Unsychronised single frequency network.

[colly0410]

I'm on hols at Primrose Valley near Filey Yorkshire, I was having a tune around the medium wave & found the 1215 KHz SFN (ex 247 metres Radio 1) of Absolute radio. It seemed to have multiple TX's coming in with clearly discernible echos's, I'd say it's of zero entertainment value unless you like lots of reverb & echo effects. I was here two years ago & then there was just selective fading & mush zone distortion. (I made a comment about it on a thread on another now closed site) I understand when the BBC ran the 1215 SFN they were very strict about frequency stability & time delay matters. I'm wondering if Absolute feed some of there TX's from DAB or satellite ?

[Refugee]

There is a timing difference between radio4 FM and there LW output.

[colly0410]

Read somewhere that the BBC adjusted the timing & phase of the Radio 1 SFN TX's to move the mush zones into less populated areas. They also ran some of their TX's at more that 100% modulation using asymmetrical amplitude modulation. Does anyone know if Absolute Radio still use Asymmetrical AM or some modern version of it?

[Nowhere-Man]

Maybe be able to answer you in 2 or 3 months. I'm currently looking into amplitude modulation systems. I'm still on plate modulation. The system I looked at uses a crystal microphone and push pull. The only station I tune into these days is Kid Jenson today on Signal 2. He does old chart replays.

[radioman]

Here in South Ayrshire, BBC Radio 5-Live has a strange 'phasing' like effect on the audio, a bit like listening through a long tube.
Presumably, I'm receiving signals from two different transmitters so must be in one of these 'less populated areas' !
Absolute radio does sound rather distorted with excessive treble but not as bad as 5-live subjectively.

Andy

[Pat Pending]

Radio five and absolute echo here in central Norfolk after dark, as the effect can often be canceled by nulling the weaker transmission, I had assumed without ever checking that the same frequency was being transmitted from multiple sites, a very unpleasant listening experience.

Andy.

[Terry]

You say Central Norfolk but the dominant factor is probably how far you are from the Postwick transmitter as far as Radio 5 Live is concerned.

The most likely competition would be Droitwich which despite the much greater distance is 150kW compared with Postwick's 10kW.

As far as Absolute is concerned, Postwick is only 1.2kW and not intended to serve Central Norfolk so perhaps you are tuned to Boston which should, at least cover NW Norfolk and further at night, despite only being 2kW. Interference source at night is most likely to be from Stockton although it's a bit of a haul at only 1kW.

Of course, what fou haven't said is what frequencies you are using for both of these stations. I've included full transmitter listings below which are taken from http://www.frequencyfinder.org.uk/AM_Stations.pdf

Something else you might find useful is this map which shows the relative locations of different transmitters on the same frequency.

I haven't investigated the situation in South Ayrshire but the same information should be useful.

Absolute now has transmitters on 5 frequencies but back in BBC Light Programme days it was just one: 1214kHz with 14 synchronised transmitters covering the main population centres with Droitwich on 200kHz covering the entire country. I note that there are still 14 transmitters on 1215kHz but Dartford Tunnel was most definitely not one of the original 14! All those extra transmitters should have improved coverage considerably even if, as the above posts indicate, it isn't perfect!


         

[Pat Pending]

Just to validate Terry's comments, I've checked out where the offenders are transmitted from.
R5L on 693KHz so Droitwich and Postwick,
Absolute on 1215KHz so Droitwich and Postwick......also, not that I'm a listener
Talksport on 1053KHz was very bad, echo machine bad, also Droitwich and Postwick.
Quarter of a mile up the road in any direction, things are fine, relatively.
(Swaffham, BTW.)

Andy.

[Terry]

Your original comment about being in central Norfolk had me confused as it conflicts with your 'near Kings Lynn' location - I would describe Swaffham (and Kings Lynn) as north-west Norfolk!

So, Postwick is most definitely not your first choice for Absolute. What is Boston on 1242kHz like? After all, the list I posted does claim it covers Kings Lynn.

Again, the local transmitter for Talksport  is Boston (1107kHz). What is that like? Admittedly it is only 1kW, though

With a massive 400kW, Brookmans Park (1089kHz) might be worth trying. Moorside Edge - also 400kW - might be a problem but being on an entirely different bearing, it should be possible to null it out if you are using a ferrite rod aerial.

On a slightly different topic, concerning power and distance, when I was camping with the scouts at Anzio in 1964, the only UK transmitter I could receive there was Radio Caroline North!

Only 10kW, but I imagine the Irish Sea made a good ground reflector. I used to tune in to Murph the Surf's Midnight Surf Party after Radio Prague closed down. About 1250 miles from the Isle of Man, I estimated at the time!

[Terry]

Of course, co-channel interference isn't limited to transmitters broadcasting the same station as this little tale describes.

Anyone remember Radio Tirana?