Monthly Archives: July 2013

End of the Summer, But Not The End

We’ve finished our ten weeks for the summer, and the balloon still hasn’t been launched. That doesn’t mean we’re won’t launch, however. We’re extremely close to being ready!

Our payload currently reads the GPS, temperature, pressure, and humidity from the appropriate sensors, converts that data into an APRS sentence, converts that sentence into an AFSK that is fed into our SRB MX-145 which then generates our signal. This signal is radiated by our quadrifilar helix antenna. With a basic dipole for the 2 meter band, we’re able to receive and decode our signal with a 2-meter transceiver and our computer’s sound card. That means it works!

Unfortunately, there are still problems. We tried decoding our signal with a different computer, and it didn’t work. Thanks to some help from Bill N3DOU and the Physics Department, we’ve determined that our audio signal is too strong. We worked on attenuating it, but ran out of time.

Don’t worry, though – the balloon will still go up! We’ll figure it out when we reconvene at the start of the school year. Even if we did get that last bug smoothed out, we would have postponed the launch until the start of the school year anyway, so that everyone who wants to see it can schedule for it.

Getting our SWR Down!

First, a huge shout out to N3DOU, Bill Clark, for the use of his incredible expertise and the amazing magic box the MFJ 269 RF Analyzer. With this we were able to see that our QFH antenna was resonant at a lower frequency than we needed by about 3MHz which amounts to about 2 inches in wavelength and each of our segments was roughly a wavelength. With a quick rearrange to our antenna, we had our SWR down from several hundred to 1.4. With a few snips we were down to 1.2. And with one last tiny nibble, we were down to 1.0! The image shows the first two snips and the little particle on the right is our final snip! So we are now good to go with this antenna! The image below has 4 blocks per inch and so you can see our last snip is less than a quarter inch.


Hack HD Full Battery test. Taking 3 AA Energizer “Pile Alkaline” batteries at full charge, we pushed them into the HackHD and hit continuous record.
The recording lasted 29min 32seconds of mostly static images (it was pointed up and the only thing changing was a corner of my computer screen). The audio was dynamic. The file size is 2.7GB which ranks in at about 1GB per 10 minutes. This is as we expected.

At the start, the batteries had 1.55V each and at the end 1.405V each. The HackHDs will power up at this point (since the batteries are still quite usable), but only for 30s-60s of video and then they’ll save the video and power down. This is a great feature to save your current video when power gets low but from what I can tell, there should still be enough voltage to push on. This is going to be a serious problem! I’ve some ideas and I’ve contacted HackHD to figure out how the power curves affect when the shutoff will occurr.

In other news, we’re now on APRS. You can check and search for my call KC3AWU to see us working hard here in the Toll Science Building at Washington College.

Lastly, we’re building antennas! Our QFH had some serious SWF but we’re working on that and a whip antenna! More news (by others) on that progress coming soon hopefully.

A Change in Cameras

We bought some hackhd cameras but are having some problems with them currently and working with the manufacturer and vendor. Because of our time crunch, we’re probably going to ditch our effort on there. So, this is where we’re going. A stand alone video camera. We just hit record at launch time.

1) Enough battery life to record for a solid 4 hours – although 6 hours preferred.
2) As lightweight as possible as the payload has weight restrictions
3) If it uses AA’s that’s best because we have AA’s that are safe at that altitude (other batteries might work, but we’d have to research)

Preferences – although these aren’t game breaking:
1) HD !
2) Wide angle if at all possible, but not required.

Downfalls or Detriments
1) Temperature   — The camera is going really high. Most camera’s aren’t rated for full exposure to space. We’re not actually fully exposing this thing to space, but the temps will still be lower than usual. So, normal batteries may not cut it and will probably fail at full altitude. The camera itself (being electronic) might fail as well. Lowest temps we expect are -40 C.
2) Payload Loss – We’re tracking this thing with radio and GPS. However, we might lose it or it might get wrecked on landing. We’re using a parachute so this shouldn’t happen, but it could.