FM aerials

DrMartin

DrMartin

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I've just had an FM aerial installed on my roof. I was having a Freesat dish put up so I thought I might as well get them to put an FM aerial up while they were up there. I have been using one of those 300 ohm indorr 'tape' dipole things for years but I get a bit of hiss with that so I was looking forward to some really clear reception with the new outdoor aerial.

Oh dear, it's not to be. With the old indoor tape aerial I was getting around 54 db signal strength on BBC Radio 2 on my Sony Tuner. With the brand new outoor FM aerial this drops to around 32db!!! I tried a few different stations and they are all worse on the outdoor aerial.

I just don't understand how this can be the case?

The aerial is one of those omni-directional folded dipole jobs. Are they worse than useless? Has anyone else got one of these and it works well?
 
Sounds like a break in the cable or a fault with the connection in either the plug or connection into the aerial assembly.
 
Rob is probably right. Check first the plug on the end of the coax cable. You will have a problem if there is a cable connection issue higher up.

You mention the use of a 300ohm tape aerial. Was that connected to the Sony Tuner with a pair of screws? The 300 ohm input.

Your new aerial should be 75ohm using coax cable and a Belling-Lee Coax Plug inserted into a matching socket. If the coax from the aerial is connected to a pair of screws on the back of the tuner you will have an impedance mis-match, and that will give you a poor signal. You can get matching transformers.

Other observations:

Those circular aerials are not the best for HiFi, a three or five element directional aerial would have been better, but if you need to pull in stations from different directions the omni is a suitable compromise.

But do notice that, given a good external DAC connected optically to the Freeview Box the Freeview Radio signal should be at least as good as FM. Internet Radio streamed from a computer or other device through a good DAC will better both.
 
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Interesting replies, thanks both.

The whole job was done yesterday and I assumed it was all done properly for £360!

The connection to the tuner is via a 75 ohm coax fly lead from the coax socket fitted to the wall yesterday into a coax socket on the tuner. I've tried a few different fly leads but they make no difference.

Brian, I know what you mean about those screw type aerial terminal because I've had those on other tuners. this Sony STA3ES has 2 x coax sockets and the 'T' - shaped tape aerial (that came with the tuner) has a moulded coax plug to connect to the tuner - perhaps it isn't 300 ohm? - I assumed all those T - shaped tape aerials were? Either way, it works a whole lot better than the brand new outdoor one. After years of trying in different places I actually have it running vertically by a window behind the curtains!!! It is not even horizontal.

I'm going to give them a call and ask them to check the FM connections all the way through. I'm sure the outdoor should be better than the indoor - even if it is just a folded dipole and not a 7 element yagi beam ...

I've got an old Freeview box with a pair of analogue outs and I put those through the Quad last night and the radio didn't sound bad at all. However, I thought that Freeview Radio was digital radio and therefore DAB radio - is that not the case?
 
Searching the recesses of my memory:

The ribbon is indeed a 300ohm cable. A single open dipole will have an impedance of around 300 ohms, but add a reflector, or fold it into a loop (as your tape areal will be configured) and the impedance falls to about 75ohm. The short length of tape down to the tuner is badly matched, but clearly it is doing a better job than your new aerial. You had better have them back, but it may be worth trying another tuner first to avoid a red face.

Freeview (DVB-T) and Freesat (DVB-S) Radio feeds are, like DAB, coded at MP2 though with higher bitrates, so should better DAB. If you can get either of those streams digitally connected to a decent DAC you will notice an improvement over the analogue out of a set-top box.

The BBC iPlayer audio streams are now coded in AAC+ and do sound very good. Radio 3 is now offered as a so called "HD" stream at 320kb/s AAC+ which is as good as you will get anywhere.

You have to use a computer for that stream, or a Squeezebox or other internet radio streamer.

But, as I said, the Freeview and Freesat MP2 streams via a decent DAC should be as least as good as FM.

FM transmissions used to be horizontally polarised, but I think they are also transmitted with vertical polarisation for the sake of car radio reception.

Where are you in the IOW? The main transmitter is a t Rowridge and is very powerful. There is a low power repeater for TV at Ventnor which suggests a bind spot in part of the island.

In Southampton, as a temporary measure, I have my Quad 77 FM Tuner hooked up to the flat communal aerial - Classic FM is fine but Radio Three is often unusable - both must come for Rowridge. Very odd.
 
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I would second Brian's comments re iPlayer, Freeview and Freesat.

For £360 I think they need to come and check their work.
A good installer will check alignment while on the roof, good strength, minimum multipath distortion etc, then do the same at the connection into your home.

