Digital Mode HF Path Simulations 

Complied by Anthony Bombardiere, K2MO
dxdx@optonline.net

Path Simulator by Moe Wheatley, AE4JY

Digital mode Software 

Fldigi
Jason
MixW
MMVari
Multipsk
WSJT

_________________________________________________

  Baseline Sensitivity Test
   Minimum SNR
    
A simulated direct path (no disturbance) was used to establish a baseline SNR for each mode. The minimum SNR was determined when all data (Pangram text) passed through the simulator without error. 

JT65(WSJT).......................-30db
Jason Turbo (Fast)...............-25db
PSKAM10..........................-20db
PSK10............................-18db
MFSK4............................-16db
Contestia 500/32.................-15db 
DominoEX-4 ......................-15db 
FEC-31...........................-15db
THROBX-4.........................-15db 
MFSK16...........................-14db
Olivia 1000/32...................-14db 
THOR11...........................-14db 
RTTYM*...........................-13db
Contestia 500/16.................-13db 
CW 20 WPM**......................-13db 
THOR16...........................-12db 
Olivia 500/16 ...................-12db 
MFSK31***........................-12db
MT63 500Hz BW....................-10db 
Olivia 500/8.....................-10db 
PSK31........................... -10db
CHIP-64...........................-8db 
DominoEX-11.......................-8db 
MT63 1K...........................-8db 
Olivia 500/4..................... -8db 
PSK63.............................-7db 
Feld Hell.........................-7db 
CHIP-128..........................-5db
RTTY 45...........................-5db 
PAX2..............................-2db
HFPacket (300baud)................+1db

         *Intermittent "bug" with RTTYM MixW Software   
         **Subjective; Morse speed dictates SNR
         ***MMVari software 
______________________________________________ 

Ionospheric Simulations

Propagation simulators are often used to test the performance of HF communication systems. Although they can't duplicate the infinite number of complex variations that take place in the ionosphere, they can mimic some of the fundamental characteristics of HF path distortion. 
Because the ionosphere is always in flux, conditions can change from one minute to the next. The ionospheric parameters of the simulator on the other hand, remain constant which makes for a more level playing field when comparing modes. 
The effects of Doppler and multipath are always present to some degree, even on quiet days. Modes that are less robust will start to show a decrease in throughput as the magnitude of the distortion increases. 
These simulations should help when choosing an alternative mode that's more likely to survive when conditions deteriorate. 

Simulation: High Latitude Moderate
Path delay: 3ms
Frequency spread: 10Hz

SNR: -8db (weak signal)

Mode                   Throughput
 
Contestia 500/16.................100% 
CW 20 WPM........................100% 
MFSK16...........................100% 
MFSK31...........................100%
Olivia 1000/32...................100% 
Olivia 500/16....................100% 
Olivia 500/8.....................100% 
RTTYM 500/32.....................100% 
Olivia 500/4......................90% 
Feld Hell*........................90% 
ThrobX-4..........................70% 
Chip-64.......................No Copy
Chip-128......................No Copy
DominoEX 4bd..................No Copy 
DominoEX 11bd.................No Copy 
FEC-31........................No Copy
PSK31.........................No Copy
Jason Turbo (fast)............No Copy
PSK10.........................No Copy
PSKAM10.......................No Copy 
PSK63.........................No Copy 
RTTY45........................No Copy 
THOR-11.......................No Copy 
THOR-16.......................No Copy 
MT63..........................No Copy 

SNR: +10db (Moderate Signal)

Chip64..........................90%
Chip-128**......................00
Feld Hell*......................90%
Olivia 500/4....................90%
RTTY45..........................90%
ThrobX-4........................70% 
DominoEX 4bd................No Copy 
DominoEX 11bd...............No Copy 
FEC-31......................No Copy
PSK31.......................No Copy
Jason Turbo(fast)...........No Copy
PSK10.......................No Copy
PSKAM10.....................No Copy 
PSK63.......................No Copy 
THOR-11.....................No Copy 
THOR-16.....................No Copy 
MT63........................No Copy 

