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Misguided installation
Thought you might like a look at todays callout.
The local business has 4 plasma screens which were breaking up badly and three radio tuners which were not performing at their best ! http://i874.photobucket.com/albums/a...didthis003.jpg http://i874.photobucket.com/albums/a...didthis002.jpg http://i874.photobucket.com/albums/a...didthis001.jpg The interesting thing was that the mechanics of the installation were quite good, with some attention to detail. The theory of it all was not so good....to say nothing of the birdsnest ! We didnt need to resite the aerial in the end as the transmitter was about 20 degrees left of where the aerial was facing, so the screening of the building turned out not to be a problem. We did, however have to spend some time with filters etc trying to get rid of very strong tetra and other locally generated interference. The radio tuners were DAB and FM so we took down the interestingly positioned halo and fitted a vertical FM dipole which gave very good results for DAB as well as it is almost exactly twice the length. |
Misguided installation
On Dec 17, 12:56*am, widgitt wrote:
Thought you might like a look at todays callout. The local business has 4 plasma screens which were breaking up badly and three radio tuners which were not performing at their best ! http://i874.photobucket.com/albums/a.../Whichprofessi... The interesting thing was that the mechanics of the installation were quite good, with some attention to detail. The theory of it all was not so good....to say nothing of the birdsnest ! We didnt need to resite the aerial in the end as the transmitter was about 20 degrees left of where the aerial was facing, so the screening of the building turned out not to be a problem. We did, however have to spend some time with filters etc trying to get rid of very strong tetra and other locally generated interference. The radio tuners were DAB and FM so we took down the interestingly positioned halo and fitted a vertical FM dipole which gave very good results for DAB as well as it is almost exactly twice the length. It's odd isn't it? -- when you find one where the installer has obviously been conscientious, but is clearly ignorant of certain basic facts about the job. I went to one the other week which had a head end that was so neat and tidy it looked like the installer had a mental problem. But the whole system was total ******** when you looked at what he's used and how he'd used it. Bill |
Misguided installation
"widgitt" wrote in message ... Thought you might like a look at todays callout. The local business has 4 plasma screens which were breaking up badly and three radio tuners which were not performing at their best ! http://i874.photobucket.com/albums/a...didthis003.jpg http://i874.photobucket.com/albums/a...didthis002.jpg http://i874.photobucket.com/albums/a...didthis001.jpg The interesting thing was that the mechanics of the installation were quite good, with some attention to detail. The theory of it all was not so good....to say nothing of the birdsnest ! We didnt need to resite the aerial in the end as the transmitter was about 20 degrees left of where the aerial was facing, so the screening of the building turned out not to be a problem. We did, however have to spend some time with filters etc trying to get rid of very strong tetra and other locally generated interference. The radio tuners were DAB and FM so we took down the interestingly positioned halo and fitted a vertical FM dipole which gave very good results for DAB as well as it is almost exactly twice the length. Good photos. I'm always trying to learn new things & improve, but quite often I see things like in your photos and it amazes me how many installers are out there with poor knowledge. Even the basic rules of a good solid installation seem to get ignored most of the time. Today I had to sort out a high gain aerial, on a 16ft mast, mounted on a single 6" chimney bracket (welded at least - not pressed). Just silly...... |
Misguided installation
Brian Gaff wrote:
Twice the length? Well this surely would be a terrible mismatch impedance wise. Brian Why, surely it would be 1/2 wave if it started at 1/4 wave, or 1 wave if started as 1/2 wave? Twice is good? -- Tony |
Misguided installation
Tony wrote:
Brian Gaff wrote: Twice the length? Well this surely would be a terrible mismatch impedance wise. Why, surely it would be 1/2 wave if it started at 1/4 wave, or 1 wave if started as 1/2 wave? Twice is good? The typical dipole to feed 75 ohms is a half-wave dipole made up from two quarter-wave elements. A quick Google search tells me that full-wave dipoles can work but shouldn't be fed directly to the coax because of the mismatch -- but this can be fixed with an air choke: http://www.hamuniverse.com/kl7jrverticaldipole.html However, this option wasn't available to the OP because the dipole's primary use was for FM, and in any case, theory is trumped by: "...and fitted a vertical FM dipole which gave very good results for DAB as well..." -- Dave Farrance |
Misguided installation
On Thu, 17 Dec 2009 18:09:49 GMT, Dave Farrance
