Why no radio reception?

[nb celestine]

About a year ago, the girlfriend was clambering about the roof and kicked my radio aerial, one of those black rubber ones, about a foot long. Up until then reception had been great. Its a quite new pioneer car radio with mp3 input, so quite modern. You could put it on scan and you could pick up loads of channels.

She had snapped it where the black rubber piece screws into the roof mounting bit. So, never mind, I said, I,ll just get a new aerial pack and screw the new black bit into the roof fitting thats still up there and away we go.

Wrong. The fitting was different so I put all the new aerial up but kept the old cable from radio to roof fitting because it was fine.

So I filed off the old paint under the aerial fitting and screwed it down tight. Reception is crap and has been for a year; I even bought a better quality rubber one and that is the same. The radio has been pulled out and the aerial cable is plugged in ok.

How can I go from fantastic reception to a point where I have to scan manually to pick up the weakest signal, just because she booted the thing off the roof.

 

Any ideas. I miss pop master with Ken Bruce.

[dor]

Are you sure that the inner cable is not shorting out to the screen or shell somewhere?

 

On a slightly different note, you mention scraping off paint to get a good earth. I understood this was bad practice as it provides an alternative earth return from the radio via the screen. The screening should still do its job as it is earthed through the radio, but any electrical device should use a wired return to avoid stray currents going through the hull (thus potentially increasing the risk of galvanic corrosion).

[philjw]

Hi,

I'd be checking that the cable is actually OK i.e. that it is not shorting out between the central core and the braided sheathing and confirming that the core has not snapped inside. Use the resistance setting on a multimeter to do both tests. You want a high resistance for the first test and low for the second.

Phil

[Titus]

First thing I'd do before fitting a new aerial is to get rid of the girlfriend !!!

 

[Keeping Up]

Are you sure that the inner cable is not shorting out to the screen or shell somewhere?

 

On a slightly different note, you mention scraping off paint to get a good earth. I understood this was bad practice as it provides an alternative earth return from the radio via the screen. The screening should still do its job as it is earthed through the radio, but any electrical device should use a wired return to avoid stray currents going through the hull (thus potentially increasing the risk of galvanic corrosion).

 

As you say, it is bad practice to have the screening, which is earthed to the radio chassis, earthed also to the hull at the aerial end. But it will also not be as effective at rejecting interference unless it is connected to the hull there at radio frequencies only by the use of a capacitor linking the disconnected braid to the metal hull (or at the radio end of the cable, by disconnecting the braid and bridging the break there with a capacitor).

 

However these are things to be investigated after the original problem has been diagnosed, by doing the tests which have already been suggested.

[Semitrad]

It is possible that the original antenna assembly incorporated an amplifier.

[nb celestine]

Thanks for all the replies guys.

I never thought a radio could be so complecated. On the building site we used to make up a box with a car battery in it, cut out a slot and put a radio in it and then couple it up to a wall tie or connect to the scaffold.

I,ve got the new cable so I,ll put that on after playing with my multimeter and see if I can understand that.

I dont think the old aerial had a amplifier; it just looked like a basic one.

Liked the quip about the girlfriend; she,s back in Cornwall now. mind you, she has blew the engine on the car since the aerial.

[nb celestine]

Thanks for all the replies guys.

I never thought a radio could be so complecated. On the building site we used to make up a box with a car battery in it, cut out a slot and put a radio in it and then couple it up to a wall tie or connect to the scaffold.

I,ve got the new cable so I,ll put that on after playing with my multimeter and see if I can understand that.

I dont think the old aerial had a amplifier; it just looked like a basic one.

Liked the quip about the girlfriend; she,s back in Cornwall now. mind you, she has blew the engine on the car since the aerial.

 

Just put the new cable on. Just the same.

Any other ideas?

Going to try a coat hanger up there now