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Raspberry Pi TNC ISS iGate
radio : by Tommy - April 8th 2014, 02:04PM
Not so long ago I completed construction of my Raspberry Pi TNC, the TNCPi. Construction of this kit was very straight forward. A few additional pictures would have made this a great kit for beginners, but still the same it's an easy build.

Building Tips
A couple of items to note regarding construction. Ensure the correct polarity of the electrolytic capacitor (C1): The negative stripe goes toward C15.
The transistor (Q1) PN2222's flat side goes away from the edge of the board.
The voltage regulator (U1) MCP1700's flat edge goes toward the edge of the board.
Crystal X2 (20MHz) is near U1. Crystal X1 (3.57MHz) is neat Q1.
Note the pin 1 position of all ICs.

Interface cable
After completing assembly of the TNC, I set to work on creating a radio interface cable to connect to the DB9 port on the TNCpi.

The pinout for the TNC Pi matches the TinyTrak cabling:
Pin 1TX Audio
Pin 3PTT
Pin 5RX Audio
Pin 6Ground

Tuning Audio Output
After creating the cable, I set the audio output level as noted in the instructions. To do this, you'll need two radios. I used 2 HTs, one that I had created the interface cable for and a spare. Tune the radios to the same frequency (I used 144.44). On the radio with the interface cable, I pressed the PTT button and heard a tone being transmitted to the neighboring radio. Adjust R7 to it's maximum volume before it begins to distort.

After tuning the audio, the TNC Pi project is complete. How you plan to implement the TNC Pi is entirely up to the software you choose. For many, this may be Xastir for an APRS GUI. For others, it may be aprx to create an APRS beacon, iGate, digipeater or any combination of the three.

tags: raspi aprs ariss iss tnc raspberrypi

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HOWTO: ISS Viewing
outdoors : by Tommy - October 5th 2011, 09:08PM
The fact that there's a space station orbiting above the globe right now has become somewhat passe in pop culture. Not many people are truly wowed at the news of it. Within seconds, a few clicks of a mouse will take you to hundreds of pictures and videos of the International Space Station; but did you know you can see the space station yourself? No binoculars or telescopes needed! I figured I would write up a HOWTO for the uninitiated. It isn't hard, it just takes a little know how.

For starters, you need to know a few terms used when talking about satellites (the ISS is a satellite of the planet Earth).

The first term when dealing with satellites is azimuth. Azimuth is a technical term that means the same thing as heading, bearing or direction. Most people are comfortable with the cardinal directions North, South, East and West. The cardinal directions are fine for general directions, but to know exactly where something is we need to be more specific. When dealing with an azimuth, a number of degrees is stated. 0 is North, 90 is East, 180 is South, 270 is West, and on around to North again. Kinda get the picture? It's a full circle divided into 360 degrees. (Also note, there's technically no such thing as 360 when dealing with Azimuth, because 360 would be the same as North, but that's already 0.)

It's not entirely what you think. Sure altitude means height, but we're not talking in feet or meters here. Remember, we're dealing with observational angles here, so knowing how high something is is of little consequence to us. Altitude in astronomy means "angle above the horizon". Altitude is expressed in degrees, just like azimuth. 0 is at the horizon, 90 is straight up. 45, you guessed it, is right in the middle.

Continue reading...

tags: iss space astronomy satellite howto

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