Using the SDR-IQ and continuum mode to measure Sun/cold sky ratio

(Or how to gain 2dB of Sun noise without even trying)

Since I started EME I have always wondered why I never got close to the sun/cold sky results with my system compared to VK3UM's predictions with EME calc?

I use an SDR-IQ and Spectravue in continuum mode on the 8.25MHz 190kHz wide IF of my K3.

 

 

In the last hour or so I have been playing with the SDR-IQ IF and RF gain settings to try and minimise some spikes that are picked up at IF from my DRIACS controller when it's doing PWM.

I normally have the IF gain set at +24 and the RF gain of the SDR-IQ at +10. i.e flat out!

Have you guessed what's coming next?

Sun/cold sky at 6cm from VK3UM  =  10dB

Sun/cold sky at 6cm with original high gain settings = 6.5dB

Drop the RF gain to -10dB and IF gain to 0dB and

Sun/cold sky at 6cm with new settings = 8.5dB!

Clearly overloading the ADC in the SDR-IQ all these years! D'oh!!

It also might explain why I never really ever got a sharp peak in Sun/sky when I adjust my feed positions. I'll confirm that tomorrow!

You live and learn!