Question Missing channels - Oxford Area transmitter

Steamage

Novice Member
I'm having very similar problems. Not sure if I should piggy-back on this thread or start a new one...
I live in Bletchingdom (OX5) about 5 miles north-west of the Beckley transmitter, nr Oxford. My aerial is in the roof and hasn't been changed since I've lived here (more than 20 years) so is almost certainly the normal UHF design. Around here, we could get perfectly good analogue reception with a bent coat-hanger!

I have a Humax HDR-FOX T2, which I bought when Freeview+ became available, linked by HDMI to a Panasonic Viera TV (SD Freeview only). The channel I watch most is BBC4 HD (channel 106). This has been unreliable for a year or more - often blocky, sometimes quite unwatchable.

Knowing that Freeview channels move around quite often, I retuned both TV and HDR recently, when the TV prompted me that new channels were available. Since then, BBC4 HD on 106 has gone from the HDR programme guide. Channels 105 (C5 HD), 107 (BBC News HD), 109 (C4+1 HD) and 110 (4seven HD) are all present, though 107, 109 and 110 are unreliable.

What, if anything, has happened to Ch 106-110 on the Beckley transmitter lately? What's the best thing to do about it? Thanks in advance

(PS: what's the "DiUK Predictor" mentioned above? A Google search didn't turn up anything that looked related to digital TV channels.)
 

Rodders53

Distinguished Member
I live in Bletchingdom (OX5) about 5 miles north-west of the Beckley transmitter, nr Oxford. My aerial is in the roof and hasn't been changed since I've lived here (more than 20 years) so is almost certainly the normal UHF design. Around here, we could get perfectly good analogue reception with a bent coat-hanger!
Oxford was a group C/D transmitter for analogue. Once DTT started around 20 years ago it needed a Wideband aerial to receive the lower frequencies. Some C/Ds work OK with lower frequencies as well (Triax relabelled their C/D as Wideband because it worked fine like that).

On 27th February 2018 COM6 and COM7 swapped transmit frequencies (31 and 55) at Oxford. On 23rd May 2018 COM5 and COM 8 swapped (37 & 56) and most other muxes changed to mostly lower frequencies as well. Making Oxford more of a group B transmitter with just the two HD COMs in the older high frequencies 55/56 at a low 13-14kW erp.

I have a Humax HDR-FOX T2, which I bought when Freeview+ became available, linked by HDMI to a Panasonic Viera TV (SD Freeview only). The channel I watch most is BBC4 HD (channel 106). This has been unreliable for a year or more - often blocky, sometimes quite unwatchable.
Knowing that Freeview channels move around quite often, I retuned both TV and HDR recently, when the TV prompted me that new channels were available. Since then, BBC4 HD on 106 has gone from the HDR programme guide. Channels 105 (C5 HD), 107 (BBC News HD), 109 (C4+1 HD) and 110 (4seven HD) are all present, though 107, 109 and 110 are unreliable.

What, if anything, has happened to Ch 106-110 on the Beckley transmitter lately? What's the best thing to do about it?
106 BBC Four HD is on freq ch 56 COM8. 107, 109 & 110 are on COM 7 freq ch 55.

The frequency changes in February and May last year seems to coincide with your problems quite well. Nothing has happened at Oxford since then. It suggests that the aerial system is borderline inadequate for the 55/56 frequencies at the -6dB/-9dB transmitted power cf the SD COM/PSB frequencies.

Go over all the cables and connectors with a fine-toothed comb. A loose plug/socket or joint may make a big difference. Re-make and suspect hand'made plugs. Try alternative moulded leads to see if something changes. Also look for damaged (crushed or kinked) cables and replace any like that (such damage can give very frequency selective problems).

The Humax -T2 signal condition metering is very useful and should be used to check the strength and quality numbering for each multiplex frequency you receive. Report back with all the numbers you have after checking the connections and cables.

If there's no simple 'connection fault' that helps: try relocating the aerial in the loft/roof space. Raise it higher/lower, crab left/right and fore/aft a little at a time to see if you can improve the signal strength and quality for 55 & 56 (using the Humax -T2 metering).

