Monday, May 4, 2015

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!

Friday, May 1, 2015

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