[hpsdr] New Hermes 2M Board

[Helmut]

Hi Larry,

I agree with you in a lot points, but would like to correct two items:

1. 16 Bit, 130 Msps ADCs are more than sufficient for ham radio applications
and beat most analogue radios. The typical 100 dB dynamic range refer to the
entire Nyquist zone. You have to add the process gain for narrow
band/channel operation. Cellular systems- in particular the new 5G- operate
at frequencies from 0.8 to 39 GHz and they all need an analogue up/down
conversion into the 'digital' baseband. This architecture limits the dynamic
range, not the 16 Bit ADC at the IF.
2. Don't mix frequency stability over some hours with jitter. HPSDR sampling
oscillators are VCXOs and PLL-disciplined from a central 10 MHz reference.
Every designer knows that too much jitter of the sampling oscillator will
reduce the dynamic range of the ADC performance. A typical phase noise of
-152 dBc/Hz at 10 kHz offset is fine. Long before Mr. Sherwood and others
recognized this fact, Walt Kester of Analog Devices pointed to the jitter
influence in his tutorials.

73, Helmut, DC6NY