All posts by Dave Lindsay
Below are all of Dave Lindsay's postings, with the most recent are at the bottom of the page.
Briantist: My thinking is that the Group system was devised for an engineering reason. I understood this to be because Group aerials are more sensitive than wideband ones, hence there is a trade-off.
The Group system has now been sacrificed. Is there really no engineering benefit to having it?
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Briantist: Thanks for the link on The Inversion Effect.
Will the signals reflected back down (from an normally unreceivable transmitter) only interfere with a local signal on the same UHF channel anyway? In which case, how could the Group system be of any benefit?
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Lee: Perhaps the signal going into your receiver is too high now. You are just less than 5 miles from the transmitter.
See this:
Freeview signals: too much of a good thing is bad for you | ukfree.tv - independent free digital TV advice
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Jordan P: Perhaps the muxes that were breaking up were being picked up from another transmitter, hence why the apparently correct ones are "new".
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I have an issue with one receiver freezing, when two others that are connected to the same aerial do not.
My Sony RDR-HXD870 freezes I estimate on average every five or ten minutes on C51 (less often on others). Yet the Panasonic TU-CT41 and Hauppauge TV USB dongle don't.
The Hauppauge software has a signal monitor with it and it shows how many errors. When the Sony breaks-up, no errors (correctable or uncorrectable) are shown by the Hauppauge software.
The devices are connected by short 1.5m leads so are not far apart. The Sony does it when it's the only device turned on.
Does the fact that two devices work fine suggest that the aerial and downlead are fine in my location?
The aerial is a 10 element contract wideband fitted in the loft. The downlead is a 10m long crappy coax (silver foil screen with 8 silver conductors!).
It was a DIY purchase from Argos around 15 years ago and has worked perfectly picking up DTT pre-DSO.
I know that it's a poor aerial, but could it be the cause of one receiver having problems when two others don't (on the same channel at the same time)?
I have tried attentuation and it makes no difference. Signal strength given by the Sony (without attentuation) varies between muxes: 70% to 92%
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Briantist: Thanks. I read the page about too much signal being bad a while ago and as a result, was reminded of it when I experienced repeated freezing. I got a variable antennuator (like the one shown in the photograph on that page) and even when the signal strength is attentuated to around 40% (from about 85%) on the most troublesome mux, it makes no difference.
jb38: You have confirmed the conclusion I was coming to: That is that it is an aerial/downlead problem. I'm now using another aerial and it's working just fine.
What threw me was the fact that the Panasonic and Hauppauge work perfectly fine (connected to the same aerial, tuned to the same channel at the same time). That is, listening to all three devices at the same time, only the Sony breaks-up. However, I do appreciate that not all devices are identical.
There is another loft aerial for another room and I've run a coax extension from there to the Sony's input (which was fed from my aerial). So far, so good, no break-up, even though the strength from that aerial is 85% (with no attentuator).
The reason I introduced the passive splitter was so as to allow the amp in the Sony to be turned off when it's in standby. Thus, if it didn't work (using the splitter), then there would be no need to get a powered one because I have one! (All devices are within a metre or so of one another.)
This aerial worked just fine pre-DSO, even during the snow.
I think that the most likely cause is reflections caused by a large warehouse (nearly half a mile long) which was built a number of years ago (ghosting appeared at that time). It is a couple of miles away at about 140 degrees from the direction that the aerial faces. The rooftop aerial also suffered from ghosting on analogue.
It was particularly bad (not terrible by any means though) with my loft aerial on BBC Two analogue, which was on C51, which is now occupied by the mux that is freezing the most. I think it's fair to assume that any such reflected digital signals would have been small (negligible maybe) pre-DSO and increased considerably now.
I remember watching the snooker on analogue (on BBC Two) and seeing a dark impression of the queue ball part way over the screen from the proper one. Does this suggest an inverted reflection?
Mark Fletcher: When I retuned at DSO, I made sure that my tuners were on Emley Moor. Sometimes they do get Belmont. In the past with analogue I tuned presets 5 to 9 (or 6 to 10) to Belmont. Even with the aerial being in the opposite direction, it came in quite strong.
Most Doncastrians seem to be on Emley, except for a few places where the topography doesn't allow. Belmont broadcasts different local news so I would never consider it unless there was no other option.
I've looked extensively at ATV's website. It's excellent with lots of information on how things work, as well as the online shop.
The reason for the DIY purchase from Argos in the early 90s was because that was the only real option! Now the internet has come along, there are many more choices.
I don't hesitate when say that I wouldn't buy the cheap DIY crap again!
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Mike Dimmick: That document is interesting. Why might they have decided to implement differing radiation patterns for the two channels? What was the point of this?
The chart published elsewhere by UK Free TV showing the number of homes served by Emley Moor indicates that not all will receive both PSB and commercial muxes:
The commercial multiplex after switchover: ArqA, ArqB and SDN | ukfree.tv - independent free digital TV advice
Presumably some at the fringes will only be able to receive the PSBs.
This is despite them all being listed as having the same ERP of 174kW.
Is this evidence that the radiation patterns of the PSBs and Coms are different? (DN31NJ)
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Mike Dimmick: Does each mux have its own set of panels then?
Why the gap of 11.5m?
I assumed that underneath the fibreglass shroud there would be rows of panels (without gaps) similar to these being installed at Sandy Heath:
mb21 - The Transmission Gallery (DN31NJ)
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Andy: You're about a mile from Beecroft Hill transmitter. If you're aerial is directed to Emley Moor, your receiver could have tuned to Beecroft Hill (for BBC & ITV/C4/C5) which explains why reception can be poor.
Beecroft doesn't carry the three commercial muxes, so if you get them satisfactorily, then they will be coming from Emily (as only it broadcasts them where you are).
See:
Digital Region Overlap | ukfree.tv - independent free digital TV advice (DN31NJ)
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Saturday 24 September 2011 12:35PM
If one of the networks can operate as a SFN, then why can't more of them? Is there a disadvantage to utilising an SFN which is why others are multi-frequency networks?