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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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#41
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DAB reception
In article ,
Scott wrote: On Wed, 22 Jan 2020 10:58:43 +0000 (GMT), "Dave Plowman (News)" wrote: In article , Scott wrote: It's not great, is it? I remember when it was first introduced with 'CD quality sound' and bitrate of 192 kbps. Listening to it now, it sounds like medium wave without the fade or the static. Comments like that just shows you've no real experience of either. If you say so. Could be you're simply deaf. And can't hear anything above 4.5 kHz. -- *(over a sketch of the titanic) "The boat sank - get over it Dave Plowman London SW To e-mail, change noise into sound. |
#42
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DAB reception
In article l.net,
Dave Liquorice wrote: On Wed, 22 Jan 2020 13:49:27 +0000 (GMT), Dave Plowman (News) wrote: The car has DAB, the few times I've listened to it there is something about the quality/procesing that makes it very wearing to listen to. Can't take more than half an hour or so before having to switch to something else, which can be the same station on FM that isn't wearing... Surely being a sound engineer you should be able to 'put a finger' on what sounds different? Some sort of higher frequency "edgeiness" and sounding if it's being driven into a 5:1 compressor fairly hard. It may well be hammering a compressor. Like a great deal of radio. And could have different processing from the same station on FM. -- *Puritanism: The haunting fear that someone, somewhere may be happy. Dave Plowman London SW To e-mail, change noise into sound. |
#43
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DAB reception
In message , mm0fmf writes
On 22/01/2020 12:46, Tim Lamb wrote: am not clever enough to play with a raspberry pi. Learn? :-) I'm happy to let someone else do the donkey work! ZX81 tested my limitations. Internet *radio* on order. I have some *must do* hedging before February 1st. -- Tim Lamb |
#44
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DAB reception
In article ,
Dave Plowman (News) wrote: In article , Scott wrote: On Wed, 22 Jan 2020 10:58:43 +0000 (GMT), "Dave Plowman (News)" wrote: In article , Scott wrote: It's not great, is it? I remember when it was first introduced with 'CD quality sound' and bitrate of 192 kbps. Listening to it now, it sounds like medium wave without the fade or the static. Comments like that just shows you've no real experience of either. If you say so. Could be you're simply deaf. And can't hear anything above 4.5 kHz. I havea 60dB notch at 4.5kHz, but I can definitely hear above that frequency/ My hearing aids pull it back about 40dB. -- from KT24 in Surrey, England "I'd rather die of exhaustion than die of boredom" Thomas Carlyle |
#45
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DAB reception
On 23/01/2020 11:16, Dave Plowman (News) wrote:
In article , Martin Brown wrote: DAB is dire when played back through a decent hifi even with good signal. Internet, TDTV, Freesat and even FM leave all it for dust. So how come it works in cars? The engine noise masks most of its short comings. The only thing that DAB does better than FM is the silent gaps inbetween programme material. You have the only FM receiver that doesn't suffer from multi-path, then? I don't spend a lot of time in big cities. Multipath is only a serious problem when there are large reflecting structures about. -- Regards, Martin Brown |
#46
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DAB reception
In article ,
Martin Brown wrote: On 23/01/2020 11:16, Dave Plowman (News) wrote: In article , Martin Brown wrote: DAB is dire when played back through a decent hifi even with good signal. Internet, TDTV, Freesat and even FM leave all it for dust. So how come it works in cars? The engine noise masks most of its short comings. The only thing that DAB does better than FM is the silent gaps inbetween programme material. You have the only FM receiver that doesn't suffer from multi-path, then? I don't spend a lot of time in big cities. Multipath is only a serious problem when there are large reflecting structures about. Then best to qualify your comments about any transmission system. However, many portable radios will exhibit multi-path just with a person moving about in the same room. -- *Strip mining prevents forest fires. Dave Plowman London SW To e-mail, change noise into sound. |
#47
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DAB reception
In article , Martin Brown
