Help with radio FM reception.( hope this is the right place to ask this)

dohouch

I'm in Dingle town and the local relay seems to carry the RTE radio channels but not the commercial stations. I can get both TodayFM and NewstalkFM but would like to improve their quality a bit. Any ideas, low cost, low altitude and low effort that would bring in a bit more signal??

I've no idea what an external aerial for FM radio should look like.

Would it be a rod, or something more complicated, like a tv aerial?

Could I construct something myself.

What shape, materials and dimensions.

Any links would be welcome,

Thanks.

Foggy43

FM External Directional Aerials ARE BIG! As far as I am aware in Ireland it must be vertically polarized for both RTE and Independent radio. I would love someone to say I am wrong! A 6 foot mast on your chimney would not give you enough clearance from your roof. A four element is about 1.8m long with the longest element 1.6m

Here is something to look at http://www.maplin.co.uk/Search.aspx?SD=false&C=gkw&Criteria=Aerial%20FM&U=Aerial%20FM&T=2005745&gclid=CLDu5Z-9i4kCFQTnEAodmBSAJg

Something to read! http://www.bbc.co.uk/reception/factsheets/pdfs/radio_aerials_factsheet.pdf

How is the TV doing?

dohouch

Hi Molly, thanks for your TV post and the nice pic of that antiference Hi-tec TV aerial. I've posted again in the tv thread, so better check there. Bit of a story. I think I have already downloaded most of the BBC fact sheet. They are good and easy, but tend to be a bit short on pics. Those Maplin aerials are interesting, now I know what an FM radio aerial looks like.

cast_iron

I thought all our FM was horizontally polarized.

If you are picking all stations up from one source, the 4 element VHF directional type is best. I was never madly impressed by those omni-directional things.

Also, you must have a proper unit (eg. hi-fi music centre) to accept a co-ax connection - your average portable radio won't facilitate this.

L1011

I thought all our FM was mixed polarity.... put up BOTH a horizontal and vertical and you'll be fine :P

Ulsterman 1690

Irish (and now UK) FM stations are all either mixed or vertical polorsaton

FM aerials start from £15 for a vertical dipole (single element)

FM multielement yagi's are BIG (especially if theres more than 3 elements)

Maplin and some DIY chains will sell you an FM aerial

Whatever you do DONT buy one of those ring shaped "halo" things theyre a piece of junk (dunno why anyone still makes/sells them ...presumably because there are fools out there whool buy em)

watty

A vertical aerial works fine with mixed polarity.

You can cheaply assemble an aerial in attic that seriously outperforms halo.

The 1/4 wave aerial in attic can be made out of 5 pieces of coax. Short center and outer of each piece. make each bit about 75cm long. One held up vertical by nylon cord or fishing line off beam connected to center of feed coax, the other four spread out on rafters/joists all connected to outer of coax feed to radio.


Originally before local radio and ILR, the BBC was all horizontal, for large coverage with few TX. No Mobile reception. People would have used a dipole or 2 or 3 element aerial for one TX

A Halo is only for horizontal omnidirectional. Thus ONLY an advantage for caravans or multiple old horisontal TX sites.

With advent of VHF car radios, pocket radio and ILR, the vertical or "slant/mixed" polarisation made more sense (we never had horizontal). As mobile & portable uses whips (i.e. vertical).

A Whip or Vertiical dipole is inherently omnidirectional.

The only aerial design that works poorer than a halo is no aerial.

watty

A vertical aerial works fine with mixed polarity.

You can cheaply assemble an aerial in attic that seriously outperforms halo.

The 1/4 wave aerial in attic can be made out of 5 pieces of coax. Short center and outer of each piece. make each bit about 75cm long. One held up vertical by nylon cord or fishing line off beam connected to center of feed coax, the other four spread out on rafters/joists all connected to outer of coax feed to radio.


Originally before local radio and ILR, the BBC was all horizontal, for large coverage with few TX. No Mobile reception. People would have used a dipole or 2 or 3 element aerial for one TX

A Halo is only for horizontal omnidirectional. Thus ONLY an advantage for caravans or multiple old horisontal TX sites.

