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Is this an FM aerial? Where did it come from?
Appologies for the cross posting, but despite this being OT for three
of these groups, these are the groups where I know people can answer this question! Right, sad aerial spotting time... Is this an FM aerial? http://www.david.robinson.org/pics/aerial1.jpg http://www.david.robinson.org/pics/aerial2.jpg I've seen one like this (but about twice as long, hence twice as many elements!!!) on top of a house in a village somewhere, but didn't have my camera with me. The example I've photographed is on the top of a hi-fi shop in Hitchin, Herts, UK, but the only aerial that _they_ know is on their roof is "a high gain digital TV aerial" (which this probably, unless DTT is still on VHF in Hitchin!). So what is this aerial, and where was it bought from? Can they still be bought? What is the advantage, if any, over the standard folded dipole and several elements which make up most directional FM aerials? Cheers, David. |
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#2
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wrote in message oups.com... Appologies for the cross posting, but despite this being OT for three of these groups, these are the groups where I know people can answer this question! Right, sad aerial spotting time... Is this an FM aerial? http://www.david.robinson.org/pics/aerial1.jpg http://www.david.robinson.org/pics/aerial2.jpg I've seen one like this (but about twice as long, hence twice as many elements!!!) on top of a house in a village somewhere, but didn't have my camera with me. The example I've photographed is on the top of a hi-fi shop in Hitchin, Herts, UK, but the only aerial that _they_ know is on their roof is "a high gain digital TV aerial" (which this probably, unless DTT is still on VHF in Hitchin!). So what is this aerial, and where was it bought from? Can they still be bought? What is the advantage, if any, over the standard folded dipole and several elements which make up most directional FM aerials? Cheers, David. For broadcast FM, I believe its a Galaxie Model G.17 with 10 reflectors, cicular dipole and six directors. 74" long with a gain of 15.9 dB and 45 deg acceptance angle. I have the G.20 above my roof which is 30" longer than the G17 gives extra 2dB extra gain and 28 degree acceptance angle. Sourced mine from Ron Smith Luton Beds UK. The reason for mine is a) I'm in the Scottish Highlands b) it feeds a good tuner Magnum Dynalab 'Etude'. The advantage for me is mainly gain & a good clean signal. Hope this helps, Mike |
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#3
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Mike Gilmour wrote:
For broadcast FM, I believe its a Galaxie Model G.17 with 10 reflectors, cicular dipole and six directors. 74" long with a gain of 15.9 dB and 45 deg acceptance angle. snip I can tell all this by looking at it.... Man, my hat is off Mike. TBerk |
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#4
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wrote in message
oups.com... Is this an FM aerial? http://www.david.robinson.org/pics/aerial1.jpg http://www.david.robinson.org/pics/aerial2.jpg So what is this aerial, and where was it bought from? Can they still be bought? What is the advantage, if any, over the standard folded dipole and several elements which make up most directional FM aerials? Cheers, David. Looks just like mine. It's an FM aerial and I bought it from R Smith in Luton some years ago. (and you'll see one on my previous house in Rowstock Lane, Colney Heath.) Needs a strong mast when the wind blows - 2" steel does the job. Will be using it later this evening when R3 is broadcasting Das Rheingold. -- M Stewart Milton Keynes, UK http://www.megalith.freeserve.co.uk/oddimage.htm |
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#5
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wrote in message oups.com... Appologies for the cross posting, but despite this being OT for three of these groups, these are the groups where I know people can answer this question! Right, sad aerial spotting time... Is this an FM aerial? http://www.david.robinson.org/pics/aerial1.jpg It looks like a TV aerial to me, and what an ugly one at that! -- MESSAGE ENDS. John Porcella |
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#6
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On Mon, 17 Jan 2005 18:06:11 +0000 (UTC), "John Porcella"
wrote: wrote in message roups.com... Appologies for the cross posting, but despite this being OT for three of these groups, these are the groups where I know people can answer this question! Right, sad aerial spotting time... Is this an FM aerial? http://www.david.robinson.org/pics/aerial1.jpg It looks like a TV aerial to me, and what an ugly one at that! Not exactly pretty beasts, are they? But it's definitely a Galaxie G17 FM aerial from Ron Smith of Luton. I had the G26 which was the biggest one he produced on a regular basis. G29 & G32 were available by special order. Due to cracks appearing in my gable wall, the whole thing eventually had to come down. I now have a single dipole! Marky P. |
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#7
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On Mon, 17 Jan 2005 17:43:31 -0000, "Mike Gilmour"
wrote: wrote in message roups.com... Appologies for the cross posting, but despite this being OT for three of these groups, these are the groups where I know people can answer this question! Right, sad aerial spotting time... Is this an FM aerial? http://www.david.robinson.org/pics/aerial1.jpg http://www.david.robinson.org/pics/aerial2.jpg I've seen one like this (but about twice as long, hence twice as many elements!!!) on top of a house in a village somewhere, but didn't have my camera with me. The example I've photographed is on the top of a hi-fi shop in Hitchin, Herts, UK, but the only aerial that _they_ know is on their roof is "a high gain digital TV aerial" (which this probably, unless DTT is still on VHF in Hitchin!). So what is this aerial, and where was it bought from? Can they still be bought? What is the advantage, if any, over the standard folded dipole and several elements which make up most directional FM aerials? Cheers, David. For broadcast FM, I believe its a Galaxie Model G.17 with 10 reflectors, cicular dipole and six directors. 74" long with a gain of 15.9 dB and 45 deg acceptance angle. I have the G.20 above my roof which is 30" longer than the G17 gives extra 2dB extra gain and 28 degree acceptance angle. Sourced mine from Ron Smith Luton Beds UK. The reason for mine is a) I'm in the Scottish Highlands b) it feeds a good tuner Magnum Dynalab 'Etude'. The advantage for me is mainly gain & a good clean signal. Hope this helps, Mike Would that shop be David Orton? Marky P. |
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#9
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tony sayer wrote:
In article .com, writes And here they are in all their glory!, though some of their stuff looks like it might require planning permission  http://anas.worldonline.es/ronsmith/main.htm How much are they? -- Steve - www.digitalradiotech.co.uk - Digital Radio News & Info Find the cheapest Freeview, DAB & MP3 Player Prices: http://www.digitalradiotech.co.uk/fr..._receivers.htm http://www.digitalradiotech.co.uk/da...tal_radios.htm http://www.digitalradiotech.co.uk/mp...rs_1GB-5GB.htm http://www.digitalradiotech.co.uk/mp...e_capacity.htm |
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#10
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"tony sayer" wrote in message ... In article .com, writes snip Use to have one but I found a conventional Yagi worked just as well if not a tad better, but this was a few years ago. The windload on one of those is serious stuff ...And here they are in all their glory!, though some of their stuff looks like it might require planning permission http://anas.worldonline.es/ronsmith/main.htm -- Tony Sayer So no Wideband or Group E then :-( |
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#11
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"T" wrote in message ... Mike Gilmour wrote: For broadcast FM, I believe its a Galaxie Model G.17 with 10 reflectors, cicular dipole and six directors. 74" long with a gain of 15.9 dB and 45 deg acceptance angle. snip I can tell all this by looking at it.... Man, my hat is off Mike. TBerk Nah, details were written down on the back of an old envelope after I phoned Ron and I'd filed it with his bill. Had this aerial for about 15 years on a chimney clamped 4m pole and its stood up to gales so far.. Mike. |
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#12
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"tony sayer" wrote in message ... In article .com, writes [clip[ Thats one of Ron Smiths circular polarised jobbies. Use to have one but I found a conventional Yagi worked just as well if not a tad better, but this was a few years ago. The windload on one of those is serious stuff ...The G17 has a windload of 50lbs at 100mph but the G23 gets quite serious at 72lbs And here they are in all their glory!, though some of their stuff looks like it might require planning permission http://anas.worldonline.es/ronsmith/main.htm -- Tony Sayer |
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#13
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Malcolm Stewart wrote:
snip Will be using it later this evening when R3 is broadcasting Das Rheingold. Danke schöne for the reminder, Malcolm. Nearly missed it!! Andereida |
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#14
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On Mon, 17 Jan 2005 19:12:36 GMT, "DAB sounds worse than FM"
wrote: tony sayer wrote: In article .com, writes And here they are in all their glory!, though some of their stuff looks like it might require planning permission http://anas.worldonline.es/ronsmith/main.htm How much are they? When I bought my G26 back in 1991, the price was £180. And that was just the aerial. They came & put it up on a 20 foot mast with a rotator. Marky P. |
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#15
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I used to own a Galaxie 17, later upgraded to a 23. Unless Ron Smith has
re-designed these since 1997, I must say their performance above 104 MHz is for one of a better word 'sh*te'. Granted, when he designed them the FM band only extended to 105 MHz but these days the 105-108 sub-band is heavily populated with stations and the performance is pretty poor with a 4-6dB roll off between 104 and 106 MHz. Between 90 and 101 MHz, yep, great antennas but the gain across the band isn't broad enough for my liking. As for the 'reducing multipath' bit which he quoted in his catalogue at the time, well I never experienced more multipath on strong stations (eg Holme Moss) than when using my Galaxie. Like previously mentioned by someone else, windloading is also a problem so a sturdy heavy duty rotator is required. I'm using a Triax FM8S these days, good gain between 90 and 107 with about a 1-2dB rolloff at the edges. Does anyone have much experience with Ron Smith's UHF Yagis? Interestingly, a friend of mine in the North Midlands has just ordered a Winegard FM antenna from the US, the gain is pretty impressive and flat across Band II as well. Anyone had any experiences with one of these? http://www.lashen.com/vendors/winegard/pdf/hd6065p.pdf -- Neil (Manchester, UK) "Mike Gilmour" wrote in message ... "tony sayer" wrote in message ... In article .com, writes [clip[ Thats one of Ron Smiths circular polarised jobbies. Use to have one but I found a conventional Yagi worked just as well if not a tad better, but this was a few years ago. The windload on one of those is serious stuff ...The G17 has a windload of 50lbs at 100mph but the G23 gets quite serious at 72lbs And here they are in all their glory!, though some of their stuff looks like it might require planning permission http://anas.worldonline.es/ronsmith/main.htm -- Tony Sayer |
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#16
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"Marky P" wrote How much are they? When I bought my G26 back in 1991, the price was £180. And that was just the aerial. They came & put it up on a 20 foot mast with a rotator. Marky P. With free digital radio on sky do we need these sort of aerials now apart from picking up the local BBC station? |
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#17
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"informer" wrote in message
... "Marky P" wrote How much are they? When I bought my G26 back in 1991, the price was £180. And that was just the aerial. They came & put it up on a 20 foot mast with a rotator. Marky P. With free digital radio on sky do we need these sort of aerials now apart from picking up the local BBC station? I thought "Sky" had some form of entrance fee. Let me know if I'm wrong, and how I can enjoy satellite carried "free" programmes without contributing to BSB or similar. -- M Stewart Milton Keynes, UK http://www.megalith.freeserve.co.uk/oddimage.htm |
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#18
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Malcolm Stewart wrote:
I thought "Sky" had some form of entrance fee. Let me know if I'm wrong, and how I can enjoy satellite carried "free" programmes without contributing to BSB or similar. Almost every radio station on Sky's platform is unencrypted. Therefore you can simply purchase a second hand Sky box on EBay, stick up a dish, and away you go. Better still, get any non Sky satellite receiver and use that instead, or get a DVB-S card for your PC and receive that way. Have a look at the Sky Digital FAQ: http://tinyurl.com/6u4p9 |
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#19
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"Neil" wrote in message ... I used to own a Galaxie 17, later upgraded to a 23. Unless Ron Smith has re-designed these since 1997, I must say their performance above 104 MHz is for one of a better word 'sh*te'. Granted, when he designed them the FM band only extended to 105 MHz but these days the 105-108 sub-band is heavily populated with stations and the performance is pretty poor with a 4-6dB roll off between 104 and 106 MHz. The centre frequency of most of the models is 93.0 MHz but if you wanted good performance above 104 MHz then maybe a GTE model may have suited you better whose centre frequency is 102 MHz, available on the 17, 20 & 23 models. Mike |
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#20
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In article , Malcolm Stewart
writes "informer" wrote in message ... "Marky P" wrote How much are they? When I bought my G26 back in 1991, the price was £180. And that was just the aerial. They came & put it up on a 20 foot mast with a rotator. Marky P. With free digital radio on sky do we need these sort of aerials now apart from picking up the local BBC station? I thought "Sky" had some form of entrance fee. Let me know if I'm wrong, and how I can enjoy satellite carried "free" programmes without contributing to BSB or similar. A standard digital satellite receiver, not a sky box, will bring all that is unencrypted on the "Sky" or rather ASTRA system. Have a look through this list and you can see what's clear and what's not. http://www.lyngsat.com/28east.html and from across the channel http://www.lyngsat.com/astra19.html and http://www.lyngsat.com/hotbird.html the channels with a beige coloured background are the free to view/listen ones. A standard digital sat receiver can be had for less that 100 quid and a dish and LNB aren't that expensive either... -- Tony Sayer |
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#21
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Marky P wrote:
On Mon, 17 Jan 2005 19:12:36 GMT, "DAB sounds worse than FM" wrote: tony sayer wrote: In article .com, writes And here they are in all their glory!, though some of their stuff looks like it might require planning permission http://anas.worldonline.es/ronsmith/main.htm How much are they? When I bought my G26 back in 1991, the price was £180. And that was just the aerial. They came & put it up on a 20 foot mast with a rotator. Any idea approx. how much they cost nowadays? -- Steve - www.digitalradiotech.co.uk - Digital Radio News & Info Find the cheapest Freeview, DAB & MP3 Player Prices: http://www.digitalradiotech.co.uk/fr..._receivers.htm http://www.digitalradiotech.co.uk/da...tal_radios.htm http://www.digitalradiotech.co.uk/mp...rs_1GB-5GB.htm http://www.digitalradiotech.co.uk/mp...e_capacity.htm |
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#22
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In article , Mike Gilmour
writes "Neil" wrote in message ... I used to own a Galaxie 17, later upgraded to a 23. Unless Ron Smith has re-designed these since 1997, I must say their performance above 104 MHz is for one of a better word 'sh*te'. Granted, when he designed them the FM band only extended to 105 MHz but these days the 105-108 sub-band is heavily populated with stations and the performance is pretty poor with a 4-6dB roll off between 104 and 106 MHz. The centre frequency of most of the models is 93.0 MHz but if you wanted good performance above 104 MHz then maybe a GTE model may have suited you better whose centre frequency is 102 MHz, available on the 17, 20 & 23 models. Mike As much as anyone would like to try the multi element Yagi array is a fairly narrowband device, and I don't know of anyone who's successfully changed that without substantially reducing the gain. So no surprise really.... -- Tony Sayer |
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#23
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Malcolm Stewart wrote:
"informer" wrote in message ... "Marky P" wrote How much are they? When I bought my G26 back in 1991, the price was £180. And that was just the aerial. They came & put it up on a 20 foot mast with a rotator. Marky P. With free digital radio on sky do we need these sort of aerials now apart from picking up the local BBC station? I thought "Sky" had some form of entrance fee. Let me know if I'm wrong, and how I can enjoy satellite carried "free" programmes without contributing to BSB or similar. This page gives more information about it and a list of free-to-air TV channels and radio stations: http://www.wickonline.com/fta.htm and the bit rates are significantly higher than on DAB: http://www.digitalradiotech.co.uk/in...bit_rate_table so the audio quality will be higher than on DAB on the stations that use lower bit rates. And I've listed some suitable receivers and other equipment on he http://www.digitalradiotech.co.uk/dsat_rx.htm Use S/PDIF to connect from the receiver to your hi-fi system if possible. -- Steve - www.digitalradiotech.co.uk - Digital Radio News & Info Find the cheapest Freeview, DAB & MP3 Player Prices: http://www.digitalradiotech.co.uk/fr..._receivers.htm http://www.digitalradiotech.co.uk/da...tal_radios.htm http://www.digitalradiotech.co.uk/mp...rs_1GB-5GB.htm http://www.digitalradiotech.co.uk/mp...e_capacity.htm |
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#24
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Mike Gilmour wrote:
Nah, details were written down on the back of an old envelope after I phoned Ron and I'd filed it with his bill. Had this aerial for about 15 years on a chimney clamped 4m pole and its stood up to gales so far.. Thanks for all the interesting and informative replies - especially Mike's which hit Google 30 minutes after I'd posted the original question! I've visited Ron's website and ordered the catalogue. It's interesting that two people suggest a normal dipole or yagi may be better. If I just need a dipole or very small yagi, then I might just dare to attack our brick work (though I'm not going up the chimney, or sending anyone else up there). It's a difficult choice: simple outdoor aerial (at loft height) or better aerial in the loft itself. Obviously it's easier to put something in the loft, but if that something costs more and does less, it's a waste of time. (See also the Bow Brickhill thread in uk.tech.broadcast for other issues!). I guess I'll just have to bite the bullet and try! Cheers, David. |
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#25
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In message
Mark Carver wrote: Malcolm Stewart wrote: I thought "Sky" had some form of entrance fee. Let me know if I'm wrong, and how I can enjoy satellite carried "free" programmes without contributing to BSB or similar. Almost every radio station on Sky's platform is unencrypted. Therefore you can simply purchase a second hand Sky box on EBay, stick up a dish, and away you go. Better still, get any non Sky satellite receiver and use that instead, or get a DVB-S card for your PC and receive that way. Non-Sky satellite receivers are readily available in the UK from specialist dealers -- including online ones, of course. But in addition to the UK radio services, there's a vast choice of satellite services from stations all over Europe and beyond. If you want to explore these, Malcolm, you're better off with something other than a Sky box -- Sky's receivers can't really handle more than the one satellite. -- Richard L. |
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#26
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wrote:
If I just need a dipole or very small yagi, then I might just dare to attack our brick work (though I'm not going up the chimney, or sending anyone else up there). It's a difficult choice: simple outdoor aerial (at loft height) or better aerial in the loft itself. Obviously it's easier to put something in the loft, but if that something costs more and does less, it's a waste of time. Yeah, if you look at the aerial (forward) gains for Antiference's 3-element (FM1083) and 5-element (FM1085) yagis: http://www.antiference.co.uk/fm108.htm they're 5.0 dBd and 6.9 dBd (dBd is dB relative to a dipole), and you'd lose the additional 1.9 dB due to the signal having to pass through the roof. If I were you I'd go for an Antiference FM1083: http://cpc.farnell.com/jsp/endecaSea...AFFM1083&N=401 and install it outside. -- Steve - www.digitalradiotech.co.uk - Digital Radio News & Info Find the cheapest Freeview, DAB & MP3 Player Prices: http://www.digitalradiotech.co.uk/fr..._receivers.htm http://www.digitalradiotech.co.uk/da...tal_radios.htm http://www.digitalradiotech.co.uk/mp...rs_1GB-5GB.htm http://www.digitalradiotech.co.uk/mp...e_capacity.htm |
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#27
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In article . com,
writes Mike Gilmour wrote: Nah, details were written down on the back of an old envelope after I phoned Ron and I'd filed it with his bill. Had this aerial for about 15 years on a chimney clamped 4m pole and its stood up to gales so far.. Thanks for all the interesting and informative replies - especially Mike's which hit Google 30 minutes after I'd posted the original question! I've visited Ron's website and ordered the catalogue. It's interesting that two people suggest a normal dipole or yagi may be better. If I just need a dipole or very small yagi, then I might just dare to attack our brick work (though I'm not going up the chimney, or sending anyone else up there). It's a difficult choice: simple outdoor aerial (at loft height) or better aerial in the loft itself. Obviously it's easier to put something in the loft, but if that something costs more and does less, it's a waste of time. (See also the Bow Brickhill thread in uk.tech.broadcast for other issues!). I guess I'll just have to bite the bullet and try! David, Stop being a wuss and get up 'thar on either that chimney or wall and hang on there something like a 4 element TRIAX available from www.cpc.co.uk. If your wall and or chimney is capable of even standing then either would support such an aerial. It would work for what you want it to do much better then either one of Rons big jobs or faffing around with aerials in the loft. If you can't do it then get a half decent aerial rigger in to do it. Make sure he uses CT100 don't be fobbed off with anything less and don't rely on him to provide the aerial either, as it'll be a cheapie contract jobbie and whatEVER you do don't be tempted into one of those HALO pieces of crap. Then sit back and enjoy the radio for several years to come. Write off the money on your well installed unit over say 10 years and then see what good value for money that really is  )-- Tony Sayer |
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#28
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On Tue, 18 Jan 2005 12:42:57 +0000, tony sayer wrote:
It's interesting that two people suggest a normal dipole or yagi may be better. If I just need a dipole or very small yagi, then I might just dare to attack our brick work (though I'm not going up the chimney, or sending anyone else up there). It's a difficult choice: simple outdoor aerial (at loft height) or better aerial in the loft itself. Obviously it's easier to put something in the loft, but if that something costs more and does less, it's a waste of time. (See also the Bow Brickhill thread in uk.tech.broadcast for other issues!). I guess I'll just have to bite the bullet and try! David, Stop being a wuss and get up 'thar on either that chimney or wall and hang on there something like a 4 element TRIAX available from www.cpc.co.uk. David, if you are getting satisfactory reception from your dipole, why do you want to put up a huge, heavy and expensive multi-element array? Your nearest BBC FM radio site is only 20km away and is designed to give satisfactory reception on a portable or mobile receiver in your area, so your rooftop dipole is more than adequate. The main independent radio channels also provide a normal service in your area. If you are interested for some reason in receiving distant stations outside their service areas then you will need a high-gain aerial, but you will then probably also need a rotator to drive it. Is this what you *really* need? Arthur |
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#29
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"tony sayer" wrote
Thats one of Ron Smiths circular polarised jobbies. ____________________ Although one structural shape in the aerial is roughly circular, this aerial is linearly polarised. An aerial element in the form of a small loop* is not circularly polarised; it is linearly polarised with its peak gain in the two directions normal to the plane of the loop (see Kraus, 3rd Edition, table 6-2). The presence of the parasitic elements in this array -- all in the same plane -- will remove some of the ambiguity from the pattern of the loop, and increase the peak gain of the array. Of course, the polarisation plane of the array will be the same as the physical orientation in which its elements are mounted. But it will be linearly polarised, not circularly polarised. Other designs are needed for true circular polarisation, some of which can be seen in the papers at the website linked below. *where loop circumference is ~ one wavelength RF Visit http://rfry.org for FM transmission system papers. |
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#30
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In article , Arthur
writes On Tue, 18 Jan 2005 12:42:57 +0000, tony sayer wrote: It's interesting that two people suggest a normal dipole or yagi may be better. If I just need a dipole or very small yagi, then I might just dare to attack our brick work (though I'm not going up the chimney, or sending anyone else up there). It's a difficult choice: simple outdoor aerial (at loft height) or better aerial in the loft itself. Obviously it's easier to put something in the loft, but if that something costs more and does less, it's a waste of time. (See also the Bow Brickhill thread in uk.tech.broadcast for other issues!). I guess I'll just have to bite the bullet and try! David, Stop being a wuss and get up 'thar on either that chimney or wall and hang on there something like a 4 element TRIAX available from www.cpc.co.uk. David, if you are getting satisfactory reception from your dipole, why do you want to put up a huge, heavy and expensive multi-element array? Your nearest BBC FM radio site is only 20km away and is designed to give satisfactory reception on a portable or mobile receiver in your area, so your rooftop dipole is more than adequate. The main independent radio channels also provide a normal service in your area. If you are interested for some reason in receiving distant stations outside their service areas then you will need a high-gain aerial, but you will then probably also need a rotator to drive it. Is this what you *really* need? What he really needs is an outside aerial up in the clear, and one that has some element of directivity and gain, so that his tuner is receiving a clean feed free from reflections, which unlike ghosting on an analogue TV aren't so apparent on FM, but they do affect the received audio. Preferably a bit more gain so that under lift conditions etc he will have some measure of discrimination against interferer signals and for the times when you local TX might go on low power, or fall over and be seemingly on reduced power from here to god knows when!, so all in all not a too demanding requirement. Course, if you feel you need one of Ron S's jobbies, on your head be it especially if that wall's as bad as he reckons. -- Tony Sayer |
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#31
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#32
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Arthur wrote:
David, if you are getting satisfactory reception from your dipole, why do you want to put up a huge, heavy and expensive multi-element array? Your nearest BBC FM radio site is only 20km away and is designed to give satisfactory reception on a portable or mobile receiver in your area, so your rooftop dipole is more than adequate. I don't think David has a rooftop dipole, though. Assuming he's just got an internal wire aerial for FM, if he installed an external dipole or Yagi he could vastly improve the SNR of the stations he wants to receive. -- Steve - www.digitalradiotech.co.uk - Digital Radio News & Info Find the cheapest Freeview, DAB & MP3 Player Prices: http://www.digitalradiotech.co.uk/fr..._receivers.htm http://www.digitalradiotech.co.uk/da...tal_radios.htm http://www.digitalradiotech.co.uk/mp...rs_1GB-5GB.htm http://www.digitalradiotech.co.uk/mp...e_capacity.htm |
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#33
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DAB sounds worse than FM wrote:
I don't think David has a rooftop dipole, though. Assuming he's just got an internal wire aerial for FM, if he installed an external dipole or Yagi he could vastly improve the SNR of the stations he wants to receive. If I had a simple roof-top vertical dipole, I think I'd have to filter out or reduce the two local stations before distributing the signal - they're spectacularly strong. Still, that may be the case with whatever I buy. Cheers, David. |
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#34
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Mike Gilmour wrote: b) it feeds a good tuner Magnum Dynalab 'Etude'. Whooo. Nice tuner. |
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#35
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wrote:
DAB sounds worse than FM wrote: I don't think David has a rooftop dipole, though. Assuming he's just got an internal wire aerial for FM, if he installed an external dipole or Yagi he could vastly improve the SNR of the stations he wants to receive. If I had a simple roof-top vertical dipole, I think I'd have to filter out or reduce the two local stations before distributing the signal - they're spectacularly strong. Still, that may be the case with whatever I buy. Depending on the angles of the transmitter you want to receive signals from and the transmitter with the local stations that you don't want to receive, then if you got a Yagi then it may do the filtering for you due to the directional radiation pattern of the aerial. If you look at typical antenna radiation patterns: http://www.gigaant.com/?id=246&show=434 these patterns are in the horizontal plane, so the omni-directional vertical dipole has a circular radiation pattern, because it has the same antenna gain in all directions. The radiation pattern superimposed on the dipole's pattern is for a directional aerial such as a Yagi (although the main lobe is quite narrow, so it's likely to have quite a few elements). But the important thing as far as filtering-out signals go is that if the unwanted signal is coming from an angle, say, 60 degrees relative to the desired signal then it's in one of the nulls of the antenna pattern, so it's pretty effectively filtered out, because the relative attenuation is the gain of the main lobe (which will be pointing at the desired transmitter) minus the gain at the undesired angle which, as you can see from that diagram, can be quite significant. Here's some more info on radiation patterns: http://www.astronantennas.com/radiation_patterns.html Antiference say the acceptance angle of their FM1083 3-element Yagi is 32 degrees, and they define acceptance angle he http://www.antiference.co.uk/def.htm as: "the angle from the centre line to the point where the signal falls to half power (-3dB)" The front to back ratio is specified as being 15dB, so if the unwanted signals were coming from the opposite direction to the desired signals then you've got 15dB of attenuation from the front-to-back ratio, and looking at a radiation pattern for a Yagi in a book I've got, the back lobe has the highest gain. Sack this, they say a picture tells a thousand words, so I've done a graph: http://www.digitalradiotech.co.uk/antenna_pattern.htm (There's a null (theoretically infinite loss) at +90 and -90 degrees, so to make the graph look right I've arbitrarily allocated a gain of -40 dB.) I don't know what exact antenna that is for, because it doesn't say what antenna it's for in the book other than it's a Yagi. But that'll be the typical shape of the graph of gain against direction. So, try and find out what the relative angles are of the transmitter that you want to receive from and the transmitter that the local stations are on which you don't want, and if you're lucky the unwanted signals may be coming from angles where they'd be filtered by the antenna pattern of a Yagi. -- Steve - www.digitalradiotech.co.uk - Digital Radio News & Info Find the cheapest Freeview, DAB & MP3 Player Prices: http://www.digitalradiotech.co.uk/fr..._receivers.htm http://www.digitalradiotech.co.uk/da...tal_radios.htm http://www.digitalradiotech.co.uk/mp...rs_1GB-5GB.htm http://www.digitalradiotech.co.uk/mp...e_capacity.htm |
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On Thu, 20 Jan 2005 13:53:12 GMT, DAB sounds worse than FM
wrote: (sound advice snipped) if you're lucky the unwanted signals may be coming from angles where they'd be filtered by the antenna pattern of a Yagi. If you aim the aerial to drop one of the "spectacularly strong" local transmitters into a notch, this will certainly help in listening to weaker stations. But when listening to the local station itself you may be beaming at a reflected signal with comparable strength to the direct signal. This can cause appalling distortion to FM audio reception. Arthur |
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#37
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"DAB sounds worse than FM" wrote
