FM aerial Omni vs Half Wave Dipole - UK Vintage Radio Repair and Restoration Discussion Forum

reactolite · 29th Dec 2013, 1:13 pm

Can someone help me with this problem? I recently became the proud owner of a Sony ST-5950SD Tuner (excellent bit of kit) and am very pleased with it except when tuned to Classic FM. Unlike Radio 3, which is exquisite, Classic FM is not exceptional. First there is quite pronounced sibilance in the voices and some distortion in the music and whats worse is the background swishing noise which seems worse in the evening. From what I've been reading a Half Wave Dipole would be better than my present Omni aerial I have in the loft, any thoughts? By the way I'm getting a signal reading of just over 4 with Classic FM same as with Radio 3.

Nickthedentist · 29th Dec 2013, 1:49 pm

Not what you asked, but Classic FM will always sound v. disappointing compared with R3 because of the harsh compression they use. The difference is immediately obvious even on a portable with a 2" speaker to my ears (honestly!).

N.

AndiiT · 29th Dec 2013, 2:15 pm

Hi,
In answer to your question I believe that a vertical dipole will always outperform one of the circular "omni-directional" FM aerials. I believe that the omni aerials have a gain of less than unity.

There is a little more information abut the omni aerial
here

Regards

Andrew

PaulE27 · 29th Dec 2013, 2:18 pm

It sounds as if the problem might be multipath reception, in which case the dipole will help, but only if it is mounted horizontally and facing the transmitter. If it is mounted vertically it will be no better than the Omni.

Paul

paulsherwin · 29th Dec 2013, 2:21 pm

The general opinion amongst professional riggers seems to be that horizontal halos are awful but easy to fit and adequate for many people. They are not truly omnidirectional so you may have the CFM transmitter in a dead spot, or you may be getting multipath reception from internal reflections in the loft.

A single vertical dipole is likely to be an improvement. You can make one from two 75cm lengths of wire stuck to a garden cane or suspended from a rafter with a weight at the bottom. Try a few different locations and pick the best one.

bikerhifinut · 29th Dec 2013, 2:25 pm

It may be worth investing in a decent 3 or more element directional aerial if the problems are caused by either a multipath reception issue, or, as is the case where I live in North Yorkshire, 2 very strong local commercial pop stations right next to the classic FM frequency, causing interference and lousy reception. This is very apparent using older analogue gear with less selectivity. I am not familiar with your area and location of transmitters, but Classic FM up here is not transmitted from the local transmitter at Bilsdale and I have to rely on Holme Moss in West Yorkshire or Pontop Pike in Northumberland to receive Classic FM.
However Nick is also right in his comment about the abysmal broadcast quality on Classic both FM and DAB is ****** awful. However I feel you should be able to achieve a listenable quality assuming a decent signal strength. If you were close enough I'd be able to give you my spare 4 element Band II aerial, its not worth trying to post such a large item, they don't cost that much to buy. Its always worth investing in a good outdoor aerial for FM if you are a serious listener.
You could also be suffering from all sorts of interference from other sources, a lot of digital gear and stuff using poor quality switch mode psu's can inject noise into the mains supply and some puts out appreciable RF hash.

emeritus · 29th Dec 2013, 3:29 pm

The deep null of a simple horizontal dipole can be used to reduce the effect of a strong signal source, and this might help with multipath. In the 1970's, before the FM band filled up, I made up a rotatable loft-mounted dipole, and by nulling out the English transmitters, I could usually listen to French FM stations in stereo in my home in Romford.

fetteler · 29th Dec 2013, 3:31 pm

Quote:

Originally Posted by Nickthedentist

Not what you asked, but Classic FM will always sound v. disappointing compared with R3 because of the harsh compression they use. The difference is immediately obvious even on a portable with a 2" speaker to my ears (honestly!).

Yes, I agree with you wholeheartedly but staggeringly I've spoken to some folk who actually prefer the sound of Classic FM to that of R3... I just can't fathom it!

Steve.

ThePillenwerfer · 29th Dec 2013, 3:34 pm

Quote:

Originally Posted by AndiiT

There is a little more information abut the omni aerial here

And more here: http://www.aerialsandtv.com/fmanddabradio.html

- Joe

Nuvistor · 29th Dec 2013, 3:42 pm

Something to keep in mind.
Determine where your transmitter sites for R3 and Classic FM are, they may not be co-located. If they are, a directional aerial may help, if they are not co-located and are many degrees apart you may improve Classic FM and impair R3.