wrote: On 23/01/2020 11:16, Dave Plowman (News) wrote: In article , Martin Brown wrote: DAB is dire when played back through a decent hifi even with good signal. Internet, TDTV, Freesat and even FM leave all it for dust. So how come it works in cars? The engine noise masks most of its short comings. The only thing that DAB does better than FM is the silent gaps inbetween programme material. You have the only FM receiver that doesn't suffer from multi-path, then? I don't spend a lot of time in big cities. Multipath is only a serious problem when there are large reflecting structures about. Hills can also create multipath -- from KT24 in Surrey, England "I'd rather die of exhaustion than die of boredom" Thomas Carlyle |
#48
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DAB reception
On 23/01/2020 12:07, Tim Lamb wrote:
In message , mm0fmf writes On 22/01/2020 12:46, Tim Lamb wrote: am not clever enough to play with a raspberry pi. Learn? :-)* I'm happy to let someone else do the donkey work! ZX81 tested my limitations. *Internet *radio* on order. I have some *must do* hedging before February 1st. Ha! did mine last week! -- If you tell a lie big enough and keep repeating it, people will eventually come to believe it. The lie can be maintained only for such time as the State can shield the people from the political, economic and/or military consequences of the lie. It thus becomes vitally important for the State to use all of its powers to repress dissent, for the truth is the mortal enemy of the lie, and thus by extension, the truth is the greatest enemy of the State. Joseph Goebbels |
#49
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DAB reception
On 23/01/2020 14:38, charles wrote:
In article , Martin Brown wrote: On 23/01/2020 11:16, Dave Plowman (News) wrote: In article , Martin Brown wrote: DAB is dire when played back through a decent hifi even with good signal. Internet, TDTV, Freesat and even FM leave all it for dust. So how come it works in cars? The engine noise masks most of its short comings. The only thing that DAB does better than FM is the silent gaps inbetween programme material. You have the only FM receiver that doesn't suffer from multi-path, then? I don't spend a lot of time in big cities. Multipath is only a serious problem when there are large reflecting structures about. Hills can also create multipath So can barbed wire fences And trees -- Socialism is the philosophy of failure, the creed of ignorance and the gospel of envy. Its inherent virtue is the equal sharing of misery. Winston Churchill |
#50
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DAB reception
On Thu, 23 Jan 2020 11:17:54 +0000 (GMT), "Dave Plowman (News)"
wrote: In article , Scott wrote: On Wed, 22 Jan 2020 10:58:43 +0000 (GMT), "Dave Plowman (News)" wrote: In article , Scott wrote: It's not great, is it? I remember when it was first introduced with 'CD quality sound' and bitrate of 192 kbps. Listening to it now, it sounds like medium wave without the fade or the static. Comments like that just shows you've no real experience of either. If you say so. Could be you're simply deaf. And can't hear anything above 4.5 kHz. I can assure you that upper-frequency cutoff is the least of my concerns. Have you actually listened to any of the many stations now broadcasting 80 kbps mono? On a scale with medium wave at one end and CD at the other, DAB in my assessment lies to the left of the scale. I accept that audio is subjective and you may believe that DAB sounds like CD quality. |
#51
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DAB reception
In message , The Natural Philosopher
writes On 23/01/2020 12:07, Tim Lamb wrote: In message , mm0fmf writes On 22/01/2020 12:46, Tim Lamb wrote: am not clever enough to play with a raspberry pi. Learn? :-)* I'm happy to let someone else do the donkey work! ZX81 tested my limitations. *Internet *radio* on order. I have some *must do* hedging before February 1st. Ha! did mine last week! Huh! In an effort to be nice to the RSPB farms are not allowed to trim hedges after the end of January. The only allowed exception is necessary roadside work. I have had Sheep grazing for the last few weeks and am now running out of suitable weather (no rain/drizzle as you then can't see out of the cab) and preferably no bright Sun for the same reason. -- Tim Lamb |
#52
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DAB reception
In article , F