What you have in terms of the hardware sounds fine to me if you are fairly close a transmitter.
I've had a 5 element on the roof this past 12 years (in London) and this drives every tuner I've connected to max quieting.
 
I seem to remember that the polarisation of F.M. transmissions was changed to slant polarisation some years ago,i.e. 45 degrees .In other words not quite exact for anybody but a good enough for most. I can't comment on signal strength for the I.O.W. since I don't live there but I have used a circular folded dipole for many years with no problems.
Logically, since a correctly installed outside dipole should give better reception than an internal 300 ohm tape aerial and the fact that yours does not, it would seem to point to a problem with the new installation.
Take no nonsense, for that price it should work.
 
Thanks for all the replies and info. I'm in Ryde Brian and I've got a clear line of site accross the Solent to the South Downs where there is a TV transmitter apparently. the Freeview signal is very good but I've no idea where I'm picking the FM up from?

That's interesting about the 45 degree polarisation Pete693. I'll try my ribbon at 45 to see if it improves the signal.

In the meantime, I'm definitely going to call them about the new outdoor aerial, it will be interesting to see what they say.

By the way, £368 was for:

New Freeview aerial
New Freesat Dish with Quad LNB
New FM aerial
New DAB aerial (thought I might as well get the lot for future reference)
Twin Sat sockets on internal wall
TV + FM/DAB sockets on internal wall
Triplexer
+ all cables, fittings etc.
Labour was £100 and the guy was here for at least 3 hours.
+ the dreaded VAT

Do you all think that was a bit much then?
 
You folded dipole aerial is no better than a half dipole one.

Approximate gain for the various FM antenna.

Omni round dipole -3db
Half dipole 0db
Folded dipole 0.5db
3 element 3-4db
5 element 5-8db

You would be better off having a directional aerial installed with a minimum of 3 elements. If you need to receiver radio stations from other areas you could consider a rotator.

Have a look here it may help.

http://www.aerialsandtv.com/fmanddabradio.html#BasicRadioAerialFacts
 
audioflyer said:
You folded dipole aerial is no better than a half dipole one.

Approximate gain for the various FM antenna.

Omni round dipole -3db
Half dipole 0db
Folded dipole 0.5db
3 element 3-4db
5 element 5-8db

You would be better off having a directional aerial installed with a minimum of 3 elements. If you need to receiver radio stations from other areas you could consider a rotator.

Have a look here it may help.

http://www.aerialsandtv.com/fmanddabradio.html#BasicRadioAerialFacts
Click to expand...


Very useful site that, thank you very much. I would love to have a huge full wave yagi beam on a motorised rotator but it's just not practical and it would seem that anything else is going to be a bit of a compromise if you want to pick up from more than one transmitter. It would also appear that the round, omni-directional FM aerial I've just had installed is just about the worst type you can get - oh well, back to the drawing board.

Actually, I was having a little play earlier and the new aerial did manage to pull in one station a bit stronger than the 'old' tape aerial. Unfortunately this was the local 'Isle of Wight Radio' station which I never listen to :(

Thanks again for all the replies - very helpful and knowledgable as always.
 
Speaking as a non scientist but nevertheless happy with a circular aerial I would only add the following.It is true that aerials with many correctly designed elements are capable of pulling in more distant stations but they are very directional.That is O.K. if all the stations you want to listen to come from the same transmitter but is a pain if that is not the case.
On the subject of aerial "gain" I have always thought that this is a bit of a misnomer and one should not get too bogged down with it. I would love to believe that it was possible to get "gain" from a piece of aluminium tube. It would be handy to connect a piece between our M.C. pickups and our amplifiers!
Getting back to the original point I still believe that a correctly installed external circular folded dipole (i.e.not erected on the blind side of a large building or well below the roof lines) will outperform an internal 300 ohm tape.I have never come across an instance where it did not.
Best of luck with it.
 
slightly off topic ..and really cheeky hee hee

I have a receiver, but no ariel of any kind...

has anyone got one of those 'free' ones you get with a tuner - will pay postage..

I know they're not great, but it will give me some stations.
 
bottleneck said:
has anyone got one of those 'free' ones you get with a tuner - will pay postage..
Click to expand...

Make your own from a short length of twin flex. The cheapest sort with a figure of eight cross section. Take one end and separate the conductors still in their plastic sheath. Tear the flex apart by extending your arms to the maximum. This gives you (miraculously) the required length for a half wave dipole of 1.5m or 5ft.

