I'm in need of some advice on the repair of a receiver fault where it appears to be a little deaf, in an odd way.
The receiver in question has a mute threshold of 0.25uV (or -125dBm) where a pretty noisy signal results, and 20dB quieting is achieved at 0.35uV (or -122dBm). That's only about 3dB variation between a very noisy just-able-to-open-the-mute signal and one that is essentially noise free.
Compared to a 'good' receiver in the same model of radio, a mute threshold of 0.11uV (-132dBm) and 20dB quieting at 0.28uV (-124dBm) is measured; that's an 8dB spread between a noisy just-able-to-open-the-mute signal to a noise free one, which is much more like normal.
So in the problem radio, the 20dBq sensitivity is OK, perhaps just a little bit down, but below that the signal drops off extremely rapidly. I've replaced the front end preamp active device and the first mixer active device, neither made much more than 1dB of improvement. The 1st & 2nd Local Oscillators look & sound pretty clean on the test bench.
Would I be correct in assuming symptoms like this is typical of an IF fault? Or could it still be something in the front end eg: faulty bypass caps etc?
The receiver in question has a mute threshold of 0.25uV (or -125dBm) where a pretty noisy signal results, and 20dB quieting is achieved at 0.35uV (or -122dBm). That's only about 3dB variation between a very noisy just-able-to-open-the-mute signal and one that is essentially noise free.
Compared to a 'good' receiver in the same model of radio, a mute threshold of 0.11uV (-132dBm) and 20dB quieting at 0.28uV (-124dBm) is measured; that's an 8dB spread between a noisy just-able-to-open-the-mute signal to a noise free one, which is much more like normal.
So in the problem radio, the 20dBq sensitivity is OK, perhaps just a little bit down, but below that the signal drops off extremely rapidly. I've replaced the front end preamp active device and the first mixer active device, neither made much more than 1dB of improvement. The 1st & 2nd Local Oscillators look & sound pretty clean on the test bench.
Would I be correct in assuming symptoms like this is typical of an IF fault? Or could it still be something in the front end eg: faulty bypass caps etc?