news@nowhere.? scribeth thus On 21/01/2020 20:03, tony sayer wrote: In article , F news@nowhere.? scribeth thus We have a couple of DAB radio alarm clocks. One of them will find and play radio channels, albeit with a low signal strength. The other can't get a reliable signal despite being just the other side of the bed. Both have lengths of thin wire for aerials. Is there anything I can do to get reception? I've moved the wire on the difficult one up, down, left and right but got nowhere. Yes! Try FM Not every station we listen to is on FM... How sad -- Tony Sayer Man is least himself when he talks in his own person. Give him a keyboard, and he will reveal himself. |
#53
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DAB reception
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#54
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DAB reception
On Thu, 23 Jan 2020 21:24:31 +0000, Tim Lamb wrote:
I have had Sheep grazing for the last few weeks and am now running out of suitable weather (no rain/drizzle as you then can't see out of the cab) and preferably no bright Sun for the same reason. Get yer billhook out an' lay 'em properly. Stock proof, RSPB friendly. Of course you can't lay 'em properly as there's nothing to lay, having been flailed for the last few decades... B-( -- Cheers Dave. |
#55
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DAB reception
On Thursday, 23 January 2020 14:19:49 UTC, Dave Plowman (News) wrote:
However, many portable radios will exhibit multi-path just with a person moving about in the same room. That's really better described as the standing wave pattern in the room changing. Bill |
#56
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DAB reception
On Thursday, 23 January 2020 14:42:55 UTC, charles wrote:
Hills can also create multipath I've always thought (or assumed) that rounded hills don't so much reflect the signal as screen it, thus making reflections from other things more significant. Having messed around with directional aerials in mountainous areas I've come to believe that rocky outcrops reflect signals more than other features. I've seen very striking examples of that. Bill |
#57
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DAB reception
On Thursday, 23 January 2020 18:33:32 UTC, The Natural Philosopher wrote:
On 23/01/2020 14:38, charles wrote: Hills can also create multipath So can barbed wire fences And trees I've never been able to blame reflections on barbed wire, but I'm sure it's possible. Trees seem to cause more problems by simply screening the signal, or sometimes by passing it through and providing a secondary transmission path. Bill |
#58
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DAB reception
On 23/01/2020 21:24, Tim Lamb wrote:
In message , The Natural Philosopher writes On 23/01/2020 12:07, Tim Lamb wrote: In message , mm0fmf writes On 22/01/2020 12:46, Tim Lamb wrote: am not clever enough to play with a raspberry pi. Learn? :-)* I'm happy to let someone else do the donkey work! ZX81 tested my limitations. **Internet *radio* on order. I have some *must do* hedging before February 1st. Ha! did mine last week! Huh! In an effort to be nice to the RSPB farms are not allowed to trim hedges after the end of January. The only allowed exception is necessary roadside work. Trim? I was PLANTING I have had Sheep grazing for the last few weeks and am now running out of suitable weather (no rain/drizzle as you then can't see out of the cab) and preferably no bright Sun for the same reason. I thought the cut off was Mach 1st. Farmer here cut his last year on March 2nd... -- "If you dont read the news paper, you are un-informed. If you read the news paper, you are mis-informed." Mark Twain |
#59
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DAB reception
On 24/01/2020 02:19, Bill Wright wrote:
On Thursday, 23 January 2020 14:19:49 UTC, Dave Plowman (News) wrote: However, many portable radios will exhibit multi-path just with a person moving about in the same room. That's really better described as the standing wave pattern in the room changing. Bill its exactly te same thing Except with FM the wave doesnt stand does it? -- "If you dont read the news paper, you are un-informed. If you read the news paper, you are mis-informed." Mark Twain |
#60
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DAB reception
On 24/01/2020 02:31, Bill Wright wrote:
On Thursday, 23 January 2020 18:33:32 UTC, The Natural Philosopher wrote: On 23/01/2020 14:38, charles wrote: Hills can also create multipath So can barbed wire fences And trees I've never been able to blame reflections on barbed wire, but I'm sure it's possible. Trees seem to cause more problems by simply screening the signal, or sometimes by passing it through and providing a secondary transmission path. Bill YOU set up TV aerials. I fly model planes. The barbed wire fence glitch is well known Of course rusty fences have effective diodes in them. So you get intermodulation of reflected signals as well. -- The ultimate result of shielding men from the effects of folly is to fill the world with fools. Herbert Spencer |
