FM signal problem

[johnb]

My Bristolian friends told me that my problem was due to the aerial I lived in

I know that many people use portable FM radios but if someone is using a 'fixed' tuner or receiver then an external aerial on the roof is infinitely better than relying on something in the box or in the room. It is the standard standard advice that comes with almost all such tuners.

[doversoul1]

Thank you again for all your advice. I am sorry to keep on about it but the problem is not the quality of the reception. This is apparently a very good area for radio reception and I only have a piece of wire for an aerial attached to the receiver which works perfectly well. The signal is steady and strong. No interference or drifting at any time. It just these odd cut-offs. Although not for the reason S-A suggested, that seems to be what it is: I am blocking the signal (but not with the bulk ).

Ah well. As salymap says she has the same problem, it can’t be something I am doing. I shall be content at that.

[johnb]

This is apparently a very good area for radio reception and I only have a piece of wire for an aerial attached to the receiver which works perfectly well. The signal is steady and strong. No interference or drifting at any time. It just these odd cut-offs. Although not for the reason S-A suggested, that seems to be what it is: I am blocking the signal (but not with the bulk ).

Sorry, but it is patently not the case that your piece of wire works perfectly well.

It seems that, during 'normal' circumstances, the signal that the piece of wire provides is just marginally sufficient to operate your tuner. When the strength of the FM signal that the aerial receives drops for any reason (and the reasons can be as simple as changes in the atmospheric conditions) the piece of wire just can't cut it.

You need an external aerial.

All good FM tuners really need an external aerial in order to perform to their full specification - that's what they are designed for.

(If you are determined to use a piece of wire, or if your circumstances mean there is no alternative, get one of the 'pieces of wire' designed for FM. These are in the shape of a "T" where the vertical of the "T" connects to the tuner. FM is usually horizontally polarised so, to get the most out of the wire, the arms of the T should be horizontal and should face, front-on, the direction of the transmitter, i.e. not end-on to the transmitter.)

[doversoul1]

John
Thank you for your advice. That makes sense. There may have been some changes somewhere along that caused the problem to start. Or my receiver is getting old. I used to have one of those T shaped wire for my old receiver but was advised by someone who knew (claimed to know) these things that we didn’t need it in this area. As it is, I have few problems in general so I shall leave things as it is for the time being.

But if you are still there: I am curious. Does human body work as anti-conductor? Or can any other solid materials obstruct the signal? But then, it has got through the brick wall… (please don’t bother to answer if you think it’s far too basic to deserve your time)

[Don Petter]

jb is absolutely right!

To save me having to recompose my previous thoughts, and in the hope that it may be of some use, here is a post I made to a similar thread last year:



My main aerial is indeed a proper FM one with attached reflector rods, albeit only laid on top of the loft insulation, with the right orientation for Wrotham, rather than fixed to the chimney. (It’s in a loft which has no other content, unlike that in the other half of the house!)

For the kitchen radio, however, I made up a simple dipole from two lengths of wire laid along the picture rail (remember those?) as the wall is near enough at right angles to the Wrotham direction. The length of wire is not terribly critical, but if my maths are right for R3 at 91.3 MHz, the theoretical figure for a quarter wave is 32.3 inches each. The inside ends of the two wires are joined to the inner and outer of a coax cable which feeds into the set.

Even this jury rig will give vastly better results than an internal aerial or a little chrome telescopic type.


Addendum

If your radio has a balanced aerial input available (shown by a pair of twin terminals rather than a coaxial socket), making the home-made dipole becomes even easier, as you can use just a length of twin flex with no joining.

Obtain a suitable length of side-by-side twin flex and for 32 inches at one end, separate the two insulated wires to form the arms of the dipole. The remainder of the flex is then the downlead to connect to the set. (In case this is not clear, you should end up with a ‘T’ shape, the two top arms are single wire, and each approximately 32 inches long, the stem of the ‘T’ is the twin wire down to the radio.)

If you don’t have my conveniently orientated picture rail, the thing can become a bit flimsy and unwieldy. One solution is to tape the horizontal wires along a length of wooden dowel or light batten. You can then hold it aloft to find a good position for reception by experiment. How you fix it in that position I leave to your ingenuity. It must be admitted that the end product is more suited to a study than the drawing room.

[Serial_Apologist]

Ah well. As salymap says she has the same problem, it can’t be something I am doing. I shall be content at that.

Indeed, my picture of saly is as a tall, slim, imposing lady!!!

[johnb]

But if you are still there: I am curious. Does human body work as anti-conductor? Or can any other solid materials obstruct the signal? But then, it has got through the brick wall… (please don’t bother to answer if you think it’s far too basic to deserve your time)

The human body doesn't act as an anti-conductor as such.

The walls of your house, and indeed your own body, are only partially transparent to FM radio waves. This means that they all affect the radio wave field. Reflections occur between the walls, etc which can creat standing waves with maxima and minima. These are apparent when you move a portable radio around a room - in some positions the reception will be good but in other positions it will be bad. Added to that your own body distorts the radio wave field so that as you move around the effect is to sometimes reinforce and sometimes deplete the signal where the piece of wire is situated.

