Description USB interface
After I have built the 100 and 500 MHz spectrum analyzer, both designed by PA3EKN, I wanted to read the measured signals into a PC. The USB interface for this and other analyzers is briefly described here. Look for detailed information in the download section.
I used the FT245RL of FTDI for the USB communication. This chip is fairly simple to control with Visual Basic and only requires one additional PIC the 18F2520. This processor has enough ports and also a fast A/D converter.
The operation of the interface is fairly simple, the process is determined by the Pen Lift pulse of the analyzer. During the first puls the settings of the interface such as sample time and number of samples are read and then the "fixed" values, switch positions and center frequency, are measured and sent to the PC. If the puls is finished the values of the Vertical output are measured and also sent to the PC. It is the intention that the number of samples and the sample time are chosen so that just before the beginning of the next puls the measurement stops. (see Figure 1)
In the PC, the measured values are converted and displayed on the screen. The program has a lot of possibilities to get additional information from the displayed values such as signal averaging, peak hold, markers, save a measured line, measuring from a reference line, etc. See the main screen to get additional details. The measurements can also be stored for later analysis.
The interface and program can also be used for other spectrum analyzers which provided an output for the vertical signal and the Pen Lift pulse. The settings of the analyzer must however set manually on the PC screen. Personally, I use a HP8558B with an 182T display.
The program runs on both Windows XP, Windows Vista and Windows 7. It is a fairly heavy load on the processor of a somewhat older PC, a Pentium 4 1.7 GHz is about the minimum.