1. Amateur Radio Digital Modes Focus on Field Day Use
Which bands?
Why now?
Amateur Radio Digital Modes Focus on Field Day Use
N6MDV K6VHY
November 14, 2017
How much power?
When and who can I talk to …?
What mode?

2. Field Day 2018 Digital Modes It has been suggested we do more digital modes in 2018
Why?
Enables contacts on higher bands despite poor sunspot propagation
Lower SNR required than phone contacts
Develop additional skills for weak signal emergency communication
Easier to learn than CW for weak signal use
May be fun to learn and try new things
Possibly attract additional operators who don’t do CW or Phone
Why not?
Takes effort to prepare for new radio connections, software, …
Good use of operator time?
Contact rate is slower than with a good CW or Phone operator
Additional equipment needs: decoding computer, TNC
Operators need to learn new skills
Interference with other W6HA radio stations in FD ops
RFI or scheduling of equipment

3. Sunspot Values Continue to Decline Reduce propagation at 20M and above
Sunspots affection ionization
Ionosphere refract radio waves
Bends waves back to earth
Responsible for long range propagation
Declining propagation has reduced our contacts on higher frequencies
CW and digital modes need less SNR than phone
To maintain higher contacts need to
Use modes that need less SNR
CW would be best
Use lower frequency bands
80 and 40 meters
Smoothed Sunspot Numbers – Predict Propagation
Next few years will be lower than last few years
2017

4. Digital is a Small Part of FD Traffic But still an opportunity for many contacts
We have about 1200 contacts. If we add same ratio we will have another 100 contacts -> 400 points

5. Chart Suggests that PSK31 needs 20 dB less SNR than SSB
Mode SNR Net data speed Needed Eb/N0
in 2500 Hz in bits/s
SSB voice * +31 dB
CW (ZRO-test, by ear) dB**
CW (QRSS-3, waterfall ) dB**
CW (RSCW, 12 wpm ) dB**
OPERA dB***
RTTY dB
PSK dB
WSPR dB****
WSPR dB****
JT65 (for EME) dB****
Coherent BPSK on VLF dB Theoretical limit dB
*very crude estimate
** based on peak average power; peak power 3 dB higher
*** peak power is 3 dB higher; 2 dB lower if counting CRC-bits as information
**** not counting energy in synchronization bits; otherwise 3 dB more
Chart Suggests that PSK31 needs 20 dB less SNR than SSB

6. SNR relative to noise in a 2.5 kHz SSB bandwidth
MODE BW(Hz) THRUPUT SNR(ave) SNR(pk) SNR(ave) Hz wpm dB dB dB at 1 char/sec
SSB
CCW (12 wpm = 1 c/s)
Hell
WSJT
PSK
RTTY
Chart Suggests that PSK31 needs 20 dB less SNR than SSB
However, other factors likely apply:
Lower transmit power
Congestion and overlap in the digital modes area of band
General noise floor increase on field day
May just need to try it to see if modeling projections are correct.

7. PSK31 Test Results Based on experiment of two HF rigs, noise generator, attenuator
SNR
Perfect copy of 12 lines of text.
Perfect copy of 9 lines of text.
Perfect copy of 16 lines of text.
Near perfect copy of 13 lines of text message.
9.90 Much of the 11 lines of text are intelligible
However, there are missing characters and a few missing words,
8.96 Much of the 12 lines of text are intelligible
7.70 Message text is readable but with considerable difficulty.
7.08 Message text is barely readable, occasional words distinguishable.
6.38 Message text is barely readable, occasional words distinguishable.
However, much of the time Digipan was not able to demodulate and decode the message.
5.1 At this SNR the message text is not readable.
Digipan was not able to demodulate and decode any of the message. But, I could still here the PSK31 signal.
This experiment suggests that the previous charts are possibly 10dB too conservative
Source: James A. Frazier, Jr., KC5RUO

8. FD Propagation 7PM Phone Blue, Yellow, Brown, Red. Digital all colors
Blue is at SNR 45 dB – recommended value for SSB and consistent with previous experience
Gray is modeled at SNR 30 dB – likely area for PSK31. CW would be better yet.
Based on PSK 31 needing 20dB less SNR and
Transmit power set at 25W vs 100W for SSB i.e., 6dB
( ~ 30 dB)
VOAAREA modeling

9. 20M Propagation FD 2018 Phone Blue, Yellow, Brown, Red
20M Propagation FD 2018 Phone Blue, Yellow, Brown, Red. Digital all colors
Phone
Phone
5PM
9AM
Phone
Phone
Blue is at SNR 45 dB – recommended value for SSB and consistent with previous experience
Gray is modeled at SNR 30 dB – likely area for PSK31. CW would be better yet.
Based on PSK 31 needing 20dB less SNR and
Transmit power set at 25W vs 100W for SSB i.e., 6dB
( ~ 30 dB)
VOAAREA modeling

10. Common Digital Modes – Potential for FD Use
RTTY Radio TeleTYpe
Two tones: 2295/2125 Hz
Transmission speed: 45 baud, 5 bit characters => 60 WPM
Bandwidth: 250Hz
Typically at xx.080 – xx.099 part of the band
PSK31
Phase shift
Transmission speed 31 baud, varicode, => 50WPM
Lower case characters are fewer bits
Bandwidth: 60Hz
Typically at xx.070 portion of band
MFSK16
16 frequencies with Forward Error Correction (FEC)
Transmission: baud 16-FSK, Hz spaced tones
Bandwidth: 384Hz => 30WPM with FEC
Known for contesting and faster
Known for long rag chew – brag tapes
Photos courtesy of See that page for sounds also.

