Image frequencies around 520 AM on some KiwiSDR's

[Ray Lalleu]

on 522 on KiwiSDR in Gerwisch
on 519.4 on KiwiSDR in Weston
(see European MW Pirate forum)

[Ray Lalleu]

New test on Weston SDR, midday on 26th of May :

image on 519.428 with BBC Radio 5 audio
strong BBC 5 signals are on 693.000.0 and on 909.000.0
so not a direct intermodulation

by comparison, on the Wessex SDR not far away, there is only a very faint carrier on 519.43 approx (too weak for AM sync mode), with even stronger BBC R5 on the 'low VHF' SDR (Kiwi clone)

guessing that those images are generated in the ADC or later stages, with some internal frequency mecanism (not very disturbing if limited to 520 kHz, except for maritime DXers, and for false reports on Internet forums), but maybe there are other images elsewhere

[ZL/KF6VO]

Sorry, I don't check this forum very often.

This is actually a software/firmware bug. I have a solution simulated in software that works. But the actual fix needs to go into the FPGA. And so far I have been unable to get that working. And I don't understand why. So I don't know when this problem might be resolved.

Regards,
John, ZL/KF6VO
KiwiSDR