Category: Ham Radio

How to make a weather station really work.

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So I got all the pieces together since my last post about weather satellite images. The hardware update is I got a very nice antenna:

Click the photo to see on Amazon.com

That alone improved reception, by eliminating a lot of noise. Also added an LNA:

Click the photo to see on Amazon.com

That’s placed right at the feed point of the antenna, it amplifies the raw signal, filters it for just the 137mhz band, and amplifies it again. (note, if you intend it for all weather operation, you’ll have to do something to weatherize this unit)

Those two things gave me the most clear satellite images I’ve gotten yet, and more importantly, it pulls the signal in from lower satellite elevations, so I get more of the pass, meaning I get more of an image in the north/south direction. You can see with this photo, I get almost from the arctic down to a good chunk of Florida on a good pass:

Now it was time to make this work in the garden for real. So I have a back corner garden, it has the biggest view of the sky in my yard, and gets a good amount of sun for the solar panel… So I’ve had a setup of a 25 watt solar panel, a 21 amp hour gel battery, and a charge controller that I’ve used to put other experiments out in the garden… however those experiments were done with a small circuit board with a relatively cheap ESP32 on it… That draws maybe 400ma… and I was able to run that experiment (A magnetic field logger) pretty far into the winter before it quit.

Now the the Raspberry PI 4 can draw up to 3 amps, which is significantly more than the panel/battery combo was designed for… but I gave it a try. I had it attached in such a way that the charge controller would cut power to the PI if the battery dropped below 10.5 volts — to save the battery… It’s a deep cycle battery, but it should not be drawn down to zero.

For waterproofing… the battery and charge controller are in a plastic battery box that has 2 downward facing vents on it. But there’s a problem… on a night when the dew is strong, it gets moisture condensing in the box… this is not good. It really needs a fan for airflow.. but I’m not sure if I can afford the power…

So since I don’t want my pie to get damp, I bought a waterproof electrical box… put the PI and the SDR radio in it and all looked happy. Then a sunny day came, and wow great for the solar panel, but not so great that the waterproof box has no where to dissipate heat… running compute intensive stuff with the radio and LNA running caused the PI to detect an overheat situation. Also at the same time it drained the battery down and the charge controller shut the whole show down…

So I tried again… Now I have a task that runs once a minute on the PI. it uses “vcgencmd” to get the throttle state of the PI… if it detects a persistent under-voltage, or over heat it kills all the satellite tasks and hopes for things to cool down before the next pass.

Ok so another very hot day came along, and at least the task shutdown worked, and the pi began to cool off. But not fast enough for me… So I moved the whole thing into the battery box again, and now the task is…figure out how to get heat out of a sealed plastic box.

I’ve done calculations and the panel should be able to more than keep up with the PI, meaning it should result in a net charging up of the battery… The problem is.. when a processor runs hot it draws more current than normal. And it’s probably why when the first heat situation hit, and was runaway, it drained the battery down below the threshold.

One more thing… I have an RTL_SDR dongle… if you turn the bias tee on to power the LNA.. well it stays on even when you’re not using the radio.. It stays on until you explicitly turn it off… That never happens in Raspberry-NOAA-V2.. so I inserted a command to shut the bias tee down between passes. This saves 300ma which is significant.

So now also on order is a “Witty PI” — which is a daughter board you attach to the PI.. it does nifty power management, like,, shut the pi down on low voltage, hight temperature, and or on a schedule… That’s exactly what I need… I can ditch the charge controller low voltage system and use the Witty PI’s version… if voltage goes to low it will do a graceful shutdown of the pi, and wait till voltage charges back up again, if the temp goes too high, it will do the same,… and for extra power saving, I can shut the pi down on a schedule, since the satellites have a consistent morning and evening schedule…there’s a good 8 hours of no passes, that I can basically shut down and draw zero power during.

By the way.. the pi itself has no real way to shut down and come back on again on it’s own because it has no real time clock. also when you halt a PI 4, it still consumes 300ma on it’s own just to sit and do nothing. The Witty PI will bring that down to an absolute zero for the pi because it controls the PI power source. The Witty PI itself draws less than 10ma when idle.

More about weather sat reception

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The whole image covered the entire east coast USA. I cropped the usable piece out. The raw image looks like white clouds on a gray background. Processing software inserts land and water coloration and state borders and precipitation probability.

Ok, Here is more info about receiving weather satellite images…

What you need (for NOAA APT and Meteor LRPT sats):
1. a radio that can receive in the area of 137 to 138 MHZ
2. a suitable antenna, tuned for that band
3. some way to capture the audio
4. some software that converts the captured audio to an image.