*diffuse text - readable 
**Intermittent decode problem with Chip-128

_______________________________________________________ 

Simulation: High Latitude Disturbed
Path delay: 7ms
Frequency spread: 30Hz 

SNR: -3db (weak signal)

Mode                 Throughput
 
Contestia 500/16.................100% 
CW 20 WPM........................100%
Olivia 1000/32...................100% 
Olivia 500/16....................100% 
Olivia 500/8.....................100% 
Olivia 500/4......................95% 
RTTYM**...........................95% 
MFSK31........................... 90% 
MFSK16............................75% 
RTTY..............................40%
Chip-64...........................10% 
Chip-128**....................no copy
DominoEX-4....................no copy 
FEC-31........................no copy
Jason Turbo (Fa...............no copy
MT631K........................no copy
PSK10.........................no copy 
PSKAM10.......................no copy
PSK31.........................no copy 
PSK63.........................no copy
Thor-11.......................no copy 
ThrobX-4......................no copy 
Feld Hell....................Readable 

SNR: +10db (Moderate Signal)

Olivia 500/4......................100%
Feld Hell*.........................90%
Chip64.............................75%
Chip-128**.........................75%
RTTY45.............................50%
ThrobX-4.......................No Copy 
DominoEX 4bd...................No Copy 
DominoEX 11bd..................No Copy 
FEC-31.........................No Copy
PSK31..........................No Copy
Jason Turbo (fast..............No Copy
PSK10..........................No Copy
PSKAM10........................No Copy 
PSK63..........................No Copy 
THOR-11........................No Copy 
THOR-16........................No Copy 
MT63...........................No Copy 

* diffuse print - readable 
** Intermittent decode problem Chip-128
________________________________________________________

                

Simulation: Mid-Latitude Disturbed
Path delay: 2ms
Frequency spread: 1Hz

SNR: -8db SNR (weak signal)

Mode                  Throughput
 
Contestia 500/16.................100% 
MFSK16...........................100%
Olivia 1000/32...................100% 
Olivia 500/16....................100%
Thor-11..........................100%
Thor-16..........................100%  
CW 20 WPM.........................90%* 
DominoEX 4bd......................90% 
Feld Hell.........................90% 
MFSK31 ...........................90% 
MT63 1K...........................90% 
Olivia 500/8......................90% 
Olivia 500/4......................90% 
RTTYM 500/32......................90% 
ThrobX-4..........................90% 
DominoEX 11bd.....................80% 
FEC-31............................70%
PSK31.............................70% 
PSK63.............................50% 
PSKAM10...........................50%
Jason Turbo (Fast)................35%
RTTY45............................20% 
PSK10.............................20%
Chip-64...........................20%
Chip-128**.........................00

SNR: +10db (Moderate Signal)

DominoEX 11bd.....................100%
Feld Hell*........................100%
FEC-31............................100%
MT63..............................100%
Olivia 500/4......................100%
THOR-11...........................100% 
THOR-16...........................100%
ThrobX-4..........................100%
SK63...............................95%
Chip64.............................90%
PSK31..............................90%
PSKAM10............................90%
RTTY45.............................90%
DominoEX 4bd.......................90% 
Chip-128**..........................00
Jason Turbo (fast).............No Copy
PSK10..........................No Copy

              * diffuse print - readable 
** Intermittent decode problem Chip-128
 
______________________________________________________________ 

               
Simulation: Low-Latitude Disturbed               
Path Delay: 6ms              
 Frequency Spread: 10Hz

SNR: -8db SNR (weak signal)

