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Sutton and Lichfield
I've been working today at Burntwood, Staffs. SC and Lichfield are
both clearly visible. I haven't measured it but I'd guess they're 5 or 6 miles away. They are about 35deg apart. It is not possible to receive the TV signals from both on one aerial, without compromising quality. What a silly state of affairs. Bill |
Sutton and Lichfield
Well, lets move Sutton coldfield for you then, would give you a lot of work
re-aligning all those aerials! Actually, I suppose there are a lot of places around which fall between stations in this way, presented with the historical siting of these masts, I suppose its inevitable no matter how carefully you choose channels to attempt to get around it. I think one of the most annoying things about freeview boxes and sets is that there seems to be no way to get the set to only look out for multiplexes from one source when auto tuning. IE I'd imagine built into the coding must be a site descriptor of some kind which the set could be told to look out for and ignore other multiplexes. Brian -- Brian Gaff - Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! " wrote in message ... I've been working today at Burntwood, Staffs. SC and Lichfield are both clearly visible. I haven't measured it but I'd guess they're 5 or 6 miles away. They are about 35deg apart. It is not possible to receive the TV signals from both on one aerial, without compromising quality. What a silly state of affairs. Bill |
Sutton and Lichfield
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Sutton and Lichfield
I think one of the most annoying things about freeview boxes and sets is
that there seems to be no way to get the set to only look out for multiplexes from one source when auto tuning. IE I'd imagine built into the coding must be a site descriptor of some kind which the set could be told to look out for and ignore other multiplexes. It's a good point. I don't know if the Freeview specs support that but if they do then surely the newer boxes will have this because after digital switchover it will be chaos in many places. Or perhaps I should "retrain" as a Freeview installer - is 50 quid a call-out plus cup of tea too much to charge? Paul DS. |
Sutton and Lichfield
"Brian Gaff" wrote in message
... I think one of the most annoying things about freeview boxes and sets is that there seems to be no way to get the set to only look out for multiplexes from one source when auto tuning. IE I'd imagine built into the coding must be a site descriptor of some kind which the set could be told to look out for and ignore other multiplexes. I think the name of the main station where the encoding takes place is included but any relays will have the ID of the main station. -- Brian Gregory. (In the UK) To email me remove the letter vee. |
Sutton and Lichfield
On Tue, 27 Apr 2010 08:00:56 +0000, Richard Tobin wrote:
Yes, I've been complaining about geometry for a long time Including the curvature of space? |
Sutton and Lichfield
On 27/04/2010 15:08, Brian Gregory [UK] wrote:
"Brian wrote in message ... I think one of the most annoying things about freeview boxes and sets is that there seems to be no way to get the set to only look out for multiplexes from one source when auto tuning. IE I'd imagine built into the coding must be a site descriptor of some kind which the set could be told to look out for and ignore other multiplexes. I think the name of the main station where the encoding takes place is included but any relays will have the ID of the main station. In most cases the encoders feed several main stations anyway, so for instance all main and relay stations in Wales carry the ID, 'Wales'. Slightly less confusing than the old ID of 'Wenvoe' though ! -- Mark Please replace invalid and invalid with gmx and net to reply. http://www.paras.org.uk/ |
Sutton and Lichfield
On Apr 27, 9:00*am, (Richard Tobin) wrote:
In article , wrote: I've been working today at Burntwood, Staffs. SC and Lichfield are both clearly visible. I haven't measured it but I'd guess they're 5 or 6 miles away. They are about 35deg apart. It is not possible to receive the TV signals from both on one aerial, without compromising quality. What a silly state of affairs. Yes, I've been complaining about geometry for a long time, but no one ever does anything about it. *If we had a few more dimensions, we could ensure that everywhere was within walking distance of everywhere else. -- Richard Geometry doesn't worry me; I'm used to it now. My complaint was about two main stations with the same nominal coverage area being so far apart. Not a matter of universal physical law, like geometry; just a matter of human affairs being imperfectly conducted. Bill |