#61
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DAB reception
"The Natural Philosopher" wrote in message ... On 24/01/2020 02:31, Bill Wright wrote: On Thursday, 23 January 2020 18:33:32 UTC, The Natural Philosopher wrote: On 23/01/2020 14:38, charles wrote: Hills can also create multipath So can barbed wire fences And trees I've never been able to blame reflections on barbed wire, but I'm sure it's possible. Trees seem to cause more problems by simply screening the signal, or sometimes by passing it through and providing a secondary transmission path. Bill YOU set up TV aerials. I fly model planes. The barbed wire fence glitch is well known With low powered ground based transmitters, sure. but I dont believe it is with FM or DAB transmitters. |
#62
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DAB reception
In message l.net,
Dave Liquorice writes On Thu, 23 Jan 2020 21:24:31 +0000, Tim Lamb wrote: I have had Sheep grazing for the last few weeks and am now running out of suitable weather (no rain/drizzle as you then can't see out of the cab) and preferably no bright Sun for the same reason. Get yer billhook out an' lay 'em properly. Stock proof, RSPB friendly. Of course you can't lay 'em properly as there's nothing to lay, having been flailed for the last few decades... B-( Hedge laying died out with WW2 on this farm. Food production took priority and Land Army girls did not have the skills. I took on linear spinneys! A downside of laying a hedge is that it can only then be flailed *down the grain* otherwise the machine picks up and eats whole limbs! An upside here is that no hedges have been lost and birds do find enough cover to nest. Various permutations of CAP payments have encouraged a range of managed hedges to cater for nesting preferences. -- Tim Lamb |
#63
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DAB reception
In message , The Natural Philosopher
writes On 23/01/2020 21:24, Tim Lamb wrote: In message , The Natural Philosopher writes On 23/01/2020 12:07, Tim Lamb wrote: In message , mm0fmf writes On 22/01/2020 12:46, Tim Lamb wrote: am not clever enough to play with a raspberry pi. Learn? :-)* I'm happy to let someone else do the donkey work! ZX81 tested my limitations. **Internet *radio* on order. I have some *must do* hedging before February 1st. Ha! did mine last week! Huh! In an effort to be nice to the RSPB farms are not allowed to trim hedges after the end of January. The only allowed exception is necessary roadside work. Trim? I was PLANTING Watch out for Rabbits. I have had Sheep grazing for the last few weeks and am now running out of suitable weather (no rain/drizzle as you then can't see out of the cab) and preferably no bright Sun for the same reason. I thought the cut off was Mach 1st. Farmer here cut his last year on March 2nd... You are quite correct! I can relax:-) -- Tim Lamb |
#64
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DAB reception
In article , Andrew
writes On 22/01/2020 10:58, Dave Plowman (News) wrote: In article , Scott wrote: It's not great, is it? I remember when it was first introduced with 'CD quality sound' and bitrate of 192 kbps. Listening to it now, it sounds like medium wave without the fade or the static. Comments like that just shows you've no real experience of either. You live in London though where DAB is fine while FM can be a problem because of illegal transmitters, buildings etc. Many parts of the country have better FM reception than DAB. DAB is OK here. Use it in the house and car. More stations available, Talksport 2 or 5Livex for continuous cricket commentary. -- bert |
#65
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DAB reception
On 24/01/2020 09:51, Tim Lamb wrote:
In message , The Natural Philosopher writes On 23/01/2020 21:24, Tim Lamb wrote: In message , The Natural Philosopher writes On 23/01/2020 12:07, Tim Lamb wrote: In message , mm0fmf writes On 22/01/2020 12:46, Tim Lamb wrote: am not clever enough to play with a raspberry pi. Learn? :-)* I'm happy to let someone else do the donkey work! ZX81 tested my limitations. **Internet *radio* on order. I have some *must do* hedging before February 1st. Ha! did mine last week! *Huh! In an effort to be nice to the RSPB farms are not allowed to trim* hedges after the end of January. The only allowed exception is necessary* roadside work. Trim? I was PLANTING Watch out for Rabbits. I have had Sheep grazing for the last few weeks and am now running out* of suitable weather (no rain/drizzle as you then can't see out of the* cab) and preferably no bright Sun for the same reason. I thought the cut off was Mach 1st. Farmer here cut his last year on March 2nd... You are quite correct! I can relax:-) Phew. So can I since he is off in the Caribbean now as the fields are too wet and there is sod all else to do -- The New Left are the people they warned you about. |
