This is how I hand-track polar-orbiting weather satellites using an old equatorial mount telescope tripod and a 1.7 GHz grid dish. This may not be the best way to do it, and other ideas are welcome!
If you're unfamiliar with HRPT reception, this is not the right place to learn about it. Head over to https://sgcderek.github.io/blog/beginner-hrpt-guide.html for that. This write-up only focuses on hand-tracking to record a baseband.
The crux of the "tracking" design is the equatorial mount. These are not cheap to buy new, it's destructive to mount a dish to it, and the mount is not used the way it's designed - but for my needs, it works! I had an old one from the early 1990s lying around, so it was convenient and essentially free. Of course, you can use another mount - but you'll need to ask for someone else's opinion on how that works since equatorial is all I know 😄.
Here is what my dish and tripod setup looks like:
The 3 axes to adjust
- Sets the max inclination of the dish
- The main axes that follows the satellite across the sky. For the most part, you're just steadily pulling along this axis to follow the satellite
- Swivels the dish around the horizon. Used to initially point the dish at the right spot on the horizon, then used to account for the arc of the satellite. On a 90 degree pass, this will not be used at all. The lower the elevation of the pass, the more this axis needs to be adjusted during the pass
All from Nooelec - even though this Gist is not sponsored
- 1.7 GHz parabolic grid dish, or a modified commercial dish like you can find instructions for here. I use Nooelec's Dish which is available on Amazon.
- An SDR. I use a NooElec SMArTee XTR which is RTL-SDR based, and has an always-on Bias-T.
- An LNA/Filter. I use the NooElec SAWbird+ GOES amilifier/filter.
- A USB extension cable to connect the SDR to the laptop. As you'll see below, I have my SAWBird and SDR connected directly to the pigtail on the dish to minimize signal loss over a coax.
- A laptop fast enough to record a baseband that may be slightly over 4GB (if recording 8-bit samples at 2.56 Msps). This does not require much processing power, but your storage write speeds need to be up-to-snuff.
- A weather satellite willing to give its data for you. NOAA-18, NOAA-19, and METEOR-M2-2 are the easiest to get.
You can get NOAA-15, MetOp-B, and MetOp-C with this hardware as well. NOAA-15 has a weak transmitter that require more precision aiming. The MetOps work better with a higher-end SDR due to their bandwidth, so I've had limited success with these birds.
- Something to predict satellite passes and show where the satellite currently is in the sky. I prefer to use a device separate from the computer recording the signal, so I use Look4Sat on an old Android phone
- Something to record the baseband on your computer. I recommend SDR++ or SatDump. SatDump will allow you to decode the pass live, but I prefer leave decoding until later.
Now that you have all your hardware and software, let's get started!
-
Use Look4Sat to find the next pass of a satellite you're interested in. In this example, it's METEOR M2-2. The most important things to take note of are:
- The start time of the pass
- The AOS (where the satellite will be at on the horizon when it rises)
- The max elevation (in degrees)
- Whether the satellite is passing to your east or west
Look4Sat gives you most of the required info on the pass list, but you may want to tap into a pass's details to see if the pass is to your East or West
-
Before the pass starts, set up your tripod so it's pointing roughly north or south, depending on where the satellite will rise
-
Point the dish straight up using axis 2 (as shown above)
-
Loosen the knob closest to where the dish is mounted (axis 1 above), and rotate the dish as shown here so the dish boom's inclination is the same as the satellite's max elevation. In this example, METEOR M2-2 will be 59 degrees up, so the dish is also pointed 59 degrees up. You can easily measure this by measuring the boom's inclination with a smartphone level app or inclinometer.
-
Rotate the tripod's main axis back down. Then, swivel the dish (axis 3 above) so the dish is pointing at the horizon where the satellite will rise. You can measure this by lining a compass up with the dish boom. I usually just use my iPhone's compass.
-
Connect the SDR to the laptop, and start recording a baseband when the satellite rises. I sweep the dish 5-10 degrees along the horizon around where the satellite should be until I see the signal, then hone in on where it's the strongest. This is in case my initial aim was a bit off.
Keep Look4Sat open on the compass view during the pass. This is indispensable to keep track of what the satellite's current elevation should be.
-
Once the signal appears, use the counterweight of the equatorial mount as a handle to rotate the dish along the tripod's main axis (axis 2 above). This will follow the satellite across the sky - of course, the speed is up to you! You may also need to adjust the dish slightly on axis 3 during the pass on lower elevation passes.
-
Once the signal disappears over the horizon (or, in my case, behind the many houses around me), stop recording and pack up your setup.
-
Decode the baseband. SatDump and LearnHRPT can both do this, so play around with what works best for you. Here is the image I got on this example pass. I lost the satellite for a few lines shortly after the satellite peaked. Looks like I have some more practice to do!
- The most important thing to watch is the signal strength, followed by the Look4Sat's current predicted location. Look4Sat does a great job of telling you where it thinks the satellite's at on its path, but the signal strength should guide your hand more than anything.
- Satellites move slower when they're closer to the horizon, and faster when overhead. This means the dish will need to be moved slowly at first, then speed up as the bird reaches its max elevation, then slowed down again as the satellite sets. This makes 90 degree elevation passes harder to "keep up" with when overhead since the max elevation is higher.
- Every so often, "wiggle" the dish a degree or two on both axes to make sure you're pointed as close to the satellite as you can be. This will result in a slight "bounce" in your SNR when decoding, but I'd rather that than realize I only received the signal at half strength the entire pass!