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FM/DAB
I have a Cambridge azur 650T tuner. I have a single coaxial cable that at
present feeds from a loft aerial (external is not possible) into the FM input via a coax connector. The DAB has an F type connector. I would like to be able to use both FM and DAB from the single cable. 1. If it is possible, what would be the most effective way of setting this up? 2. Is there an aerial that would support both FM and DAB? (I live in Wareham, Dorset - BH20 5BB) Thanks, Gordon |
FM/DAB
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FM/DAB
In message , tony sayer
writes In article , Gordon MacPherson gordon.macph scribeth thus I have a Cambridge azur 650T tuner. I have a single coaxial cable that at present feeds from a loft aerial (external is not possible) into the FM input via a coax connector. The DAB has an F type connector. I would like to be able to use both FM and DAB from the single cable. 1. If it is possible, what would be the most effective way of setting this up? 2. Is there an aerial that would support both FM and DAB? (I live in Wareham, Dorset - BH20 5BB) Thanks, Gordon Generally an FM vertical dipole, not that abortion known as a halo, works quite well on DAB in a lot of areas. You should get a very good signal from the Rowridge TX on the Isle of Wight. I believe that BBC DAB is from there and the commercial from Chillerton down in the same isle!.. Even if you used a 3 element Yagi I suspect there'd still be sufficient DAB signal as well as enhancing the FM ones.. I think that there are FM/DAB Splitters around, never used one as this is a DAB free zone!, do not use just a simple splitter as this will halve the available signal on each band... I think that the first questions a 1. What is the existing loft aerial (vertical, horizontal, dipole, groundplane, random piece of dangling wire etc)? 2. Have you tried connecting the existing FM feed (which presumably has a traditional Belling Lee connector) to the DAB F input (using an adapter)? If you already get good FM, and the DAB also seems good, then you may get away with a simple 2-way splitter (preferably a 'proper' 3.5dB splitter, and not a cheaper 6dB resistive job). If not, an even more-proper low-loss filtered splitter/diplexer would be better. [However, if you really do need a filtered job, signal levels must be rather marginal.] If you don't get good DAB using the existing FM, aerial, then you'll have to think about improving things - but only cross that bridge when you come to it. -- Ian |
FM/DAB
In message , RJH
writes On 30/07/2013 12:17, tony sayer wrote: In article , Gordon MacPherson gordon.macph scribeth thus I have a Cambridge azur 650T tuner. I have a single coaxial cable that at present feeds from a loft aerial (external is not possible) into the FM input via a coax connector. The DAB has an F type connector. I would like to be able to use both FM and DAB from the single cable. 1. If it is possible, what would be the most effective way of setting this up? 2. Is there an aerial that would support both FM and DAB? (I live in Wareham, Dorset - BH20 5BB) Thanks, Gordon Generally an FM vertical dipole, not that abortion known as a halo, works quite well on DAB in a lot of areas. You should get a very good signal from the Rowridge TX on the Isle of Wight. I believe that BBC DAB is from there and the commercial from Chillerton down in the same isle!.. Even if you used a 3 element Yagi I suspect there'd still be sufficient DAB signal as well as enhancing the FM ones.. I think that there are FM/DAB Splitters around, never used one as this is a DAB free zone!, do not use just a simple splitter as this will halve the available signal on each band... I was looking into this, and: http://www.aerialsandtv.com/fmanddab...fFM&DABAerials looks useful. Useful maybe, but I always worry a little when I see comments like this: "The round FM “Omni” type antennas do not perform as well as the half wave dipole and this reflects their design, which gives a theoretical minus 3 dBd gain figure. That's why we think they're crap and we don't stock them." There's nothing wrong with these omnidirectional 'halo' aerials provided the user knows what the performance is, and knows that he can tolerate the 3dB of signal loss compared with a straight halfwave dipole. But being horizontally polarised, they are probably pretty useless when it comes to the 'accidental' reception of vertically polarised DAB signals. -- Ian |
FM/DAB
One thing that everyone has missed is that DAB is vertically
polarised. Thankfully all FM transmissions in the UK are now of mixed polarisation (i.e. they have both horizontal and vertical components) so turning your FM aerial vertical (if necessary) will not be a problem (electronically - might be physically!) As others have said a simple single half-wave vertical VHF dipole is the best as (a) it is just about a full wave at DAB frequencies so will work albeit with a mismatch and (b) it is near enough omni-directional so will not limit you to your source Tx station. -- Woody harrogate three at ntlworld dot com |