Sutton and Lichfield
On Apr 27, 9:06*am, Mark Carver wrote:
On 26/04/2010 23:47, wrote: I've been working today at Burntwood, Staffs. SC and Lichfield are both clearly visible. I haven't measured it but I'd guess they're 5 or 6 miles away. They are about 35deg apart. It is not possible to receive the TV signals from both on one aerial, without compromising quality. What a silly state of affairs. I suppose the same is probably true for Pontop Pike and Burnhope, and perhaps Crystal P and Croydon in some locations for Ch1-4/C5 analogue ? I assume you were trying to get the temporary DVB-T2 mux from Lichfield, along with the six T1 muxes from SC ? -- Mark Please replace invalid and invalid with gmx and net to reply. http://www.paras.org.uk/ No, the temporary mux is of no interest, since there is no terrestrial HD in the building and won't be for the next year. However it did cross my mind that it could cause a problem had the circumstances been different. The problem was a few old tellys that needed analogue C5. In the end we decided to scrap them. That was a better use of money than a seperate aerial and channel filter! Bill |
Sutton and Lichfield
http://www.paras.org.uk/ No, the temporary mux is of no interest, since there is no terrestrial HD in the building and won't be for the next year. However it did cross my mind that it could cause a problem had the circumstances been different. The problem was a few old tellys that needed analogue C5. In the end we decided to scrap them. That was a better use of money than a seperate aerial and channel filter! Bill I had the same problem many years ago in Shirley, Southampton. I fitted a new aerial and combiner for a mate to receive analogue C5 from Fawley as his Rowridge aerial was only able to provide ghosty mush from Rowridge OR Fawley. As I recall they were about 45 degrees apart. |
Sutton and Lichfield
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Sutton and Lichfield
On Tue, 27 Apr 2010 21:23:44 +0100, "Doctor D"
wrote: http://www.paras.org.uk/ No, the temporary mux is of no interest, since there is no terrestrial HD in the building and won't be for the next year. However it did cross my mind that it could cause a problem had the circumstances been different. The problem was a few old tellys that needed analogue C5. In the end we decided to scrap them. That was a better use of money than a seperate aerial and channel filter! Bill I had the same problem many years ago in Shirley, Southampton. I fitted a new aerial and combiner for a mate to receive analogue C5 from Fawley as his Rowridge aerial was only able to provide ghosty mush from Rowridge OR Fawley. As I recall they were about 45 degrees apart. That was a very common problem. Many people within the potential service area of Fawley couldn't get it with their existing aerials on Rowridge, and didn't want C5 enough to pay for additional aerials. |
Sutton and Lichfield
In article , Java Jive
scribeth thus It'll be carrying SC's DVB-T2/HD mux at least until DSO. I suspect that after DSO it will indeed drop out of use, but I'm sure Mark will be along in a while to confirm or correct. Umm.. So whys it carrying that instead of SC.?. Aerial space or cost?.. -- Tony Sayer |
Sutton and Lichfield
In article ,
Brian Gaff wrote: If they are only that far away, you almost need a very wide beam width Arial. I recall, many moons ago achieving this by actually sawing off an Antiference Arial so there were only two directors left! Are you using speech input? It seems to think you're talking about a font rather than an antenna! -- Richard |
Sutton and Lichfield
On 27/04/2010 22:52, lid wrote:
I fitted a new aerial and combiner for a mate to receive analogue C5 from Fawley as his Rowridge aerial was only able to provide ghosty mush from Rowridge OR Fawley. As I recall they were about 45 degrees apart. That was a very common problem. Many people within the potential service area of Fawley couldn't get it with their existing aerials on Rowridge, and didn't want C5 enough to pay for additional aerials. I actually lived where both Fawley and Rowridge were to within a gnat's difference on the same bearing. However, that was no good either, because BBC 1 on E31 came banging in about 20dB above C5 on E34. Therefore BBC 1 would 'splash' over C5. I faffed about with filters etc for ages, and finally obtained satisfactory results, however the next day C5 popped up crystal clear on Astra 19.2, so I needn't have bothered ! I thought at the time, how handy it would be to have the other four channels on satellite too ;-) -- Mark Please replace invalid and invalid with gmx and net to reply. http://www.paras.org.uk/ |
Sutton and Lichfield
No, but the spellcucker was on auto that time.
