Duplex Communications Without a Repeater

Thoughts on radio communications in a WROL situation:
Communications have historically been a critical target for totalitarian governments.  In a crisis, all methods of communications are important, but radio operators have historically been the most difficult to control in chaotic times.  I believe it is important for at least some of us in every community to become proficient at radio communications.  The only way to become really proficient is to practice the craft.  Study the theories and apply them in your own real-world setting until you understand how the theoretical interfaces with the practical.  In our nation today, there are a great many job hunters and employers who value training and certification above ability.  I cannot overstate the danger of this thinking when it comes to emergency communications.  There is no substitute for practice.  It is not enough to know that the connection works.  We must understand as well as we are able, why it works.  This way when things change, we will better understand our options.

My first ham radio purchase was a 2 meter/70 centimeter handheld transceiver.  These are so inexpensive that anyone, no matter what their financial status, can afford one.  The distance and operating modes limitation of these bands was good for me because it forced me to focus on what could be done with them.

Both bands are popular with ham clubs and there are local repeaters to extend the range in most cities.  In addition, many of these repeaters are tied together, either through radio links to other repeaters, through the Internet or a combination.  There are even satellite repeaters if you care to experiment.  My first thoughts were upon how two people could use these to establish secure communications in a SHTF situation.  It is worth noting at this point that the FCC forbids any encryption or other attempts at obfuscation of communications on amateur bands, so these ideas are “what if” thoughts on how someone might communicate in the absence of a functional government.  I am a believer in law and order and I will support and defend the Constitution of the United States against all enemies foreign and domestic.  I will do this to my last breath and without hesitation.  I am not advocating anyone violate the law.

Frequency hopping: While programming my handheld transceiver (HT) to communicate via the local repeater, I noticed that all of these little radios are capable of transmitting on one frequency while receiving on another.  The receive channel doesn’t even have to be on the same band.  Even the cheapest of these radios have 128 programmable “channels”.  I envision a scenario where two stations want to maintain the ability to communicate locally while limiting eavesdroppers.  A series of 62 frequencies would be selected pretty much at random between the two bands.  Radio one would be programmed with 31 transmit channels and 31 receive channels to the first 31 “channel” memory on the radio.  Radio two would be programmed the same as radio one except that the send and receive frequencies would be reversed.  The day of the month would determine the starting channel and either at preset times during the conversation or by some other signal, both radios would switch to the next higher channel, looping back to channel 1 when leaving channel 31.  At the end of the conversation, both radios are advanced to the next channel.  This continues until midnight, when both radios would be re-started at the channel corresponding to the new date.  During the entire conversation, someone might hear a couple of minutes of one side of a conversation, but it would be very difficult to monitor both sides even briefly, let alone overhearing the entire conversation.