Mode                   Throughput 
 
Contestia 500/16................100% 
MFSK16..........................100% 
MFSK31..........................100%
Olivia 1000/32..................100%
Olivia 500/16...................100% 
RTTYM 500/32....................100% 
CW 20 WPM........................90% 
Olivia 500/8.....................90% 
Olivia 500/4.....................90% 
Throbx-4.........................70% 
Feld Hell.................Poor Copy* 
Chip-64......................No Copy
Chip-128.....................No Copy
DominoEX 4bd ................No Copy 
DominoEX 11bd................No Copy 
FEC-31.......................No Copy
Jason Turbo (Fast)...........No Copy
MT63 1k......................No Copy
PSK10........................No Copy 
PSKAM10......................No Copy 
PSK31........................No Copy 
PSK63........................No Copy
RTTY45.......................No Copy 
Thor-11bd....................No Copy 
Thor-16bd....................No Copy 

SNR: +10db (Moderate Signal)

Olivia 500/4.....................100%
Feld Hell........................90%*
Chip64............................90%
Chip-128.........................??**
RTTY45............................70%
ThrobX-4......................No Copy 
DominoEX 4bd..................No Copy 
DominoEX 11bd.................No Copy 
FEC-31........................No Copy
PSK31.........................No Copy
Jason Turbo (fast)............No Copy
PSK10.........................No Copy
PSKAM10.......................No Copy 
PSK63.........................No Copy 
THOR-11.......................No Copy 
THOR-16.......................No Copy 
MT63..........................No Copy 

* Characters diffuse difficult to read. 
 
** Intermittent decode problem Chip-128

__________________________________________________________

NVIS
Near Virtical Incidence Skywave

       *NVIS waves penetrate deeper into the ionosphere
        than waves that are beamed at low angles. The 
        increased interaction with the plasma tends to 
        slow the wave down increasing the time-of-flight. 

        NVIS sky waves can 'mix' with ground waves due to  
        the close proximity of the stations. This causes 
        internal timing issues for some digital modes as 
        the two signals interact. 

               Simulation: Mid-Latitude NVIS 
               Path Delay: 20ms*
               Frequency Spread: 1Hz 
               SNR: +10db

Mode                   Throughput

Contestia 500/32.................100%
CW 20 WPM........................100%
MFSK16...........................100%
MFSK31 (MMvari)..................100%
MT63 1K..........................100%
Olivia 1000/32...................100%
Olivia 500/16....................100%
RTTYM 500/32.....................100%
THOR11...........................100%
THOR16...........................100%
Contestia 500/16..................95%
Olivia 500/4..................... 95%
DominoEX-4 .......................95% 
DominoEX-11.......................85%
Feld Hell**.......................80%
RTTY 45...........................80%
Chip-64...........................75%
DominoEX-22.......................60%
THROBX-4..........................60%
PSK31.............................10%
PSK63.............................10% 
FEC-31............................nil
PSKAM10...........................nil
PSK10.............................nil

ARQ Modes (Unproto)

ALE400............................10%
Pax...............................nil
Pax-2.............................nil
HFPacket (300baud)................nil
HFPacket (300baud)................nil

       *Worse case scenario -- 20ms 
       **Hellschreiber text ghosting - difficult to read

__________________________________________________________

  ARQ Modes

  Minimum SNR 

(Direct Path no Ionospheric distortion)
         
PAX (UNPROTO)...................-11db  
ALE400 (UNPROTO).................-8db 
PAX2 (Unproto)...................-7db
HF Packet (300 baud Unproto).....+1db

_______________________________________________

Ionospheric Simulations

Throughput SNR for complete Pangram decode
*Indicates partial decode
Partial decode criteria: => 50%

Simulation: High Latitude Moderate
Path delay: 3ms
Frequency spread: 10Hz

Mode                Throughput

ALE400 (Unproto).............-1db /  -6db*
PAX (Unproto)................-4db / -10db*
PAX2 (Unproto)...............+2db /   0db*
HF Packet (Unproto 300bd)......NO DECODE