Sorry bout that. One has no idea when the word is read if its been got at of course! Brian -- Brian Gaff - Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! "Richard Tobin" wrote in message ... In article , Brian Gaff wrote: If they are only that far away, you almost need a very wide beam width Arial. I recall, many moons ago achieving this by actually sawing off an Antiference Arial so there were only two directors left! Are you using speech input? It seems to think you're talking about a font rather than an antenna! -- Richard |
Sutton and Lichfield
In message , Brian Gaff
writes If they are only that far away, you almost need a very wide beam width Arial. I recall, many moons ago achieving this by actually sawing off an Antiference Arial so there were only two directors left! I'm sort-of guessing, but I would have thought that you could obtain a wide beamwidth by adding the polar diagrams of two medium-gain, identical aerials. These would be co-located, but mounted with the required angle of 35 degrees between them (each pointing at its required transmitter). The aerials would need to be combined using feeders of identical lengths. The actual lengths would not matter, so the two feeders could be brought to an accessible place, where the combiner would be located. At only 5 or 6 miles from the transmitters, there should be more than sufficient signal, so the combiner could be a bit lossy. A standard TV 2-way splitter (reversed) could be used, incurring a loss of around 4dB*. Obviously, this technique will only be 'sound' for relatively narrow angles. With a wider beamwidth, there's a greater risk of ghosting. Later on, when one of one of the signals was no longer required, the unwanted feed could be disconnected from the combiner, restoring the polar diagram to that of a single aerial. The unused port can be terminated, or the combiner removed and a barrel put in. *It would only as high as 4dB if two different signals were being combined. If the two aerials were being used to obtain more gain, with no angle between them, two essentially identical signals would be presented to the combiner input ports. In this case, there would be no power loss in the combiner (other then the unavoidable 1dB or so in the transformers). Or am I talking rubbish? -- Ian |
Sutton and Lichfield
On Wed, 28 Apr 2010 05:11:30 +0100, "Brian Gaff"
wrote: Yes, what youn need here is the spherical version of a mobious loop. Brian For sale: Klein bottle. Apply within. -- Tim |
Sutton and Lichfield
On Apr 28, 2:11*pm, Ian Jackson
wrote: I'm sort-of guessing, but I would have thought that you could obtain a wide beamwidth by adding the polar diagrams of two medium-gain, identical aerials. These would be co-located, but mounted with the required angle of 35 degrees between them (each pointing at its required transmitter). They would have to have the dipoles in the same vertical axis. One dipole would have to be exactly above the other, and they would have to be fairly close together. This is how some tx aerials achieve the desired polar response. In Scotland somewhere there used to be a self helf where they'd tried this technique but had put the aerials side by side. The result was a series of nulls across the field, each null being 'infinitely' deep. Basically, as you went down the street every so often there was a house with zero reception. Bill |
Sutton and Lichfield
In message
, " writes On Apr 28, 2:11*pm, Ian Jackson wrote: I'm sort-of guessing, but I would have thought that you could obtain a wide beamwidth by adding the polar diagrams of two medium-gain, identical aerials. These would be co-located, but mounted with the required angle of 35 degrees between them (each pointing at its required transmitter). They would have to have the dipoles in the same vertical axis. One dipole would have to be exactly above the other, and they would have to be fairly close together. This is how some tx aerials achieve the desired polar response. In Scotland somewhere there used to be a self helf where they'd tried this technique but had put the aerials side by side. The result was a series of nulls across the field, each null being 'infinitely' deep. Basically, as you went down the street every so often there was a house with zero reception. I can see that, if the aerials were side-by-side, splayed, and separated by a foot or so, each would dipole be somewhat further away from one transmitter or the other. There would be bound to be some phase cancellation, leading to the production of nulls. But I don't think that deep nulls will suddenly appear in the main lobe as splay is progressively increased from zero. Instead, there will come a point when the ever-broadening main lobe starts to develop a hole in the middle. Presumably you mean that the Scottish self-help aerials developed nulls close into the edges of the main lobe which, in the case of the aerial required for SC and Lichfield, might be in the direction of the two transmitters. I suppose that even with one aerial above the other, the two dipoles might still not quite be co-located, so some cancellation would occur. But (with luck), the null problem should be less. -- Ian |
