Omnidirectional Station How To

This How-To is written to get you quickly receiving satellite data with an Omnidirectional antenna (an antenna that does not move).

Prerequisites/Background

I'm assuming that you are a bit familiar with amateur radio, or linux in general, or you already have a Raspberry Pi.

Expectation Management

First off, I'd like to set some expectations around a SatNOGs station with an omnidirectional antenna. Yes, you will be able to hear satellites, Morse code beacons, maybe even some voice contacts on a FM transponder. But for CubeSats with 1 watt transmitters at 9600 baud, it's going to be really difficult to actually decode any data with an omni antenna. You'll definitely see squiggly lines on the waterfall plot, but demodulating the signal and extracting satellite telemetry is going to be pretty difficult.

The only way to get more signal is a better antenna. A better preamp will not help, see LNA section below.

Hardware Required

This is a list of the hardware for indoor/testing purposes:

Raspberry Pi
- Power supply + cable (see note below)
- Up to 16 GB Micro SD card
- Ethernet cable
RTL SDR Blog v3 dongle
Various short lengths of coax
Preamp/LNA - Or not if your coax is short, see LNA section below
Omnidirectional antenna - just a dual mag-mount on a cookie sheet will work OK for stronger satellites

For permanent mast-mounted installation, I would recommend adding:

PoE splitter
PoE injector
Large mast-mounted waterproof case
Waterproof cord grips, both to keep out the rain but also spiders
Desiccant
Mastic tape for weatherproofing antenna connectors
Better omnidirectional antenna

Setting up the Raspberry Pi

I chose the Raspberry Pi 3 Model B for my station. There is a Model B+ on the market right now, with a faster processor. But it takes a lot more power and apparently the Ethernet port is a USB device, which is causes some problems, according to the forums. Both are the same price, the procedures are the same.

Downloading/Writing the SD image

The SatNOGs team has done a great job creating a Raspbian image with all the required software. Simply navigate over to the latest tag on Gitlab, and click on the "Zipped image" link under the latest tag. It's about 650 MBytes.

For linux:

Unzip the downloaded file: unzip image_2018-08-03-Raspbian-SatNOGS-lite.zip
Figure out which device is the SD card. SD cards are usually start with mmcblk. sudo lsblk
Write the image. This will take a while. Make sure you don't overwrite your host OS: sudo dd if=2018-08-03-Raspbian-SatNOGS-lite.img of=/dev/mmcblk0

Power notes

Thinking I could save a few bucks, I used a no-name generic 2.4 amp "tablet" USB power supply I got as a freebie, and a micro-USB cable I use for charging my phone. What a mistake! The Micro-USB cable wire gauge was too small, so there was too much voltage drop on the cable, so the Raspberry Pi reported power problems every time it was doing anything.

Power problems are indicated by either on the monitor in the upper right (lightning bolt appears), or the red power LED flashes on the board itself. If The Raspberry Pi is pretty forgiving of power droops because it runs at 3.3 volts. But the 5v USB ports are directly tied to input power, so undervoltage conditions will cause problems for USB devices, such as the RTL SDR dongle.

Software Configuration

Creating a SatNOGs Network account

There are several different accounts you will want to make. (Why aren't they all linked??)

Required: Network: for registering your station and adding data to the network.
Recommended: Forums: for asking questions.
Optional: Database: Only if you want to add satellites/modes. Not necessary for receiving satellite data.

Booting and Configuring Raspbian

After you have the image burned onto a Micro-SD card, boot it! I would recommend hooking up a keyboard and HDMI monitor, you can watch the boot process. If it doesn't boot at all, double check that you wrote the SatNOGs Raspbian image correctly.

After a successful boot, log in with username pi and password raspbian:

Change your password! passwd
Update and upgrade raspbian strech: sudo apt update then sudo apt upgrade
You'll probably update a lot of packages and get a new kernel, so reboot after this: sudo reboot
Run sudo raspi-config to set up the base OS. Tab switches between the options and select.
1. 4 Localisation Options: I1 Change Locale: en_US.UTF-8 UTF-8
2. 4 Localisation Options: I2 Change Timezone: None of the above: UTC
3. 4 Localisation Options: I3 Change Keyboard Layout:
4. 7 Advanced Options: A1 Expand Filesystem
  This will expand the ~2GB Micro-SD card partition to fill the entire SD card.

The Raspberry Pi needs to reboot to expand the filesystem, so do this now. It might take a while. 'sudo reboot

Disabling WiFi and Bluetooth

To disable WiFi and Bluetooth, edit the /boot/config.txt file, and add the following lines at the bottom:

# Disable WiFi and bluetooth
dtoverlay=pi3-disable-wifi
dtoverlay=pi3-disable-bt

Then reboot again. To make sure that it worked, run ifconfig and make sure that wlan0 isn't listed. I'm not sure how to tell if bluetooth is turned off.

Additional software

I like to install this additional software with sudo apt install package

bmon - a graphical network usage analyzer.
vnstat - keeps track of your bandwidth usage
vim - the world's best text editor ;)
irssi - a terminal IRC client, for chatting on the #satnogs IRC channel

If you can't tell by now, I'm always a big fan of rebooting. It certainly doesn't take that long... sudo reboot

Configuring the satnogs-client

Once you have the base Raspbian Strech OS installed, updated, and looking good, you can configure SatNOGs.