The evaluation of FM radios designed primarily for analog voice traffic, but used for data transmission, requires operation over a wide range of data rates and modulation formats. A versatile full-duplex baseband modem has been built which interfaces with tactical VHF radios and operates from 75 bits/s to 16 kbits/s. The choice of modulation formats, modem implementation, and some performance results are presented in this paper.

This paper discusses the theory and design of a tactical channel simulator (TCS) built to simulate land-mobile VHF radio links. The instrument is one of the first such units based on the stored channel principle, which permits the actual medium to be recorded and played back. The key application of the TCS simulator is to realistically reproduce field conditions in a laboratory. Tests on the TCS simulator should be in good accord with performance encountered in the field, unlike results obtained in the standard back-to-back tests which ignore effects of the propagation channel. Experimental results show that the evaluation of modem performance must take into account the effects of propagation over the VHF channel, as data tests are measurably affected by channel conditions. The TCS simulator will be particularly useful in the comparative evaluation of various highspeed, high-performance modems now being introduced into the inventory.