Sutton and Lichfield
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Sutton and Lichfield
"Brian Gaff" wrote in message
... If they are only that far away, you almost need a very wide beam width Arial. I recall, many moons ago achieving this by actually sawing off an Antiference Arial so there were only two directors left! Brian snip top post If you are going to do that you might as well use just a dipole A pair of small yagis each pointing at their respective transmitters, matched with a coax phasing harness would probably be the best solution Steve Terry -- Get a free Three 3pay Sim with £2 bonus after £10 top up http://freeagent.three.co.uk/stand/view/id/5276 |
Sutton and Lichfield
" wrote in message ... On Apr 28, 2:11 pm, Ian Jackson wrote: I'm sort-of guessing, but I would have thought that you could obtain a wide beamwidth by adding the polar diagrams of two medium-gain, identical aerials. These would be co-located, but mounted with the required angle of 35 degrees between them (each pointing at its required transmitter). They would have to have the dipoles in the same vertical axis. One dipole would have to be exactly above the other, and they would have to be fairly close together. This is how some tx aerials achieve the desired polar response. In Scotland somewhere there used to be a self helf where they'd tried this technique but had put the aerials side by side. The result was a series of nulls across the field, each null being 'infinitely' deep. Basically, as you went down the street every so often there was a house with zero reception. It's interesting the way the aerials are configured on this local relay, I don't pretend to know anything about the transmission side of things, so why are they passing through one another? Also the lower two log periodics, which I presume almost certainly to be, receiving aerials, pointing towards Mendip, appear to be in closer proximity to one another than I've seen you recommend (because of interaction) is there a reason why the same rule doesn't apply as for a domestic installation? http://tx.mb21.co.uk/gallery/backwell.php |
Sutton and Lichfield
On Wed, 28 Apr 2010 09:17:33 +0100, Mark Carver
wrote: On 27/04/2010 22:52, lid wrote: I fitted a new aerial and combiner for a mate to receive analogue C5 from Fawley as his Rowridge aerial was only able to provide ghosty mush from Rowridge OR Fawley. As I recall they were about 45 degrees apart. That was a very common problem. Many people within the potential service area of Fawley couldn't get it with their existing aerials on Rowridge, and didn't want C5 enough to pay for additional aerials. I actually lived where both Fawley and Rowridge were to within a gnat's difference on the same bearing. However, that was no good either, because BBC 1 on E31 came banging in about 20dB above C5 on E34. Therefore BBC 1 would 'splash' over C5. I faffed about with filters etc for ages, and finally obtained satisfactory results, however the next day C5 popped up crystal clear on Astra 19.2, so I needn't have bothered ! I thought at the time, how handy it would be to have the other four channels on satellite too ;-) C5 were desperate to have some coverage on the south coast. Due to the well-known planning restrictions Fawley was about the only available site and they went for it. I doubt if it was ever an economic proposition. |
Sutton and Lichfield
lid wrote:
C5 were desperate to have some coverage on the south coast. Due to the well-known planning restrictions Fawley was about the only available site and they went for it. I doubt if it was ever an economic proposition. Indeed not, and in fact the C5 Tx there was closed in March 2009, because Rowridge needed E34 for DTT in a re-shuffle resulting from Stockland Hill's DSO. -- Mark Please replace invalid and invalid with gmx and net to reply. www.paras.org.uk |
Sutton and Lichfield
tony sayer wrote:
In article , Java Jive scribeth thus It'll be carrying SC's DVB-T2/HD mux at least until DSO. I suspect that after DSO it will indeed drop out of use, but I'm sure Mark will be along in a while to confirm or correct. Umm.. So whys it carrying that instead of SC.?. Aerial space or cost?.. SC is currently being ripped apart and re-built for DSO next September, with some transmissions coming from a temporary mast. I'm told it was less of a faff about to simply transmit this special 7th HD mux from Lichfield, which has plenty of mast space, and is nice and 'quiet'. Come DSO in Sept 2011, the HD Mux will of course replace SD Mux B, and along with the other muxes, transmit from SC at high power. -- Mark Please replace invalid and invalid with gmx and net to reply. www.paras.org.uk |
Sutton and Lichfield
On 28/04/2010 16:35, Ivan wrote:
" wrote in message ... On Apr 28, 2:11 pm, Ian Jackson wrote: I'm sort-of guessing, but I would have thought that you could obtain a wide beamwidth by adding the polar diagrams of two medium-gain, identical aerials. These would be co-located, but mounted with the required angle of 35 degrees between them (each pointing at its required transmitter). They would have to have the dipoles in the same vertical axis. One dipole would have to be exactly above the other, and they would have to be fairly close together. This is how some tx aerials achieve the desired polar response. In Scotland somewhere there used to be a self helf where they'd tried this technique but had put the aerials side by side. The result was a series of nulls across the field, each null being 'infinitely' deep. Basically, as you went down the street every so often there was a house with zero reception. It's interesting the way the aerials are configured on this local relay, I don't pretend to know anything about the transmission side of things, so why are they passing through one another? Also the lower two log periodics, which I presume almost certainly to be, receiving aerials, pointing towards Mendip, appear to be in closer proximity to one another than I've seen you recommend (because of interaction) is there a reason why the same rule doesn't apply as for a domestic installation? http://tx.mb21.co.uk/gallery/backwell.php Standard crossed log configuration for relays, with angles of 90, 120 and 150 degrees being the most usual. IIRC, 120 gives a nearly cardioid pattern. The crossing point is where the log is 'active' in the middle of the channels used. Backwell is standard Group B, so the crossing is where channel 25 (approx) is active. The receive antenna are probably spaced to give a narrow VRP, though I don't know why. Phil |
Sutton and Lichfield
On Apr 28, 3:54*pm, charles wrote:
met that from Winter Hill once in parts of Bolton/Horwich. The solution? Bill |
Sutton and Lichfield
On Apr 28, 4:35*pm, "Ivan" wrote:
It's interesting the way the aerials are configured on this local relay, I don't pretend to know anything about the transmission side of things, so why are they passing through one another? It's to get the 'active zones' in a vertical line so the outputs of the two stacks keep in phase with each other. There's a BBC paper about it somewhere. Also the lower two log periodics, which I presume almost certainly to be, receiving aerials, pointing towards Mendip, appear to be in closer proximity to one another than I've seen you recommend (because of interaction) is there a reason why the same rule doesn't apply as for a domestic installation? I don't think they're all that close, looking at it. I've played around with logs and I'd say you can put them half a wavelength at the lowest frequency apart (HP one above the other; VP side by side) before anything seriously wierd happens. I regularly stack them one wavelength apart. Bill |
Sutton and Lichfield
On Apr 28, 3:39*pm, Ian Jackson
wrote: I can see that, if the aerials were side-by-side, splayed, and separated by a foot or so, each would dipole be somewhat further away from one transmitter or the other. There would be bound to be some phase cancellation, leading to the production of nulls. But I don't think that deep nulls will suddenly appear in the main lobe as splay is progressively increased from zero. Instead, there will come a point when the ever-broadening main lobe starts to develop a hole in the middle. In fact, the positions of the nulls and the shape of the main lobe of each aerial are not related related in that way. Consider a pair of 18 element yagi receiving aerials, side by side, exactly equidistant from the TX. They are as close together as they can be consistent with not encroaching in each other's reception aperture. They are combined using equal feeder lengths and a combiner that has equal loss on both legs. With the aerials both aligned on the tx the forward lobe will be much the same as for a single aerial, but the gain should be slightly better. The nulls caused by the phasing of the two aerials will be outside the forward lobe. Now suppose the two aerials are, say, 15 wavelengths apart. The first nulls will now be within the common forward lobe. Since nulls caused by phase cancellation are theoretically infinitely deep, even in reality they will be very deep; far deeper than the opposing effects of the aerials' forward gain will be able to conteract significantly. The same thing applies if the aerials are pointing in different directions. Yes, as long as the forward lobes overlap there will be some broadening, but the positions of the nulls are fixed by the inter- aerial spacing and the wavelength, and if they co-incide with the broadened forward lobe they will just dig a big hole in it. With unfortunate inter-aerial spacing you could well have a null in the direction of one transmitter. Presumably you mean that the Scottish self-help aerials developed nulls close into the edges of the main lobe which, in the case of the aerial required for SC and Lichfield, might be in the direction of the two transmitters. No, they had used two horizontally polarized logs (chosen for their broad forward lobe) mounted around a metre apart, side by side, (as I recall) and aligned about 25deg apart. Each aerial had its own main amplifier and to be honest I don't think anyone had worried about cable length or anything. I have also seen one that used a pair of four bay vertically polarized BB Grids, mounted side by side. So there were 8 radiating dipoles with no particular phase relationship. Results were, apparently, 'patchy'. And also one that had two TC18Bs pointing about 120deg apart, and there seemed to be no problems at all with that. Bill |
