[CALV-AUXCOMM] Calvert AUXCOMM Net Wednesday Aug 17 at 7:30pm

[Shawn Donley]

All,

We'll have a net instead of a meeting this month.  We'll meet on the 146.985 repeater at 7:30pm on Wednesday, August 17.

After the voice net we'll try to have a round table discussion using the MT63-2000L digital mode, again using the 146.985 repeater for coverage. 

If you have a sound card interface between your 2M FM radio and your computer, that's great.  Use it.  But you can run MT63-2000L with no cables at all.   Just let the computer's microphone "hear" the speaker on your radio, and when you transmit, let the rig's microphone "hear" the computer's speaker.   Probably the hardest part of this approach is holding PTT down and typing at the same time.  See the Youtube link below for a demo.  MT63-2000L is one of the many digital modes available in the free FLDIGI software package found at http://www.w1hkj.com/

https://www.youtube.com/watch?v=Mwepl8rBhKY

One of the aspects of MT63 that is different is the latency time between going into transmit and data actually being sent, as well as that data showing up at the other end.  Takes a bit to get use to.  When sending, watch for your message going out on the FLDIGI screen and you can switch back to receive as soon as the complete message text has been sent. 

Changeover from transmit to receive and vice–versa is therefore considerably slower than most modes due to the data latency in the decoder as the buffers are flushed. It therefore, requires some skill and patience in a QSO as it is not a “break–in” mode as you would think of CW or PSK that have virtually no latency time. Correctly decoded text can take up to 15 seconds to appear on the screen. A clue to synchronized reception can sometimes be gleaned if the software has a digital squelch facility (software based vs. hardware squelch). If the squelch is set up to be closed when no MT63 signal is present, it can often be seen to open as soon as it finds MT63 and ideally the text will follow quite a number of seconds later! In order to make the decoder start printing valid text as soon as possible, software should be chosen that has an effective squelch, so as to minimize feeding the decoder garbage before valid text. Latency in this mode is considerably longer than other 2FSK or multi–AFSK modes like MFSK16 or even MFSK64L. For instance the shortest latency time for MT63 is 3.2 sec. in short interleave 2K transmission mode. The latency time for RTTY is 330 ms. Unlike OLIVIA and MFSK16 the narrower 500 Hz operational modes are much slower using MT63 than the wide (2K) mode. OLIVIA is several times faster and more noise tolerant in the narrow band mode yielding a lower latency, while conversely MT63 becomes much more robust and has a longer latency time in the wide band mode. Accurate text copy can be obtained from MT63–2K when the tones are near or below the noise level under optimal conditions similar to PACTOR III, although at a much lower text throughput.

N3AE
Calvert EC