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In this section

Wednesday, 25 September 2013

11:36 PM

JLM,Ely: Thanks for the update on the situation, and pleased to see in your latest (09.46pm) posting that all is still indicating OK.

Although the reason for your problem, and with the rectification of, somewhat indicating that you must be located in a good area for reception otherwise the signal received using an aerial of that design when having been mounted in error as far as polarity is concerned would have been very poor right from the start, although the fact of your reception dipping in the evenings was an indication that the signal could not have been that stable, which of course is only to be expected with any aerial mounted incorrectly polarity wise and especially where slight distances are involved, as the aerial will try to grab as much of the signal as possible meaning that it will be prone to picking up reflections from the horizontally polarised signal that get bounced off objects along the way, and signals of that nature are always sensitive to changes in reflective surfaces that generally occur between day and later evenings caused by such things as moisture etc.

Of course slight signal drop off in the evenings is something commonly experienced in many installations and indeed will still be occurring, but with the effects of not now being noticed because the strength / quality that your signal will now be running at will be well in excess of the receivers cut off threshold level.

By the way the differences referred to would not be noticed on a Panasonics signal check screen, as Panasonics (and I use one) are inclined to indicate levels as being far higher than they really are when checked against say a Humax PVR, one of the few devices around whose indications are more in line with that obtained from a more professional signal strength meter albeit that its indications are in dB/m and not percentages such as indicated on a Humax.

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jb38's 7,179 posts GB flag
Thursday, 26 September 2013
6:24 PM

@jb38. I am happy that my situation is resolved but unhappy because I have suffered with generally poor reception for over a year; since my incorrectly polarised aerial installation in fact. Until I purchased the outdoor aerial, I was using an indoor aerial. I purchased and installed the outdoor aerial then called BT because the reception had not improved as much as I expected. The BT engineer came during the afternoon and tested my newly installed outdoor aerial and said the signal was low but acceptable. At the time, I asked him about polarity and he said I had installed the aerial properly. Thus, for more than a year I was under the (now mistaken) impression that my aerial was correctly installed and thus I suffered with intermittent issues as previously described.

Back to now. Wolfbane ( suggests I can expect around 52dBV/m for my location, TL532760.

May I take advantage of your skills one last time? I read (recently in the Technika ARLSSS1103 aerial booklet) that some receivers provide 5V at the antenna connector which means in such situations, a booster is not required. Does either or both of my Panasonic TX-32LXD1 and/or my BT Vision integrated digital terrestrial receiver model DIT7421/05 provide such a voltage on the aerial connection? I think it is also known as phantom powered aerial socket.

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JLM,Ely's 5 posts GB flag
JLM,Ely's: mapJ's Freeview map terrainJ's terrain plot wavesJ's frequency data J's Freeview Detailed Coverage

8:51 PM

Personally I would be very surprised if any TV set provided a DC voltage at the aerial input socket. The normal connection via a coaxial cable to the aerial would be compromised by having a voltage present. The aerial system presents a DC short circuit but a 75 Ohm impedance circuit to RF signals in the wanted design frequency range (around 450 MHz to 800 MHz). [DC continuity is a standard test for intermittently poor signals as it would be likely to show any cable breakages if they are present when tested.]

Any DC power required to operate an aerial amplifier would normally be provided by a power supply unit designed to add the required DC voltage, typically 5 Volts, using an input socket with the DC voltage present and an output socket that has no DC voltage (that output socket connecting into the TV RF input). Normally, the aerial amplifier would be fitted close to the aerial (so it only amplifies wanted signals from the aerial and not the 'noise' picked up on the coaxial cable) and is between the aerial itself and the power supply - so as close as possible to the aerial. That allows the supply to be in a convenient place for an electrical supply connection that is indoors and away from wet weather, etc. The masthead amplifier is weather sealed so should not allow water ingress if the connections are made properly.

Any terrestrial receiver would, therefore, be very unlikely to have this supposed 5 Volts present at the aerial input socket. (Satellite receivers do have voltages present at the input connections from the LNB on the dish, somewhere between 12 and 18 volts. That is set by the receiver so it can select horizontally or vertically polarised signals are received by the LNB. Freesat receivers also provide these voltages to operate the LNB on the dish.)

Thinking in 'first principles' terms, a 5 volt DC supply connecting into a 0 Ohms at DC circuit will potentially have infinite current flowing in the circuit! That would rupture any fuse! Formula I=V/R, so I=5/0, hence I=infinity!

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MikeP's 3,056 posts GB flag

9:10 PM

MikeP: sorry but some tv do have output voltage but they are normaly portable tv and cheap brands have seen lots.

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mazbar's 384 posts GB flag

11:16 PM

JLM,Ely: The 5 volt via the aerial socket facility is intended to supply power to remotely positioned amplifiers such as mast head types etc and with this being irrespective of whether or not they are actually mounted on the mast or in the loft, the main difference with those types being that none of have internal power supplies as their amplifiers extract the DC power for the amplifier from the coax without having any effect on the RF signal being fed back to the TV, however this facility is only found on certain model numbers within only one or two brands but with Panasonic's not being one of them, at least not as far as any that I am personally aware of nor did I see this facility mentioned in any of their manuals picked at random from the range I use for reference purposes, this also applying to your particular model of BT vision box.

With regards to the comment made by the BT engineer when referring to signal strength, this somewhat backs up my own statement regarding you being in a good area for reception, because if you were not then you would most likely have experienced reception problems right from day one due to the polarity error, the fact of the BT engineer not having picked up on this can only in my opinion, be put down to the possibility that he hasn't actually seen one of those types before, although I would have thought that the fact of the device having been mounted facing upwards towards the Sky might have caused him to latch on to the possibility that something was not quite correct about the installation.

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jb38's 7,179 posts GB flag
Friday, 27 September 2013
r veitch
4:16 PM
Newcastle Upon Tyne

how to connect btvisionbox and dvdplayer plus a cvr to sony braviatv

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r veitch's 1 post GB flag
r's: mapR's Freeview map terrainR's terrain plot wavesR's frequency data R's Freeview Detailed Coverage
7:19 PM

Hello can you tell me why i cant watch create and craft live on my computer for the last 2 weeks

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V PHILLIPS's 1 post GB flag
Pauline beer
7:36 PM

Can you tell me why I.t.v. Stations have been particularly bad this for many hours at a time

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Pauline beer's 1 post GB flag
Pauline's: mapP's Freeview map terrainP's terrain plot wavesP's frequency data P's Freeview Detailed Coverage
Pauline Beer
7:39 PM

Why are my I.T.V channels breaking up badly this week for many hours at a time, totally unable to watch

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Pauline Beer's 1 post GB flag
Pauline's: mapP's Freeview map terrainP's terrain plot wavesP's frequency data P's Freeview Detailed Coverage

8:37 PM

Pauline Beer: The problem referred to is likely still to be as a result of the continuing high pressure interference that has been plaguing viewers in various Southern areas, as although you reside @ 24 miles away from the Midhurst transmitter in an RH10 location and report problems with your ITV channels, another viewer located in an RH20 location @ 13 miles from the same transmitter posted a comment six minutes earlier to the effect that all his channels were OK except HD.

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jb38's 7,179 posts GB flag
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