#66
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DAB reception
In article ,
Bill Wright wrote: On Thursday, 23 January 2020 14:19:49 UTC, Dave Plowman (News) wrote: However, many portable radios will exhibit multi-path just with a person moving about in the same room. That's really better described as the standing wave pattern in the room changing. Oh, indeed. But the audible results are similar. And the same sort of problems with an inside aerial in VHF TV days. Each transmission medium has its own individual problems. -- *i souport publik edekashun. Dave Plowman London SW To e-mail, change noise into sound. |
#67
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DAB reception
On 23/01/2020 23:30, tony sayer wrote:
In article , F news@nowhere.? scribeth thus On 21/01/2020 20:03, tony sayer wrote: In article , F news@nowhere.? scribeth thus We have a couple of DAB radio alarm clocks. One of them will find and play radio channels, albeit with a low signal strength. The other can't get a reliable signal despite being just the other side of the bed. Both have lengths of thin wire for aerials. Is there anything I can do to get reception? I've moved the wire on the difficult one up, down, left and right but got nowhere. Yes! Try FM Not every station we listen to is on FM... How sad ?? -- F |
#68
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DAB reception
On 22/01/2020 21:17, Brian Reay wrote:
Andrew wrote: On 22/01/2020 11:19, The Natural Philosopher wrote: On 22/01/2020 11:17, F wrote: On 21/01/2020 20:03, tony sayer wrote: In article , F news@nowhere.? scribeth thus We have a couple of DAB radio alarm clocks. One of them will find and play radio channels, albeit with a low signal strength. The other can't get a reliable signal despite being just the other side of the bed. Both have lengths of thin wire for aerials. Is there anything I can do to get reception? I've moved the wire on the difficult one up, down, left and right but got nowhere. Yes! Try FM Not every station we listen to is on FM... Use a raspberry pi or other computer to listen to them on the internet Better still buy a Roberts Stream94 and avoid ALL the awful Linux garbage. The iStream94 is an excellent radio but I think you will find the software is Linux based- I stumbled across some details of the software when researching models. So is my Humax HD FOXT2 PVR but I don't need to interact with it directly. For a bedroom radio you want something that is easy to use even with the lights off !! Unlike some of the cheaper Internet Radios, the user interface is very straight forward and, above all, stable. I use mine in DAB, Internet Radio, and Media mode - very occasionally in FM. |
#69
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DAB reception
On Friday, 24 January 2020 02:37:09 UTC, The Natural Philosopher wrote:
I fly model planes. The barbed wire fence glitch is well known I haven't heard of this and I'm very interested. Please tell us more. Bill |
#70
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DAB reception
On Friday, 24 January 2020 13:47:19 UTC, Dave Plowman (News) wrote:
In article , Bill Wright wrote: On Thursday, 23 January 2020 14:19:49 UTC, Dave Plowman (News) wrote: However, many portable radios will exhibit multi-path just with a person moving about in the same room. That's really better described as the standing wave pattern in the room changing. Oh, indeed. But the audible results are similar. For VHF FM, a standing wave causing complete or near-complete signal cancellation obviously results in what is effectively weak or zero signal at the receiver. You'd expect degradation into noise pure and simple but there's usually another weak signal path from a reflection external to the room. With the direct path almost or completely cancelled out that signal becomes more significant so the audible result is often the high frequency audio distortion (lisping) that is also caused by simple signal reflections. In the case of analogue TV, standing waves within the room (or loft)can, by the same mechanism, cause ghosting rather than simple weak signal. Bill |
