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Join Date: May 2010
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FM Sensitivity

09/26/2010 9:31 AM

After installing a modern Blauplunkt stereo in a 1992 Volvo, I was disappointed that the station sensitivity was much worse than an old Alpine that came to us in a 1985 Volvo 240. The antenna appears to be in good shape, and the wiring is complete with no obvious damage and is well insulated from ground. Can any of you buffs suggest the next place to look? We were wondering if we need to somehow check capacitances, or resistance, but we don't have a clue what these values should be. We also do not have access to a signal injector, which in conjunction with a diagnostic oscilloscope (which we also don't have) might shed some light on signal distortion to the radio. By the way, the antenna is at the left rear of a station wagon.

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#1

Re: FM Sensitivity

09/26/2010 10:35 AM

Well first I would check the web to compare the old versus new radio sensitivity specifications. No need trying to "fix" something that is already working as best it can. Remember new does not always mean better and Alpine made some very good products. Now from my experience most car radio antenna matching problems exist with the AM band and not the FM band. Many radios use to have a front end tuning capacitor that could be adjusted with a low capacitance tool. Since audio levels would improve with a stronger AM signal the adjustment trick to work without instruments was to tune to a weak AM signal somewhere near mid-band and adjust the capacitor until you found the strongest audio levels.

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#2

Re: FM Sensitivity

09/26/2010 12:30 PM

on the back of some radios for vehicles there is somtimes an ariel trimmer.

you can find it normally near to where the airiel socket is it is behind a small hole in the casing and looks like a small screw inside the casing normaly looks like a brass colored

I suggest if you find it tune to a very weak station with the ariel fully extended the using a small screw driver turn the screw slowly clock/and anti clockwise untill sound improves.

by the way the plucg that goes into the ariel should when metered between the inner and outer show no connection at all.

the inner point on the plug to the ariel should read like a short

and the outer part of the plug like wise should when metered to the chassis also read as a short or very low ohms if not a low ohms reading then there is a fault on the ariel wires

Like This One

Behind the casing

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#3

Re: FM Sensitivity

09/26/2010 3:30 PM

Temporarily connect a known good antenna, preferably a telescopic one and experiment with the length.

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#4
In reply to #3

Re: FM Sensitivity

09/26/2010 3:34 PM

My apologies, could not delete the previous post.

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#5

Re: FM Sensitivity

09/26/2010 11:31 PM

I agree, the new radio may not just simply be as good.

People have become spoiled with perfect signal qualities, so manufacturers don't bother makinhg hot front ends anymore.

Take an old AM car radio from the 60's and it will blow away anything that is made now days.

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#6

Re: FM Sensitivity

09/27/2010 7:38 AM

Having been thru this problem recently, I offer this advice. Check the antenna cable from the antenna base all the way to the radio. i found a connection mid cable that was a winner. Classic radio plug and socket except that there was a spring on the centerpin. When the shell finally cracked, the spring just pushed them apart and the sensitivity went to pot. I thought it was the radio and put in a new one only to have the same problem. Thats when I found the problem. Now have a spare radio for the car.

New one is nice. It has HD and blue tooth as well as taking input from the IPOD.

Only used the IPOD once, but use the bluetooth frequently.

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#7

Re: FM Sensitivity

09/27/2010 11:24 AM

"The antenna appears to be in good shape, and the wiring is complete with no obvious damage and is well insulated from ground."

Although it appears good as you claimed it to be, your best bet is to do an actual measurements to verify antenna continuity and mechanical connections using an ohmmeter. You will need to verify also that your antenna's center conductor is not shorted to ground or chassis of your car! The antenna wire is supposed to be isolated and physically not touching the car's metal body.

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#8

Re: FM Sensitivity

09/28/2010 3:03 PM

Check the Blaupunkt owners manual. Maybe there's a 'local' and 'distance' setting that needs to be set correctly.

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