With advent of VHF car radios, pocket radio and ILR, the vertical or "slant/mixed" polarisation made more sense (we never had horizontal). As mobile & portable uses whips (i.e. vertical).

A Whip or Vertiical dipole is inherently omnidirectional.

The only aerial design that works poorer than a halo is no aerial.

lawhec

The only FM Radio sites in the Irish Republic that are mixed polarity I believe are the RTÉ sites on Kippure, Three Rock and Holywell Hill along with some of the Red FM TX sites in Cork. The rest are all vertically polarised.

Vertical polarisation allows for better mobile reception of FM VHF signals, especially for car radios that often change direction.

Horizontal polarisation was originally chosen by the BBC for FM as it was more immune to electrical interference from car engines etc. and to multipath, though it also has the properties of having better directional properties for receiving and can propagate over the horizon better. It was designed to be received by home receivers (sometimes combined with a television) using a 2-4 element aerial on a rooftop. The advent of the transistor portable radio in the 1960's changed the future plans for the network - it probably saved MW & LW radio from being shut down for the forseeable future and when the ILR stations started broadcasting on FM with mixed polarisation, the BBC started following suit in the early 1980's.

One way to improve reception is with a single 1/2 wave dipole (around 1.5 metres on VHF Band II) on the roof or an attic which will be omidirectional but will provide no protection from multipath interference. There is also a "loop aerial" which can be found at the link below that looks interesting but I've yet to try it.

http://www.skywaves.info/index.php?entityType=HTML&id=139

As for connections to a hi-fi, if it isn't designed to accept an external aerial, one way around it is for the end of the downlead to have a crocidile clip connected to the inner of the lead with the outer shield trimmed and taped back as not to make contact with the clip. This can then either be attached to a whip (extendable) aerial or to a wire coming out at the back by stripping around 3-4 cm of insulation at the end of it and wrapping it around one jaw of the clip before clamping it. Its not ideal, especially and the impedance will very likely mismatch, but its much better than nothing.

dohouch

watty wrote:

You can cheaply assemble an aerial in attic that seriously outperforms halo.

The 1/4 wave aerial in attic can be made out of 5 pieces of coax. Short center and outer of each piece. make each bit about 75cm long. One held up vertical by nylon cord or fishing line off beam connected to center of feed coax, the other four spread out on rafters/joists all connected to outer of coax feed to radio.

Thanks all. This is truly a discussion forum :eek: I like DIY, rather than buying off the shelf in Maplin,etc. Having a bit of a problem, visualising what watty is describing "Short center and outer of each piece." Have Hi-Fi with aerial input. I think watty's idea is probably enough for my needs as a ghetto blaster on another window of the house does allright with NewstalkFM. Will reread it but if anybody has diagram of layout. Put up new TV aerial with different cable run so I have wall plug with cable end free lying above in the attic.

watty

Convert each of the five cut off 0.75m / 75cm pieces to a ordinary fat piece of wire by shorting out the inner wire and outer braid at both ends.

4 pieces lie flat radiating out from outer of main coax feed (braid).

5th piece stands up straight held by tape, thread, cord etc to overhead beam, connected to inner core.

Foggy43

Over 20 years ago RTE Tech sent me a list of all the RTE radio transmitters. You needed a vertically polarized aerial for all except 2 transmitters.
1. Three Rock - Mixed
2. Clermount Cairn - Circular - I still to this day do not know what this means.

I still have the document but it is in Ireland and as it is over 20 years old things may have changed.

Around then there were a few 4 to 8 element directional Band 11 aerials but they were horizontally polarized as you could then get BBC FM radio from Nothern Ireland.

dohouch

Northern Correspondent wrote:

There is also a "loop aerial" which can be found at the link below that looks interesting but I've yet to try it.

http://www.skywaves.info/index.php?entityType=HTML&id=139

:cool:
Great link Northern Correspondent with pics. Looks like a great aerial. Learning the limitation of my Google search techniques, I wasn't able to find 1 single DIY FM aerial. :mad:

Thaks watty for clearing me up on "short". I now the term just using it to refer to joing screen and core of coax didn't sink in.