Sutton and Lichfield
On Apr 28, 7:46*pm, phil wrote:
On 28/04/2010 16:35, Ivan wrote: " wrote in message .... On Apr 28, 2:11 pm, Ian Jackson wrote: I'm sort-of guessing, but I would have thought that you could obtain a wide beamwidth by adding the polar diagrams of two medium-gain, identical aerials. These would be co-located, but mounted with the required angle of 35 degrees between them (each pointing at its required transmitter). They would have to have the dipoles in the same vertical axis. One dipole would have to be exactly above the other, and they would have to be fairly close together. This is how some tx aerials achieve the desired polar response. In Scotland somewhere there used to be a self helf where they'd tried this technique but had put the aerials side by side. The result was a series of nulls across the field, each null being 'infinitely' deep. Basically, as you went down the street every so often there was a house with zero reception. It's interesting the way the aerials are configured on this local relay, I don't pretend to know anything about the transmission side of things, so why are they passing through one another? Also the lower two log periodics, which I presume almost certainly to be, receiving aerials, pointing towards Mendip, appear to be in closer proximity to one another than I've seen you recommend (because of interaction) is there a reason why the same rule doesn't apply as for a domestic installation? http://tx.mb21.co.uk/gallery/backwell.php Standard crossed log configuration for relays, with angles of 90, 120 and 150 degrees being the most usual. *IIRC, 120 gives a nearly cardioid pattern. *The crossing point is where the log is 'active' in the middle of the channels used. *Backwell is standard Group B, so the crossing is where channel 25 (approx) is active. That'll be 45? Bill |
Sutton and Lichfield
" wrote in message ... On Apr 28, 7:46 pm, phil wrote: On 28/04/2010 16:35, Ivan wrote: " wrote in message ... On Apr 28, 2:11 pm, Ian Jackson wrote: I'm sort-of guessing, but I would have thought that you could obtain a wide beamwidth by adding the polar diagrams of two medium-gain, identical aerials. These would be co-located, but mounted with the required angle of 35 degrees between them (each pointing at its required transmitter). They would have to have the dipoles in the same vertical axis. One dipole would have to be exactly above the other, and they would have to be fairly close together. This is how some tx aerials achieve the desired polar response. In Scotland somewhere there used to be a self helf where they'd tried this technique but had put the aerials side by side. The result was a series of nulls across the field, each null being 'infinitely' deep. Basically, as you went down the street every so often there was a house with zero reception. It's interesting the way the aerials are configured on this local relay, I don't pretend to know anything about the transmission side of things, so why are they passing through one another? Also the lower two log periodics, which I presume almost certainly to be, receiving aerials, pointing towards Mendip, appear to be in closer proximity to one another than I've seen you recommend (because of interaction) is there a reason why the same rule doesn't apply as for a domestic installation? http://tx.mb21.co.uk/gallery/backwell.php Standard crossed log configuration for relays, with angles of 90, 120 and 150 degrees being the most usual. IIRC, 120 gives a nearly cardioid pattern. The crossing point is where the log is 'active' in the middle of the channels used. Backwell is standard Group B, so the crossing is where channel 25 (approx) is active. That'll be 45? Backwell is a group 'A' transmitter so maybe a typo? |
Sutton and Lichfield
On 28/04/2010 21:04, Ivan wrote:
" wrote in message ... On Apr 28, 7:46 pm, phil wrote: On 28/04/2010 16:35, Ivan wrote: " wrote in message ... On Apr 28, 2:11 pm, Ian Jackson wrote: I'm sort-of guessing, but I would have thought that you could obtain a wide beamwidth by adding the polar diagrams of two medium-gain, identical aerials. These would be co-located, but mounted with the required angle of 35 degrees between them (each pointing at its required transmitter). They would have to have the dipoles in the same vertical axis. One dipole would have to be exactly above the other, and they would have to be fairly close together. This is how some tx aerials achieve the desired polar response. In Scotland somewhere there used to be a self helf where they'd tried this technique but had put the aerials side by side. The result was a series of nulls across the field, each null being 'infinitely' deep. Basically, as