[hpsdr] Mercury and 28 MHz receive

[h-hartfuss at t-online.de]

Hi Phil,

similar observations here:
Mercury with Alex_RX in front and 50 Ohm, ATT = 0 
(calibrated at 14 MHz: S9 = -73 dBm).
Noise power density less than -145 dBm/bin over the whole band 28 - 30
MHz, no ripple, nice baseline. S-Meter gives -126 dBm within 2.7 kHz.

Two birdies half an S-unit above S1 = -121 dBm found: 

at 28.416 MHz :  -119 dBm
at 28.320 MHz :  -118 dBm

A few others are present, however, just visible, close to the noise
level,
clearly below S1.

The difference between the two frequencies is 96 kHz which is the
sample rate. All other birdies appear at 96 kHz difference.
Switching to 192 kHz SR generates birdies with 192 kHz difference
frequency. Again the strongest is at 28.416 MHz.  
All others are as before much weaker, below S1.

73, Hans, DL2MDQ.