Will probably have a go a the Loop Aerial from NC's post. Might take a while before I can report back on reults.

watty

Molly Dawson wrote:

Over 20 years ago RTE Tech sent me a list of all the RTE radio transmitters. You needed a vertically polarized aerial for all except 2 transmitters.
1. Three Rock - Mixed
2. Clermount Cairn - Circular - I still to this day do not know what this means.

I still have the document but it is in Ireland and as it is over 20 years old things may have changed.

Around then there were a few 4 to 8 element directional Band 11 aerials but they were horizontally polarized as you could then get BBC FM radio from Nothern Ireland.

Vertical Receive will work with Mixed
Anything except the reverse direction of circular works with circular.
I can explain it any one REALLY interested.

You still can get VHF from NI with a big aerial, or for a few days a year ordinary aerial even in Limerick.

Foggy43

Watty!
I am proably the only one! I would like to know how circular works.

Mixed, I think, is where you can receive with your aerial polarized either in vertical or horizontal.

cast_iron

I'm interested too, Watty. (God, how sad we are:D )

Thanks.

watty

Vertical (0 Degrees) and Horizontal (90 degrees) are what they say. "Mixed" usually means 45 degrees and can be + or - from vertical.

At 45 degrees to the actual polarisation you get about 1/2 the signal. At 90 degrees to actual polarisation (using a plane aerial) you get nearly no signal.

This explains why a Halo is useless here as it is a negative gain horizontal only aerial. A whip is always "vertical" and a Dipole can be mounted at any angle. With Vertical a halo gets nothing. With even Slant/mixed/circular a whip can do 3dB to 6dB better than a halo. A Dipole does a bit better still. With horisontal TX a whip gets nearly nothing. A dipole gets nothing if vertical or up to 9dB better than a Halo if it is horizontal.

A vertical dipole, like a whip is omnidirectional in horizontal direction. It has a null below the mast and straight up into sky . A horizontal dipole has a null in both directions along the rod.

If you mount a vertical dipole and a horizontal dipole and feed them with exactly the same signal you will get + or - 45 degrees (or slant polarisation). Obviously either a vertical or horizontal aerial will receive it. A same angled slanted dipole will get twice the signal.

If the two dipoles (H and V) are fed with a two signals where one is delayed by 90 degrees the polarisation is Circular. It can be Clockwise or Anticlockwise depending on which dipole has the delayed signal.

No matter WHAT angle the receive dipole is at, you get 1/2 the signal. If you have a circular polarised receive aerial it receives either ALL the signal, or if phased the opposite way, no signal.

At higher frequencies a Corkscrew shaped wire is used as an aerial and the direction of the helix decides if it is clockwise or anticlockwise.

The phased V and H dipole (or X yagi) with two feed cables (you can buy these) can thus be connected to a switch box with a length of coax in it to delay by 90 degrees at the desired frequency, which allows selection of:
Vertical
Horizontal
-45 (Mixed / slant)
+45 (Mixed / Slant)
Left handed Circular
Right handed Circular

(I can't remember If Left handed is clockwise or anticlockwise!)

Why?
Things that don't work with H or V or Mixed but do with Circular:
:: Early satellites spun to stabalise themselves.
:: C band transmission polarisation is rotated by chaning atmospheric conditions
:: Long VHF paths the polarisation can rotate with weather
:: Over sea paths the polarisation can change with tide
:: Mountainous regions the polarisation can change with reflection. Using Circular, it swaps direction of rotation.

Foggy43

Watty!
Thank you for your reply. It is going to take me a while to take it all in. I will need to read it a few times.

cast_iron

Yes, cheers Watty. It'll take a couple of reads alright.

