DAB reception oddities

L1011

About two weeks ago, Mux 12A got a lot harder to get here in Maynooth. Could position the radio funny and get about 85 Arbitary Pure-decided Reception Units which was enough to just about lock. 12C seemed fine.

Now, I've shoved a 6 element log-periodic band III in the attic and... 100"%" on 12A but I've lost 12C - about 20"%". Now, I listen almost solely to Phantom, Newstalk and TodayFM, so this is no big deal - but its just bloody strange.

Anyone any idea? They're meant to be on the same mast and I'd guess the same power.

Antenna

HAve you made the mistake of having the aerial horizontally polarised?, (all DAB is vertical)

If thats OK, just try repositioning the aerial elsewhere in the attic?

L1011

I've slightly more cop on than that!

And no, not yet. Its in a nasty position that requires loads of crawling over dodgy 20+ year old marine ply thats starting to give...

Radio|Man

The Mux with the local Dublin stations and two National independents is from 3 rock only.

The RTE mux is from both 3 rock and CMC.

You are obviously getting the CMC signal and not the 3 Rock which would explain your dilema.

Keep trying though as changes are likely to be made with regard the syncing of the two sites that may affect which signal you are receiving.

Hope this helps.

L1011

No, I'm getting the Dublin/Local mux and NOT the RTE mux - what you're describing is the reverse.

Radio|Man

Hi,

Sorry, I mis-read your post.

I'm guessing its still a timing issue causing this. I'll see what I can find out for you.

Antenna

MYOB wrote:

No, I'm getting the Dublin/Local mux and NOT the RTE mux - what you're describing is the reverse.

It sounds like the two RTE DAB transmitters (Three Rock and Clermont Cairn) are destructively interfering with each other in your area. Try aiming your aerial a bit off-beam to the south, it might help cut out the interference from Clermont Cairn, whilst still getting the Dublin transmissions with enough strength.

Booms

Could the dipole be located at the null point of a standing wave for the 12c frequency? Or doesn't that apply to digital signals?

L1011

Antenna wrote:

It sounds like the two RTE DAB transmitters (Three Rock and Clermont Cairn) are destructively interfering with each other in your area. Try aiming your aerial a bit off-beam to the south, it might help cut out the interference from Clermont Cairn, whilst still getting the Dublin transmissions with enough strength.

Its entirely possible - the joys of SFN, eh? :rolleyes: CC is strong enough here for UHF and FM so it could be for DAB too.

I'll try the repositioning a bit. Nothing major as I rarely listen to the traditional RTE channels but I'd like to be able to play with the trial services. Phantom still wakes me up sucessfully

watty

Reflections, ghosts, Nulls, standing waves do affect "digital" signals. The signals are actually still analogue radio waves. The effect depends on modulation scheme, symbol rates, etc etc, COFDM vs single carrier etc.

Just as 28k modems, DSL modems, ISDN all do analogue signals to get the digital data across the phone wires.

Morse code is probably the only truly digital RF signal. It's either there or it isn't.

L1011

Back to listenable now. Timing tightened up I wonder?

lawhec

It would be unlikely, but there might have been an outside chance of a transmission from Britain on 12C interfering in roughly the same direction towards Three Rock. Atmospherics might cause it.

More than likely is that the timing of the signals from CC & 3R were slightly out. The BBC DAB Transmitters in N.Ireland are slightly ahead of their counterparts in Britain so that in times of tropospheric enhancement over there SFN time delay receiving problems are minimised - of course it means that signals here are more vunerable!

L1011

Lasted about two weeks so atmospherics is a bit unlikely.

Radio|Man

Timing has been adjusted.