[R-390] Doubts about R-390A sensitivity

[Ing. Giovanni Becattini]

Hi Friends,

I believe that this is a theme already afforded, but I could not find a precise answer, so I ask kindly if someone would help to cure my ignorance.

The manual NAVSHIPS 0967-063-2010 (4. 3.1 Procedure Q1- Measure Receiver Sensitivity) states: “Connect the RF OUTPUT jack of Signal Generator AN/URM-25 to receiver ANTENNA UNBALANCED jack J103”.

This doesn't seem correct to me, as I believe that in this way the signal generator and receiver’s impedances don't match. To confirm this, the TM 11-856A manual (94. Over-all Receiver Gain Test) states that the DA-121/U dummy load must be used for the connection from the signal generator to the R-390A antenna when you check the overall gain.

According to my measurements, the difference between using it and not using it is not small: more than 10 dBm, as I could expect. 

Using the DA-121/U at 7,500 kHz, I measured for my R-390A a sensitivity of -100 dBm (2.1 µV) for 10 dB S/S+N ratio. 

It is compliant with the official specification, but I read that it should be much better.

Thanks

Gianni