Oh and you’ll need to somehow get satellite tracking information

But in my case specifically I’ve gotten and done this:
1. got an RTL-SDR Blog V3 sdr radio (already had one for short wave listening). This is a USB device, you hook an antenna to it, and hook it to a usb port, you can use the suite of software in the rtl_sdr linux package to do basic radio listenning
2. Well I’ve been in the antenna hacking stage, right now I have it hooked up to a dipole antenna of mine that just happens to have low SWR in the area of 137.5MHZ. But ever hating fussing with antenna construction, I ordered what’s called a V-Dipole built just for NOAA weather sat reception. So a V-Dipole is just a dipole but the two elements in this case are set at an angle of 120 degrees to each other, rather than having them in a straight line. By doing this it basically get omnidirectional reception and also reception from UP, where the sats are. The actual antenna to use for this is a helical antenna built for the weather sat band, Unfortunately I cant’t find clear instructions online to build, and I see no one selling one, I did see at a legit ham radio store site, that you could pay $300 for a built one for another band. Uhm… No.
3. and 4. To capture the audio and process it I am using Raspberry-NOAA-V2, findable on Github. basically you devote a raspberry pi 2 or greater to have a fresh OS install, and install that software, It does the full job of tracking sats, and listening at the right time, and converts the audio to sat images with various “enhancements”.

NOAA sats, NOAA 15, 18 and 19, are in a polar orbit, sun synchronous , meaning they fly pole to pole, with a period of about 90 minutes, and they keep themselves aligned with the sun, so that their images always have the same lighting on the day side. They don’t have a normal camera in them, they have more or less a single line Earth scanner in them… so as they fly they are scanning a line of the earth perpendicular to their path, and they put out about 2 scan lines a second. The signal is analog, AM modulated on a 2400hz carrier, the whole shebang is FM modulated somewhere in the 137mhz band, a different channel for each sat. The Meteor sat is a Russian sat that uses a digital encoding, but it’s the same basic scanning idea, just a different scan line encoding.

You don’t really need to know all that, you use software to decode the signals, and generally you can expect NOAA images to be like old time TV, sometimes a clear signal, sometimes snowy. And the Meteor, being digital, will be clear, but with black lines where the decoder failed to hear a decent signal.

Well, Raspberry NOAA V2 (RN2), is a great package that just handles everything for you to track, record and decode the 3 NOAA sats and a Meteor sat. I’m running mine on a headless RPi 4, with minimal OS (no GUI). RN2 runs a web server on the pi so you can check schedules and look at captured images.

Well we have to talk about the Meteor M2 saga.. It seems that Meteor M2, was giving great results — looking back at other people’s posts and videos about it, but it has failed… and it’s replacement ? Failed. So now we’re up to the newly launched Meteor N2-3. Support for that sat in RN2 is in beta development. I took a peek at that code, and found that, yes, once it is released I can expect amazing sat photographs from it.

And we should talk about the realities of antennas and Raspberry PIs….

I have played with radios since I was in grade school. Always putting a lot of energy into the question — why is my reception so bad? I have played with antennas and long ago came to the conclusion that they are magic, and a kind of magic I can’t grasp. Sure there are formulas, and calculators, and simulators all for designing the perfect antenna, but when it comes down to it, you never have the perfect antenna, and you never have the perfect antenna installation.

So these few days have been spent fussing with antennas. And as I said.. I ordered one, and hope it does it’s magic, but in the mean time, this above is the best image I got so far, and it was done with a hacked together v-dipole from an old TV rabbit ears, at ground level (Some say go as high as possible, some say no.. it needs to be between .4 and .6 meters off the ground.)

Mind you… as far as antennas and SDR and RPi’s go… the PI itself is a noise source. USB is a noise source… so I have two chokes on the USB cable to the SDR dongle, I have a choke on the power going in to the PI, and I have everything stretched out so the SDR dongle is as far from the PI as possible, and the antenna is as far as possible away.

Earlier today, I used my 40M OCF Dipole, (installed in my garage):

So you can see my motivation… that image says I have the potential to get images from the gulf of mexico up to way north in canada…

My next steps: Once the actual antenna comes in, install it properly. Also I have a 137mhz band pass filter on order. Also have a much better radio on order. Ultimately this is all going into a waterproof box in my garden. I had put together a 12v battery, a solar panel and a charge controller, for a past experiment… Now it will be re-purposed as the beginning of my garden weather station.

Get Weather Satellite Photos onto your Raspberry PI?

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I’ve had a side track for a couple days… I did some work on the solar tracker project and got stuck waiting for parts, and so took a look at YouTube and since I am also into Ham Radio, YouTube suggested a video on how to receive photos from weather satellites.

Ok wow. I already had all the components I needed… A Raspberry PI, an SDR USB dongle (software defined radio), an antenna.

Basically with the right software installed, and some internet access, you can tune the SDR to a NOAA satellites downlink frequency, wait for it to fly overhead, and record the audio received. From there you can give that audio file to a program that decodes the tones in the audio into a photograph.

There’s also software that automates the process so all you have to do is configure things and sit back while your Raspberry PI collects images from satellites as they fly overhead.

I’m not giving details on how to do this.. there’s so many ways to accomplish the task, and fortunately many websites and videos explaining how to do things.

Here is a link to the video that got me started.