#71
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DAB reception
In article , Bill
Wright scribeth thus On Thursday, 23 January 2020 14:42:55 UTC, charles wrote: Hills can also create multipath I've always thought (or assumed) that rounded hills don't so much reflect the signal as screen it, thus making reflections from other things more significant. Having messed around with directional aerials in mountainous areas I've come to believe that rocky outcrops reflect signals more than other features. I've seen very striking examples of that. Bill Edge diffraction there is a good article on it somewhere, can't think of it right now tho.. -- Tony Sayer Man is least himself when he talks in his own person. Give him a keyboard, and he will reveal himself. |
#72
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DAB reception
On 24/01/2020 20:34, Bill Wright wrote:
On Friday, 24 January 2020 02:37:09 UTC, The Natural Philosopher wrote: I fly model planes. The barbed wire fence glitch is well known I haven't heard of this and I'm very interested. Please tell us more. back in the days of 35MHz NBFM it was well known that flying at reasonable range over rusty fences would cause momentary loss of or corruption of signal. Generally seen as a massive twitch on all flight surfaces and a loss of throttle. 35MHz was never the best of mediums anyway but club fliers got to know that certain places were prone to this effect. Whether it was multipath, or diodic mixing causing intermodulation I cannot say - or both. For more information, the signal modulation on FM RC is/was a series of frequency excursions marking the edges of a series of channel frames about 1ms long with the lengh of a frame being the position of the associated servo - in the range of 0.5ms to 1.5ms. A very long frame - 10ms or so - was used as a synchronisation frame., This form of modulation has only one benefit. A simple CMOS shift regsiter could decode the pulse train to the servos. But as an interference rejecting schema it was pants. Loss of a frame edge meant one channel got two channels worth of info and the subsequent channels got te wrong info. Hence the massive glitch/twitch. Bill -- "It is an established fact to 97% confidence limits that left wing conspirators see right wing conspiracies everywhere" |
#73
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DAB reception
In article , The Natural Philosopher
scribeth thus On 24/01/2020 20:34, Bill Wright wrote: On Friday, 24 January 2020 02:37:09 UTC, The Natural Philosopher wrote: I fly model planes. The barbed wire fence glitch is well known I haven't heard of this and I'm very interested. Please tell us more. back in the days of 35MHz NBFM it was well known that flying at reasonable range over rusty fences would cause momentary loss of or corruption of signal. Generally seen as a massive twitch on all flight surfaces and a loss of throttle. 35MHz was never the best of mediums anyway but club fliers got to know that certain places were prone to this effect. Whether it was multipath, or diodic mixing causing intermodulation I cannot say - or both. For more information, the signal modulation on FM RC is/was a series of frequency excursions marking the edges of a series of channel frames about 1ms long with the lengh of a frame being the position of the associated servo - in the range of 0.5ms to 1.5ms. A very long frame - 10ms or so - was used as a synchronisation frame., This form of modulation has only one benefit. A simple CMOS shift regsiter could decode the pulse train to the servos. But as an interference rejecting schema it was pants. Loss of a frame edge meant one channel got two channels worth of info and the subsequent channels got te wrong info. Hence the massive glitch/twitch. Bill Interesting! Time for OFDM perhaps;?.. -- Tony Sayer Man is least himself when he talks in his own person. Give him a keyboard, and he will reveal himself. |
#74
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DAB reception
On Saturday, 25 January 2020 00:02:48 UTC, tony sayer wrote:
In article , Bill Wright scribeth thus On Thursday, 23 January 2020 14:42:55 UTC, charles wrote: Hills can also create multipath I've always thought (or assumed) that rounded hills don't so much reflect the signal as screen it, thus making reflections from other things more significant. Having messed around with directional aerials in mountainous areas I've come to believe that rocky outcrops reflect signals more than other features. I've seen very striking examples of that. Bill Edge diffraction there is a good article on it somewhere, can't think of it right now tho.. Edge diffraction! Six miles from a high powered TV tx. Rounded and bare heap of colliery waste in way. Move the rx aerial vertically up and down and there will be distinct peaks and nulls. Bill |