The comments about putting the aerial outside are worth considering, get the aerial as far as possible from local interference and reflections in the attic.

reactolite · 29th Dec 2013, 4:48 pm

Interesting to note that when I push the Multipath button in (which is spring loaded and does not stay in) the signal strength needle waivers between 1 & 2 biased mainly towards 2. On Radio 3 the needle drops back to less than 1 and hovers around between zero and 1.

gramofiend · 29th Dec 2013, 5:07 pm

Unfortunately it seems you have two problems. One of which you can do something about in optimising the reception of the signal by moving your aerial either to a different area of your loft or even taking it outside and placing same in a new location.

What unfortunately you cannot do is to compensate for the ignorance of the artists who somehow cannot use a microphone properly to save their lives. You would think they might take a pride in placing themselves at a proper distance from the, very expensive, large diaphram capacitor microphones employed in the studios of Classic FM and other broadcasters. The sibilance and popping heard daily is pathetic! Subsequent processing by the station equipment especially in the case of Classic promotes the overall effect. Bear in mind however that the major listening audience for this was to potable radios and car systems. You cannot make a silk purse from a sow's ear.

Mike

G6Tanuki · 29th Dec 2013, 5:08 pm

Quote:

Originally Posted by Nuvistor

Something to keep in mind.
Determine where your transmitter sites for R3 and Classic FM are, they may not be co-located. If they are, a directional aerial may help, if they are not co-located and are many degrees apart you may improve Classic FM and impair R3.

FM-broadcast [and TV] reception does depend a lot on local issues too: if there's some significant signal-reflector in the area [a tower-block, a hill, any big industrial-complex like an oil refinery/steel-mill or an old-fashioned 'gasometer'] it can introduce multipath reflections and give the sort of scratchy sibilance the original poster mentions.

[I recall some time spent living in one of the Medway towns where the best FM reception was by pointing my 5-element beam at a block of flats a mile or so away, and getting the 'indirect' signal from Wrotham rather than the direct signal]

Old-ish FM radios were particularly susceptible to multipath: indeed, according to "The Setmakers" quite a few early purchasers of FM receivers complained about the 'scratchy' or 'tinny' multipath-perturbed reception they got when using their radios' internal foil-strip antennas and were fobbed-off by dealers who said that was just the 'extended quality' the BBC were broadcasting.

If you really want to do the job properly you may need to install a multi-element antenna and a rotator, just as I did a few decades back [so I could get good-quality LBC and Capital FM, then swing the beam and listen to Radio Boulogne Littoral when I wanted to]

paulsherwin · 29th Dec 2013, 5:28 pm

In most cases, sibilance-inducing multipath results from nearby reflections and is consequently much, much worse with an indoor aerial of any type. You really do need a correctly installed external aerial to get rid of it completely.

If you must use a loft aerial, positioning can make a huge difference and it's well worth taking the time to experiment.

Horizontal halo omnis as used by the OP seem particularly bad for multipath sibilance, much worse than an omnidirectional vertical dipole. I've tried both (and several other types) in my own loft.

reactolite · 29th Dec 2013, 7:17 pm

I'm being guided toward a half wave dipole which is fine as I've discovered they are not very expensive. One question; will my 75 ohm coaxial work with this aerial or should it be 300 ohm?

G6Tanuki · 29th Dec 2013, 7:33 pm

What does your radio have as an antenna-connection?

If it's got a concentric coaxial socket like this:

http://upload.wikimedia.org/wikipedi...nectorjack.jpg

then it's expecting a 75-ohm feed.In which case something like

http://cpc.farnell.com/1/1/729-radio...tiference.html

will work.

reactolite · 29th Dec 2013, 9:57 pm

Thank you. Yes my tuner accepts this type of aerial connection although it is a screw on type. Thanks for the link - great stuff!

paulsherwin · 30th Dec 2013, 12:11 am

As I said in #5, just make a dipole and connect it in your loft instead of your halo. If you attach the wires to a cane or stick with vinyl tape you can try it horizontally or vertically.

reactolite · 30th Dec 2013, 9:04 am

Great idea and I may try this, but does it matter type of wire used e.g. stranded or solid core & what gauge or number of strands or does it not matter and any old bit of copper wire will do? Also I might try re positioning my halo aerial in the loft by moving it about a bit while my young son keeps an eye on the signal strength meter whilst pressing the multipath button and we will keep in contact via his 'walkie talkie set' which will be the first time he will have used them for a serious purpose. Wow real boys own stuff, can't wait! Roger that!

SteveCG · 30th Dec 2013, 11:34 am

Am I alone in not understanding what function a 'Multi-path' button could provide and how it achieves it (if that is possible)?

