VI Operation in External Mode
1. Basics#
The tone that the DMX-40 is looking for is NOT 600 or 650 Hz, tones normally used for
listening to CW. Rather, it is 1300 Hz. Why did we mess your ears over by choosing
1300 Hz? Because we can lock onto a weak signal buried in noise twice as fast?
Because we can send and receive code twice as fast? We thought that was good
reason enough. Naturally, we would have loved to go even higher, but we had mercy
on your ears.
What does this mean? It means a typical CW filter will not work - will cause the DMX-40
to not work. Rather, set your rig to SSB. If you check in the PreppComm Community,
some have found adding a 1300 Hz filter helps, or their transceiver has the ability to
create a filter around 1300 Hz that is not too sharp and thus causing the decoder to fail
due to filter ringing, but most just use the SSB setting.
Essentially, if you are not tuning so the decoder is hearing 1300 Hz, the CW IN LED will
not light up, and nothing will decode. This can be quite a shock if you are not expecting
it, as you are used to decoding by hearing at just about any tone.
If you do a lot of CW, you are used to trying to isolate a single CW station so you can
'hear" only it, and thus decode it in your head. Here, it is quite different. You are
feeding a fairly wide audio signal to the DMX, and so it is doing the isolating via its very
narrow hearing ability around 1300 Hz. You can experiment with your filter settings if
you want to try to also isolate it for your hearing, but be careful not to tighten it up so
much that you cause ringing and decoder failure.
You also need to set up your transceiver so that it goes into transmit mode when the
KEY IN is activated. Otherwise, you will have to switch manually between transmit and
receive mode on your transceiver in addition to operating the DMX-40, which is, in a
word, not going to work for you. Full or partial breaking is fine.
2. Decoder Only Use#
If you only plan to use the internal decoder, and not use the encoder, including the CALL
and ANSwer functions, automatic call sign capture, keyboard texting and type-ahead
buffer, and microprogramming for customization of operating methods, then all you
need to remember is to press the SPACE bar after tuning in the station of interest,
making sure first that you are roughly in the center of the 1300 Hz bandpass of
approximately 100-150 Hz. The SPACE bar restarts the decoder by clearing the cache
of any information from previous signals. Also, while in decode mode, remember that
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