FM/DAB
In article , Woody
wrote: One thing that everyone has missed is that DAB is vertically polarised. Thankfully all FM transmissions in the UK are now of mixed polarisation (i.e. they have both horizontal and vertical components) so turning your FM aerial vertical (if necessary) will not be a problem (electronically - might be physically!) You beat me to commenting on the polarisations. I suspect that having a VHF antenna 'work' for DAB may simply be using its coax as the DAB antenna because the actual antenna is a hopeless match at DAB frequencies. :-) That said, I just made a DAB antenna using two bits of wire taped to a wooden stick. (Flower support from the garden center.) 8-] Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
FM/DAB
Gordon MacPherson wrote... The DAB has an F type connector. I would like to be able to use both FM and DAB from the single cable. 1. If it is possible, what would be the most effective way of setting this up? It depends on your existing signal level, if it is good then you could use a simple passive splitter but you may need to use a signal booster to compensate for the loss incurred in the splitter. I'm in a similar situation, in that our communal aerial system provides a single combined (very good) FM/DAB feed. I tried various ways of getting this to to my FM & DAB tuners including a couple of passive splitters and they were fine for DAB but degraded the FM signal too much compared to a direct connection. In the end I got one of these 1 in 2 out amplifiers http://www.philex.com/catalogue/prod...d=116&cat=1069 which works well for both DAB and FM. It has a variable gain control which allows you to fine tune things. Here are the results of using that on the end of a much derided FM halo. http://goo.gl/maps/sF9Yh -- UnsteadyKen |
FM/DAB
In message , Woody
writes One thing that everyone has missed is that DAB is vertically polarised. No we haven't. That's why I asked what the existing FM aerial was (but you've snipped it all). Thankfully all FM transmissions in the UK are now of mixed polarisation (i.e. they have both horizontal and vertical components) so turning your FM aerial vertical (if necessary) will not be a problem (electronically - might be physically!) As others have said a simple single half-wave vertical VHF dipole is the best as (a) it is just about a full wave at DAB frequencies so will work albeit with a mismatch and (b) it is near enough omni-directional so will not limit you to your source Tx station. If the existing FM aerial is horizontal, to get DAB it would be better if it could be turned vertical. It should still work well for FM. As you say, its length will be a complete impedance mismatch for DAB, but it might work well enough. If not, that's the time that the OP needs to think about doing things a bit 'more properly'. -- Ian |
FM/DAB
In message , Jim Lesurf
writes In article , Woody wrote: One thing that everyone has missed is that DAB is vertically polarised. Thankfully all FM transmissions in the UK are now of mixed polarisation (i.e. they have both horizontal and vertical components) so turning your FM aerial vertical (if necessary) will not be a problem (electronically - might be physically!) You beat me to commenting on the polarisations. I suspect that having a VHF antenna 'work' for DAB may simply be using its coax as the DAB antenna because the actual antenna is a hopeless match at DAB frequencies. :-) Aerial impedance mismatch doesn't cause pickup on the coax. However, if the receiver is getting a reasonable signal, it's possible that a lot of it isn't coming from the aerial, but is being picked up on the coax. That said, I just made a DAB antenna using two bits of wire taped to a wooden stick. (Flower support from the garden center.) 8-] Indeed, most true enthusiasts will have done something similar. Bamboo canes also play an important part in such experimentation. Wire coathangers (straightened, of course, and cut to size!) can also be used as aerial elements. Unfortunately, the OP hasn't come back yet to say what his present FM aerial consists of. -- Ian |
FM/DAB
In article , Ian Jackson
wrote: In message , Jim Lesurf writes In article , Woody wrote: One thing that everyone has missed is that DAB is vertically polarised. Thankfully all FM transmissions in the UK are now of mixed polarisation (i.e. they have both horizontal and vertical components) so turning your FM aerial vertical (if necessary) will not be a problem (electronically - might be physically!) You beat me to commenting on the polarisations. I suspect that having a VHF antenna 'work' for DAB may simply be using its coax as the DAB antenna because the actual antenna is a hopeless match at DAB frequencies. :-) Aerial impedance mismatch doesn't cause pickup on the coax. I'm afraid that it does when the cause is essentially an irregular bunch of bits of metal connected to the end. The point here is that the mismatch comes from an arrangement that is nothing like a correctly unbalanced and matched arrangement. Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