wrote: Tony wrote: Brian Gaff wrote: Twice the length? Well this surely would be a terrible mismatch impedance wise. Why, surely it would be 1/2 wave if it started at 1/4 wave, or 1 wave if started as 1/2 wave? Twice is good? The typical dipole to feed 75 ohms is a half-wave dipole made up from two quarter-wave elements. A quick Google search tells me that full-wave dipoles can work but shouldn't be fed directly to the coax because of the mismatch -- but this can be fixed with an air choke: http://www.hamuniverse.com/kl7jrverticaldipole.html However, this option wasn't available to the OP because the dipole's primary use was for FM, and in any case, theory is trumped by: "...and fitted a vertical FM dipole which gave very good results for DAB as well..." In a large proportion of cases where an inappropriate or just plain wrong aerial is fitted, it gives perfectly good service simply because of a sufficiently high field strength. In such an environment the proverbial length of wet string would do just as well, with or without a balun or correct impedance match. |
Misguided installation
On Dec 17, 6:09*pm, Dave Farrance
wrote: Tony wrote: Brian Gaff wrote: Twice the length? Well this surely would be a terrible mismatch impedance wise. Why, surely it would be 1/2 wave if it started at 1/4 wave, or 1 wave if started as 1/2 wave? *Twice is good? The typical dipole to feed 75 ohms is a half-wave dipole made up from two quarter-wave elements. *A quick Google search tells me that full-wave dipoles can work but shouldn't be fed directly to the coax because of the mismatch -- but this can be fixed with an air choke: http://www.hamuniverse.com/kl7jrverticaldipole.html However, this option wasn't available to the OP because the dipole's primary use was for FM, and in any case, theory is trumped by: "...and fitted a vertical FM dipole which gave very good results for DAB as well..." -- Dave Farrance Vertical FM dipoles without a balun work so well on DAB it's not always obvious which feed is which is you've fitted a DAB dipole as well. But FM dipoles with baluns are crap for DAB. However, since DAB coverage is based on indoor aerials the field strength on the roof is often enough for a very inefficient aerial to work well. In fact, most DAB dipoles feeding head ends do so via a 6dB or 12dB attenuator. Or they should. Often they don't and the result is that the DAB signals are launched at the same level as the analogue TV. Bill Bill Bill |
Misguided installation
Dave Farrance wrote:
"...and fitted a vertical FM dipole which gave very good results for DAB as well..." I use my vertical FM dipole for DAB reception. I was surprised to receive distant muxes with it. I lashed up a dipole cut for Band III Ch 11, and compared the results. There were no differences, only that the Band III was crap at Band II (which you would expect). -- Mark Please replace invalid and invalid with gmx and net to reply. www.paras.org.uk |
Misguided installation
"Mike Henry" wrote in message ... In , "-GB-Carpy" wrote: Good photos. I'm always trying to learn new things & improve, but quite often I see things like in your photos and it amazes me how many installers are out there with poor knowledge. Even the basic rules of a good solid installation seem to get ignored most of the time. Today I had to sort out a high gain aerial, on a 16ft mast, mounted on a single 6" chimney bracket (welded at least - not pressed). Just silly...... For my untrained eye, could I tentatively ask what is wrong with the TV aerial part? I can see that the radio aerial is wrong, but all I can think that's wrong with the TV aerial is that it's too close to the radio aerial. TIA :-) Pity there's isn't a number 4, "after", picture! TV aerial looks ok - certainly better than most! |
Misguided installation
"-GB-Carpy" wrote in message ... "Mike Henry" wrote in message ... In , "-GB-Carpy" wrote: Good photos. I'm always trying to learn new things & improve, but quite often I see things like in your photos and it amazes me how many installers are out there with poor knowledge. Even the basic rules of a good solid installation seem to get ignored most of the time. Today I had to sort out a high gain aerial, on a 16ft mast, mounted on a single 6" chimney bracket (welded at least - not pressed). Just silly...... For my untrained eye, could I tentatively ask what is wrong with the TV aerial part? I can see that the radio aerial is wrong, but all I can think that's wrong with the TV aerial is that it's too close to the radio aerial. TIA :-) Pity there's isn't a number 4, "after", picture! TV aerial looks ok - certainly better than most! I wonder what the metal paneling is doing to it's polar diagram, and I don't fancy the impulses from the air conditioning motor directly underneath it. |
Misguided installation
wasn't it the birds nest and 20 deg misalignment, in conjunction with bad
tetra. Paul T "Doctor D" wrote in message o.uk... "-GB-Carpy" wrote in message ... "Mike Henry" wrote in message ... In , "-GB-Carpy" wrote: Good photos. I'm always trying to learn new things & improve, but quite often I see things like in your photos and it amazes me how many installers are out there with poor knowledge. Even the basic rules of a good solid installation seem to get ignored most of the time. Today I had to sort out a high gain aerial, on a 16ft mast, mounted on a single 6" chimney bracket (welded at least - not pressed). Just silly...... For my untrained eye, could I tentatively ask what is wrong with the TV aerial part? I can see that the radio aerial is wrong, but all I can think that's wrong with the TV aerial is that it's too close to the radio aerial. TIA :-) Pity there's isn't a number 4, "after", picture! TV aerial looks ok - certainly better than most! I wonder what the metal paneling is doing to it's polar diagram, and I don't fancy the impulses from the air conditioning motor directly underneath it. |