If you have a coax TV plug, attached it to the other end, or otherwise bodge a connection to the tuner

If you have a spare coax to coax TV lead, snip the plug off one end and attach a wire to the central conductor and one to the screen. The wires should be 0.75m or 2ft6in long.

Experiment with positioning the dipole. Try it horizontally and vertically. If you can't spread it five feet, let the ends dangle.

If you are not in a difficult reception area you can do a lot with a bit of wire. Iv'e done it often.

There are quite a few webitses - google DIY FM aerial (Do spell aerial correctly!)

Or you could go for bust:

http://radio.meteor.free.fr/us/yagi_fm.html

But by the time you have bough the bits you could have bought an aerial!
 
bottleneck said:
slightly off topic ..and really cheeky hee hee

I have a receiver, but no ariel of any kind...

has anyone got one of those 'free' ones you get with a tuner - will pay postage..

I know they're not great, but it will give me some stations.
Click to expand...



Well that's what I'm using at the moment and, as I said earlier, it gives me better reception than the outdoor one. To give you an idea, the signal strength meter on my Sony Tuner says 54db (Radio 2) from that aerial (vertically polarised) and the maximum reading you can get on that is 75db according to the manual, so it's not doing too badly at all really. Radio 3 however is a completely different story - much weaker at around 32db - so I presume they're coming from different transmitters? which seems a bit odd to me. In fact no two stations give the same reading.

Thanks for all the other comments & suggestions everyone. I'm going to try some experiments at the weekend when I can source some aluminium tubing. Should be fun.
 
DrM: You should be receiving FM from Rowridge

http://www.thebigtower.com/live/Rowridge/Index.htm

http://txlib.mb21.co.uk/v/bbc-national-fm-radio/1902-8-9211.jpg.html?g2_imageViewsIndex=2


I am tuned to Rowridge from Southampton, and it should be line of site. Classic FM is fine and Radio 3 awful, yet they are both supposed to be radiating 250kw from the same mast.

I note the analogue TV is to be turned off in 2012, and a new mast will be erected. I guess at that pont the power of the digital TV broadcast will be increased.

Perhaps they are already some compromises - on FM.

The flat I live in are about to have a communal sat dish installed. At that pont I will swap to Freesat and access radio off sat, or by internet.

The FM Tuner will go.

Anyone want to buy a fine Quad 77 FM Tuner? It draws poer from the Quadbus, so is only of interest to other Quad owners.

But why R3 FM is so poor from Rowridge, I dont know.
 
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Hi Brian, yes that is odd about R3, and it's interesting that you seem to have the same symptoms regarding a drop in signal on R3.

The aerial installer did say that the Freeview signal was going to be pumped up quite a lot when the analogue signal was turned off. He mentioned this when I asked about a mast-head amp for my freeview aerial. He said that I didn't really need one now but that if he fitted one I would be asking him to come and remove it in about a year's time because the signal would be too strong!

I'm getting a good Freeview signal ATM, much better than with my old TV aerial, but I know it can play up when there is High atmospheric pressure. Well, it did with the old one so I'll see if it's any better with the new one. So far son good on that front.
 
DrMartin said:
Hi Brian, yes that is odd about R3, and it's interesting that you seem to have the same symptoms regarding a drop in signal on R3.
Click to expand...

I emailed complaint about R3 reception to the BBC. Let's see if they respond.
 
DrMartin said:
Hi Brian, yes that is odd about R3, and it's interesting that you seem to have the same symptoms regarding a drop in signal on R3.
Click to expand...

The BBC has answered me

I understand you've encountered problems with your Radio 3
reception recently.
The Rowridge transmitter is undergoing a period of planned
upgrade work essential for the digital switchover (DSO). At
present maintenance is being carried out on the radio apparatus
and is the most likely explanation for your poor signal.
For future reference, you can find details of current engineering
work and known faults by visiting the links provided:
http://www.digitaluk.co.uk/how_do_i_switch/your_aerial/engineering_works
Click to expand...

I did chhck for transmitter faults online before asking them, but nothing showed.
 
Ah well, at least you tried - and got a response!

That website could be useful in future.


Off topic (ish)

I've just been looking to see when we'll get Freeview HD (I've just bought a new TV with Freeview HD & Freesat HD tuners built-in) and it looks like most of the South East is last on the list in 2012.

At least the Satellite dish they installed at the same time as the FM aerial appears to be working ok, so that's a blessing.
 
With the BBC now rolling out the so called 'HD' radio I'd expect the online feed to surpass FM. It does already on many stations with only R3 & R4 being better on FM via a good tuner.

Radio at 320kbs (or 256) can sound very good indeed.
 

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