2007 ARRL International EME Competition
The Digital/Analog Divide
by H. Ward Silver, N0AX
What is all the fuss about digital and analog scores? There certainly is a lot of vigorous discussion about the relative merits of each mode, with each camp holding firm to its position and operating habits. (There are a number of operators and teams that use both digital and analog moonbounce techniques, of course.) To an EME newcomer or the casual reader, the reason for the differences of opinion may not be so obvious.
Analog, in the context of moonbounce, means the use of human hearing and brainpower as the means by which audio from the received echoes is translated into callsigns and messages. The two modulation techniques used are CW and SSB. Of the two, SSB requires the strongest signal strength. CW signals can be detected by a highly trained and sensitive pair of ears (certainly not the author's) down into the receiver noise floor and slightly beyond in exceptional cases and circumstances. The resulting EME station is very much an alloy of operator and machine.
Digital moonbounce is dominated by the use of signal processing in the form of special protocols and codes known as JT65, part of the WSJT software suite developed by Joe Taylor K1JT (http://physics.princeton.edu/pulsar/K1JT). In these modes, the received audio is translated into callsigns and messages by signal processing software that uses a PC sound card to digitize the audio. JT65 can dig a lot farther into the noise to recover signals than can even the best human ear. This extra ability to recover a signal is known as "processing gain."
By using JT65 codes, a much more modest station can successfully complete moonbounce contacts than is required for analog modes.
As a result, many more stations are now making moonbounce contacts.
Somewhat justifiably, this rankles some analog operators who feel their operations are distinct from those of the software-driven systems. Digital techniques continue to evolve and so more stations are likely to try their hand at moonbounce in the future. To accomodate both views and techniques, different categories have been established in the ARRL EME Contest.
Another point of divergence between groups is the use of the Internet to coordinate contacts in nearly real-time. On-line "chat rooms", such as http://www.on4kst.com/chat/start.php are often used to set up or schedule EME contacts. Stations are sometimes observed "talking each other in" until they are able to complete a contact. This is a big change from "random"
QSO's, in which one station calls CQ off the moon and then listens for replies without knowing who may be calling or when. Random QSO's are definitely more difficult to complete, but as with digital mode contacts, smaller stations can complete contacts with this form on on-line assistance.
As you might imagine, random QSO proponents consider contacts made with the aid of the Internet much less difficult and thus less worthy of note.
As long as one is clear about the techniques used to make QSO's, there are plenty of stations to work, big and small, on both sides of the digital/analog fence. Although the traditional analog mode dominance is being eroded, its practitioners can take some solace from the fact that as digital mode operators become more proficient, they may want to add CW and even SSB to their capabilities. The moon is big and does not care what type of signal it reflects - there is room for all.
Page last modified: 10:05 AM, 15 Apr 2008 ET
Page author: contests@arrl.org
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