[vinteuil]

The human body doesn't act as an anti-conductor as such.

The walls of your house, and indeed your own body, are only partially transparent to FM radio waves. This means that they all affect the radio wave field. Reflections occur between the walls, etc which can creat standing waves with maxima and minima. These are apparent when you move a portable radio around a room - in some positions the reception will be good but in other positions it will be bad. Added to that your own body distorts the radio wave field so that as you move around the effect is to sometimes reinforce and sometimes deplete the signal where the piece of wire is situated.

... thanks, johnb!

I have a similar problem to that of doversoul with the small radio I use in the kitchen. I have discovered that if I tune it perfectly to R3 - and then walk away - it's out of tune and fizzling - but if I go back - retune it a smidgeon upwards - it sounds out of tune and fizzling - but when I step back - it's perfect and in tune...

But these oddities seem to vary with a) time of the year b) time of day c) climatic conditions (barometric pressure?)

[doversoul1]

Thank you johnb

I feel much better now that the mystery is solved.

[ed] vinteuil
Ah, so you do the step round the radio, too

[Gordon]

Thank you all for your information (and interference, Ariosto ). I am afraid I have no idea where the transmitter is but I’ll find out. What puzzles me is:

1. I have had this receiver/tuner for some ten years but never before had this problem.

2. It is not the kind of poor reception or interference but the break up is definitely to do with my movement.

3. The receiver generally works perfectly well, and even when the signal cuts off, when it comes back the sound quality is not affected.

Well, at least it looks as if I haven’t gone quite mad, which is a relief.

Posts 18 and 20 are right, your problem shows the classic symptoms of poor signal strength. The fact that your presence near the receiver affects reception is the key indicator. Changing the location of the receiver, if possible, might help especally of you can increase its height above ground eg upstairs or get it close to a window.

Why it has apparently got worse lately is puzzling but if you live in the midlands or parts of E Anglia you may have reduced signal strength because of TV Switchover work on the masts that also carry FM antennae. Some FM transmitters - eg Wrotham in Kent - don't share with TV facilities.

It would be helpful if you could say where you live [the area or town not your address] and then we can find the local transmitter. It is possible that the receiver has been retuned and your receiver is now tuned to a more distant station than before? Try retuning around where the receiver is currently set. Check what frequency it is tuned to for R3 - an electronic readout is more precise than an old fashioned dial - and then cross check that with the BBC web site tables of transmitters at: http://www.bbc.co.uk/reception/transmitters/radio/

At this time of year we are moving towards the high pressure weather conditions that enhance interference so it is just possible that your receiver has been tipped over the edge by low level background interference.

[BetweenTheStaves]

Here you go...entering your postcode will tell you about any work

https://faq.external.bbc.co.uk/templates/bbcfaqs/emailstatic/interferencePage

There isn't an FM tx at Crystal Palace..so you;re either picking up Wrotham or one of it's satellites

[doversoul1]

johnb, Don Petter and Gordn
Thank you all for your advice. If I am perfectly honest, I am beginning to half wish I hadn’t asked: a) things are getting rather too technical for me and b) I had been perfectly content with the sound quality of my receiver but now it looks as if it can be improved…

Don
My receiver is in my study so your solution will cause no problem although this is one room without picture rails. I have copied your instruction and saved in my Reference file.

Gordon
My screen name is where I am. In fact, there is a mast quite nearby which, I think, is a transmitter (of some kind). My receiver knows no other station. It was tuned electronically and that was it.

BetweenTheStaves
Thank you for the link. I shall try it and see how far I can get to.

Once again, thank you everyone for all your advice.

[salymap]

Indeed, my picture of saly is as a tall, slim, imposing lady!!!

Blimey,just come across this, I'm being watched. Tall, slim yes, imposing never in my life so far. 5.2 females have a much better time. If a woman is fairly tall, she is 'capable'. Still can't grumble

[Don Petter]

Gordon
My screen name is where I am. In fact, there is a mast quite nearby which, I think, is a transmitter (of some kind). My receiver knows no other station.

(With apologies to Only Fools and Horses)

I just hope you don't end up with the Calais ferry arriving in your study...

[johnb]

Your FM is probably Swingate (grid ref TR334429) if your frequencies are as follows:

Radio 1 99.5
Radio 2 90.0
Radio 3 92.4
Radio 4 94.4

By the way, my neighbour once mentioned her small FM radio was playing up. It turned out that she had a "T" shaped wire draped vertically. I explained the best approach and she put one arm of the T along the picture rail of one wall (~15 degrees off) and the other arm along the picture rail of the adjoining wall (~ 75 degrees off) and it worked fine.

What I'm getting at is that there is no need to get everything exact - just try a few things out and you might find that some small changes help. (Maplin has a FM T indoor wire aerial for £4.99 - it might help, if you want to experiment.) Swingate has mixed polarisation, so you can try both verticle (say up a corner) and horizontal orientations.