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What signal strength is too strong? - Do I need an ariel attenuator?


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Old 13-06-2011, 12:31
bahjan
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Hi,

I'm in Central Scotland and I believe my Transmitter is most likely Black Hill but it could also be Craigkelly. I have a hi-gain arial mounted in the attic, a set-up which has worked fine for a number of years.

I use a Pioneer Freeview Box DBR-TF100, an older model I know, but I really like the features and design compared to all others I've seen, I've looked on various sites to see if this is specifically mentioned as unsuitable for post-switchover, and it isn't on any list (I know other models may be affected).

Switichover began last week and since then I have noticed intermittent pixalation and tearing on portions of the picture, bottom edge, middle. It only occurs for a few seconds, but I have noticed it happens on channels BBC 1, 2, where the signal strength is at 88% + - other freeview channels which are as low as 44% work fine with no such interference. For this reason, I've ruled out interference from electrical devices as the picture would be effected on all channels no matter the signal strength.

To try and remedy the situation, I turned the box off overnight, have re-tuned several times and replaced channels, the only thing I haven't tried is a factory re-set/retune. Is a signal strength of 88-91% too strong?

Switchover as far as I know is due to end this Wednesday when another re-tune will be necessary. It's possible the issue may disappear, but I am begining to wonder whether I need a variable attenuator to knock back the signal a bit - trouble is my lower strength channels will be affected and I might lose them.

Anyone else had this experience during switchover?
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Old 13-06-2011, 12:36
tellytart1
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With digital TV signal strength isn't anywhere near as important as signal quality.

Does your receiver report the signal quality? This can be affected by an aerial that isn't aligned properly, and is picking up lots of multipath reflections.
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Old 13-06-2011, 12:46
bahjan
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Yes, along with signal strength, signal quality is reported as 100% on all channels, regardless of signal strength. I have noticed that the problem I'm getting seems to be with the BBC channels and red button channels. I haven't tried BBC 3 or 4 yet, but I expect they are affected too. As an experiement, I kept the signal check up and watched for any changes when a 'fault' occurred, but there were none - neither signal quality or strength seemed to dip significantly. I don't think I mentioned eariler, it's not only a picture issue, sometimes the sound is affected too.

Could it be since swtich over started I'm getting interference between signals from Craigkelly and Black Hill? If so, wouldn't it affect all channels not just the BBC ones? My first thought when the issue started was to check for Transmitter maintainance, but there was none reported as on going.

Last edited by bahjan : 13-06-2011 at 12:59. Reason: addition
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Old 13-06-2011, 13:21
Peter Rhea
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Old 13-06-2011, 13:42
Ray Cathode
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Is it different on the Mux B channels? Ie BBC Four/CBeebies, Parliament found in the 800s as duplicates?
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Old 13-06-2011, 18:09
bahjan
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Is it different on the Mux B channels? Ie BBC Four/CBeebies, Parliament found in the 800s as duplicates?
On 800 channels signal strength 28% and signal quality 9-20% are both very poor with consequent poor reception....

CBeebies on regular channel 071 strength is backup to 81% quality 100% issue still occurs I have tried reporting it to tec at BBC - I'll see if they reply. On Saturday evening I discovered a fault on my taped programmes - picture but no sound. It wasn't my equipment (I checked) all seemed okay on Sunday. Don't know if it relevent to the issue, but I reported it a anyway.
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Old 13-06-2011, 19:01
Dr.OliverTwich
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That Pioneer is one of the few OnDigital boxes that claimed 8k compatibility. Wait until the second retune and see if things are OK or the same on all the new muxes. By then all muxes will be at 100kW erp rather than just the BBC one.

The Black Hill power increase is from 20kW to 100kW - 5x or approximately 7dB. IF an attenuator is needed a 6dB one will get you back to roughly the pre-DSO levels. (A cheap nasty passive splitter will lose 3-4dB if you have one lying around - but don't buy one instead of a proper attenuator.).

Craigkelly erps go from 4 or 2kW to 20 or 10 kW also 5x so the same amount of attenuation would be needed if necessary.
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Old 13-06-2011, 23:37
Hector
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I have a similar problem on 1 box:
http://forums.digitalspy.co.uk/showp...&postcount=125
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Old 14-06-2011, 00:14
reslfj
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....... The Black Hill power increase is from 20kW to 100kW - 5x or approximately 7dB. ....
Craigkelly erps go from 4 or 2kW to 20 or 10 kW also 5x
You forget that the 4 analogue channels have/had a much higher power output - typical 5 times above the final post-DSO level (max analogue comes in short bursts).

Don't think overload of the inputstage is a major problem. Regulate the amplification down as much as possible - before even thinking of adding an attenuator.