FM/DAB
In message , Jim Lesurf
writes In article , Ian Jackson wrote: In message , Jim Lesurf writes In article , Woody wrote: One thing that everyone has missed is that DAB is vertically polarised. Thankfully all FM transmissions in the UK are now of mixed polarisation (i.e. they have both horizontal and vertical components) so turning your FM aerial vertical (if necessary) will not be a problem (electronically - might be physically!) You beat me to commenting on the polarisations. I suspect that having a VHF antenna 'work' for DAB may simply be using its coax as the DAB antenna because the actual antenna is a hopeless match at DAB frequencies. :-) Aerial impedance mismatch doesn't cause pickup on the coax. I'm afraid that it does when the cause is essentially an irregular bunch of bits of metal connected to the end. The point here is that the mismatch comes from an arrangement that is nothing like a correctly unbalanced and matched arrangement. If a balanced (or even sort-of balanced) aerial is connected to an unbalance feeder, indeed there will be pickup (or radiation) from the feeder. However, that doesn't really have anything to do with impedance mismatch. Connect a perfect, balanced 75 ohm dipole directly to perfect 75 ohm coax, and you will get feeder pickup/radiation effects. Connect a perfect, balanced 300 ohm dipole via a balun 75 ohm to coax, and you won't. [However, your signal will be 8db lower than if it was a 75 ohm dipole.] -- Ian |
FM/DAB
"Ian Jackson" If a balanced (or even sort-of balanced) aerial is connected to an unbalance feeder, indeed there will be pickup (or radiation) from the feeder. ** Which merely makes the polar pattern a bit lop sided. However, that doesn't really have anything to do with impedance mismatch. Connect a perfect, balanced 75 ohm dipole directly to perfect 75 ohm coax, and you will get feeder pickup/radiation effects. Connect a perfect, balanced 300 ohm dipole via a balun 75 ohm to coax, and you won't. [However, your signal will be 8db lower than if it was a 75 ohm dipole.] ** That is ambiguously worded. Is the balun a 300ohm to 75 ohm type ? If so, there is no significant loss of signal level. If it is a 75ohm to 75 ohm type, then the loss is 8dB compared to using to correct balun. NB 1: If the antenna has passive elements ahead and behind the folded dipole - all bets are off regards correct matching. See the maker's specs for advice. NB2: Long as the co-ax cable is matched at the receiver, there is no problem with standing waves. ..... Phil |
FM/DAB
In message , Phil Allison
writes "Ian Jackson" If a balanced (or even sort-of balanced) aerial is connected to an unbalance feeder, indeed there will be pickup (or radiation) from the feeder. ** Which merely makes the polar pattern a bit lop sided. However, that doesn't really have anything to do with impedance mismatch. Connect a perfect, balanced 75 ohm dipole directly to perfect 75 ohm coax, and you will get feeder pickup/radiation effects. Connect a perfect, balanced 300 ohm dipole via a balun 75 ohm to coax, and you won't. [However, your signal will be 8db lower than if it was a 75 ohm dipole.] ** That is ambiguously worded. Is the balun a 300ohm to 75 ohm type ? If I had meant a 300 to 75 ohm balun, I would have said so. If so, there is no significant loss of signal level. If it is a 75ohm to 75 ohm type, then the loss is 8dB compared to using to correct balun. Which is why I said "8dB". NB 1: If the antenna has passive elements ahead and behind the folded dipole - all bets are off regards correct matching. See the maker's specs for advice. When I said a 75 ohm dipole, I meant a 75 ohm dipole. When I said a 300 ohm dipole, I meant a 300 ohm dipole. That's why I said a 75 ohm dipole and a 300 ohm dipole. NB2: Long as the co-ax cable is matched at the receiver, there is no problem with standing waves. No one mentioned problems with standing waves. You're missing the whole point about the effects of connecting a balanced aerial directly to coax. -- Ian |
FM/DAB
In article , Ian Jackson
wrote: In message , Jim Lesurf writes I'm afraid that it does when the cause is essentially an irregular bunch of bits of metal connected to the end. The point here is that the mismatch comes from an arrangement that is nothing like a correctly unbalanced and matched arrangement. If a balanced (or even sort-of balanced) aerial is connected to an unbalance feeder, indeed there will be pickup (or radiation) from the feeder. However, that doesn't really have anything to do with impedance mismatch. Connect a perfect, balanced 75 ohm dipole directly to perfect 75 ohm coax, and you will get feeder pickup/radiation effects. Connect a perfect, balanced 300 ohm dipole via a balun 75 ohm to coax, and you won't. [However, your signal will be 8db lower than if it was a 75 ohm dipole.] The theory is fine, based on presuming only one factor isn't optimised. But the reality is that the two factors will tend to be wrong, in a related way, and each then has an impact on the results from the other. Hence the reality can be that signals may be picked up from the coax acting as a vertical antenna. Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
FM/DAB
"Ian Jackson" Phil Allison "Ian Jackson" If a balanced (or even sort-of balanced) aerial is connected to an unbalance feeder, indeed there will be pickup (or radiation) from the feeder. ** Which merely makes the polar pattern a bit lop sided. However, that doesn't really have anything to do with impedance mismatch. Connect a perfect, balanced 75 ohm dipole directly to perfect 75 ohm coax, and you will get feeder pickup/radiation effects. Connect a perfect, balanced 300 ohm dipole via a balun 75 ohm to coax, and you won't. [However, your signal will be 8db lower than if it was a 75 ohm dipole.] ** That is ambiguously worded. Is the balun a 300ohm to 75 ohm type ? If I had meant a 300 to 75 ohm balun, I would have said so. ** Pedantic crap. Your post has a glaring error that creates the ambiguity. If so, there is no significant loss of signal level. If it is a 75ohm to 75 ohm type, then the loss is 8dB compared to using to correct balun. Which is why I said "8dB". ** No fooling ???? Who woulda thunk ..... NB 1: If the antenna has passive elements ahead and behind the folded dipole - all bets are off regards correct matching. See the maker's specs for advice. When I said a 75 ohm dipole, I meant a 75 ohm dipole. When I said a 300 ohm dipole, I meant a 300 ohm dipole. That's why I said a 75 ohm dipole and a 300 ohm dipole. ** More autistic, boring pedantic crap. Can you spell the word "ambiguous" for me? NB2: Long as the co-ax cable is matched at the receiver, there is no problem with standing waves. No one mentioned problems with standing waves. ** I did. To head off those with the usual misconceptions before they ****ing posted them. You're missing the whole point about the effects of connecting a balanced aerial directly to coax. ** You have yet to post anything non-ambiguous about that too. But I'm not holding my breath waiting. ..... Phil |
FM/DAB
In article , UnsteadyKen
scribeth thus Gordon MacPherson wrote... The DAB has an F type connector. I would like to be able to use both FM and DAB from the single cable. 1. If it is possible, what would be the most effective way of setting this up? It depends on your existing signal level, if it is good then you could use a simple passive splitter but you may need to use a signal booster to compensate for the loss incurred in the splitter. I'm in a similar situation, in that our communal aerial system provides a single combined (very good) FM/DAB feed. I tried various ways of getting this to to my FM & DAB tuners including a couple of passive splitters and they were fine for DAB but degraded the FM signal too much compared to a direct connection. In the end I got one of these 1 in 2 out amplifiers http://www.philex.com/catalogue/prod...d=116&cat=1069 which works well for both DAB and FM. It has a variable gain control which allows you to fine tune things. Here are the results of using that on the end of a much derided FM halo. http://goo.gl/maps/sF9Yh Think how much better it would be with a decent Vertical dipole;-).. In fact we did some tests on one of they and they did do better than a coat-hanger .. which incidentally wasn't resonant;-!.. That design, if you can call it that, was used for some IBA transmit aerials waay back before they devised better mixed polarisation ones but it has got a relative loss compared to the straight half wave dipole.. As regards matching alluded to elsewhere its worth remembering that a simple half wave dipole has a typical impedance at resonance of 73 ohms but when folded this rises to close on 300 hence the need for a transformer to wind that down to a more useful value and also to an unbalanced cable as 300 ohm.. does anyone use that anymore in the UK I rather suspect not. Sadly most all FM aerials made in the UK dispense with any attempt at a balun device apart from some Triax ones. Antiference use another odd arrangement. If you NEC model a half wave fm dipole whilst the SWR does go high at DAB frequencies the gain oddly enough improves around the DAB sector. I have seen reports by Bill Wright of Wright's aerials saying that they very often get decent DAB signals off vertical FM dipoles in the UK. Whilst on the humble Halo and V and H polarisation it is true to say that most all main stations and higher power relays do use Mixed polarisation but some relays and most all community stations use Vertical only hence another reason for the implementation of a vertical dipole RX aerial.. -- Tony Sayer |