Depending on the angles of the transmitter you want to receive signals from and the transmitter with the local stations that you don't want to receive, then if you got a Yagi then it may do the filtering for you due to the directional radiation pattern of the aerial. (etc) _________________ Other considerations are the frequency separation between the desired and undesired station, and the field strength of the undesired station. A very strong local station on a nearby freq can de-sensitise a receiver, making it difficult to receive adjacent channels. The carrier ratio between local and distant stations easily can be 50dB or more. Even the best FM rx antenna will have difficulty reducing the field strength of the local station below that of the distant one. Reflections of the local station can arrive via multipath along with the distant station, on the pointing axis of the rx antenna. The reflection itself may only be 10-15 dB reduced from the direct wave -- still far above that of the distant station -- and there is no way to get rid of it using the antenna pattern alone. There are methods of introducing a sample of the interfering signal into the output of the rx antenna line, and adjusting its amplitude and phase so as to null the interfering RF wave. Usually this is not practical for other than commercial applications. RF Visit http://rfry.org for FM transmission system papers. |
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#38
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Arthur wrote:
On Thu, 20 Jan 2005 13:53:12 GMT, DAB sounds worse than FM wrote: (sound advice snipped) if you're lucky the unwanted signals may be coming from angles where they'd be filtered by the antenna pattern of a Yagi. If you aim the aerial to drop one of the "spectacularly strong" local transmitters into a notch, this will certainly help in listening to weaker stations. But when listening to the local station itself you may be beaming at a reflected signal with comparable strength to the direct signal. This can cause appalling distortion to FM audio reception. Fair enough. Mark Carver said it might be these: Chiltern 96.9 and BBC 3CR 95.5, so I assumed he wouldn't want to ever listen to them. -- Steve - www.digitalradiotech.co.uk - Digital Radio News & Info Find the cheapest Freeview, DAB & MP3 Player Prices: http://www.digitalradiotech.co.uk/fr..._receivers.htm http://www.digitalradiotech.co.uk/da...tal_radios.htm http://www.digitalradiotech.co.uk/mp...rs_1GB-5GB.htm http://www.digitalradiotech.co.uk/mp...e_capacity.htm |
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#39
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Richard Fry wrote:
"DAB sounds worse than FM" wrote Depending on the angles of the transmitter you want to receive signals from and the transmitter with the local stations that you don't want to receive, then if you got a Yagi then it may do the filtering for you due to the directional radiation pattern of the aerial. (etc) _________________ Other considerations are the frequency separation between the desired and undesired station, and the field strength of the undesired station. A very strong local station on a nearby freq can de-sensitise a receiver, making it difficult to receive adjacent channels. The carrier ratio between local and distant stations easily can be 50dB or more. Even the best FM rx antenna will have difficulty reducing the field strength of the local station below that of the distant one. Reflections of the local station can arrive via multipath along with the distant station, on the pointing axis of the rx antenna. The reflection itself may only be 10-15 dB reduced from the direct wave -- still far above that of the distant station -- and there is no way to get rid of it using the antenna pattern alone. There are methods of introducing a sample of the interfering signal into the output of the rx antenna line, and adjusting its amplitude and phase so as to null the interfering RF wave. Usually this is not practical for other than commercial applications. Very interesting, thanks. -- Steve - www.digitalradiotech.co.uk - Digital Radio News & Info Find the cheapest Freeview, DAB & MP3 Player Prices: http://www.digitalradiotech.co.uk/fr..._receivers.htm http://www.digitalradiotech.co.uk/da...tal_radios.htm http://www.digitalradiotech.co.uk/mp...rs_1GB-5GB.htm http://www.digitalradiotech.co.uk/mp...e_capacity.htm |
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#40
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DAB sounds worse than FM wrote:
Arthur wrote: If you aim the aerial to drop one of the "spectacularly strong" local transmitters into a notch, this will certainly help in listening to weaker stations. But when listening to the local station itself you may be beaming at a reflected signal with comparable strength to the direct signal. This can cause appalling distortion to FM audio reception. Fair enough. Mark Carver said it might be these: Chiltern 96.9 and BBC 3CR 95.5, so I assumed he wouldn't want to ever listen to them. I did, I only posted that reply in alt.radio.digital, so to avoid confusion I suggested making a couple of quarter wave stub filters, and place them in the downlead. |
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