MARS Automated HF Modem Switch

Accessories connectors are hardly standard.  Some are DIN connectors, mini-DINs, D-Subs of various pin counts, and even high density D-Sub connectors are present radios use in MARS service.  None of these are rated for a large number of “mate-demate cycles.”  And some are fragile too.  A single mate-demate cycle with some angular misalignment will cause the receptacle contacts to “open up” and become intermittent.

There are technical issues as well.  While most amateur HF transceivers use unbalanced audio inputs (at various levels and impedances), some MARS operators have gone to high quality commercial or military communications gear that uses balanced 600 Ohm audio interfaces with levels usually around 0 VU.  HF modems have this same issue.  Typical amateur HF modems are unbalanced with levels similar to those needed by amateur transceivers.  But more and more MARS members are transitioning to commercial and military HF modems.  These offer many more modes, many with high speed and error detection and correction.  Of course these have the balanced 600 Ohm audio interfaces that would match a comparable military HF transceiver.

But that is only the beginning.  Every HF modem receiver has a signal level range that affords maximum performance.  And, of even more concern, every HF transceiver needs transmit audio levels in a certain range or either low power or a distorted signal is sent to the antenna.

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