[hpsdr] mercury/diversity19 - calibration/readings

[Georg Prinz]

Hallo Joe, Phil,

thanks for explanation. Checking the circuit drawing it was clear that 
no preamp is available. The LTC6400 is a driver for ADC, only.

What I was astonished, is the discrepancy between RX1 Meter reading 
(Signal) and Panadapter. Therefore I made following measurements:

Program: diversity19
Settings: Panadapter: AVG
Preamp: on
Mercury2: input signal
Mercury1: 50 Ohm load
Frequency: 10,14 MHz
Demod: AM
Filter: 4 KHz

Calibration at: 10,14 MHz and level -140dBm

Signal Source     RX1     Pan        all in dBm
====================================

         -140            -141      143,0
        -120             -135     -123,0
        -100             -117     -103,8
       -   80             -  97      -  84,3
       -   60             -  77      -   63,7
        - 40              -  57      -   44,2
        - 20              -  37      -   23,7
        - 12              -  29      -  15             Overload on (with 
pream on is ok)
            0               -  27     -  13,6         0dBm input checked 
with HP 435B

Calibration at: 10,12 MHz and level -70dBm

       -140            -124        -140            noisefloor at -143dBm
       -120           -118         -120
       -100           -100        -100
        -80              -80          -80
        -60              -60          -60
        -40              -40          -40
        -20             -20           -20
       +10             +10          +10           preamp off ADC overload

1. The discrepancy is obvious, if calibrated at a different level!
2. According to the performance data the ADC overload shoud be at +8dBm 
with preamp off. So that is ok, too.
3. 0 dBm is ok.
4. At -120dBm nonlieanrity starts.

As a result, you should follow the proposed calibration parameters.

Vy 73, Georg - dl2kp