Radio reception - engine on

After what seems years of experimenting with aerials to achieve a consistent DAB signal I abandoned the stick-on system and went for a Halfords magnetic aerial for a tenner. Not ideal aesthetically and you have to remember to put it on and away again when you leave the car, but being external the signal difference was palpable so well worth it.

Now recently, tested out at length on the trip to Holland and back, it's started to misbehave - eventually traced seemingly to whether the engine is running or not. It's picking up a good signal with engine off but disappears 80% of the time with engine on, even in parts of the country where you'd think reception was optimum such as the flat east coast.

Can anyone make any sense of this? Is it the aerial cable coming into close proximity with something it shouldn't?

The obvious culprit would be noise from the alternator. Question is though; has the aerial seen its day and therefore more susceptible to noise or has perhaps your alternator worn to a point it's very noisy (brushes and slip rings)

The aerial is less than a year old....never occurred to me about the alternator; I'll have to make enquiries as to whether it was changed during restoration, but I think not...?

Is it noise or signal? They used to talk about suppression back in thee olde days which usually equated to electrical interference from suppressor caps or spark plugs. TBH I've never found DAB to be any good round here as the signal is pathetic or non existent.

Hi Simon,

I Also have a magnetic dab aerial. It's on the boot and works perfectly fine. That said, you need a good head unit to work properly. I bought a Pioneer headunit and reception has been fine ever since. Worth a try putting a pioneer head unit in. You could have seen it working at Viva Italia being parked up next to my coupe....

Henk

If we all could see the future, Henk!

Yes, this is my first idea, to relocate it as far from the engine/alternator as possible.

It's odd that 6 months ago it was fine, but then if the alternator's suppressor (assuming it has one) is failing that may be the problem.

Oddly enough, I had very few problems with my stick-on DAB aerial cunningly concealed behind the mirror, with the power and signal lead running under the window rubber to the left and then into the warren behind the dash. Conveniently, it provided better FM signal than the factory apology on the rear window.

DAB is a bit weird and wonderful: it uses a thing called trellis encoding where the instantaneous phase of the radio signal is measured around two million times a second. Because it's digital, it basically works or it doesn't; it doesn't understand graceful failure as FM does. If the signal is strong enough it works, if it isn't, it stops.