presumably the digital 1 kHz-to-baseband conversion is done in an FPGA or DSP in realtime. The associated periodic processing activity or register content could lead to a 1 kHz component radiated by the FPGA itself or it's DC power lines. This could then leak into the analog audio input to the ADC. Try sniffing around the FPGA with a capacitive or inductive probe.

 

Downconverting from a soundcard on a PC in software usually does not suffer from such coherent leakage, as there are variable delays due to buffering and multitasking which effectively remove the periodicity in the CPU activity.  

 

Best 73,

Markus

 

-----Ursprüngliche Mitteilung-----
Von: Andy Talbot <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: Do, 10 Dez 2015 11:23 am
Betreff: Re: LF: LF EbNaut test from JN80 on 137370

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