FM/DAB
In message , Jim Lesurf
writes In article , Ian Jackson wrote: In message , Jim Lesurf writes I'm afraid that it does when the cause is essentially an irregular bunch of bits of metal connected to the end. The point here is that the mismatch comes from an arrangement that is nothing like a correctly unbalanced and matched arrangement. If a balanced (or even sort-of balanced) aerial is connected to an unbalance feeder, indeed there will be pickup (or radiation) from the feeder. However, that doesn't really have anything to do with impedance mismatch. Connect a perfect, balanced 75 ohm dipole directly to perfect 75 ohm coax, and you will get feeder pickup/radiation effects. Connect a perfect, balanced 300 ohm dipole via a balun 75 ohm to coax, and you won't. [However, your signal will be 8db lower than if it was a 75 ohm dipole.] The theory is fine, based on presuming only one factor isn't optimised. But the reality is that the two factors will tend to be wrong, in a related way, and each then has an impact on the results from the other. Hence the reality can be that signals may be picked up from the coax acting as a vertical antenna. The screening effect of coax 'works' because as far as the impinging RF signals (hitting the coax) are concerned, at any position on the coax, the voltage on the inner conductor is (or should be) the same as the RF voltage on the outside of the shield (ie there is RF potential between inner and the outside of the shield). By itself, well-screened coax only delivers RF signals to the receiver input if the shield isn't properly (solidly) connected to the reference ground/chassis of the receiver. If there is any impedance in the way (isolation capacitors, lead lengths etc) at the receiver end, the outside of the shield can be at an RF voltage (from RF fields impinging on the length of the coax shield). As the RF voltage on the inner is the same as that on the outside of the shield, any RF voltage on the outer of the shield also appears on the inner - and this gets fed (whether by direct connection or by stray coupling) into the 'RF live' side of receiver input. [Well, that is my understanding things!] -- Ian |
FM/DAB
tony sayer wrote... Think how much better it would be with a decent Vertical dipole;-).. Who knows why they use these halos?, DAB is a V dipole, it is the standard council communal installation round here for sheltered housing and flats, consisting of a large sat dish, FM halo, DAB dipole and two TV aerials; one pointing north for Waltham and one south for Sandy Heath all mounted on a sturdy pole. Receiving two different TV regions with equally strong signals confuses a great many Freeview boxes and TV sets, plus their elderly owners. Equipment which detects this and allows you to choose a region cope fine, but lots end up with the whole 70 channels duplicated in the 800's In fact we did some tests on one of they and they did do better than a coat-hanger .. which incidentally wasn't resonant;-!.. It gets those results through the use of massive amplification, whole swathes of the VHF band are obliterated by the resulting harmonics from the local main transmitters, (Peterborough and Geddington) -- UnsteadyKen |
FM/DAB
tony sayer wrote... I have seen reports by Bill Wright of Wright's aerials saying that they very often get decent DAB signals off vertical FM dipoles in the UK. We seem to be in a sweet spot for DAB reception round here, especially since the Northamptonshire service started earlier this year from the transmitter at Geddington. The communal system also pulls in the Leicester, Nottingham and Cambridge muxes as well as the locals, A portable DAB radio will work on a bit of wet string and I can only clear the memory of my DAB tuner by shorting the aerial input. Bubbling mud, wossat? -- UnsteadyKen |
FM/DAB
In article , UnsteadyKen
scribeth thus tony sayer wrote... Think how much better it would be with a decent Vertical dipole;-).. Who knows why they use these halos?, Simple, easy to mount, and above all they get them cheap... I think some aerial "riggers" don't have that much idea of what the do or are doing other than "we wire this up and it usually works" DAB is a V dipole, it is the standard council communal installation round here for sheltered housing and flats, consisting of a large sat dish, FM halo, DAB dipole and two TV aerials; one pointing north for Waltham and one south for Sandy Heath all mounted on a sturdy pole. Receiving two different TV regions with equally strong signals confuses a great many Freeview boxes and TV sets, plus their elderly owners. Equipment which detects this and allows you to choose a region cope fine, but lots end up with the whole 70 channels duplicated in the 800's Why are they doing that? ITV 1 is much the same anywhere in that area apart from the news I'd have thought Waltham is more your backyard rather than the outpourings of Narwich.... In fact we did some tests on one of they and they did do better than a coat-hanger .. which incidentally wasn't resonant;-!.. It gets those results through the use of massive amplification, whole swathes of the VHF band are obliterated by the resulting harmonics from the local main transmitters, (Peterborough and Geddington) Ah!, I'm sure Bill Wright, not on this ng, could give you chapter and verse of what they find wrong when asked in to sort these "systems".... -- Tony Sayer |