Other than the good advice already given here, is there the possibility that your are also receiving a weaker adjacent channel transmission to your desired Classic FM transmission? Where I live the local transmission is only 200 Kc/s away on the dial from another weaker version from a more distant transmitter. This does give curious sound effects on some portable sets using their own telescopic aerials. There is no problem with my reception when I use a good directional loft aerial.

29th Dec 2013, 1:13 pm	#1
reactolite Retired Dormant Member Join Date: Dec 2013 Location: North Somerset, UK. Posts: 59	FM aerial Omni vs Half Wave Dipole Can someone help me with this problem? I recently became the proud owner of a Sony ST-5950SD Tuner (excellent bit of kit) and am very pleased with it except when tuned to Classic FM. Unlike Radio 3, which is exquisite, Classic FM is not exceptional. First there is quite pronounced sibilance in the voices and some distortion in the music and whats worse is the background swishing noise which seems worse in the evening. From what I've been reading a Half Wave Dipole would be better than my present Omni aerial I have in the loft, any thoughts? By the way I'm getting a signal reading of just over 4 with Classic FM same as with Radio 3.

29th Dec 2013, 1:49 pm	#2
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,861	Re: FM aerial Omni vs Half Wave Dipole Not what you asked, but Classic FM will always sound v. disappointing compared with R3 because of the harsh compression they use. The difference is immediately obvious even on a portable with a 2" speaker to my ears (honestly!). N.

29th Dec 2013, 2:15 pm	#3
AndiiT Octode Join Date: Aug 2005 Location: Saltburn-East, Cleveland, UK. Posts: 1,786	Re: FM aerial Omni vs Half Wave Dipole Hi, In answer to your question I believe that a vertical dipole will always outperform one of the circular "omni-directional" FM aerials. I believe that the omni aerials have a gain of less than unity. There is a little more information abut the omni aerial here Regards Andrew

29th Dec 2013, 2:18 pm	#4
PaulE27 Pentode Join Date: Jul 2010 Location: London, UK. Posts: 222	Re: FM aerial Omni vs Half Wave Dipole It sounds as if the problem might be multipath reception, in which case the dipole will help, but only if it is mounted horizontally and facing the transmitter. If it is mounted vertically it will be no better than the Omni. Paul

29th Dec 2013, 2:25 pm	#6
bikerhifinut Octode Join Date: Nov 2013 Location: Penrith, Cumbria, UK Posts: 1,993	Re: FM aerial Omni vs Half Wave Dipole It may be worth investing in a decent 3 or more element directional aerial if the problems are caused by either a multipath reception issue, or, as is the case where I live in North Yorkshire, 2 very strong local commercial pop stations right next to the classic FM frequency, causing interference and lousy reception. This is very apparent using older analogue gear with less selectivity. I am not familiar with your area and location of transmitters, but Classic FM up here is not transmitted from the local transmitter at Bilsdale and I have to rely on Holme Moss in West Yorkshire or Pontop Pike in Northumberland to receive Classic FM. However Nick is also right in his comment about the abysmal broadcast quality on Classic both FM and DAB is ****** awful. However I feel you should be able to achieve a listenable quality assuming a decent signal strength. If you were close enough I'd be able to give you my spare 4 element Band II aerial, its not worth trying to post such a large item, they don't cost that much to buy. Its always worth investing in a good outdoor aerial for FM if you are a serious listener. You could also be suffering from all sorts of interference from other sources, a lot of digital gear and stuff using poor quality switch mode psu's can inject noise into the mains supply and some puts out appreciable RF hash.

29th Dec 2013, 2:21 pm	#5
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,965	Re: FM aerial Omni vs Half Wave Dipole The general opinion amongst professional riggers seems to be that horizontal halos are awful but easy to fit and adequate for many people. They are not truly omnidirectional so you may have the CFM transmitter in a dead spot, or you may be getting multipath reception from internal reflections in the loft. A single vertical dipole is likely to be an improvement. You can make one from two 75cm lengths of wire stuck to a garden cane or suspended from a rafter with a weight at the bottom. Try a few different locations and pick the best one.

29th Dec 2013, 3:29 pm	#7
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,345	Re: FM aerial Omni vs Half Wave Dipole The deep null of a simple horizontal dipole can be used to reduce the effect of a strong signal source, and this might help with multipath. In the 1970's, before the FM band filled up, I made up a rotatable loft-mounted dipole, and by nulling out the English transmitters, I could usually listen to French FM stations in stereo in my home in Romford.

29th Dec 2013, 3:42 pm	#10
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: FM aerial Omni vs Half Wave Dipole Something to keep in mind. Determine where your transmitter sites for R3 and Classic FM are, they may not be co-located. If they are, a directional aerial may help, if they are not co-located and are many degrees apart you may improve Classic FM and impair R3. The comments about putting the aerial outside are worth considering, get the aerial as far as possible from local interference and reflections in the attic.