(PS: what's the "DiUK Predictor" mentioned above?
DiUK Predictor was probably a clickable link to the digitaluk website? This link: http://www.digitaluk.co.uk/coveragechecker/main/trade/OX53dh/old/0/NA is the reception prediction for a shop in your village. For that same postcode Wolfbane predicts 71dBuV/m at 8 m above the ground for the 50kW erp COM SD muxes; 74 dBuV/m for the 100kW PSBs and around 65dBuV/m for the two HD COMs (7 & 8) which are giving you trouble. Typically roof tiles or slates will lose at least 6dB of the signal cf outside. Even so, those numbers are high. Possibly high enough to cause overload issues** with a sensitive receiver like the Humax -T2?
So the numbers you get would be really useful if you can't sort things out easily.

** Overload = too much signal = distortion of the signal = breakup and poor quality / no signal indication which is much like how a lack of signal manifests itself.
 

Steamage

Novice Member
Thanks for the info. It will be Tuesday before I get a chance to play with cables, aerial, etc. I'll report back later in the week
 

Steamage

Novice Member
Coax cables all have moulded plugs and all appear to be properly connected.
My TV is finding ordinary DVB stations on channels 22, 29, 31, 37, 41 and 44.

Humax settings/installation/manual search gives strength & quality by channel:
DVB-T
22: S 27; Q 100
29: S 42, Q 100
31: S 52, Q 100
37: S 55, Q 100
41: S 50-51; Q 100
42: S 10; Q 10
44: S 42; Q 100

DVB-T2
47: S 48-50; Q 100
48-54: S 0; Q 0
55: S 36; Q 100
56-69: S 0; Q 100

I've not been up in the loft yet to play with the antenna but that seems like a bit of a long shot. Surely if that just needed a few tweeks, Ch 56 would be showing up with low power?

Thanks in advance
 

grahamlthompson

Distinguished Member
Coax cables all have moulded plugs and all appear to be properly connected.
My TV is finding ordinary DVB stations on channels 22, 29, 31, 37, 41 and 44.

Humax settings/installation/manual search gives strength & quality by channel:
DVB-T
22: S 27; Q 100
29: S 42, Q 100
31: S 52, Q 100
37: S 55, Q 100
41: S 50-51; Q 100
42: S 10; Q 10
44: S 42; Q 100

DVB-T2
47: S 48-50; Q 100
48-54: S 0; Q 0
55: S 36; Q 100
56-69: S 0; Q 100

I've not been up in the loft yet to play with the antenna but that seems like a bit of a long shot. Surely if that just needed a few tweeks, Ch 56 would be showing up with low power?

Thanks in advance

Basically you likely have a group aerial with UHF channels above 47 which are now out of band. Replace it with a log periodic.
 

Rodders53

Distinguished Member
Sorry for not replying sooner. Been away in the caravan and had no internet access.

Those numbers are not a group C/D aerial response issue: Oxford was originally and until very recently (February/May 2018) still was a group C/D transmitter. Frequency channel 22 is from a very distant CP not OX so indicates good gain at low frequencies, but should be ignored/deleted as reception will be poor. But it suggests a wideband aerial is already fitted (some C/Ds work quite well at group A frequencies, too). 42 is from Hannington (Meridian ITV/C4 in SD) and again should be ignored/deleted as reception will be very poor.

The Oxford numbers don't quite conform to the levels being similar for the 3 x 100kW erps : 41, 44, 47; and also similar, but lower, for the 50kW: 29, 37, 31 and in-between for the 84/82kW erp for 55 and 56 respectively. I believe they show classic signs of 'standing wave' reception cancelling/reinforcing on different frequencies. It may account for the lack of 56 and the low level of 55. But a dodgy connection on the aerial may also give some issues and that's the first thing to check.

NB As well as missing 56 the Local TV frequency ch 34 has not been found; but that is not directed towards your location. See the transmit patterns at the end of Oxford (Oxfordshire, England) Full Freeview transmitter

As the existing aerial is in the loft then a new aerial can be d-i-y fitted as easily as checking the aerial connection / cable and re-positioning it. But also look around: are trees giving problems? (Grown up in front of the aerial). Has / is building work ongoing? Scaffolding around homes very nearby. A loft conversion of a close neighbour upsetting your reception by obstructing a clear view of Beckley?

BUT and it's quite a big BUT... The levels you have on the HDR-Fox-T2 with the existing aerial are toward the marginal level in my view. Ideally you want over 60 on the signal level for the weakest received frequency. So what does the current aerial look like? You may need one with more gain than the existing aerial. Or moving outside and higher.

A good local aerial installer may be worth consulting though. Just ensure any new aerial is a quality brand and not a 'contract' aerial with a pressed aluminium rectangular plate for its reflector!
 

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