FM/DAB
In article , UnsteadyKen
scribeth thus tony sayer wrote... I have seen reports by Bill Wright of Wright's aerials saying that they very often get decent DAB signals off vertical FM dipoles in the UK. We seem to be in a sweet spot for DAB reception round here, especially since the Northamptonshire service started earlier this year from the transmitter at Geddington. The communal system also pulls in the Leicester, Nottingham and Cambridge muxes as well as the locals, A portable DAB radio will work on a bit of wet string and I can only clear the memory of my DAB tuner by shorting the aerial input. Bubbling mud, wossat? Well!, checking out where you are on the terrain database that's some 125 Metres above ordnance datum which by most standards for that area is bloody high!. Its not surprising that you get good reception. There are quite a few areas in East Anglia where 'bubbin mud is a well worn tune!... Not everyone is so well blessed with such a decent area to live in .. well with regards to height that is;!.. -- Tony Sayer |
FM/DAB
In message , UnsteadyKen
writes tony sayer wrote... Think how much better it would be with a decent Vertical dipole;-).. Who knows why they use these halos?, 1. Halos are compact and very easy to mount on (around) a vertical mast. They don't clutter up the space required for other aerials too much. 2. Halos have a well-defined, pretty well omnidirectional gain of around minus 3dBd. The fact that that there a minus sign there doesn't necessarily indicate that it doesn't perform adequately. -- Ian |
FM/DAB
In article , Ian Jackson
wrote: In message , UnsteadyKen writes tony sayer wrote... Think how much better it would be with a decent Vertical dipole;-).. Who knows why they use these halos?, 1. Halos are compact and very easy to mount on (around) a vertical mast. They don't clutter up the space required for other aerials too much. 2. Halos have a well-defined, pretty well omnidirectional gain of around minus 3dBd. The fact that that there a minus sign there doesn't necessarily indicate that it doesn't perform adequately. Depends on how you define 'adequately'. ;- Yes, the user may still get enough signal to keep them happy. Although for VHF - as people have said - a vertical dipole will probably provide more gain. Another way to look at the halo is to wonder where the power goes if you try to use one as a TX antenna. This may give a clue to the inefficiency when used for the task for which they are fitted. I'd have on my list of reasons for why they are used: N) Because they look to the punter like they are getting something more impressive than a 'bit of wire' (i.e. a dipole). So the installer can charge more for them. and also sometimes: N+1) So the installer doesn't have to spend any time aligning them toward a local TX. Fit, down the ladder, present the invoice. Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
FM/DAB
"Ian Jackson" wrote in
message ... In message , UnsteadyKen writes tony sayer wrote... Think how much better it would be with a decent Vertical dipole;-).. Who knows why they use these halos?, 1. Halos are compact and very easy to mount on (around) a vertical mast. They don't clutter up the space required for other aerials too much. 2. Halos have a well-defined, pretty well omnidirectional gain of around minus 3dBd. The fact that that there a minus sign there doesn't necessarily indicate that it doesn't perform adequately. -- Ian Come on Ian, they are crap (unless the Tx is line of sight) and you and everyone else on here knows it. -- Woody harrogate three at ntlworld dot com |
FM/DAB
In message , Jim Lesurf
writes In article , Ian Jackson wrote: In message , UnsteadyKen writes tony sayer wrote... Think how much better it would be with a decent Vertical dipole;-).. Who knows why they use these halos?, 1. Halos are compact and very easy to mount on (around) a vertical mast. They don't clutter up the space required for other aerials too much. 2. Halos have a well-defined, pretty well omnidirectional gain of around minus 3dBd. The fact that that there a minus sign there doesn't necessarily indicate that it doesn't perform adequately. Depends on how you define 'adequately'. ;- 'Adequately' could be that even if you put up a 'better' aerial, reception is not noticeably - and in many cases, not measurably - improved. Yes, the user may still get enough signal to keep them happy. Although for VHF - as people have said - a vertical dipole will probably provide more gain. 