GOES 17 Project Update

Having now received most of the items needed, missing the SAWbird (Low Noise Amplifier (LNA) plus a band pass filter) and an adaptor (I’ve one I’m using elsewhere which I can borrow), I’ve been having my first attempts to pick up signals from GOES 17.

Part of the fun of getting things set up is that you need to get the positioning pretty accurate, to within about a degree for bearing and elevation. So I determined the target angles:

• Magnetic bearing – 38 degrees
• Elevation – 22.5 degrees

I’d mounted the antenna on a temporary mount, which is a pedestal fan mount which isn’t being used at the moment since it is winter here in New Zealand, I just pointed it in roughly the right direction and had a look at the signal.

With a lot of luck, I’d got it pointing at the satellite and you can see a very definite signal being picked up. So thinking this seemed to be a bit easier than expected I tried to get it a bit better and spent most of the next half hour trying to get anything like what I’d captured.

Even when I got something which showed a distinct signal with a good waterfall (the pattern below), keeping it locked in position was far from simple as keeping the mounting slack enough to move around was conflicting with getting it tightened up without moving it.

I then spent the next hour or two trying hard to improve on this, but without anything better for more than a few minutes. When connecting the signal to the Raspberry Pi decoder software every time it resulted in there being no signal detected.

So thinking about the problem, what is making it hard to detect a good signal is the SNR (Signal to Noise Ratio) which is effectively how strong is the signal compared to the background noise. A value of around 6dB isn’t enough with most guides showing you need about twice this value.

But then it was a good start in aiming a dish at a satellite which is over 30,000Km away.

Another thought also hit me in that what can be a problem in picking up weak signals is anything strong nearby (relative to the distance to the satellite) and I remembered that the Auckland Sky Tower is about 30Km away and it broadcasts multiple FM radio signals with over 50KW of power per signal. So I tried tuning the SDR to the FM band and within a few seconds I was listening to the Queen song “Hammer to Fall”. It wasn’t perfect audio, but pretty good and the SNR was more than double what I could pick up from GOES 17.

So now I’m waiting for the SAWbird to arrive to make a significant difference. But of course I’ll give it a go today which is sunny, a far cry from Saturday which had constant showers. That isn’t a good mixture for using computers and electronics with no weather proofing.