All posts by Dr. John Pritchard
Below are all of Dr. John Pritchard's postings, with the most recent are at the bottom of the page.
Correction to my last posting: Maps suggest there are No G4 transmission services in this area (Thanet) but the maps may be out of date.
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Thank you, Dave Lindsay! The stub roads are still stubs, and you are right in noting that the Westwood Cross development is growing. However, the copse and park to the South of us are scheduled to remain as local amenities for the foreseeable future. My guess is that the stub roads will lead into a new Sainsbury (for deliveries) and out to Newington Road along an existing hedgeline, probably replacing an existing footpath between two schools. All a bit bizarre, but there we are.
From line of sight when sitting on the roof next to the ariels (real sight, not through a telescope) there does not appear to be any obstruction in the way. My cabling is all WF125 with F-plugs so on a presumption, now, that my signal strength is too strong, not too weak, I'm going to try an adjustable attenuator and taking my preamp/splitter out of the circuit with the best aeriel see if that may help in bringing the Dover Transmitter's 80 kw MUCS within tolerances that my HDMI television can accept. I'll also see if the attenuator will do the decent thing in downgrading a less powerful aeriel to our kitchen tv to make to restore domestic harmony there, too. And your suggestion regarding the b&w/colour shifts on our bedroom computer makes sense: I've checked the RF lead to the digibox (it, too, is WF125) and the plugs at each end are fine, but the digibox connects to the tv via a ribbon SCART lead that runs up the back of the tv case to the digibox on top of the set. So the SCART lead now seems to me the most likely culprit as that's the only analogue link in the chain. If that fails, I guess the next suspects are (1) the digibox itself notwithstanding the fact that it is the only one in the house that is now delivering all channels from Dover, or (2) the 20-year-old set which must be getting near its end of life anyway. Anyway, your advice that the b&w/colour shifts must be an analogue problem is hugely helpful. I'll report on the outcome of these changes in case that helps others!
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Oh, one more thing: Manston Airport does lie less than a mile away and the incoming flights do cross my line of sight to Dover. Strangely enough, this has never affected my reception at all, even during Air Shows (and be it remembered that in the distant past, Manston was capable of launching whole squadrons of Hurricanes & Spitfires all abreast, and later the place was used by lumbering great B-52s. Nowadays, while the debate over Boris Island continues, Manston seems fated to remain underused until the powers that be build a parkland station there and upgrade our tracks to suit our existing local Javelin 140mph train services on the line to St. Pancras International via Ashford. At present, however we don't have as much as one single scheduled flight a day into or out of Manston's 8000 foot nunways and the odd freighters that use the airport really cause no perceptible nuisances at all save to a few homes that sit right under the flight paths (most of which end up out over the Channel or the North Sea except for periods that can be measured in seconds.
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The Hi-gain aerial for my HDMI tv is a Televes DAT 45; the aerial for the kitchen tv is a wideband high gain 52-element aerial from a leading supermarket (ahem). The oldest aerial is a straight-forward group C/D 18-element log without any balun but with a "solid" flat-sheet reflector (with slots): I think it might be an old Antiference: not sure. The Televes and log aerials share the same cranked pole, and I'll see if I can increase the distance between them to avoid possible resonances or other interactions between them. Dave, any advice on how far apart they should be?
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Thanks, Dave. This is exceedingly helpful.
Changing the SCART lead didn't help on the analogue colour shifts: you're right. It did appear to make the colours more intense, which was unexpected. I'll check the other things out, by swopping the ancient tv for another that I can put in that bedroom. Adding the attenuator to the kitchen tv immediately brought back two of the three missing MUCs, including the BBC and ITV stations. I'll fine-tune the adjustable attenuation and see if the fifth MUC can be recovered, too. The power bricks and AC cabling appears to be affecting hum levels on the tv audio in the kitchen: more careful positioning dropped that back to a fraction of what it was. The aerial fly lead to the decoder is very poorly shielded (I'd ignored that before): the rest of the cabling is WF125 but that last two metres is a joke, especially as it is in close proximity to poorly shielded rfi sources. I'll just make up a new MF 125 cable and see what happens. I expect that to sort out the hum problem, at least!
What you say about the height of the aerial is highly relevant. I kept it low deliberately in part because there's a large aerial array not far from us (behind a local fire station on the Margate Road) and I felt keeping the aerials low helps to shield us from any rear lobe on our aerials. But the copse about 100m between us and the route to the Dover transmitter has grown like crazy in the past few years. All you've said on that score and on reflections from other near-ground topographical features between us and our horizon makes sense. In the case of the copse in particular, that extra 15 - 20 feet of height added in the past six years since we moved here won't be doing us any favours. Likewise two tall trees on our property line with our neighbour nearest to my best aerial have grown rapidly, too, and their span as well as their height could be adding all kinds of reflections, not least because there's a catenary cable between the bottom of the aerial pole and outbuildings to the rear: that catenary line carries two CAT 6e signal cables but when the trees and cabling are wet and swinging, well, probably not good. In the spring I hope to be able to put that cabling into underground conduits. One of the trees is also likely to go. Raising the pole will also happen as soon as I get another wall-bracket to take part of the weight and dampen oscillations in windy conditions. But tomorrow I'll also be testing the effect of the adjustable attenuator on our HDMI decoder and main tv: with a little luck that will restore domestic bliss within our household until the other work can be done with the weather improves!
In case all of this helps others, and just to offer further feedback, I'll record here any further developments as I continue to try to sort this out in the days or weeks ahead. Meanwhile, thanks, Dave!
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PS, Dave: I've taken onboard your observations about Log periodics, Yagis and high-gain one-size-to-fit-all models like my Televes DAT 45 (which to the unitiated is like the model shown on the chimney in the photo to the left of this forum). Having looked at the stats and your remarks, it all does make sense to me. The Televis was probably over-kill, but in the pre-switchover years when freeview was just building up, the Televes was highly recommended by one of our best local electrical supply houses. Very glad I was sensible enough not to go for the DAT 75 model. Those are beautifully crafted products, however, and I did have in mind the possibility of multipath problems that the Televes are said to cope with well.
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Thanks, Dave. the answer is certainly yes, re. Tetra base stations. I suspect you will be right about 4G. There are certainly 3G aerials on all of the high buildings in the vicinity including the sites of the two vertically polarised television sites for Margate (80 watt) and Ramsgate (50 watt), but as you will know those sites offer a very limited number of channels.
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Sunday 17 February 2013 9:04AM
Ramsgate
We have three digiboxes, each of a different make and generation. The most primitive, on a basic aeriel, serves a small 20-year old tv and is prone to shifting back and forth from colour to B&W. The other two, less than a year old, worked fine before and after digital switchover but have BOTH become unusuable. All BBC channels, most ITV channels and all news channels apart from Sky News suddenly switched off and on the one digibox that supports HDTV, all HD channels are gone. Some other channels are listed but report no signal. Dover transmitter reports no problems and is 28 miles away but still in line of sight. Maps suggest there are G4 but the maps may be out-of-date. Resets aren't working. Others but not everyone in Thanet are experiencing the same problems. What are our remedies to restore all of our services: do we need to contact trading standards?