title_body: Drone with SDR for HF antenna field strength measurements, I need a Raspberry Pi based drone kit that I can just buy I have very little time until I get to the USA to buy the material to put together a drone which I want to use to measure antenna gain patterns for HF radio. Example, a 20m band half-wavelength dipole antenna is 10 m wide and should be mounted 10 m above ground, probably it will have to be less. Additional parasitic elements of about 10 m wide spans are added around the main driven element to achieve directional gain.
  The issue is measuring this gain for which one needs to get two wave lengths away and up all around the antenna assembly, which is easily 100 m all around. And for 40m, 80m, 160m band antennas it would scale accordingly.
  The measurement device we would need to lift up is an SDR (software defined radio) device, which can be as small as a USB dongle, along with some small receiving antenna. The drone would fly around the transmitting antenna and would measure the antenna's gain pattern on a set of chosen frequencies and transmit power while we would be intermittently transmitting our call sign in Morse code like a beacon. Given the fact that it's an experimental antenna assembly, the drone should re-take the same flight path several times as we adjust the setup.
  Since an SDR dongle needs to be plugged into a USB port of a computer running some Linux, the Raspberry PI comes to mind. And to avoid having to carry that as extra payload, I want to have a drone which has a PI as its main control and communication module.
  I have seen several PI drone projects, dating as far back as 2016, but even after all that time I have not seen an affordable kit. It should be around $200, as even in 2016 a ZDnet article talked about a DIY PI drone in that budget. Since I have very little time to get the parts together while on a short visit to the USA before returning to South America where everything is twice as expensive, I would like to find something that I can just buy. Do you know of a kit or a state of the art shopping list that is based on a generic drone kit?
  [Hey Stack-Exchange police: this is not just a shopping question, it is a state of the art question.]
  What is the state of the art in Raspberry Pi drones now? Much has happened since 2016.
  How can I tell from looking at drone kits on Amazon for example, how much payload they are able to carry? This is not reported in the specs that I can see.
  I would like to avoid the RC gear and just use WiFi to control the drone and receive the telemetry data.
upvoted_answer: You might check out this video on using a Pixhawk and a rPi with Python.  The video just walks you through the serial connection and some Python code for basic control.  The Pixhawk is doing all the real time control (Linux isn't good for that part) and the rPi is talking to it over a serial port.
  You might also look at the MicroHawk reference in:  Do drones with inflight API access for control inputs exist? (although the link seems to be broken at the moment).