Lars
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Old 14-06-2011, 10:16
Dr.OliverTwich
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You forget that the 4 analogue channels have/had a much higher power output - typical 5 times above the final post-DSO level (max analogue comes in short bursts).

Don't think overload of the inputstage is a major problem. Regulate the amplification down as much as possible - before even thinking of adding an attenuator.

Lars
I did not forget (although I never mentioned them). {Someone once taught me to Keep It Simple S....)

As DSO stage 1 has happened there 5 analogues have dropped to 4. As the 5 analogues gave no problems to the OP with 7 pre-DSO muxes, analogue is unlikely to be cause of the issue (in my opinion).

OP made no mention of amplification, but that a valid point.

Perhaps the Pioneer isn't actually 8k compliant? Perhaps it doesn't like mixed 8k/2k signals (why, though??)? Hopefully at DSO2 on the 22nd all will come good.

[NB I now realise the OP must be on BKH because Craigkelly started on 1st June and DSO2 there is tomorrow.]
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Old 14-06-2011, 10:46
Winston_1
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The strength/quality readings from a STB are meaningless apart from a guide. There is no standard and one makers 100% could be anothers 70%.
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Old 14-06-2011, 12:31
bahjan
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Thanks for all the advice, much appreciated. I will wait until swtichover ends, and see what I have after that. There is no added amplification to my digital box, until now, it ran fine straight off the ariel. My issues started on June 8th so I think I must be BKH, two dates were mentioned - is the final phase on the 22nd? Would it gain me anything to do a factory reset then retune the box?
Thanks again - I'll post later and let you know what happens.
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Old 19-06-2011, 14:01
mim1946
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You should do the factory reset procedure both now and on 22nd June.

This is often (not always) a requirement for equipment to function correctly at switchover.

Samsung (with 'plug and play'), Panasonic (with 'shipping condition'), Humax (with 'default settings') recommend a factory reset at switchover, although some models will cope perfectly well with 'auto search', 'auto store' etc.
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Old 24-06-2011, 13:38
bahjan
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Unfortunately, retuning a switchover didn't seem to sort my problems. I tried a 6db attenuator but it didn't make any difference.
I emailed the BBC, they shunted me to OnDigital - and basically there live chat 'help' gave me a download of my freeview box user manual (basically, 'here's the instructions for retuning') which I'd already done - kicked the box back to factory defaults and now BBC1 on ch 46 which in is BKH (27 is Craigkelly). I checked all the channel numbers and they match for BlackHill.

Found this online utility:
http://www.wolfbane.com/cgi-bin/tvd.exe?

I put in my postcode and results were:

Transmitter Black Hill
BBCA UHF 46 100k
PSB 2 43 100k
A Com 1 41 100k
B PSB 3 BBC B 40 100k
C (Com) 2 Arqiva A 44 100k
D (Com)3 Aquiva B 47 100k
Gp B PL - H
Grid Ref NS******
Field 33 * distance 42 Bearing 235
Atenna (suggestion) Amplified extra hi-gain

* - where the field strength is asterisked, there is a possibility of multipath reception effects. It might be worth trying again with a greater antenna height.

Craigkelly which my box dosen't seem to pick up is only 13 miles distant, so is my problem down to multipath reception? Not sure I can increase the antenna height - however, as far as I know the hi-gain aerial isn't amplified - as far as I recall, pre-switchover the aerial didn't need anything added to it. My signal strength is reported as minimum 85% - can't see why an amp is needed. Could it be the aerial is now too strong? I suppose if that had been the case, the attenuator might have worked?

I was beginning to think it was my freeview box, but apart to reception issues it is picking up channels and acting normally. Oddly I have no 800 channels on my box - to be exact, I only have ch 800.

I also found this website that some may find useful.
http://www.stevelarkins.freeuk.com/F...v_channels.htm
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Old 24-06-2011, 14:29
bahjan
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I've just checked with On digital site for post swtichover aerial advice
Craigkelly
1 June 2011 15 June 2011 Group A aerial Wideband aerial
Black Hill
8 June 2011 22 June 2011 Group B aerial Group B aerial

I believe I have a Group E wideband which according to this should still work
http://www.aerialsandtv.com/blackhilltx.html

Is the aerial now the wrong type? Still confused.....
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Old 24-06-2011, 14:42
chrisjr
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Ignore Wolfbane's aerial recommendation. I suspect they only have the one option as every time I use it it gives the same answer. I suspect they would recommend Amplified Extra High Gain if you had the aerial mounted three feet from the top of the transmitter mast!

Anyway. There is a chance that signal strength has nothing to do with your problem at all. There are other causes of interference affecting the picture and sound on digital telly that have nothing to do with the broadcast signal.

