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uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions. |
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I understand the general principles of how to rig this, but I was
wondering if the riggers here would have any particular make they swear by. Note: Up here it can get VERY, VERY windy! -- ================================================== ====== Please always reply to ng as the email in this post's header does not exist. Or use a contact address at: http://www.macfh.co.uk/JavaJive/JavaJive.html http://www.macfh.co.uk/Macfarlane/Macfarlane.html |
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Java Jive wrote:
I understand the general principles of how to rig this, but I was wondering if the riggers here would have any particular make they swear by. Note: Up here it can get VERY, VERY windy! Go for galvanised, welded stuff. Tell me what you're fixing (height, loading) and the condition of the brickwork and size of chimbley and I'll tell you what you need. ATV Sheffield is a good source of info and place to buy. Bill |
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Thanks Bill ...
On Wed, 23 Sep 2015 15:36:47 +0100, Bill Wright wrote: Java Jive wrote: I understand the general principles of how to rig this, but I was wondering if the riggers here would have any particular make they swear by. Note: Up here it can get VERY, VERY windy! Go for galvanised, welded stuff. Tell me what you're fixing (height, loading) and the condition of the brickwork and size of chimbley and I'll tell you what you need. To receive most probably from the local relay with a clear line of sight just under 5 miles away, 2.6W ERP, Gp B Vertical, though first I will probably investigate the very faint possibility of the main TX over the hills and far away, 34 miles, 20kW, also Gp B but Horizontal, but I'd be amazed if I were actually to get anything. Conveniently, they're almost in the same direction. The chimneys are currently being rebuilt, which is why I'd like to do the job now. ATV Sheffield is a good source of info and place to buy. I'll probably investigate Inverness first, as my experience up here of suppliers south of the border is that the moment you tell them you're in the Highlands, they double the delivery charges. -- ================================================== ====== Please always reply to ng as the email in this post's header does not exist. Or use a contact address at: http://www.macfh.co.uk/JavaJive/JavaJive.html http://www.macfh.co.uk/Macfarlane/Macfarlane.html |
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On Thu, 24 Sep 2015 13:34:17 +0100, Java Jive
wrote: Thanks Bill ... Oh, and about 10 - 15m above ground. -- ================================================== ====== Please always reply to ng as the email in this post's header does not exist. Or use a contact address at: http://www.macfh.co.uk/JavaJive/JavaJive.html http://www.macfh.co.uk/Macfarlane/Macfarlane.html |
#5
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Java Jive wrote:
Thanks Bill ... To receive most probably from the local relay with a clear line of sight just under 5 miles away, 2.6W ERP, Gp B Vertical, Some relays are very directional. The erp figure is the best you might get! Really, a lot of relays should be specified as 0 to 2.6W erp! A look at the relevant relay on MB21 might be interesting. Anyway, you probably ought to go for a grouped 18 element aerial such as this. http://www.blake-uk.com/sr-yagi/404-...e-aerials.html I have known reception of such low powered txs at 5 miles be problematic! though first I will probably investigate the very faint possibility of the main TX over the hills and far away, 34 miles, 20kW, also Gp B but Horizontal, but I'd be amazed if I were actually to get anything. Conveniently, they're almost in the same direction. Sounds like both would be good? But how to combine? Ah there's the rub! The chimneys are currently being rebuilt, which is why I'd like to do the job now. Wait at least four days before fixing a lash kit to new mortar. ATV Sheffield is a good source of info and place to buy. I'll probably investigate Inverness first, as my experience up here of suppliers south of the border is that the moment you tell them you're in the Highlands, they double the delivery charges. I don't think Blake charge extra. Have a look. In any case what matters is how much you pay in total. A local outfit could mark up the goods a lot more than the extra carriage might be. Assuming a reasonable chimney with no big overhangs or excessively tall pots a good fixing for the aerial above, in a very windy region, would be a nine foot x 1.5" mast. A set of double chimney brackets and lashing kits, bkts about 2ft apart. Trim the mast if it's too long; no point in having the aerial too high. But it does need to be well above any smoke or fumes from the chimney, and also well above interference from the house (because the field strength will be low). Low field strength means more risk of 'swamping' type interference problems including TETRA and 4G, so a grouped ae would be my choice. I'd seriously consider a low gain masthead amp. If you do trim the mast save the offcuts for bonfire night. Good for rocket launchers! Bill |
#6
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Java Jive wrote:
On Thu, 24 Sep 2015 13:34:17 +0100, Java Jive wrote: Thanks Bill ... Oh, and about 10 - 15m above ground. The chimney? That sounds good. Hope the scaff is still up. |
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On Thu, 24 Sep 2015 15:42:53 +0100, Bill Wright
