DAB car reception query

occasional post · 14/02/13 - 16:39

Just curiosity on this one....
I often drive on the M4, and therefore often drive past Membury Services, which has (what I presume is) a radio and/or TV transmitter mast next door.
If listening to DAB, I have no issues going eastbound (on the carriageway next to the transmitter). However when travelling westbound I lose the signal. The duration varies a bit but can be from about half a mile before reaching the services to as much as 2 or 3 miles afterwards.
Any idea why this should be? No problems on FM or AM, and it's affected both my current car (Jag) and my previous (Audi) - both of which have factory fitted DABs.
Thanks

hanssolo · 14/02/13 - 16:57

http://stakeholders.ofcom.org.uk/broadcasting/radio/coverage/dab-coverage/
It's a site where D1 will add DAB to, but no date and surprised it has taken so long being on a major motorway?

Inkblot · 14/02/13 - 17:04

This problem has been mentioned a few times here. I believe it is because the Membury mast transmits the BBC national multiplex and this kills reception of Digital 1 within a small area around the mast. Not sure why, perhaps someone can explain, is it because in-car DAB sets are easily overloaded when the signal is too strong?

Bangers · 14/02/13 - 17:18

It's called adjacent channel interference (ACI), and typically only causes problems within a couple of hundred meters of a transmitter. The problem here is that Membury TX is literally right next to a major road! When Digital One do finally join the TX then the problem will go away.

chrisjr · 14/02/13 - 17:26

I have had that virtually every time I drive past Membury in a variety of cars over the years. But can't say it's been more than a few hundred yards either side of the mast itself. Certainly not for miles either side anyway.

More of a minor irritation than a major problem really.

mill9 · 14/02/13 - 19:19

Inkblot wrote: »

This problem has been mentioned a few times here. I believe it is because the Membury mast transmits the BBC national multiplex and this kills reception of Digital 1 within a small area around the mast. Not sure why, perhaps someone can explain, is it because in-car DAB sets are easily overloaded when the signal is too strong?

In the 1980's I added an amplifier to my car radio to improve the FM reception which worked well but sometimes weaker stations would be killed off when you drove past an FM transmitter. So its nothing new.

jaffboy151 · 15/02/13 - 11:16

It happens Alot to me on my old jvc db1000 dab add on tuner, if I travelled along the m54 to Shrewsbury driving past the Wrekin TX listening to now wolves/salop the signal would break up for about half a mile, also the same thing happens when driving on the m6/m5 past Turner Hill, the now multiplex is broadcast from these sites as long with MXR WM, D1 & BBC, plus ce Birmingham from Turner hill, bit of a fault with dab that it has such a dramatic effect, though saying that, can't recall it happening on the other mux's, just now wolves.. Have changed my radio now so will have to see if this one is effected..

makeba72 · 15/02/13 - 11:59

I'm thinking of updating my in-car radio (to include DAB and a plug-in for my cheap MP3 player, so I can listen to podcasts).

How is DAB reception in-car in (North) London? Would I wasting my money, or is it good?

Thanks in advance

vinnielo · 15/02/13 - 12:51

occasional post wrote: »

... going eastbound.... travelling westbound....

You should be reading the traffic news on the radio!

vinnielo · 15/02/13 - 12:53

makeba72 wrote: »

How is DAB reception in-car in (North) London? Would I wasting my money, or is it good?

It's very good because of BT Tower and Alexandra Palace.
Shouldn't get any breakup even without a roof-mounted aerial (although I'd still recommend getting one).

makeba72 · 15/02/13 - 13:29

vinnielo wrote: »

It's very good because of BT Tower and Alexandra Palace.
Shouldn't get any breakup even without a roof-mounted aerial (although I'd still recommend getting one).

thank you

Kiko H Fan · 15/02/13 - 14:43

occasional post wrote: »

Just curiosity on this one....
I often drive on the M4, and therefore often drive past Membury Services, which has (what I presume is) a radio and/or TV transmitter mast next door.
If listening to DAB, I have no issues going eastbound (on the carriageway next to the transmitter). However when travelling westbound I lose the signal. The duration varies a bit but can be from about half a mile before reaching the services to as much as 2 or 3 miles afterwards.
Any idea why this should be? No problems on FM or AM, and it's affected both my current car (Jag) and my previous (Audi) - both of which have factory fitted DABs.
Thanks

I have asked this question before.

I listen to Planet Rock and for about a 2-3 mile radius, it drops completely, both west and east bound.

I use a Pure Highway with an external magnetic mount aerial.

Gerry1 · 15/02/13 - 17:38

occasional post wrote: »

I have no issues going eastbound... However when travelling westbound...

vinnielo wrote: »

You should be reading the traffic news on the radio!

Absolutely not ! :eek:

You travel west; it's the carriageway that's westbound.

It's a very common tautology, almost as irritating as "the time is now five minutes before the hour of four o'clock..." when "it's five to four" would suffice.

(I'll get my coat.)

Vectorsum · 15/02/13 - 18:27

chrisjr wrote: »

I have had that virtually every time I drive past Membury in a variety of cars over the years. But can't say it's been more than a few hundred yards either side of the mast itself. Certainly not for miles either side anyway. More of a minor irritation than a major problem really.

This is an instance where D1 wouldn't actually need to install a full transmitter, only an On Frequency Repeater for a fraction of the cost. BBC R&D looked at this 'hole punching' problem back in 2005 in a white paper called 'Digital On-Channel Repeater for DAB'. This references a hole-repair trial based around the Mapperly Ridge TX.

There is also an excellent study by Ægis on behalf of Ofcom, 'The feasibility of DVB-T on-channel repeaters for coverage repair on channel 60'. While this examines the use of OCRs to repair holes punched in DTT channel 60 coverage by adjacent 3G/4G signals, it also summarises much DAB OCR work and references a coverage-oriented DAB OCR deployment at Otford.

Membury being a substantial mast, it should be perfectly possible to obtain 80-90 dB isolation between source and coverage side antennas.

vinnielo · 15/02/13 - 20:02

Gerry1 wrote: »

Absolutely not ! :eek:

You travel west; it's the carriageway that's westbound.

My point is that it seems to be the standard accepted on the radio, even though it's horrendously wrong.

Bangers · 16/02/13 - 10:19

You may have a point vinnielo because I note that weather forecasts (which have been around since before the car was invented) refer to westerly winds as to those coming from the west to the east, not the other way around. However I think most people get the gist of what westbound means.

occasional post · 19/02/13 - 08:29

Thanks for all of the replies - I'll try to get my grammar correct next time!

Hey there!

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