For example when my mum first went digital her set top box at the time muted the audio every time she opened the fridge door and the light came on! Any sort of iffy electrical equipment can radiate all sorts of mush either through the air or via the mains wiring that potentially can cause interference. Even changing weather conditions can cause problems.

Tracking it down could be a problem. If it was consistently at the same time every day then it could be something like a heating thermostat switching on or some other device on a time switch for example. I've seen posts on DS where problems have been reported when the street lights outside turn on. So it could be some electric appliance in your home, a neighbour's home or just about anywhere nearby that is causing the problem.

As I say finding out what could be a bit of a pain to put it mildly You could turn everything electrical off in your home except for the box and telly and see if that cures it. Then switch things back on one at a time till you find the culprit. But as I said it might not be in your home anyway.

Something you can do is to double check everything in your installation is in order. Check the cable run as much as you can to ensure there are no signs of damage. And make sure you are using decent double screened cable for the best results. That includes any cable from a wall connector box to the set top box.

Also make sure the aerial lead is kept as separate as possible from any other cables to minimise the chances of interference. Especially if you do have a wall box and use a cheap and nasty thin cable with poor screening to hook up the set top box.
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Old 24-06-2011, 14:44
chrisjr
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I've just checked with On digital site for post swtichover aerial advice
Craigkelly
1 June 2011 15 June 2011 Group A aerial Wideband aerial
Black Hill
8 June 2011 22 June 2011 Group B aerial Group B aerial

I believe I have a Group E wideband which according to this should still work
http://www.aerialsandtv.com/blackhilltx.html

Is the aerial now the wrong type? Still confused.....
Group B is UHF channels 35 to 53. Group E is UHF 35 to 68. So as you can see a Group E will work in a Group B area.
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Old 24-06-2011, 15:26
bahjan
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Been onto On Digital again - they are recommending Group W aerial for BKH in my area - as I said I think I have a group E - however, according to earlier link website info an E should work... Can anyone out there illuminate me?
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Old 24-06-2011, 15:33
chrisjr
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The UHF channels used by Black Hill are entirely consistent with a Group B or a Group E aerial. So unless they are considering either moving the mux channels out of band at some point or adding more out of band muxes either a B or E aerial should suffice.

Looking at the channel numbers pre- DSO 2 then a group B aerial may not have picked up all the muxes, whereas a Group E would. But again no real need for a wideband even then.
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Old 24-06-2011, 15:37
ejstubbs
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Been onto On Digital again - they are recommending Group W aerial for BKH in my area - as I said I think I have a group E - however, according to earlier link website info an E should work... Can anyone out there illuminate me?
"Group W" is just wideband ie not grouped. Post-DSO all Black Hill channels are well within the Group E UHF channel range.

Have a look at this page for more information about aerials, groupings etc.
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Old 25-06-2011, 12:21
King Bear
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No need to search any further.

http://forums.digitalspy.co.uk/showt...795&highlight=

You will just have to live with it I am afraid. I moved the Pioneer to a small bedroom tv and replaced it with a PVR on the main tv.
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Old 25-06-2011, 13:05
bahjan
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Yes, I found that thread too - I am like so many other owners very annoyed that all it needs is a firmware update (which Pioneer don't seem to be interested in) - My next question is - is there a box out there like the Pioneer? Here's a link to the specs

http://www.pioneer.eu/uk/products/ar...0GB/index.html
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Old 26-06-2011, 12:52
bahjan
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It seems with my Pioneer box DBR-TRF100 - I am now stuck in the hinterland between 2x and 8x compliancy. Despite being DVB badged - without the right OTA firmware (fat chance) it's only x2 compliant - I hate weazle-words in industry!!

Worst of all, not sure Pioneer make freeview boxes anymore. I bet there's nothing out there as well built these days......(another thing I hate...)
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Old 26-06-2011, 15:55
David (2)
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this was the plan all along with the move from ATT to DTT, turn the tv or box into a sort of PC, and then people will be stuck on a never ending upgrade path. This means a much improved way of making money (you have to buy new equipment a lot more often than before).
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Old 27-06-2011, 09:55
Richard Fusniak
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There is a chance that signal strength has nothing to do with your problem at all. There are other causes of interference affecting the picture and sound on digital telly that have nothing to do with the broadcast signal.
Just to add to that it may even be due to a strong radio frequency signal being radiated nearby that is not even on the same frequency. Sometimes harmonics from radio transmitters can be a cause. Check and see if there are any local radio amateurs in the neighborhood, commercial businesses, etc.

If you have an old medium/longwave receiver with a ferrite rod in it, tune this to a weak station and leave it near the mains lead of your telly. If it crackles when you get the interference then it's quite likely it is some sort of mains born interference.

You could try one of those mains suppression multi socket leads with inbuilt spike protection, the type commonly sold to protect PC's.
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