wrote: Anyway, you probably ought to go for a grouped 18 element aerial such as this. http://www.blake-uk.com/sr-yagi/404-...e-aerials.html That is way bigger than any of my neighbours' aerials, and up here windage is a VERY significant factor. However ... I have known reception of such low powered txs at 5 miles be problematic! .... Yes, my own site confirms that the relay is possibly too weak to give a usable signal at 5 miles. though first I will probably investigate the very faint possibility of the main TX over the hills and far away, 34 miles, 20kW, also Gp B but Horizontal, but I'd be amazed if I were actually to get anything. Conveniently, they're almost in the same direction. Sounds like both would be good? But how to combine? Ah there's the rub! Well, I'll buy an aerial aimed at the relay, but before finally mounting it, I'll see what happens when I try and receive the main. ATV Sheffield is a good source of info and place to buy. I'll probably investigate Inverness first, as my experience up here of suppliers south of the border is that the moment you tell them you're in the Highlands, they double the delivery charges. I don't think Blake charge extra. Have a look. In any case what matters is how much you pay in total. A local outfit could mark up the goods a lot more than the extra carriage might be. Assuming a reasonable chimney with no big overhangs or excessively tall pots a good fixing for the aerial above, in a very windy region, would be a nine foot x 1.5" mast. A set of double chimney brackets and lashing kits, bkts about 2ft apart. Trim the mast if it's too long; no point in having the aerial too high. But it does need to be well above any smoke or fumes from the chimney, and also well above interference from the house (because the field strength will be low). [out of original order] I'd seriously consider a low gain masthead amp. If you do trim the mast save the offcuts for bonfire night. Good for rocket launchers! There are a number of properties very similar to mine in this area. When first I came to mine, from the thickness of the walls I thought it older than it actually is, that it dated from times when the cattle were kept at one end of the building and the people in the other. Then I realised that this couldn't be, because there was a chimney at *each* end, and anyway the dwelling was unnecessarily high for this style of dwelling. In fact, I've since discovered that this reasoning was correct, and these houses are all much more recent and date from immediately after WW1 - local land was parceled up into crofts and the houses built on them to provide livings for returning, newly demobbed, soldiers. Thus they were built in a hurry, using whatever was to hand, and completely re-harling the wall the other end from the proposed aerial siting has shown that the build of the walls and the mortar in them is not of the first grade of work - for example, there is no point in completely removing the rendering to expose the underlying stone, because the original stone work wasn't anywhere near good enough to justify such expense. Although the tops of the chimneys have been rebuilt, the rest of them are as was, so frankly the thought of a 9' mast in the sort of gales we had last January would be just unthinkable. So many dwellings old and new were damaged in those gales that local builders are still repairing them, which is why they've only just come to mine. Many lost parts of their roofs, many were damaged by falling trees which often, bitterest of ironies, were planted originally as shelter belts! Here's a pic, pre-harling, of the rebuilt chimney on the gable end facing the transmitters, which are over the left shoulder from the vantage point, around 7 o'clock on a ground plan with 12 o'clock being the direction in which the shot was taken. For scale, the part of the chimney pot above the coping will be about 68cm high: www.macfh.co.uk/Temp/HouseWork.jpg (2MB) In summary, most of the aerials around here are just large enough and no more, and hunkered down on very short masts, sometimes even well below the apex of the roof, so as to be shielded from the wind. Low field strength means more risk of 'swamping' type interference problems including TETRA and 4G, so a grouped ae would be my choice. TETRA is unlikely to be a problem here, it's too remote, and we still haven't got decent 3G, let alone 4G (nor FTTC come to that)! Although I was careful to preserve the functionality of the downstairs chimneys, both fireplaces are walled up, while the upstairs fireplaces are exposed, but I've allowed the chimneys to be blocked off, because I can't see anyone ever wanting actually to light a fire in them. Consequently, chimney smoke is not likely to be a problem for the present, and if and when I do have open fires, the aerial will be windward of the prevailing wind direction. Is an 8" chimney bracket one where the two cables around the chimney are 8" apart? Given that there's a 2" coping overhang, I reckon from the ATV site: 8" Mitre Chimney Bracket, possibly 2 and aerial between them 3' Mast thickest guage practically obtainable (I have a section of scaffolding pole about that length, that was originally used to mount a satellite dish, but whether a chimney bracket fastening could mount anything of that diameter, I don't know) Aerial still to choose. Can you suggest one with less wind-resistance? -- ================================================== ====== Please always reply to ng as the email in this post's header does not exist. Or use a contact address at: http://www.macfh.co.uk/JavaJive/JavaJive.html http://www.macfh.co.uk/Macfarlane/Macfarlane.html |
#8
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Java Jive wrote:
http://www.blake-uk.com/sr-yagi/404-...e-aerials.html That is way bigger than any of my neighbours' aerials, and up here windage is a VERY significant factor. However ... Whether or not an aerial is blown down by the wind is not related to the size of the aerial. It is dependent on whether or not it's been properly installed. If you see an aerial that's been damaged by the wind, either it's very old indeed or it wasn't properly installed. Sounds like both would be good? But how to combine? Ah there's the rub! Well, I'll buy an aerial aimed at the relay, but before finally mounting it, I'll see what happens when I try and receive the main. Yes, but both would be good. Except you can't combine them. There are a number of properties very similar to mine in this area. When first I came to mine, from the thickness of the walls I thought it older than it actually is, that it dated from times when the cattle were kept at one end of the building and the people in the other. Then I realised that this couldn't be, because there was a chimney at *each* end, and anyway the dwelling was unnecessarily high for this style of dwelling. In fact, I've since discovered that this reasoning was correct, and these houses are all much more recent and date from immediately after WW1 - local land was parceled up into crofts and the houses built on them to provide livings for returning, newly demobbed, soldiers. Thus they were built in a hurry, using whatever was to hand, and completely re-harling the wall the other end from the proposed aerial siting has shown that the build of the walls and the mortar in them is not of the first grade of work - for example, there is no point in completely removing the rendering to expose the underlying stone, because the original stone work wasn't anywhere near good enough to justify such expense. Although the tops of the chimneys have been rebuilt, the rest of them are as was, so frankly the thought of a 9' mast in the sort of gales we had last January would be just unthinkable. So many dwellings old and new were damaged in those gales that local builders are still repairing them, which is why they've only just come to mine. Many lost parts of their roofs, many were damaged by falling trees which often, bitterest of ironies, were planted originally as shelter belts! Here's a pic, pre-harling, of the rebuilt chimney on the gable end facing the transmitters, which are over the left shoulder from the vantage point, around 7 o'clock on a ground plan with 12 o'clock being the direction in which the shot was taken. For scale, the part of the chimney pot above the coping will be about 68cm high: www.macfh.co.uk/Temp/HouseWork.jpg (2MB) In summary, most of the aerials around here are just large enough and no more, and hunkered down on very short masts, sometimes even well below the apex of the roof, so as to be shielded from the wind. Re-read what I said. Use a 9ft mast because that's the shortest length you can buy heavy gauge 1.5" masting. Use a set of double chimney brackets and lashing kits, bkts about 2ft apart. This enormously reduces the strain on the stack. Trim the mast if it's too long; no point in having the aerial too high. Remember there's only 7ft above the top bracket, and you shorten it even more. But it does need to be well above any smoke or fumes from the chimney. It's corrosion from smoke and fumes that brings aerials down. If no smoke, you can mount the aerial just above the stack. But not really close to a pot because it will affect it. Is an 8" chimney bracket one where the two cables around the chimney are 8" apart? No it's a single bracket 8" high. You need a pair of 'double chimney brackets' mounted 2ft apart. Given that there's a 2" coping overhang, I reckon from the ATV site: 8" Mitre Chimney Bracket, No no no. One lashing wire will stress the stack. You must use a double lashing kit and double bracket pair. 3' Mast thickest guage practically obtainable (I have a section of scaffolding pole about that length, that was originally used to mount a satellite dish, but whether a chimney bracket fastening could mount anything of that diameter, I don't know) The thickness of the mast is only one factor. The tube wall (gauge) is important. The double bracket sets all take scaffold tubes. Scaff tubes are a good idea, but steel ones are so heavy they bring their own problems. Use alloy ones. Regarding the idea of mounting the aerial just above the roof: By far the strongest winds occur when the wind is blowing onto a pitched roof and it goes up the roof and at the apex and just above it is like a hurricane. But three feet higher you are out of that stream and the wind is much the same as it is at ground level. Mounting an aerial in that danger zone is asking for trouble. Aerial still to choose. Can you suggest one with less wind-resistance? No. The aerial I recommend is centre mounted. Anything smaller will be end mounted and thus far more vulnerable. The aerial I recommend was chosen because it combines good gain and directivity combined with small windage. Please don't go and buy one of those end mounted 'high gain' wideband pieces of **** as sold by the DIY shops. If you do I will come round and rip it down and ram it up your arse. Just accept that I've been fixing aerials in very windy places for the last 45 years and my advice is good. Your location is not so exceptional. Try standing on top of a 20 floor block of flats when it's windy. Bill |
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On Fri, 09 Oct 2015 23:52:09 +0100, Bill Wright wrote:
Please don't go and buy one of those end mounted 'high gain' wideband pieces of **** as sold by the DIY shops. If you do I will come round and rip it down and ram it up your arse. If this happens, please can you let me know and sell me a ticket for the spectacle? |
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