#75
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DAB reception
On Saturday, 25 January 2020 10:28:47 UTC, The Natural Philosopher wrote:
On 24/01/2020 20:34, Bill Wright wrote: On Friday, 24 January 2020 02:37:09 UTC, The Natural Philosopher wrote: I fly model planes. The barbed wire fence glitch is well known I haven't heard of this and I'm very interested. Please tell us more. back in the days of 35MHz NBFM it was well known that flying at reasonable range over rusty fences would cause momentary loss of or corruption of signal. Generally seen as a massive twitch on all flight surfaces and a loss of throttle. 35MHz was never the best of mediums anyway but club fliers got to know that certain places were prone to this effect. Whether it was multipath, or diodic mixing causing intermodulation I cannot say - or both. For more information, the signal modulation on FM RC is/was a series of frequency excursions marking the edges of a series of channel frames about 1ms long with the lengh of a frame being the position of the associated servo - in the range of 0.5ms to 1.5ms. A very long frame - 10ms or so - was used as a synchronisation frame., This form of modulation has only one benefit. A simple CMOS shift regsiter could decode the pulse train to the servos. But as an interference rejecting schema it was pants. Loss of a frame edge meant one channel got two channels worth of info and the subsequent channels got te wrong info. Hence the massive glitch/twitch. Thank you. Bill |
#76
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DAB reception
On 25/01/2020 13:37, tony sayer wrote:
In article , The Natural Philosopher scribeth thus On 24/01/2020 20:34, Bill Wright wrote: On Friday, 24 January 2020 02:37:09 UTC, The Natural Philosopher wrote: I fly model planes. The barbed wire fence glitch is well known I haven't heard of this and I'm very interested. Please tell us more. back in the days of 35MHz NBFM it was well known that flying at reasonable range over rusty fences would cause momentary loss of or corruption of signal. Generally seen as a massive twitch on all flight surfaces and a loss of throttle. 35MHz was never the best of mediums anyway but club fliers got to know that certain places were prone to this effect. Whether it was multipath, or diodic mixing causing intermodulation I cannot say - or both. For more information, the signal modulation on FM RC is/was a series of frequency excursions marking the edges of a series of channel frames about 1ms long with the lengh of a frame being the position of the associated servo - in the range of 0.5ms to 1.5ms. A very long frame - 10ms or so - was used as a synchronisation frame., This form of modulation has only one benefit. A simple CMOS shift regsiter could decode the pulse train to the servos. But as an interference rejecting schema it was pants. Loss of a frame edge meant one channel got two channels worth of info and the subsequent channels got te wrong info. Hence the massive glitch/twitch. Bill Interesting! Time for OFDM perhaps;?.. we have now gone 2.4GHz. Essentailly the wifi band. This uses a collision detection algorithm and spread spectrum. Also some frequency hopping. Since the frame rate is low - a complete model only needs 64 bits every 20 ms - a massive data rate of 3200 bits per second - the way the systems work is to transmit a frame with error correction and a transmitter ID, and back off if there is collision. The comms is bi directional so the receivers request retransmits if a frame is corrupt. Loss of a frame simply means that the model carries on doing whatever it was doing - the actual perception is that it's sluggish and unresponsive. Ther is usally a watchdog tomer that will move the controls to user configurable preset positions - usully cut throttle and mild level turn - in the event of total signal loss. Since every transitter has a unique MAC code, operation of dozens of models simultaneously is possible - all too many transmitters does, is slow the data rate down a bit. Its like having a shared wifi network. I used to get some issues flying through a tight beam from the local radio mast that you know of all too well. Lets hope te 2.4GHz stuff is more resilient -- "Strange as it seems, no amount of learning can cure stupidity, and higher education positively fortifies it." - Stephen Vizinczey |
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