RSP1A not calibrated below 1 MHz, 37 db wrong at 1 kHz

[bb1]

SDRplay claims that RSP1A is calibrated and shows correct signal amplitude measured in dBm.
They also claim valid frequency range for RSP1A to be from 1 kHz to 2 GHz.

I applied -30 dBm CW signals of different frequencies from DG1022z to the input of RSP1A.

At 10 MHz the screenshot SDRuno_10MHz_-30 dbm_dec1.png of SDRuno indeed shows signal level of -30 dBm and SNR ratio of about 80 db.
When the frequency is decreased, SDRuno still shows correct signal level down to 1 MHz.

However, below 1 MHz the signal level shown by SRDuno starts to decrease. At 100 kHz it becomes about -38 dBm, at 10 kHz -41 dBm.
At the lowest end of the frequency range claimed by SDRplay, 1kHz, the signal level shown by SDRuno is very low 67 dBm, as can be seen on the attached sdrUno_1kHz_-30dbm_dec32.png.
The SNR is also decreased to 60 db.

SDRplay support admitted absence of calibration below 1 MHz, while SDRuno does use lower frequency ranges Broadcast LW and part of MW, and Ham Lower 2200 and 630.

[ejeffrey]

I would normally expect "not calibrated" to mean that the signal can have an error of a couple dB.  37 dB too low isn't a missing calibration, it sounds more like an AC coupled signal path with a significantly higher cutoff frequency.