All posts by Colin R
Below are all of Colin R's postings, with the most recent are at the bottom of the page.
Colin R: In my previous post I didn't make suggestions for fixing the problem. Well, short of writing to Ofcom and your MP to complain, you might try:
a) experimenting with different levels of gain on the amplifier, if your amplifier has variable gain, and if not, trying an alternative variable gain amplifier. Turning down the gain may just reduce the unwanted weaker signal to a level that lets your TV or PVR receiver resolve the stronger signal without interference and lock on.
b) experimenting with rotating the aerial by up to about fifteen degrees either way, possibly combined with a higher amplifier gain. This will reduce the main signal, assuming that the aerial is currently perfectly pointing at your preferred transmitter, but hopefull not so much as to make it too weak for the receiver, particularly with a bit more amplification. Crucially though, it may move the other transmitter into a a low gain or null lobe of the aerial's reception polar plot, thus significantly reducing or eliminating that other unwanted signal.
c) experimenting with pointing the aerial at the other transmitter, e.g. if currently pointing at Crystal Palace then point it at Hannington instead, and vice-versa, possibly also combined with a) and b) above.
d) if your aerial is in the loft, try it outside, combined with a), b) or c) above if necessary.
A useful gadget when doing the above if your budget stretches to about 35 quid is a Sathero or equivalent digital terrestial finder. These are more expensive than other so-called signal finders, but the advantage is that it will show the signal strength and quality on each channel separately, whereas the cheaper models just show, or claim to show, overall signal strength across all channels.
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NICKADSLUK: I agree with you about the hassle of switching between Freeview and Freesat.
Unfortunately those of us with both Freeview and Freesat receivers, e.g. many recent model TVs, and group A aerials for Crystal Palace, suffered a double whammy this year when firstly Channel 4 removed Channel 4 HD from Freesat, and then just a month later, the Com7 and Com8 at CP moved to channels 55 and 56.
This means that either you have to keep switching between Freesat for e.g. BBC News HD, and Freeview for e.g. Channel 4 HD, or you have to shell out hard-earned cash to get a wideband aerial, because Freeview won't give you a free wideband aerial if you have satellite capability - perhaps a triple whammy!
Also, if you want to watch Channel 4 + 1 HD and 4seven HD then then the only option is a wideband aerial because these are not on group A channels any more, and nor are they on Freesat.
So the government might be raking in billions in licences for 5G, but it is 'taxing' some of the four and a half million people that are served by Crystal Palace who now have to shell out money for new wideband aerials, or put up with at least some channels lost, if they have both Freeview and Freesat.
Miffed of Weybridge!
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Colin R: .... and then, just when you have forked out for a new wideband aerial and you think it is safe to go back into the kitchen (or wherever else your telly is)....
... you get co-channel interference because all the transmitters are being changed to broadcast Com7 and Com8 on the same channels 55 and 56! Aaarrgghhh!!
It's really is the final straw, isn't it?
Extremely miffed of Weybridge
Dear Philip Hammond MP........
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Colin R: .... and sadly, no, it's not even the final straw. It has been said that channels 55 and 56 have been chosen for Com7 and Com8 because they will lie in a narrow gap of the 700Mhz band (743 - 757MHz) that won't be used for 5G, at least initially from 2020.
But that still means that frequencies from 700-740MHz and 760-800MHz will probably be used for 5G. If you happen to have a mobile antenna mast nearby your home, or on the line of sight to your TV transmitter (my nearest mast is 600 metres from my house at about 20 degrees off the line of sight) then your TV receiver is likely to be swamped by the strong adjacent 5G signals, thus losing reception of channels 55 and 56.
This is because TV terrestial receivers are actually designed to receive all of the 700MHz band (and the 800Mhz band as well up to channel 68 at 850MHz), and being consumer electronics, and not professional communications receivers costing thousands that have special band-pass and notch filters to filter out strong local transmissions on adjacent frequencies, the so-called automatic gain control in the receiver will probably desensitise it so much because of the relatively strong local 5G signals that TV channels 55 and 56, ususally broadcast with much lower power than the other multiplexes anyway, will no longer get through other than for people who live quite close to the TV transmitter.
So after all this hassle and wideband aerial cost, come 2020 many of us might find that we can't receive the Com7 and Com8 muxs after all, and our new aerial purchase only lasted to get us these channels for a couple more years!
It is also said, that by 2022 Com7 and Com8 might move again, presumably to lower channels / frequencies that are below the 700Mhz 5G and 800MHz 4G bands. This just leaves Baldrick to explain why they were ever moved to ch55 and 56 in the first place!
Does anyone get the feeling, like I do, that the government would like to sell off the entire UHF TV specturm to mobile data serivces sometime in the next ten or twenty years, and shut down terrestial TV altogether? All these recent less-than-user-friendly changes may be a way of 'encouraging' people to switch to satellite TV, or in due course to most TV being delivered by broadband Internet. It may be no coincidence that Ofcom recently set OpenReach and other broadband infrastructure providers a target of a minimum of 10Mb/s broadband to all homes, i.e. sufficient bandwidth to be able to watch any television channel of your choice. It may be feasible, and it may even be reasonable by then, but it would be nice if there was some open and honest communication of the strategy, if this is indeed the case.
