Tuning a Telemetry Antenna with a VNA
As part of my Vertical Trajectory System I am adding another telemetry downlink from the rocket, and for that I need an antenna. I want something robust and simple so I chose to just make a simple dipole that can be taped to the outside, or inside, of the rocket airframe. This was accomplished by just using a SMA pigtail and stripping the coax. This however had to be tuned to the correct frequency.
I grabbed my Nano VNA, and quickly calibrated it for a frequency range of 1-3GHz, to suit my target frequency of 1.28GHz.
Connecting the commercial antenna to it quickly confirmed the center frequency of that antenna at 1.24GHz.
Next up I grabbed my roughly-trimmed dipole and connected it, revealing a frequency of 1.1GHz in air (look for the resonance dip in the yellow trace. That is where more energy is going out into the air).
I then taped the antenna to the airframe, simulating its final mounting to some degree. The frequency was shifted to below 1GHz due to the fiberglass dielectric in proximity to the dipole.
Based on the reduction of frequency due to the fiberglass and the low frequency from the first attempt I calculated the length required and cut the dipole. The result is an antenna on the 1.28GHz I wanted.
I took the antenna and taped it to the stick of a Q-tip for now. It will be quite adequate for bench testing.
I really can’t wax lyrical enough about the VNA. Such a handy tool to have around, and the whole process of tuning the antenna took around 15 minutes. Totally amazing!
As part of my Vertical Trajectory System I am adding another telemetry downlink from the rocket, and for that I need an antenna. I want something robust and simple so I chose to just make a simple dipole that can be taped to the outside, or inside, of the rocket airframe. This was accomplished by just using a SMA pigtail and stripping the coax. This however had to be tuned to the correct frequency.
I grabbed my Nano VNA, and quickly calibrated it for a frequency range of 1-3GHz, to suit my target frequency of 1.28GHz.
Connecting the commercial antenna to it quickly confirmed the center frequency of that antenna at 1.24GHz.
Next up I grabbed my roughly-trimmed dipole and connected it, revealing a frequency of 1.1GHz in air (look for the resonance dip in the yellow trace. That is where more energy is going out into the air).
I then taped the antenna to the airframe, simulating its final mounting to some degree. The frequency was shifted to below 1GHz due to the fiberglass dielectric in proximity to the dipole.
Based on the reduction of frequency due to the fiberglass and the low frequency from the first attempt I calculated the length required and cut the dipole. The result is an antenna on the 1.28GHz I wanted.
I took the antenna and taped it to the stick of a Q-tip for now. It will be quite adequate for bench testing.
I really can’t wax lyrical enough about the VNA. Such a handy tool to have around, and the whole process of tuning the antenna took around 15 minutes. Totally amazing!