Always a fountain of (odd, but interesting) knowledge.:D

dohouch

watty wrote:

Convert each of the five cut off 0.75m / 75cm pieces to a ordinary fat piece of wire by shorting out the inner wire and outer braid at both ends.

4 pieces lie flat radiating out from outer of main coax feed (braid).

5th piece stands up straight held by tape, thread, cord etc to overhead beam, connected to inner core.

Today got around to making and connecting the above suggested design. It has improved things. TodayFM seems like solid stereo,:D but Newstalk while much improved is not stereo.
Just wondering, as the coax came off a roll and is somwhat curvy, should I go to a bit of trouble getting the 4 floor lying stands absolutely straight, (maybe blobs of silicon on a a large sheet of cardboard would hold them, or cable clips into the rafter beams.) Probably, hmm?

Again really appreciate the help with these DIY solutions

Mayo Exile

Newstalk while much improved is not stereo.

I think they might only broadcast in Mono FM. They probably don't see the need to broadcast in stereo due to the nature of their programming.

dohouch

Mayo Exile wrote:

I think they might only broadcast in Mono FM.

You could be right there. But on the LCD display of my mini-hifi, the other FM stations diplay TUNED whereas with Newstalk this doesn't come up and my impression is that Newstalk is just that little bit shaky.

Is there any information available to the public, (lousy license payers) as to what strength Various TV/Radio transmitters output their programmes at.

Ulsterman 1690

Newstalk is transmitted at lower power than the other national Irish stations.

Also its transmissions are crammed closer together on the band which is another reason for them to be mono.

When the layout of the FM band was originally planned Ireland and the UK decided to allow for five national networks each plus some local stations (At the time Ireland only had two networks and the UK three so five seemed plenty for future needs)

So when it came to setting up a sixth network (Newstalk) they basically had to squeeze it in wherever they could without affecting existing services.

This also meant lower power, less coverage (about 80%) and mono (stereo signals take up slightly more "room" on the band)

watty

dohouch wrote:

Is there any information available to the public, (lousy license payers) as to what strength Various TV/Radio transmitters output their programmes at.

Radio licence abolished a long time ago. RTE will send you a list of the their TV sites and TX powers free if you tell them on phone you install aerials. It didn't used to have TV3 info. You get that from TV3. Not all RTE sites carry TV3 as they won't pay for all of them.

Antenna

this maybe of interest

http://mysite.wanadoo-members.co.uk/freq_find/IRE_txt.pdf

However some of the info for local radio is inaccurate or out of date. They seem to wrongly assume some local stations are co-located with RTE. For example Red FM on 106.1 is NOT from Spur Hill!

Ulsterman 1690

Pretty good list that as regards frequency info but as well as the gaffes RE: site locations they also have a couple of mistakes RE: Start dates.

Some of the original batch of ILR stations theyve listed as "1990/91" actually started in late 1989 and IIRC the Gaeltacht station started in 1972 not 1974 (In response to very early pirate stations)

dohouch

Why should LyricFM be so strong around here. When I got my last mobile phone I made sure there was a radio on it. Turns out to be faily useless around here, but regardless, if I'm going to get a good signal it's going to be LyricFM.

So is this a peculiarity of the phone, Nokia 6230i, or are RTE giving this station a super boost.

watty

Where is "Here"?

dohouch

watty wrote:

Where is "Here"?

I suppose the Dingle town area ,North, South, West for about 10 miles. Not East as that is the Conor Pass, not sure how high, probably 500 Meters.

EDIT: If I were to go east I'd be on the north side of the peninsula with 7 to 800 meter mountains at my back and would be receiving , I imagine from very different transmitters.

Ulsterman 1690

Its not unusual for signals from one radio/TV station to be a lot better/worse than others even when all are eminating from the same site and operating at the same power level.
Several possible reasons among the are
1) Variations in aerial directional/gain characteristics by frequency
2) Standing wave patterns

Another possibility is that the Lyric FM transmitter is newer and possibly more efficent (although the difference would usually be slight)