Saturday, 16 December 2017

AM Bandstop evaluation

I had my first opportunity today to assess the AM Bandstop, which should reduce the strength of signals on the Medium Wave band and hopefully clean up the receiver.

378-1880 kHz - 3 dB attenuation

526-1710 kHz - 9 dB attenuation

KiwiSDR1 on the left, KiwiSDR2 with AM bandstop on the right.

Unfortunately, the addition of the bandstop was not enough to stop ADC overload on the KiwiSDR when the attenuator was removed. As this was the primary purpose of its procurement its continued retention in circuit will have to be justified by improvements in other areas, which will require further observations.

Other strong signals outside of the Medium Wave band could be the cause of the ADC overload or it could be because of the aggregate strength of all the signals being fed in from the loop across the LF/MF/HF range.

Reducing the circumference of the loop would give the KiwiSDR an easier time, however this would affect the Red Pitayas which can tolerate larger signal inputs. A compromise is therefore needed.

Further observations were made in the early morning of Sunday 17th December. A snapshot taken at 0610z of the 80m band shows a real improvement with the bandstop fitted. The improvement is so marked that continued retention of the AM bandstop is justified.

KiwSDR1 on the left, KiwiSDR2 with AM bandstop on the right.

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