29th Dec 2013, 4:48 pm	#11
reactolite Retired Dormant Member Join Date: Dec 2013 Location: North Somerset, UK. Posts: 59	Re: FM aerial Omni vs Half Wave Dipole Interesting to note that when I push the Multipath button in (which is spring loaded and does not stay in) the signal strength needle waivers between 1 & 2 biased mainly towards 2. On Radio 3 the needle drops back to less than 1 and hovers around between zero and 1.

29th Dec 2013, 5:07 pm	#12
gramofiend Pentode Join Date: Aug 2010 Location: Cowbridge, Vale of Glamorgan, UK. Posts: 137	Re: FM aerial Omni vs Half Wave Dipole Unfortunately it seems you have two problems. One of which you can do something about in optimising the reception of the signal by moving your aerial either to a different area of your loft or even taking it outside and placing same in a new location. What unfortunately you cannot do is to compensate for the ignorance of the artists who somehow cannot use a microphone properly to save their lives. You would think they might take a pride in placing themselves at a proper distance from the, very expensive, large diaphram capacitor microphones employed in the studios of Classic FM and other broadcasters. The sibilance and popping heard daily is pathetic! Subsequent processing by the station equipment especially in the case of Classic promotes the overall effect. Bear in mind however that the major listening audience for this was to potable radios and car systems. You cannot make a silk purse from a sow's ear. Mike

29th Dec 2013, 5:28 pm	#14
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,965	Re: FM aerial Omni vs Half Wave Dipole In most cases, sibilance-inducing multipath results from nearby reflections and is consequently much, much worse with an indoor aerial of any type. You really do need a correctly installed external aerial to get rid of it completely. If you must use a loft aerial, positioning can make a huge difference and it's well worth taking the time to experiment. Horizontal halo omnis as used by the OP seem particularly bad for multipath sibilance, much worse than an omnidirectional vertical dipole. I've tried both (and several other types) in my own loft.

29th Dec 2013, 7:17 pm	#15
reactolite Retired Dormant Member Join Date: Dec 2013 Location: North Somerset, UK. Posts: 59	Re: FM aerial Omni vs Half Wave Dipole I'm being guided toward a half wave dipole which is fine as I've discovered they are not very expensive. One question; will my 75 ohm coaxial work with this aerial or should it be 300 ohm?

29th Dec 2013, 7:33 pm	#16
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: FM aerial Omni vs Half Wave Dipole What does your radio have as an antenna-connection? If it's got a concentric coaxial socket like this: http://upload.wikimedia.org/wikipedi...nectorjack.jpg then it's expecting a 75-ohm feed.In which case something like http://cpc.farnell.com/1/1/729-radio...tiference.html will work. Last edited by G6Tanuki; 29th Dec 2013 at 7:44 pm.

29th Dec 2013, 9:57 pm	#17
reactolite Retired Dormant Member Join Date: Dec 2013 Location: North Somerset, UK. Posts: 59	Re: FM aerial Omni vs Half Wave Dipole Thank you. Yes my tuner accepts this type of aerial connection although it is a screw on type. Thanks for the link - great stuff!

30th Dec 2013, 12:11 am	#18
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,965	Re: FM aerial Omni vs Half Wave Dipole As I said in #5, just make a dipole and connect it in your loft instead of your halo. If you attach the wires to a cane or stick with vinyl tape you can try it horizontally or vertically.

30th Dec 2013, 9:04 am	#19
reactolite Retired Dormant Member Join Date: Dec 2013 Location: North Somerset, UK. Posts: 59	Re: FM aerial Omni vs Half Wave Dipole Great idea and I may try this, but does it matter type of wire used e.g. stranded or solid core & what gauge or number of strands or does it not matter and any old bit of copper wire will do? Also I might try re positioning my halo aerial in the loft by moving it about a bit while my young son keeps an eye on the signal strength meter whilst pressing the multipath button and we will keep in contact via his 'walkie talkie set' which will be the first time he will have used them for a serious purpose. Wow real boys own stuff, can't wait! Roger that!

30th Dec 2013, 11:34 am	#20
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: FM aerial Omni vs Half Wave Dipole Am I alone in not understanding what function a 'Multi-path' button could provide and how it achieves it (if that is possible)? Other than the good advice already given here, is there the possibility that your are also receiving a weaker adjacent channel transmission to your desired Classic FM transmission? Where I live the local transmission is only 200 Kc/s away on the dial from another weaker version from a more distant transmitter. This does give curious sound effects on some portable sets using their own telescopic aerials. There is no problem with my reception when I use a good directional loft aerial.