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!

24GHz anomalous propagation

Since 1114 UTC today, and despite no visible trace whatsoever on the WSJT-X waterfall display I've been getting continuous, averaged decodes from GB3PKT's 24GHz JT4G signal via "Drizzle scatter" :-)

This is over a 77km, totally obstructed path from Sea level here on the Fen Edge to Sea level at Clacton over the "Essex/Suffolk Alps". Signals vary from -19 to -21dB.

So much for the "experts" who that say that 24GHz is a water absorption band and only works when the atmosphere is dry.

I'm now monitoring the beacon 24/7 using a Raspberry pi running WSJT-X and a Funcube Dongle behind my transverter and it's popping up all sorts of interesting propagation. Followers of my Twitter feed @g4bao will have read my reports of "late night, after a hot day" propagation last week.

We need more home stations on the band (or portables prepared to get wet!) to experiment with these modes and make some digimode QSOs on this seriously under-used and underestimated band.

In a recent "GHz bands" I reported that G8ACE and G4LDR have shown that this type of drizzle Scatter/ Cloud scatter propagation (call it what you will) even works on 47GHz with decent eqiupment.         

You miss SO much by only coming on during contests and activity periods and working the "usual suspects" over the usual line of site paths. Do the sums as to how the probability of anomalous conditions falls when you operate on the fixed days determined by the contest committees! Anyway in these days of "No Tropo" it's something to keep you interested!

Here ends my appeal for more experimentation than competition!