If you can transfer data via a radio link (Ham or otherwise), can't you encrypt the text files (Via an encrypted Zip format for example) and send them as data files to get around the encrypted limitation on those frequencies. (Your not encrypting the voice traffic). The HF/VHF Tactical Radio System features software-programmable L3Harris Sierra™ II encryption, providing secure Type 1 interoperability among U.S., Coalition and Partnership for Peace forces. The manpack is fully compatible with L3Harris Falcon II
It replaces the KY-65 for HF radio applications (2.4 k bits/sec). It also replaces the KY-57 in most VHF and UHF applications (12 or 16 k bits/sec). Note the "Narrowband" in ANDVT means that this unit is not optimum for VHF and UHF radios where the bandwidth is much wider than for HF radios.