New project Idea - Solar, GSM, Off Grid

I thought that would catch a few eyeballs.

I have been asked by work to setup at least 2 of these base stations. I would love to make them stand alone, self sufficient units as they will be in remote locations in the desert. Before I go about inventing this in my shop, has anyone done this before? Could you reach out to me if you have?

Here are a small list of things i’'m getting started with. Please feel free to add to my list of things you think I need to make it the ultimate.

PI zero W
Pi aware pro dongle
Pi aware Filter for 1090Mhz
Airspy Saw Preamp (Ceramic always seem out of stock)
Solar panel (size has yet to be determined)
18650 battery pack (size has yet to be determined)
Solar charge controller
Water resistant case (not sure how im doing the active cooling just yet)

What else would YOU add to make this even more stable and amazing?

A small fan inside the case to circulate air and aid in cooling.

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Circulating the air will just heat up the whole enclosure.
I think it needs an aluminum radiator, on the shaded part, to dissipate that heat passively.

Depends on how the fan is doing it’s job.

If it is inside, the air circulation needs to go from one side to the other, both sides with holes where the air can come in and leave the case.

Just doing it inside a case without holes doesn’t make sense indeed

May want to consider adding a sunshield.
Inexpensive, and a simple way to reduce the heat.

Temperature difference with sunshield

It’ll reduce the temperature differential between the housing and the pi.
Thus you can get lower temperature differential to the outside.

I’m not sure why people think a fan in a box doesn’t help to keep something cool that is producing heat in the box.
Especially when the box is large enough to passively exchange quite some heat with the outside relative to the heat load.

And yeah kinda obvious that you’d mount it in the shadow of the solar panel :slight_smile:

It does make sense, see temperature differential above.

So it’s easiest to work in temperature differences.
Let’s say we have 5 W of heat load (the power the pi is dissipating) and that heat needs to leave that box.
For the heat to leave that box the box needs to be hotter than the air surrounding the box.
That temperature differential won’t be changed by a fan.

But the temperature difference betweent the pi and the box can be massively changed by the fan.
Due to the box having a large area, it’s usually not a limiting factor in heat dissipation.
Bigger boxes will do better of course.

No need for Pi aware Filter for 1090Mhz, the dongle already has a filter and in the desert there are not likely to be too many high power local RF sources to interfere.

What’s your plan for Internet access?

They mention GSM in the thread title - I assumed that they meant cellular - 3G.


Because plastic boxes don’t radiate heat. Fan spinning might even add more heat than that box can dissipate.
That’s why I suggested a proper radiator.

The air inside the box will reach thermal equilibrium with or without that fan, if the thermal resistivity of the case is high. Like voltage drop over a high resistor, the temperature gradient across that plastic wall will remain high.

GSM cellular radio connected to the raspberry pi.

Heat moves by three modes: Radiation, Convection, and Conduction. The relatively thin thickness of the box affect the Conduction of the heat out where the heat is removed by radiation and convection. Painting the outside a flat black will help radiation, and thins the air layer over the box increasing convection effects. Inside the box, without a fan, you have limited convection created by the temperature differences in the box, not much conduction, and radiation will remove lesser amounts of heat, Adding a circulation fan means the convection part goes up much more, especially if you use heat sinks on hot parts. Stay out of the sun, helps, just remember the back side of a solar panel can get quite hot, so use a shield between any direct path for radiation heat from the solar panels on to the Pi enclosure. My vote goes to the circulation fan, and keeping the enclosure away from heat sources. The fan does not have to be a high power fan, moving the air is the important thing, Without the fan, the hot air becomes trapped and slow convection currents limit heat removal. Physicist background from college and USAF days, now happily retired.

I see a small green bias tee on some setups. Is that even needed if Im using the “1090 MHz ADS-B Filter/Preamp” ? If I use this do i even need the blue version SDR or can i go with the cheaper version? Then i also dont need the other filter as well?

Metal enclosure for sure. Painted white.
Be aware that the bottom of the solar panel can be very hot. On a 95°F day my solar panels for the house measured 125 °F on the back side.
Since you’ve got a cellular connection, make the box a bit bigger and find some way to get telemetry about the outside temperature, the temperature in the box, and the battery voltage. Even a once a minute sending of this data could tell you if there was a problem or give you more information about what’s going on.
A simple I2C Analog to Digital converter and some LM50 analog temperature sensors could go on the I2C pins of the PI. There are various 4 to 8 input parts out there. Search for some PI Hats, see what you can find. If you can find one with a relay output, or use a spare GPIO, you could put a driver for a fan on that.
Pre-punch the enclosure for a 40 to 60 mm fan and another for exhaust. Then if you need to exchange air with the outside it’s an easier update in the field.
Leave room between the antenna feedline (boy that spell checker hates that word…) and the USB SDR for a Pi Aware filter in case your cellular is de-sensing your ADSB receiver.

You need a source of 5VDC power for the amplifier. You could use an RTL-SDR Blog or Nooelec NESDR SMArtee (not the XTR which has a coverage gap at ADS-B’s frequency) to provide this power as neither of the FA dongles provide bias-T power. Or you can use an external bias-T supply board like this one for example and power it via USB from your Pi or any other source of 5 volts DC, then you can use pretty much any SDR dongle you want to.

Ill be honest, due to all the issues listed above, I might just look into moving the unit into an airconditioned building!

So this is where I get confused. It says it wants 12v+ pref 13.8VDC
And the frequency isnt right. Can you show me where to get one that works in the 1090Mhz range?


Exactly which one are you talking about? Brand and model.

What wants this? The LNA? Pi? Fan?