Digital Radio Modes

Brooke Clarke, N6GCE 2001 - 2013


Background
Modes
    CW
    Coherent CW
    High Speed CW
    Radio Teletype
    PSK31
    Olivia
    Weak Signal Propagation Reporter
        Configuration
        A Note on USB
        Operation
        Reports
    Chirp
    Automatic Link Establishment
    Digital Voice
    Frequency Hopping
    Spread Spectrum
Military Designations
Related
Test Equipment
Links

Background

By using a digital mode where the signal bandwidth is narrower than the standard 300 Hz to 3,000 Hz voice bandwidth the signal to noise ratio can be improved thus working where voice will not work.

Modes

A classical problem is getting a message to the desired recipient without any errors in the presence of noise.  In the analog world that was best done by minimizing the signal bandwidth and using a receiver with that same bandwidth.  But, as the bandwidth is narrowed so is the amount of information per unit of time reduced.

Another concept is that it's better to transmit something than nothing.  So modulation schemes that are always transmitting work better than schemes where the transmitter is turned off.

In the digital world there are new things that can be done.  Multiple frequency-shift keying (Wiki) is an outgrowth of the development of dial-up modems (Wiki) where it was desired to send as much data as possible over a bandwidth limited to about 3 kHz.  At the beginning 200 baud was that best that could be done, but ended up at 56,000 baud in that 3 kHz bandwidth.  Later DSL (Wiki) would provide 6,000,000 baud over phone lines.

Continuous Wave (Wiki: CW)

This is the oldest digital mode also knows as On Off Keying (OOK).  This mode suffers from a number of problems.  For example when the transmitter is turned off no information is being sent, so modes that are always transmitting are better.  There is no synchronization in terms of the on/off edges or in terms or timing relative to the carrier.

Coherent CW (CCW)

The idea is for both the transmitting station and the receiving station to have a precise clock and the start and stop edges of all the symbols fall at known points in time.  This allows automated detection of CCW at lower signal to noise ratios than ordinary CW.

High Speed CW

During WWII the enemy could use Direction Finding (DF) receivers to locate transmissions that were being made by spies.  In order to reduce the time it takes to transmit a message High Speed CW sets were developed and later used as late as View Nam.
GRA-71 and and English version of the GRA-71 use a magnetic tape that is recorded manually and then played to the transmitter at about 300 Words Per Minute.

Radio Teletype (Wiki: RTTY)

Also knows as frequency shift keying (FSK).  Involves transmitting on one of two frequencies.  This mode has been around for a very long time. Problems: If the shift is too wide the signal takes up more bandwidth than is needed relative to the keying rate.  Minimum Shift Keying (Wiki: MSK) is better in this regard.  The early demodulators required both Mark and Space signals in order to work and if one or the other was garbled the output was garbled.  Frederick Electronics and I assume others offered advanced demodulators that would work with either Mark or Space signals.

Note that the transmitter is always transmitting something so more power is being used per bit than in a mode like CW where the transmitter has off time.

By using a number of different forms of diversity the reception of HF RTTY signals could be radically improved.  A common system was to use two receiving antennas, two receivers and two demodulators.  If the antennas have different polarity and/or are separated by a distance that's a few wavelengths then the signals tend to fade at different times on the two systems and a combiner automatically selects the best signal so the output is the best of both signals.  Another form of diversity is to use a common antenna but have the two receivers tuned to different frequencies that are both transmitting the same message.  Another form of diversity is time.  The MD-1142 sends a number of versions of the same message offset in time and modulation tone frequency.  The idea is that fades only last a short time and the message can be reconstructed.

The CV-89A/URA-8A is a Military tube type FSK converter with a CRT type tuning indicator.
The CV-483/URA-17 is a Military solid state FSK converter with a CRT type tuning indicator.
The Frederick 1203 a solid state FSK Demodulator that works with either Mark or Space or both
The MD-1142 uses time diversity and multiple audio channels

PSK31 (Wiki)

This is a digital mode that's optimized for human generated characters, very narrow bandwidth and the transmitter is always on.

Olivia (Wiki)

Is similar to PSK31 but includes multiple copies of the message offset in time, similar to the MD-1142 and is more robust.

WSPR (Wiki)

"Weak Signal Propagation Reporter" Intended for propagation analysis and/or antenna testing, does not include provision for data communication.
Official web page - http://physics.princeton.edu/pulsar/K1JT/wspr.html - software designed to be used with SSB HF radio and a computer sound card.
wsprnet.org - maps and logging

QRP-Labs - has a relay filter bank as an option for their WSPR transmitter (6 Tx frequencies) as well as a GPS receiver for keeping time, RF frequency & Grid square.
WSPRlite - SotaBeams: UK based standalone WSPR single frequency transmitter- Classic SB or Flexi -

Photo

WSPRlite beacon
                  transmitter at base of TCI-651 antenna
WSPRlite Flexi beacon transmitter at base of TCI-651 antenna
With Power Bank recommended for GoPro camera where my existing power bank did not work.  SotaBeams says some power banks turn off if they don't see enough load.

