Radio suppression

I've got the original LR radio/CD player in my 55 plate 1.8 and I get loads of interference on MW (old school I know!). What sort of suppressor do I need and where do I wire it up ? - thanks

Years ago it used to be the dynamo causing this, haven't experienced this since my old MK2 Cortina in the early 80's.

Not to sure if you can fix a suppressor adapter on the aerial to the radio could be wrong

In order to suppress such interference, the first job is to track down where it's coming from; alternator, another motor, ignition circuits or even more strangely, something like tyre "noise" (yes it does exist although it's almost unheard of these days).
Only once the noise source has been identified can suppression begin.
The first question must be what does it sound like and does it change with engine revs and so on.
Over to you.

brian47 said:

In order to suppress such interference, the first job is to track down where it's coming from; alternator, another motor, ignition circuits or even more strangely, something like tyre "noise" (yes it does exist although it's almost unheard of these days).
Only once the noise source has been identified can suppression begin.
The first question must be what does it sound like and does it change with engine revs and so on.
Over to you.

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Excellent guidance / advice. My radio which is mainly on the FM bands loses reception fairly quickly and as it does so there is a lot of crackle interference. I suspect the antenna's earth connection and your could be worth a check too. I read on here some time ago about this very thing.

Mine normally went haywire when Posh Spice or her clone Cheryl Cole sang. Many a day fiddling with my knob to fine tune

The two most important things to combat FM reception problems and interference are:
A: good ground connection at each end of the cable.
B: a good centre core connection between the aerial and receiver.

MW reception is different to FM because, as a rule, the signal doesn't come from the vehicle aerial. MW normally needs a really long aerial to receive a signal with a long wavelength. This is normally fitted inside the radio itself and is in the form of a coil, wound round a ferrite rod. The coil can extend to over 20ft if unwound!
There are a couple of issues with this setup. First a MW aerial works best with the receiver case connected to ground. This obviously can't happen in a car because of the tyres. Additionally the aerial rod is inside the car body, which is also being used as a "floating" ground. This basically means that the aerial is almost insulated from the signal you are trying to receive. For correct MW and LW reception, the receiver needs a good solid ground connection.
This "floating ground" reduces the signal strength massively. This low signal is compensated for in the receiver by using a powerful pre-amplifier. However amplification of a week signal, also amplifies general electrical noises nearby, hence the interference heard.

thanks for the replies.............
The reception general is poor which I think is done to what Nodge68 is saying, if I go under a bridge I lose reception altogether. There is no difference if the engine is running or at higher revs, it gets much worse when electrical components are used - wipers, brakes and really noticeable with indicators. So I guess I need to suppression on the electrical circuit ?

Where is the aerial earth point ?

scotty57 said:

Where is the aerial earth point ?

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Directly to the body, below the aerial. You access it by removing the interior light.

Guys this is MW we are talking about - as noted above it'll probably be a ferrite rod. Fiddling with the external antenna may be pointless.

Check first the following.

1. Do you lose of change reception if the external antenna is unplugged (just to check if it is an internal antenna or not)
2. What causes the noise and what is it? Whines are usually switching components like a rectifier diode pack in an alternator. Crackles are impulse broadband noise - like sparking on a commutator from a motor. (alternators rarely spark as the current isn't interrupted as such). Does things like wiper motors, washer pumps etc get picked up? If it's continually crackling an electric fuel pump can be the cause.
3. If you put your hand flat on the front of the head unit does the station strength get louder or the crackles become less? The hand applies earthing capacitance - if this test has a marked effect it's usually very obvious. In which case you need to earth the radio. Usually it either has a slide in earth connection, or the mount collar is earthed and it relies on a contact there. Either way you want a small wire - doesn't need to be much current .25sqmm is more than enough and connected to earth.

Thanks both. I know its only MW and I may need to go down the DAB route for better reception but I'll check what Chris suggests.