you went down the street every so often there was a house with zero reception. It's interesting the way the aerials are configured on this local relay, I don't pretend to know anything about the transmission side of things, so why are they passing through one another? Also the lower two log periodics, which I presume almost certainly to be, receiving aerials, pointing towards Mendip, appear to be in closer proximity to one another than I've seen you recommend (because of interaction) is there a reason why the same rule doesn't apply as for a domestic installation? http://tx.mb21.co.uk/gallery/backwell.php Standard crossed log configuration for relays, with angles of 90, 120 and 150 degrees being the most usual. IIRC, 120 gives a nearly cardioid pattern. The crossing point is where the log is 'active' in the middle of the channels used. Backwell is standard Group B, so the crossing is where channel 25 (approx) is active. That'll be 45? Backwell is a group 'A' transmitter so maybe a typo? Sorry, I was in service planning mode, where group A is 21, 24, 27, 31 and group B is 22, 25, 28, 32 etc. Usually, but not always, made relay planning easier. Phil |
Sutton and Lichfield
On Wed, 28 Apr 2010 12:20:43 -0700 (PDT), "
wrote: On Apr 28, 3:39=A0pm, Ian Jackson wrote: I can see that, if the aerials were side-by-side, splayed, and separated by a foot or so, each would dipole be somewhat further away from one transmitter or the other. There would be bound to be some phase cancellation, leading to the production of nulls. But I don't think that deep nulls will suddenly appear in the main lobe as splay is progressively increased from zero. Instead, there will come a point when the ever-broadening main lobe starts to develop a hole in the middle. In fact, the positions of the nulls and the shape of the main lobe of each aerial are not related related in that way. Consider a pair of 18 element yagi receiving aerials, side by side, exactly equidistant from the TX. They are as close together as they can be consistent with not encroaching in each other's reception aperture. They are combined using equal feeder lengths and a combiner that has equal loss on both legs. With the aerials both aligned on the tx the forward lobe will be much the same as for a single aerial, but the gain should be slightly better. The nulls caused by the phasing of the two aerials will be outside the forward lobe. Now suppose the two aerials are, say, 15 wavelengths apart. The first nulls will now be within the common forward lobe. Since nulls caused by phase cancellation are theoretically infinitely deep, even in reality they will be very deep; far deeper than the opposing effects of the aerials' forward gain will be able to conteract significantly. The same thing applies if the aerials are pointing in different directions. Yes, as long as the forward lobes overlap there will be some broadening, but the positions of the nulls are fixed by the inter- aerial spacing and the wavelength, and if they co-incide with the broadened forward lobe they will just dig a big hole in it. With unfortunate inter-aerial spacing you could well have a null in the direction of one transmitter. This certainly *sounds* very impressive and scientific to the lay reader, but I'd like to look at the evidence for myself. Perhaps Bill or another expert would care to provide some. Hopefully if an expert does contribute, he will not offer as evidence one of his own articles. --- news://freenews.netfront.net/ - complaints: --- |
Sutton and Lichfield
Please note that the previous post was NOT written by me.
If in doubt, just compare the headers. I think we can all guess which poster would attempt such childish tricks. |
Sutton and Lichfield
On Friday, April 30th, 2010 17:18:06 +0100, Nemo wrote:
If in doubt, just compare the headers. How can one know which header lines are valid, and which are forged? The path line indicates that the posting originated from the news.netfront.net server which is in Hong Kong. The NNTP posting host indicates a subscriber to B$kyB broadband services via Easynet. The message id indicates the machine is on a host affiliated to a domain registered by somebody in Saltash, Cornwall. |
Sutton and Lichfield
On Fri, 30 Apr 2010 18:44:57 +0200, J G Miller
wrote: On Friday, April 30th, 2010 17:18:06 +0100, Nemo wrote: If in doubt, just compare the headers. How can one know which header lines are valid, and which are forged? Who cares? Most of the spurious message's header lines are different from mine, which is enough to demonstrate that it is not genuine. No doubt with sufficient effort it could be faked up to look exactly the same as mine. If he wants to waste that much time he's welcome. I can't be arsed to discuss it further. |
Sutton and Lichfield
On Apr 30, 5:18*pm, wrote:
Please note that the previous post was NOT written by me. If in doubt, just compare the headers. I think we can all guess which poster would attempt such childish tricks. * You can tell by the style anyway. Bill |
Sutton and Lichfield
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