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C
Crystal Palace (Greater London, England) Full Freeview transmitSunday 29 April 2018 2:43PM
Weybridge
Peter K: StevensOnln1 is probably right if you have recently installed an amplifier or extra amplifier. But if nothing has changed in your setup and suddenly you are getting this problem then apart from cable or connection faults, it is possible that it is co-channel interference from the recent transmitter channel changes. However this doesn't explain you having this problem on all muxes, so it may well be a signal strength or an intermittent cable / connection fault.
You said that you live far down in Hampshire, so-channel interference may be experienced on channels 55 and 56 because Hannington is since 18 April transmitting Com7 and Com8 on these channels which, for those in the overlap area between Hannington and Crystal Palace, now conflict with Crystal Palace which has been broadcasting these muxes on channels 55 and 56 since 21 March.
You may also experience co channel interference on channel 35 if you are close to the Lambourne repeater transmitter, and / or channel 30 if you are close to the Tidworth repeater, both of which have had channel changes on 18 April that now conflict with Crystal Palace.
Did you start getting your problems from 18 April onwards? If it was earlier then your problem is unlikely to be co-channel interference.
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Chris Roberts: Great news Chris. However, for some others in this Crystal Palace thread I am sad to repeat my previous tongue-in-cheek comment "Just when you though it was safe to go back in the kitchen.... (or whereever else in your house that your TV is)!"
The reason is that these channels changes to various transmitters are going to go on apace for the rest of the year. The next change that may cause Crystal Palace viewers of Com7 on channel 55 problems is that Rowridge main transmitter (big and powerful like CP and Hannington) on the Isle of Wight is going to start transmitting Com7 on ch 55 on 2 May -Wednesday this week.
Fortunately for you Chris in GU1 and others in the Sonning area etc that have had problems with the Hannington co-channel interference since 18 April, Rowridge signals shouldn't bother you except on the few ocassions a year when there is a 'Tropospheric lift' that allows UHF signals to travel much further than normal, for a few hours or a day or so.
However, people in the overlap between Crystal Palace and Rowridge - roughly north-west to south of Basingstoke and down to a line east of Winchester - who currently choose to watch London programmes from Crystal Palace may possibly start to suffer the same co-channel interference that has affected the Hannington / CP overlap area recently, unless the authorities get the phasing right.
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For Crystal Palace viewers who are wondering if the authorities planning and implementing these channel changes for the 700MHz clearance are entirely competent, you may be astonised to read the following excerpt from DigitalUK's Industry Briefing dated Feb 2018, updated Mar 2018 which talks about all of the channel changes in several regions including London, i.e. including Crytal Palace:
Most aerials are expected to be capable of receiving a reliable signal following the changes. However, some grouped aerials - notably group C/D - may need to be updated. A wideband model is generally recommended.
So, notice how this paragraph completly fails to recgnise that everyone tuned to Crystal Palace who have a group A aerial will most likely not be able to receive Com7 and Com8 on ch55 and ch56, unless they live quite close to the transmitter.
How can anyone have any confidence in DigitalUK if they fail to give correct guidance on even the most basic principles that group A aerials are not only not designed to receive 740-760MHz (ch55 & 56), these aerials are actually specifically designed to reject these signals!
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Monday 23 April 2018 8:50PM
Steve & Chris Roberts: This may be co-channel interference if you can get both Hannington and Crystal Palace. The trouble with the 'subtle and cunning plan' of the transmitting authorities to put Com7 and Com8 on channels 55 and 56 everywhere is that, unless the signals are perfectly sychronised at all transmitters, then out of phase signals start to cancel each other out (completely at 180 degrees out of phase).
So it may be that the two transmissions of the Com7 mux on channel 55 at Crystal Palace and Hannington may be, by coincidence, quite out of phase, and hence the interference is causing signal quality 0, but the two Com8 mux transmissions on channel 56, may be by coincidence, in phase, and hence you can receive it.
I am in Weybridge, and although I am much closer to CP than Hannington, ever since 18 April, I am now getting intermittent pixellation on channel 55 mux channels such as BBC News HD, because of interference from Hannington off the back of my shiny new (since the March CP channel changes put paid to my old group A aerial) wideband aerial.
This is what comes of letting Baldrick design a channel strategy that breaks all of the cardinal principals that have governed UHF transmitter channel grouping and mapping for fifty years!
Or more's to the point, rather than a tongue-in-cheek reference to Blackadder, this is in fact what happens when the government goes for a dash for cash from selling off first the 800Mhz TV band for 4G mobile data, and now hastily preparing for selling off the 700MHz TV band for 5G mobile data! All the old channel and aerial groupings that were designed to prevent just this sort of interference seem to have been thrown out of the window.