Comments from Tim

Added by J. Simmons over 9 years ago

Tim asked me to post these thoughts for him a couple of weeks ago. My schedule has been so crazy lately that I just got around to posting them.. Sorry about that.


A few of my own notes from our conversation on the Mach 30 hangout:

1) It would be good to separate the "electronics" portion of this project from the "antenna" portion. We already know that a RTLSDR + suitable LNA will pick up C2 radio signals and Scott's software can decode them, when connected to a suitable antenna. Even if the GroundSphere antenna turns out to be useless, the project could still have value for us - we just connect the electronics to a better antenna.

2) J. - You asked for an estimate of total # of systems we'd need to supply our kickstarter backers with, plus for our own needs (should this actually prove workable). Please use 15 units, firm, at this point.

3) J. - You asked about providing a 915 MHz tone generator. Today, I finally managed to reach Kevin Brown (AstroDev). I have a conference call w/ him in 2 hours. I am going to get status on our 3rd C2 radio which we've had on order from him since July (!!!) If that turns out to be shippable any time soon, let's use that. As a fallback, there is the BladeRF ($420) which Scott has:

Scott - would this be adequate? can you think of any alternatives? Mach 30 just needs a way to generate a 915 MHz tone for testing purposes.

4) I have a question about the Ground Sphere antenna: it's omnidirectional. Most systems use Yagis (and hence rotators) which are directional, and need to be aimed. The advantage is that the narrow antenna beam cuts out the background noise, emission, etc. as it's pointing up at the sky. How does GroundSphere do this? It seems to me that the output from an omnidirectional antenna would contain a lot of background noise (esp. at 915 MHz) , overwhelming the very faint satellite signal. We had enough problems like this when testing in Monterey, with the yagis there pointing at the horizon. How does GroundSphere address this problem? If not ... can this possibly even work at all? Can you ask Aaron?

5) Scott has some additional work to do on the DeeDeR software, probably over the Xmas timeframe, to actually decode the tweets from space (SkyCube broadcasts them without any preamble, to save power - the current s/w needs a preamble. And it needs to handle doppler.) Scott can elaborate a bit more on that.