms of quality and strength. Tacolneston reports no problems with anything. It seems like although I have improved the issue to the point of fair usability, which is great, it's probably a compound issue with a little something else somewhere. Also the signal quality/strength are still better am than pm with this mux, there seems to be a little something still about 618 MHz. I'm intrigued (but not fussed) as to what it may be and will investigate in the fullness of time but I'm really considering that this is external to the installation as a whole. If I find it, I'll post back, meanwhile thanks again.
 

A1944

Well-known Member
As suggested by Rodders, a small movement of the aerial might also help. Good to hear that separating the aerial and HDMI cable produced some improvement.

However, it is worth noting that sometimes too high a signal can reduce the quality (which is the significant figure, not the strength) and 5 miles from a main transmitter, that could be the problem, especially as I don't think there are too many hills in that area to cause low signal reception that far away.

By the way, there is no ARQ-C Mux, I imagine you meant SDN.
 
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Rodders53

Distinguished Member
If that cable moved is a moulded fly lead type, replace with double-screened satellite grade cable and plugs.

If hand made plugs, re make them. Costs most but time and may prevent pickup of anything.

The main 6 muxes are all 100kW ERP so should be very similar in level. Do consider a small relocation adjustment - but be aware that one of the others may change for the worse, so it can need a repetitive move/check/move process to get them all perfect.

EDIT Overloading is possible but unlikely imho.

Direct connect the aerial to the one outlet will increase the signal to the TV by more than double (splitters lose 4dB), other muxes will then overload too perhaps?
If you have one, a second splitter will reduce signals by a further 4dB if inserted after the 2-way in the loft and if that improves Arq B quality to 100%... I'll have to eat my words ;)

NB Trees can be a right pain. I'm just back from a week at a caravan site in Theberton surrounded by trees and causing irregular breakup on both TAC and Aldeburgh. Reflected signals of Aldeburgh off one bank of trees were stronger than the direct signal through another copse; neither 100% reliable.
 
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RetroRocker

Standard Member
Variable signal levels suggests multipath reflected signals to me... Reflections off trees, water, etc.,. causing frequency dependent cancellation and/or reinforcement, aka standing waves.
Loft spaces are renowned for that.
So the aerial may need repositioning to give more stable consistent reception? Higher/lower, crab fore/aft and left/right in a cube of space with 1 metre sides is something to try.
Just wanted to close this thread by saying problem solved ! It was a compound issue, the first part of which, concerning the HDMI interference, was covered in a previous post. The second part was resolved by taking Rodders53's suggestion at moving the aerial around. At this point I have to make a very embarrassing confession... I have roof mounted solar panels 😬... ok, I know 🙄 but now I'll make my excuses. They were installed years ago and the aerial was there before them. I honestly had no noticeable problems with reception. Also though, as previously mentioned, it was wanting to start viewing channels in ARQ B mux which started this off. Resiting the aerial at the same height, level & angle but about 80cm further along in the loft fixed the problem completely. Prior to this the aerial was pointing just through the edge of the solar panels now it clears them... just (before running into an end wall). Result is now all multiplexes give 100% quality and 90 - 92% strength and crucially, are stable, with no further changes to the installation as a whole.
I really appreciate the help I've received, with A1944 starting it off, but Rodders53, what can I say, you go above and beyond 👍 thanks again and very best wishes
 

Rodders53

Distinguished Member
Thanks for the update, and the thanks :blush:.

I rather enjoy keeping my grey matter exercised on such problems.

I wonder what the attenuation is through a solar panel? But as it/they only affected the one frequency, I still suspect it was mainly a 'standing wave' effect and relocation to a peak rather than null has cured the problem.

Well done for the perseverance and experimentations needed to solve the riddle.

Weirdly all three COM mux frequencies were unchanged through the 2018 700MHz clearance programme. (Ignoring a positive167kHz offset on ArqB's ch 39 that was removed). So something external / internal to the loft changed to cause the reception problem (tree growth most likely).
 

RetroRocker

Standard Member
As for the attenuation through a solar panel, I don't know but I'll hazard a guess at significant 😂 Looking back at my initial post in this thread, to be honest I probably wrote my own clue... well maybe. The roof with the solar panels is due West facing, TAC from here is about 305 degrees. Goodish ARQ B reception in the morning (sun not on panels), gets worse throughout the day, bad in afternoon/evening (solar panels going full pelt), with sun finally setting about 9:20pm. Hmmm... all too much to be just a coincidence and it's really the last 2 days that pointed me hard at this because afternoon / evening ARQ B reception has been sigificantly better... and it's been very cloudy... a ha !
More lessons I've learned 😎
 

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