Channel sounder for the tactical VHF-range

The usability of tactical radio systems is strongly affected by the characteristic of the VHF mobile radio channel. The design of a channel sounder and preliminary measurements are presented. The channel sounder uses a chirp impulse compression technique based on a surface acoustic wave (SAW) filter with a bandwidth of 6 MHz in the receiver. The transmitted chirp is generated digitally and is designed for a high correlation gain, a small pulse-width and low correlation sidelobes. The chirp is fed to a mixer with a variable local oscillator frequency and transmitted in one of the subbands between 30 and 88 MHz. All local references in the transmitter and the receiver are synchronized by a 10 MHz Global Positioning System (GPS) time reference. Additionally a 1 Hz signal, also GPS synchronized, is used as a trigger signal for the transmitter and the receiver to determine the absolute delay of the different propagation paths. Due to the high stable reference the compressed chirp can be demodulated coherently and the complex position-dependent channel impulse response can be measured. The delay-Doppler power spectrum is calculated which yields the location of scatterers.