This program uses the K3 (or K2) and W1 to measure your antenna bandwidth. No, it won't replace an antenna analyzer, but to use it:
When the program starts up, choose which serial port is connected to your K3, then do the same for your W1.
Choose the start and stop frequencies as well as the number of measurements you want to take in that range. The program will sample that many SWR readings at evenly spaced frequencies. The power level should be kept low to avoid bothering others and 1 Watt is a good choice.
To start sampling click the 'play' button and you will be prompted for a file name. This is the file where the readings will be stored, and which you can then plot using your favorite graphing software.
The SWR values are read from the W1. The way the W1 works is that it reports, say, 1.1 for SWR values s where 1.1 <= s < 1.2, meaning the measurements are up to 0.1 SWR optimistic.
Run it on this page.
Here are a couple plots of my antenna bands measured this way: