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Old 07-02-2011, 7:22 PM
Join Date: Jul 2011
Posts: 7
Default Noise Floor.

I have a Truetone CY1 4834A-87 40 Channel CB made in NOV 1976.
I have a signal generator. When I apply a rf signal into the radio,the noise floor level changes, when I touch my hand to the chassis of the generator.
It goes down when I touch it and comes up again when I let go.

I replaced a broken cap from shield around rf output to chassis ground. That seemed to work for a little while but it seems to do same thing now when I touch generator.
I tested other radios with same generator and they do not experience this.

If anyone knows anything about this please let me know.

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Old 07-05-2011, 6:48 PM
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i'm not quite as experienced in this as many others probably are. but i would start by changing all of the caps that go to ground. if that radio was made back in '76 then you could probably bet that all of the caps have probably dried out.
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Old 07-06-2011, 3:33 PM
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What signal generator? The cheapies with uncalibrated attenuators? Totally shielded cables, preferably double tight shields too?

The noise floor reduces with signal due to AGC action in the receiver. The noise floor reduces when you touch the case of the signal generator due to you picking up signal leakage from the generator and inducing it into the receiver adding to the signal.
Cheers - Martin ZL2MC - Palmerston North
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