*Partial decode

___________________________________________________

Simulation: High Latitude Disturbed
Path delay: 7ms
Frequency spread: 30Hz

ALE400 (Unproto)......Incomplete / +2db*
PAX (Unproto)..................NO DECODE
PAX2 (Unproto).................NO DECODE
HF Packet (Unproto 300bd)......NO DECODE

___________________________________________________

Simulation: Mid-Latitude Disturbed
Path delay: 2ms
Frequency spread: 1Hz

ALE400 (Unproto)...............-2db /  -6db*
PAX (Unproto)..................-4db / -10db*
PAX2 (Unproto).................+1db /  -2db*
HF Packet (Unproto 300bd).........NO DECODE

_____________________________________________________

Simulation: Low-Latitude Disturbed               
Path Delay: 6ms              
 Frequency Spread: 10Hz

ALE400 (Unproto)................0db /  -5db*
PAX (Unproto)...................0db /  -6db*
PAX2 (Unproto)....................NO DECODE
HF Packet (Unproto 300bd).........NO DECODE

_________________________________________________________________

    RSID and Video I.D. Tests

     (MutliPSK Software by F6CTE) 

Minimum SNR (no Ionospheric distortion)

RSID......... -25db
Video ID.......-2db

_____________________________________

Ionospheric Simulaitons

   High-Latitude Moderate

RSID............No Decode
Video*.....Partial Decode

* Diffuse text difficult to read regardless of SNR

High-Latitude Disturbed

RSID........No Decode
Video*......No decode

*Text completely diffuse

Mid-Latitude Disturbed

RSID........-25db
Video....... +3db

Low-Latitude Disturbed

RSID...........no decode
Video*....Partial decode

* Diffuse text difficult to read

__________________________________________________________

WSJT Modes

Minimum SNR
(direct path - no ionospheric distortion)   

JT65A*...........-30db
WSPR*............-30db
JT6M.............-12db
FSK441............-2db

*On-air minimum SNR (approximate). 

Ionospheric Simulations 

High-latitude Moderate
(-8db SNR)

Mode        Throughput

JT6M.............100%
JT65..........no copy
WSPR..........no copy

High-latitude Disturbed 
(-3db SNR)
JT6M..............75%
JT65..........no copy
WSPR..........no copy

Mid-latitude Disturbed
(-8db SNR)
JT6M.............100%
JT65.............100%
WSPR.............100%

Low-latitude Disturbed
(-8db SNR)
JT6M.............100%
JT65..........no copy
WSPR..........no copy

Doppler Tolerance
JT65 / WSPR

Both modes seem to have a low tolerance for the increased doppler spread found on high / low latitude paths. 

In this test, the spread was increased until throughput was lost. Spread tolerance was roughly 1.5 Hz for WSPR and 3.5 Hz for JT65. 

A -20db SNR was used for this test since both modes are likely to be used for weak-signal work. 

Test #1
Path delay: 1ms
Doppler: 0.5 Hz
(-20db SNR)

Mode        Throughput

JT65..............100%
WSPR..............100%

Test #2
Path delay: 1ms
Doppler: 1 Hz
(-20db SNR)

JT65..............100%
WSPR..............100%

Test #3
Path delay: 2ms
Doppler: 2 Hz
(-20db SNR)

JT65..............100%
WSPR...........no copy

Test #4
Path delay: 2ms
Doppler: 3 Hz
(-20db SNR)

JT655..............100%
WSPR............no copy

Test #5
Path delay: 2ms
Doppler: 3.5 Hz
(-20db SNR)

JT655..............100%
WSPR............no copy

Test #6
Path delay: 2ms
Doppler: 4 Hz
(-20db SNR)

JT65............no copy
WSPR............no copy

_______________________________________________

WSJT Mode Description

FSK441: Intended for VHF/UHF high speed meteor scatter -- not suitable for HF. 
JT65: EME and other weak signal work (HF/VHF/UHF)
JT6M: Specifically developed for 6 meter ion / meteor scatter.  
WSPR: Weak Signal Propagation Reporter (digital beacon).