Friday, December 13, 2013

The Capabilities of Weak Signal Digital Modes

Since the beginning of the "Amateur Radio Service", we hams have almost constantly sought out news ways of doing one thing: communicating.  We switched from spark to CW for many reasons...but namely, CW was vastly more efficient.  AM is still with us, but primarily, we use SSB.  Why?  Single-Sideband "goes farther".

The same is true for the soundcard digital modes.

Some modes are better in adverse conditions than others.  Some are more efficient, and are able to convey the same amounts of information, while sometimes using less power to do so.

The following is a list of popular digital modes, and the typical minimums of signal-to-noise ratios that allow their transmitted information/signals to be copied:

JT9-30..............................-42 db ("QSOs" can last 3 hours or MORE!)
JT65...................................-30db
Jason Turbo (Fast)...............-25db
FT8.....................................-20/22db
PSKAM10..........................-20db
PSK10............................-18db
MFSK4............................-16db
Contestia 500/32.................-15db
DominoEX-4 ......................-15db
FEC-31...........................-15db
THROBX-4.........................-15db
Olivia 1000/32...................-14db
Olivia 500/16....................-14db
THOR11...........................-14db
MFSK16...........................-13db
Contestia 500/16.................-13db
CW 20 WPM......................-13db
RTTYM 500/64....................-13db
THOR16...........................-12db
MFSK31........................-12db
Olivia 500/8.....................-12db
DominoEX-8........................-11db
MT63 500Hz BW....................-10db
Olivia 500/4.....................-10db
PSK31........................... -10db
CHIP-64...........................-8db
DominoEX-11.......................-8db
MT63 1K...........................-7db
PSK63.............................-7db
Feld Hell.........................-7db
CHIP-128..........................-5db
RTTY 45...........................-5db
PSK125............................-4db
PAX2..............................-2db
PSK250............................-1db
HFPacket (300baud)................+1db
PSK500............................+3db

Right away, we see that the old-timer's MYTH that "CW gets through when no other mode will" no longer applies.  At -13 dB under perfect conditions, we see that there are AT LEAST 15 other modes than can do the job BETTER.  If a simple signal report is all that is needed, JT65 is EXCELLENT when used with QRP power, or when faced with QRM, QRN, and QSB.  Quite simply...there aren't many that are better. JT65 can be copied with almost over-lapping signals.  (JTDX 18.1.30 is arguably the most capable of the few suites that CAN do JT65).

But how about times when you want to have an actual conversation with another station...or you need to convey more than "WX1XYZ KB2HSH -12" ?  For "rag-chewing" during poor/weak-signal conditions, Olivia 500/16 or 1000/32 and Domino EX-4 are able to copy at signal levels 2 to 3 dB LOWER than CW.  This can be handy for that elusive QSO.

A few years ago, I was having a QSO with a German station on 30 meters.  We were using Olivia 500/16.  When we began the QSO, the signals were audible as well as visible on the waterfall.  As the band began to close, 30 had deteriorated to where we could no longer see or hear the signals, but we still had solid copy throughout.  It was that QSO that convinced me that digital modes were not only superior to the older, ANALOG modes, but with the QRP power levels I use...they are VITAL.

During periods of good band conditions, many use the faster modes.  There is nothing wrong with that...but when using modes such as 300-Baud Packet, or PSK125, you will simply not get the distance that you might otherwise obtain with the slower, narrow modes.  Case in point: the IS0R DX-Pedition to Sardinia recently.  Now, Sardinia isn't exactly exotic, but on 80 meters, this would have been great for my 80 meter DXCC total.  80 was in decent shape, but they were using PSK63.  I had 80-90% copy on them...and I stood a good chance of working them, IF they had used a better mode.  Instead, they switched to PSK125, and the game was over.  By the time they switched to PSK31, it was too late.  The band had gotten lousy, and the pile-up was growing larger.  The error made was when they switched to a mode that was wider, faster, and capable to -4 dB S/N.  Too bad they didn't use PSK10!

It should be noted that many of these modes are only found in MultiPSK. 

With the aid of this list, it should give the digital operator a big boost when trying to increase their DXCC totals.  Granted, some of these modes aren't very popular, and finding another station that is using them may be difficult, but using the right mode for the right time, conditions, or needed applications can be the difference in successful QSOs...or none at all.

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