11. Another Option FT8 – New Mode July 2017
FT8 similar to JT65 but 4 times faster
15 second transmit and receive intervals
Entire QSO in 1 minute
Limited payload: call signs, signal report, minimal exchange
E.g. grid squares, 73
Includes Forward Error Correction (FEC)
May be in use this field day, as it is new and hams like new
Reportedly even lower SNR needed than CW
“SNRs from my receiver below –10 dB (measured in a 2,500-Hz bandwidth). Some of the 22 QSOs may have been difficult to complete on CW.”
The new mode is named after its developers, Steven Franke, K9AN, and Joe Taylor, K1JT.
The numeral designates the mode’s 8-frequency shift keying format.
Tones are spaced at 6.25 Hz,
FT8 signal occupies just 50 Hz.
FT8 requires accurate time synchronization.
An auto-sequencing feature offers the option to respond automatically to the first decoded reply to your CQ.
Google ft8 for the software

12. How is Digital Done Computer connected to radio via TNC
Computer connection to sound card
Software on computer decodes sounds displays waterfall
Operator clicks on open frequency space to call CQ or on a call
Software auto loads other person’s call sign into macros
Press appropriate Function key to transmit macro
Four macros when running
cq fd de w6ha k
<call> 3A LAX 3A LAX de w6ha k
<call> tu
<call> agn? Agn? de w6ha k
Three macros when search and pounce
<call> de w6ha w6ha k
<call> tu 3A LAX 3A LAX de w6ha
TNC = Terminal Node Controller
MPC = Multi Protocol Controller
De = “this is”
K = “over, go ahead”
Agn = again abbreviation
fd = field day
tu = thank you

13. Computer Sound Card Connection & USB Control Connection
Example Hook Up for PSK31
ICOM 7000 Radio RIGblaster TNC
Computer sound card & USB connection
CI-V and accessory connection on radio
Strong PSK31 signal
Decoding via Digipan software
Macro buttons across the top
Multiple signal decode on right
Waterfall below
ICOM 7000 multimode radio
CI-V
ACC
Computer Sound Card Connection &
USB Control Connection
RIGblaster TNC
Sound, control, CI-V link
CW and digital modes

14. Concerns, Issues, Possible Solutions
Inter-station interference with two transmitters on same band
Band pass filters do a fine job keeping different bands separate
But not for two stations on the same band
Other groups make it work
Radios with good internal filters / selectivity / low noise (e.g., KX-3 and K3)
Careful placement of antennas
Keep them far apart and oriented so nulls point toward each other
Run rates will be slower than phone – likely true
Data from 2015 shows the following results at non-optimal time of day, i.e, few stations on the air midnight or with poor antenna propagation on Sunday morning
Digital log data
Av time between QSO 2.6 minutes
Min time between QSO 0 minutes – we might get our average time better
Phone log data
Av time 1.6 minutes per QSO (Sunday at 10 AM)
Av time 1.06 minutes per QSO (Saturday 9 PM)
AB6UI rate on FT8 was a QSO 4 minutes on average – new to mode
Expect digital may be 2X slower than phone – with practice may do better

15. FD 2015 Details: Digital Contacts PSK31
ICOM 7000 nominally Watts
Rigblaster plug and play
Lap top Windows 8.1 running digipan
Total QSO: 45
10 at midnight Saturday, just to get some
Great national antenna coverage, just few operators
35 Sunday AM starting at 7:30 AM
Limited antenna coverage at that time of day
Stats on QSO rate
Saturday night
Av minutes between QSO 4.5 minutes
Max time 9 minutes Min time 2 minutes
Sunday morning
Av minutes between QSO 3.5 minutes
Max time 10 minutes Min time 0 minutes
If throw out the long times on Sunday AM, presuming equipment or people distractions
Av time between QSO 2.6 minutes
Compared to phone run rate
10 AM Sunday 1.6 minutes per QSO
9 PM Saturday 1.06 minutes per QSO
With double points for digital, the points per minute are close with digital when number of stations has dwindled

16. FD 2015 Details: Run Rate Thoughts
20M station first 3 hours Saturday
1 minute each -- FAST
20M station 10AM Sunday
2.14 minutes each– Slowing
40M station first 3 hours Saturday
40M station Saturday 9PM
1.06 minutes each -- FAST
40M station 10 AM Sunday
1.36 minutes each Slowing
Digital station better case
2.6 minutes per QSO
Observations
When there are plenty of stations
And with good
antenna
Band
Transceiver
Operators
A run rate on phone can be 1 QSO per minute for extended periods of time
With digital PSK31, run rates appear to be close to the slower run rate on phone
Possibly could be faster with more stations???
Or possibly just use to collect additional contacts

17. Next Steps for W6HA Field Day 2018
Decide if we want to do more digital
Get interfaces and software for the rigs that will be used
Train / practice using digital modes
Decide how it will be used on field day
As a separate CW / Digital station enabled for every band
As an occasional mode on the different band stations e.g., 15, 20, 40
When should it be used?
When phone run rate drops below a certain level?
Which mode(s)
Consider pushing ARRL publications to encourage:
Digital use given low sunspots
Mode based on portion of hour, i.e., psk on the hour, RTTY on the half – FT8
As a club set up a digital / SSB experiment day in the park
Confirm that the mutual interference will be small
Hands on practice and testing of the rigs / SW

18. Questions?
Thoughts?