All posts by jb38
Below are all of jb38's postings, with the most recent are at the bottom of the page.
E. Mole: If you are referring to either a Sky or Freesat satellite installation then a 50% strength (or quality) reading is not conducive to reliable reception and can indicate that the dish is slightly out of alignment, this usually always being in the "right or left" horizontal plane, and so this aspect will require to be checked out.
However in cases where the TV can be seen from the dish, then provided that the latter is not located in a precarious position this out of alignment problem can sometimes be rectified by an able bodied viewer giving a slight nudge to either side of the dish whilst observing the results on the boxes signal check screen, preferably having slightly slackened the dishes horizontal clamps before attempting the exercise.
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les: With reference to that said at the start of "your" second paragraph regarding the one cable from the dish to the box, if you genuinely have Sky+ then you "must" have two cables unless you have the box set to single feed operation, which if you had would result in you being seriously limited in what you would be able to record, this being because that anyone using that mode can only record programmes on the same polarity as the programme that is being viewed hence the reason for twin feeds being necessary, and as mentioned by Dave Lindsay.
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K.Barrett: Well, what you are experiencing is unfortunately not that abnormal in situations such as you have described, and if a signal is always worse on a clear relatively cloud free day then its an indication that the reception at a particular location is dependant on reflective elements, something which certain types of clouds can be rather good at.
All DTT receivers operate on a threshold level whereby the spec of the tuners circuitry determines the minimum level that a signal can be decoded at, and with this level being variable between different brands of equipment, and so if an auto-tune is carried out and the scanning circuitry detects any signals, then even if they are sitting at just a fraction under the threshold level for the particular receiver being used they will either be ignored or maybe placed up in the 800 ranges dependant on how sophisticated the receiver might be.
The other and misleading (for some) aspect of this system being, that if its intended to carry out a manual tune whereby its usual to see the signal strength / quality being indicated as soon as the channel number that's intended to be scanned is entered into the box, this being seen "before" search or scan is pressed, then should it be subsequently discovered that after having pressed same that nothing had been picked up then this is caused by the threshold level circuitry referred to, and is because that as soon as search (or scan) is pressed the threshold circuitry comes into play whereas it wasn't before, as prior to pressing scan etc the tuner was just acting like a "free of restrictions" signal sniffer and why using this facility is a superior way on monitoring signal levels during any alterations being made to the aerial, i.e: by the very fact of continuous indications being seen no matter how low the signal drops to.
Taking this explanation into account you will probably have sussed out why you do not always get the same results during any tuning exercises carried out, i.e: because of you experiencing variable levels of signals from Mendip whereby Chiseldon might take the lead as far as strength is concerned on some occasions.
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K.Barrett: Just noticed that Dave Lindsay has also replied from another angle, and which if you discover that you are the only person thats having the problem could well apply, the problem possibly caused by either water having entered a junction box or even slight corrosion having developed on one of the connections, although I do appreciate that you have already indicated that you have checked on all of these possibilities.
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K.Barrett: I really think that you should consider it as priority with regards to making some checks with your neighbours, because unless its known if they are also experiencing the same type of problems as yourself there really isnt any point in you carrying out any further tests more than you have already done, which I may say is seemingly quite comprehensive.
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K.Barrett: I had also meant to add, that as Chiseldon is located so close to your area of residence then I wouldnt really bother too much about what band of aerial you are using as it doesnt really matter, but though its the fact that you also experience problems with Chiseldon that is the main thing to look into, and along the lines of ensuring that the relay is not just repeating a problem inherited from Mendip.
By the way, although no transmitter engineering should be taking place over the Christmas period faults can still occur on the transmission (relay) side that may not be instantly known about, and so it should not be automatically assumed that the station has a clean bill of health, so to say.
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K.Barrett: These are lots of myths around about aerials used for DTT reception and if one is required to cover the channels mentioned then it has to be a wideband version, but though NOT one of the high gain varieties in your situation as high gain (or so called) aerials rely on being precisely focused on the signal source, this being something that cannot really be achieved in circumstances such as yours and so using one of these types will give a slightly inferior performance (glitch wise) over that a wider acceptance angle type coupled to a booster of around 15db or so minimum.
Taking this into account I would recommend using a log 40 in conjunction with a variable booster of around the rating referred to, as should less than satisfactory reception be evident with this combination then I can say with a level of confidence that nothing will improve the situation, and with this basically being because that the problem is outwith your control.
This is a link to the type of aerial referred to.
Online TV FM DAB Aerial sales
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K.Barrett: Well I wouldn't rely too much on these terrain predictors as they take no account whatsoever of anything other than ground level, and so a person could be located behind such Sherwood Forrest or a number of tower blocks and yet it would still indicate a clear line of site.
As far as the XB22WB is concerned, all I can say is to give it a try, but though when a person is located in a difficult reception area then the secret is to try and have an aerial with as wide an acceptance angle of pick up as possible to compensate for the inevitable deviations in the angle that the signal is received at, then make up for the slight less gain by using a booster of the rating referred to.
After all it has to be appreciated that the only reason an aerial can be classed as high gain is because that the multitude of director elements located along the boom focuses the signal on the only active part of the aerial that exists, this being the element immediately in front of the reflector, whereas with log aerials all elements are active and thats why their response across the bands is so even when compared to other types of aerials.
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K.Barrett: I was just reading through your various postings again and in particular the one made at 11.41pm, should it transpire that your neighbours are also suffering from similar problems to yourself then if at all possible try and check at some location outwith your immediate area, maybe even a shop or store that sells TV's and such likes, but the main point is to be able to verify if the problem only exists in your immediate locality.
That said though, as far as interference is concerned if the problem is definitely only affecting the BBC transmissions then I very much doubt if its anything connected to local interference, as in my opinion (as an engineer) I feel that it would be a bit too coincidental (although not completely impossible!) for the BBC to be involved in both cases when two separate frequencies are involved, unless that is it was actually them at fault! because I remember a case some time ago in a Northern area of Scotland where an intermittent fault existed on a relays HD transmitter for nearly a week, this being because that the problem hadn't been noticed by the fact that it wasn't a complete breakdown in transmission.
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Tuesday 25 December 2012 9:43PM
k.Barrett: Out of all that you have reported the most significant factor is you having stated that using the Chiseldon relay did not show any improvement either, because the Chiseldon relay receives its programmes from Mendip and this could indicate that the relay is also receiving a corrupted signal, therefore I would not advise altering anything at present before making some local enquiries for purposes of finding out if others are being affected in a similar way to yourself.
By the way, the fact of having a 16 watts transmitter so close to your location "is" very likely to have an effect on your tuner by slightly desensitising it, this happening no matter what channel you are trying to receive although obviously the effect will get worse the closer you get to frequencies used by the Chiseldon transmitters, although by the fact of the two stations not being that terribly far off right angles to each other plus them being on different polarities does help.
Chiseldon: 27 - 24 - 21 (@ 323 degrees)
Mendip: (43 miles @ 243 degrees) 61 - 54 - 58 - 48 - 56 - 52, please note though that channels 54 (ITV) & 58 (HD service) are classed as variable for reception.