'In the open' (I hesitate to say 'in free space'), a vertical halfwave will have 3dB more gain than a horizontal halo. If you mount it 1/8 to 1/4 wave away from the mast (which you more-than-likely will) it will also be broadly directional (sort-of cardioidal) with up to 3dB gain, which may - or may not - be what you want. Of course, you also have to take into account the relative field strengths of the horizontal and the vertical signals, and if some of the required signals are predominantly vertical, a halo is definitely not a good choice. Another way to look at the halo is to wonder where the power goes if you try to use one as a TX antenna. This may give a clue to the inefficiency when used for the task for which they are fitted. A horizontal halo used to be popular as a radio amateur aerial for 144 and 432MHz (especially for mobile work). This is because horizontal was the norm. However, in the early 80s, the influx and immediate popularity of ready-made FM transceivers brought a move to vertical polarization - especially for relatively short-distance communication. These days, the sight of a halo (whether on a vehicle or on a building) is quite a curiosity. I'd have on my list of reasons for why they are used: N) Because they look to the punter like they are getting something more impressive than a 'bit of wire' (i.e. a dipole). So the installer can charge more for them. A properly installed vertical dipole hardly looks like a 'bit of wire'. and also sometimes: N+1) So the installer doesn't have to spend any time aligning them toward a local TX. Fit, down the ladder, present the invoice. I doubt if installers have much difficulty in pointing a directional FM aerial (of whatever type) roughly in the right direction (certainly less exacting then pointing a TV aerial). Even a vertical dipole on the side of a mast should be on the correct side. However, a halo is indeed a 100% no-brainer. -- Ian |
FM/DAB
In message , Woody
writes "Ian Jackson" wrote in message ... In message , UnsteadyKen writes tony sayer wrote... Think how much better it would be with a decent Vertical dipole;-).. Who knows why they use these halos?, 1. Halos are compact and very easy to mount on (around) a vertical mast. They don't clutter up the space required for other aerials too much. 2. Halos have a well-defined, pretty well omnidirectional gain of around minus 3dBd. The fact that that there a minus sign there doesn't necessarily indicate that it doesn't perform adequately. -- Ian Come on Ian, they are crap (unless the Tx is line of sight) and you and everyone else on here knows it. It's a case of horses for courses. Halfwave straight dipole - good? Halfwave halo - signal 3dB less - but crap? In most cases, you won't notice the difference. If a halo is more than 3dB down on a dipole, either you're doing something wrong, or the laws of physics have been changed. But if you need something better than a halo, then you need something better than a halo. -- Ian |
FM/DAB
tony sayer wrote... Why are they doing that? ITV 1 is much the same anywhere in that area apart from the news I'd have thought Waltham is more your backyard rather than the outpourings of Narwich.... Historical reasons I think. There are a couple of shallow valleys running east west through the town so the slope you live on dictates your transmitter but those on the heights; which is the majority, can choose either, and it nearly always seems to be Anglia/BBC East -- UnsteadyKen |
FM/DAB
tony sayer wrote... Not everyone is so well blessed with such a decent area to live in .. well with regards to height that is;!.. Being a new town, we're all immigrants here with no regional loyalties. Am fay Midmar http://www.geograph.org.uk/photo/486400 and our family moved here to get work, mains services such as gas and electricity were much appreciated too. Though I don't think DAB reception figured high on the list of priorities I always look on us as being East Anglians rather than East Midlanders. -- UnsteadyKen |
FM/DAB
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FM/DAB
In message , tony sayer
writes In article , Ian Jackson ianREMOVET scribeth thus In message , UnsteadyKen writes tony sayer wrote... Think how much better it would be with a decent Vertical dipole;-).. Who knows why they use these halos?, 1. Halos are compact and very easy to mount on (around) a vertical mast. They don't clutter up the space required for other aerials too much. 2. Halos have a well-defined, pretty well omnidirectional gain of around minus 3dBd. The fact that that there a minus sign there doesn't necessarily indicate that it doesn't perform adequately. Confucius he say.... .. "All bits of metal work as aerial!. But some bits of metal shaped differently work better"!... Nah "All aerials have equal gain, but some have more equal gain than others." -- (an |
FM/DAB
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