The short answer is NO you still need a dummy load or an attenuator that can handle the power from the transmitter. Then VNAs are not really designed to do spectral analysis of transmitter output. VNAs measure the characteristics of antennas, filters, and with the correct attenuator, amplifiers. They need to control the source frequency being used to measure the characteristic. A Spectrum Analyzer (SA) can measure the output of a transmitter for signal characteristics by scanning the frequencies that the receiver in the SA measures. An inexpensive SA would be the TinySA.
So a VNA is measuring the network being tested by adjusting the stimulus feeding the network and measuring the result. A spectrum analyzer scans the frequencies in question and measures what it sees regardless of what the device is sending.
Both have limits on how much power can be applied to the input before overload and damage occurs. That is why you need a dummy load and/or the proper attenuator.
You can look up NanoVNA and TinySA on the internet to find out more about these instruments.
73
Evan
AC9TU
