I’m looking into using the Jetson TX1 to build a Parrot Bebop + SkyController competitor - a drone controlled through a VR headset with a long-ish range and enough bandwidth to run a good resolution video stream. The Parrot website says that they use a 4W 2.4GHz 802.11n or 5GHz 802.11ac signal (which are legal in the US) to achieve “up to” 2km range.
- what’s the power output of the TX1 802.11ac antennas, without any addons? I ran through all the datasheets without finding any indication…
- did anybody run benchmarks on the real-life WiFi performance at a distance between 2 TX1s, and/or between a TX1 and a high-spec router?
- if (as I strongly suspect) the TX1 doesn’t support 4W natively, is there any suggested schematic and/or component to achieve it?
Please bear with my ignorance - the project is pretty much an idea in the clouds now and, while I have decent electronics skills, my ham radio knowledge is very limited.
I have not experimented with this, YMMV. In general, configurable technical parameters occur in the firmware. In /boot will be several “.dtb” files…most of those are extra and not even used. In /boot/extlinux/extlinux.conf you will see which firmware file is actually used. The default for the dev kit is “tegra210-jetson-tx1-p2597-2180-a01-devkit.dtb”. This is the binary blob file, which was compiled from the .dts source file in the kernel source. There are actually tools in the kernel source to reverse compile the dtb back into a dts, but the reverse compiled versions will lack comments and useful naming.
This particular dev kit dts file is in the kernel source at:
arch/arm64/boot/dts/tegra210-jetson-tx1-p2597-2180-a01-devkit.dts
…these are the easily accessed parameters. I do not see any kind of power setting, but if you look at the notation, there may be something listed elsewhere which this file could alter. Otherwise, alteration would be in the driver source itself.
Documentation is divided into the TX1 chip itself, the module board the chip is soldered to, and the carrier board the module is seated on. Looking at a block diagram of the module board, it appears the BCM4354 chip is part of the module board the TX1 is soldered to (half way between TX1 chip and dev carrier board). The antenna connection supports this. Documentation will probably require finding out which I/O the chip is wired to (the tegra210 chip is wired to the bcm4354, but does not directly “know” about this chip), and documentation about the chip itself. Combine that and a combination of the firmware file and/or driver source should be able to do what you want.
I seriously doubt that the Broadcom chip outputs 1 Watt of TX power. The FCC limit is 1 Watt of conducted power into a 6dBi antenna. Since 1 Watt is 30dBm, the antenna gain accounts for 6dB of the 36dBm of transmitted power in the air, which is 4 times the power or 4 watts (36dBm EIRP). By the FCC rule, you cannot increase the 1 Watt of conducted power, even if you use a lower gain antenna. You can increase the antenna gain as much as you like so long as you do not exceed 36dBm EIRP. This may require backing off the conducted power. The price you pay with antenna gain, is that the higher the gain, the more directional it becomes.
The WiFi chips on the market either have low output power ~1mW, with the expectation of using an external power amplifier, OR some WiFi chips have internal power amplifiers and typically output around 20dBm or 100mW of power. The highest WiFi power found in power amplifiers in the market is 1Watt, but these use a lot of current, which is probably not happening on the TX1 board.
In the case of MIMO, the multiple power amplifiers must not add together to more than 1W of conducted power. If two power amplifiers are used, each outputting 20dBm or 100mW of power, then the total conducted power would be 23dBm (3dB is a doubling of power) which is 200mW (<1W conducted).
If two power amplifiers with 6 dBi antennas are used then the total power in the air, or EIRP, would be 29dBm (20dBm + 6dBi + 3dB = 29dBm, slightly less than 1W). To get to 36dBm EIRP, you would need antenna gain of 13dBi. Each power amplifier outputs, for example, 20dBm connected to a 13dBi antenna for a total of 33dBm in the air. With two such power amplifiers and antennas, you would double the power which adds 3dB for a total of 36dBi or 4 Watts EIRP. However, a 13dBi antenna is very directional and you would lose omni-directional coverage.