MFSK-16/32 good for weak signal work.

We had an excellent chat on the Saturday TDRC "fun" net on 40m between one other station and I.  I had an opportunity to demonstrate the various capabilities of the FLDIGI suite to transfer files and emails from station to station.

There was some fading on the band right after the start of the net, which made higher speed PSK-125 and PSK-250 difficult.

For similar data throughput, we changed to MFSK-16 and had 100% copy at almost the same data rate.  Keep in mind that MFSK has some FEC (forward error correction) built into it, plus the mode is generally more resistant to fading and other "intermittent" sources of interference.

We may consider MFSK-32 as a mode for our APRS experiments!

Different flavors of Olivia

It would appear that most nets have standardized on Olivia 8-500, which has a decent tradeoff in terms of speed vs. reliability.

However, Olivia is not limited strictly to 8-500 (which stands for 8 carrier/500 Hz).

Was having problems copying a station last night on our net on 80m.  I was able to switch from Olivia 8-500 to Olivia 8-250.  That reduced the required s/n from -11 dB to -14 dB.  Suddenly we went from 35-50% copy to 100% copy, as the other station's signal was fluctuating between -9 and -12 dB.  Of course, we also took a 50% cut in data throughput when we reduced the bandwidth from 500 Hz to 250 Hz.  However, 100% copy at 50% speed beats 35% copy at full speed any time!

Here is a sort summary of how the different types of Olivia compare (courtesy of the W1HKJ web site for FLDIGI):

Mode	Baud	WPM	Duty Cycle	BW (Hz)	Modulation	S/N	ITU	RSID-1	RSID-2
OLIVIA-4-250	63	20	100.00%	250	4-FSK	-12 dB	250HF1B	75
OLIVIA-8-250	31	15	100.00%	250	8-FSK	-14 dB	250HF1B	69
OLIVIA-4-500	125	40	100.00%	500	4-FSK	-10 dB	500HF1B	74
OLIVIA-8-500	63	30	100.00%	500	8-FSK	-11 dB	500HF1B	72
OLIVIA-16-500	31	20	100.00%	500	16-FSK	-13 dB	500HF1B	70
OLIVIA-8-1000	125	58	100.00%	1000	8-FSK	- 7 dB	1K00F1B	116
OLIVIA-16-1000	63	40	100.00%	1000	16-FSK	-10 dB	1K00F1B	73
OLIVIA-32-1000	31	24	100.00%	1000	32-FSK	-12 dB	1K00F1B	71

3000 baud and nothing wrong!

Most VHF/UHF rigs have "9600 baud" capable ports built into them.  Without going into a long-winded explanation, the port bypasses the pre-emphasis circuitry of the radio so that 9600 bps operation is possible.  Plus, you have to get a 9600 baud TNC, like the Kantronics KPC9612.  Looking at a few hundred dollars for that.

So, most of us have grown accustomed to "1200 baud" only on non-9600 baud radios.

Scott KD5NJR and I have experimented with the new "8PSK" modes that were added last fall to the FLDIGI suite of programs.  Running 8PSK-1000 is the equivalent to running 3000 baud.  Yes, two and a half TIMES faster than a standard TNC.  I was sent him a 77K file in less than 5 minutes.

I encourage everyone to try out the super-speedy 8PSK modes on VHF/UHF, especially considering you will have no added cost outside of your soundcard interface to the radio.

FLDIGI "in depth" training PDF

Click on the attached link to learn how to get started on the FLDIGI software.  This is the five hour training presentation that was given in Tulsa and Oklahoma City over the past year:

https://www.dropbox.com/s/z54ini73fimhcio/FLDIGI%20TDRC%20Training.pdf?dl=0

APRS Messaging Training (PDF)

Click on the attached link for training on how to message in APRS:

https://www.dropbox.com/s/rgvw6bokclb4ttj/APRS%20Messaging%20TDRC%20Training.pdf?dl=0

For the next APRS net...

On this past "statewide" APRS net, I had some APRS OBJECTS that marked my station as the net control station.  I also had a couple similar OBJECTS that had in the comments field instructions to message me to check in, or to find me on a talk-in channel, etc.


Jeff has a good idea to do the same thing with APRS BULLETINS.  I think that worked even better.  I'd not tried bulletins because I was unsure how to name them.  But it's not hard. 


But here is what I want to do next time.


NCS first sends a message to ANSRVR with the contents CQ OKAPRS Let's Start the Net


Optional : A message to ANSRVR containing D OKAPRS stateside net at 1300 CDT ... or something to provide a bit of a description.


Participating stations join the net by sending a message to ANSRVR with the contents J OKAPRS


Participating stations send a message to Net Control (and everyone else, like a conference call ) with a message to ANSRVR , again with the contents of CQ APRS xx5xxx checking in ... or other traffic.

And when we're done, people can log out of the net with a U OKAPRS message sent to ANSRVR.


The NCS can check on the number of participants with a ? OKAPRS message.


Jeff pointed this out in a deck of slides he provided to Lloyd recently.


73
Scott / KD5NJR

May 2015 QST : APRS

Guys, I didn't read it yet myself, but Lloyd asked I mention the May 2015 QST as a source of information about APRS.  I have to admit, I didn't read it yet myself.


--Scott