Misguided installation
"Doctor D" wrote in message o.uk... "-GB-Carpy" wrote in message ... "Mike Henry" wrote in message ... In , "-GB-Carpy" wrote: Good photos. I'm always trying to learn new things & improve, but quite often I see things like in your photos and it amazes me how many installers are out there with poor knowledge. Even the basic rules of a good solid installation seem to get ignored most of the time. Today I had to sort out a high gain aerial, on a 16ft mast, mounted on a single 6" chimney bracket (welded at least - not pressed). Just silly...... For my untrained eye, could I tentatively ask what is wrong with the TV aerial part? I can see that the radio aerial is wrong, but all I can think that's wrong with the TV aerial is that it's too close to the radio aerial. TIA :-) Pity there's isn't a number 4, "after", picture! TV aerial looks ok - certainly better than most! I wonder what the metal paneling is doing to it's polar diagram, and I don't fancy the impulses from the air conditioning motor directly underneath it. Well I think we have to assume that's the only place to put the aerial so can't really avoid being close to the metal panelling. Yes it could be moved away from the aircon unit but this is unlikely to cause any problems. Yes a different type of aerial (and lighter) would have been better in this "enclosed" location. Yes the person looking out of that window won't be happy if they are into feng-shui. Yes galvanised brackets would have been better, and tape rather than cable ties, and stop using those awful coach bolts - but in general the TV aerial part of this installation is fine - better than most. They've got the basics right - 1.5" mast - 2 piece bracket with adequate spacing, they haven't fixed it into the top coarse of bricks as is normally the case, they've clipped the cables etc etc. |
Misguided installation
Yes, I quite agree that you wouldn't really choose to use an FM aerial
for DAB but the ones without a balun really do work quite well and in this case I took analyser readings with a true DAB dipole and with the FM one and they were so close as to make no difference. As the main pont of the call was to sort out the TV reception and it was my idea to improve the radio, the "upgrade" from the silly use of the halo was more than worthwhile. It is quite true that the FM ones with a balun are completely useless for DAB. As far as the TV aerial was concerned, there was essentially nothing wrong with the aerial. A decent Triax, solidly mounted. It was just that it was almost fully enclosed by the building and was facing slightly into it. Fortunately it was not actually facing the right way and faced away from the building when it was directed properly. I would not have chosen to fit it so close to the metal cladding and certainly not so close to the airconditioning units but apparently they were fitted after the aerial. The main problem with the TV reception was a mixture of tetra and other local radio transmission which was cured with a mixture of tetra filter, band filter and attenuators. I studied the analyser carefully as the air conditioners cut in and out and there was no noticable affect. There is another "halo" aerial mounted in the same way (vertically), on a bungalow about a mile from this one. It appeared about two years ago as part of a complete new TV and radio erection on the chimney. And then there is the "high gain" new TV aerial that has been added under the existing aerial on the mast on the house almost opposite mine, which is vertically polarised. Our transmitter is horizontally polarised and so is every aerial in sight so heaven knows why the installer thought it was right. I assume it came with the clamp mounted that way and he didnt like to change it! |
Misguided installation
In article
, wrote: Vertical FM dipoles without a balun work so well on DAB it's not always obvious which feed is which is you've fitted a DAB dipole as well. But FM dipoles with baluns are crap for DAB. I have a 4 element FM aerial with balun which was also feeding a DAB tuner. Thinking it would be theoretically better vertical for both, swung it - and got worse results on both. ;-) The DAB becoming unusable. -- *Never miss a good chance to shut up.* Dave Plowman London SW To e-mail, change noise into sound. |
Misguided installation
In message
, widgitt writes I studied the analyser carefully as the air conditioners cut in and out and there was no noticable affect. I would have thought that air conditioner units would use induction motors (or similar). If so, they shouldn't cause any interference. -- Ian |
Misguided installation
they haven't fixed it into the top coarse of bricks
as is normally the case, Yes, as I said, I have no real problem with the TV aerial apart from it facing into the building. Actually you mention the top course of bricks......if you look closely at the middle picture you can see where the installer tried that first and decided it was a bad idea. The bolt is still there. |
Misguided installation
....snip...
I noddy question but assuming the radio transmitted is in the same direction as the Tv transmitter, presumably there would be no problem with mounting the halo vertically. The problem would be that you would get nothing off-axis. Paul DS, |
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