The transmitter has microUSB for DC power and programming.
SMAf for RF out, a status LED and a start push button. A very simple setup.  But the timing of the press and hold for start needs to be accurate to maybe 0.1 seconds, 2 seconds is far enough from correct to prevent proper reception.

I have a microUSB to microUSB cable on order to allow using my cell phone to configure the transmitter in the field.  This was a mistake since the LG-998Tphone has a USB-C connector and does support OTG.

20 June 2018 borrowed a WSPRlite Flexi - has the following frequencies built-in, only one per configuration:
power out 200 mW and lower. The classic SB model has fewer frequencies but includes a couple of filters.
meters
MHz
Flexi
MHz
SB
630
0.474200

160 1.836600

80
3.592600

60
?

60
?

40
7.038600

30
10.138700
Filter
20
14.095600
Filter
17
18.160100
na
15
21.096100
na
12
24.926100
na
10
28.126100
na
6
50.294500
na
Filter: the SB has internal filters for 20 & 30 meters.  The Flexi has no internal filters.
Spectrum Plots on 4395A using a 3 foot wire as antenna.  This was done as a check that the transmitter was working.
The Wiki WSPR page says the bandwidth is 6 Hz. So what your seeing in these two plots is the SA IF BW.
80 meters 3.570125 MHz
WSPR spectrum
                plot
40 meters 7.040104
WSPR spectrum
                plot

Configuration

Prior to using the WSPRlite it needs to be programmed using the USB-micro port for both power and data.
That can be done using a standard USB-A to USB-microB cable and a laptop or desktop computer or a USB-microB to USB-microA cable and a cell phone with OTG capability.
USB On-The-Go (Wiki) allows connecting two devices where one acts as the host.  Intended for things like memory, keyboards, mouse, &Etc.  Allows the WSPRlite app to both configure the beacon transmitter and to also start it at the exact time needed.  But to remove the phone and keep the beacon transmitting requires a Y-cable.

Turns out this does NOT fit  the LG-998T phone,
connectors 6.81mm wide (Mini-B), but need to be 8.2mm (B).
This is a USB-Bmicro cable -
USB
                  On-The-Go USB-microB to USB-microA Cable
<- This is a Cable Creation p/n: CC0756
UPC: X001HH6U8R
Length" 0.2m (8")f
eBay search term: "Micro USB Male to Micro USB Male OTG Cable Data Transfer"
The cable is asymmetrical and one end is labeled "Host".
Fig 1 Cables for OTG configuration & starting

Cables
                  for WSPRlite OTG configuration & starting
Although not marked on the Y-cable, one of the
USB-A connectors only carries DC while the other
one will work for data.  To test connect WSPRlite to computer using Y-cable and see which leg supports configuration.  For this Y-cable the other leg does NOT support any data, only DC.

Note: the cable from the phone to the USB-A socket needs to
match your phone.  Mine happens to be a USB-C connector,
but prior phones have used USB-Bmini and USB-Bmicro
connectors.

Fig 2 Set-up prior to tapping Auto-Start
Cables for
                  WSPRlite OTG configuration & starting
Fig 3 Counting down for auto-start to activate beacon
Cables for
                  WSPRlite OTG configuration & starting
Fig 4 beacon has been activated
Cables for
                  WSPRlite OTG configuration & starting
Fig 5 Cell phone can be removed and beacon gets DC from
power bank.
Cables for
                  WSPRlite OTG configuration & starting


The problem is that if the start transmission function is used in the phone then the phone is powering the WSPRlite.  When the phone is unplugged the WSPRlite stops, so a "Y" cable is needed to take advantage of the app auto start function.  The Y-cable sold by SotaBeams (web page) seems to have a USBA socket and to is a two cable solution.

I have on order (eBay title: "USB OTG Power Y Cable")  It has a USB-A plug for the power bank, a USB-A socket for the existing WSPRlite power/programming cable & a USB-microB plug for the cell phone.  I'm guessing this is what the SotaBeams cable is, so it will take two cables.
To determine if yhour phone supports USB OTG use the Android app "USB OTF Checker".  The LG-VS988T does support it.

Part of the configuration is the Grid Square location of the beacon.  Here's a web page to help with that.  Note only the first 4 characters are used by WSPR.

A Note on USB

When USB first came out it was a fantastic improvement on RS-232. 

It turns out the RS-232 was an agreement to NOT have a standard.  The pin assignments (Tx on 2 or 3?), number of pins (9 or 25) in the connector and sex (pin or socket), type of handshake (hardware, ACK/NAK,, none), parity bits (none, 1, 2, even or odd) are not fixed, so in order to get two devices to talk in "RS-232" you need a custom cable or a stock cable (straight or null modem?), BAUD rate (select from a long list or auto determined) and a bunch of adapters to get it working and settings on the computer to match.  That all went away when USB was introduced because there was USB-A where the desktop or laptop computer had a USB-A socket.  The one and only cable had a USB-A plug to a USB-B plug and the other device had a USB-B socket.  But then people wanted video and USB was to slow so, Firewire came out as something different.  That didn't last long and USB got faster and then the "B" connectors started changing.  Now there are B, Bmini, Bmicro and C connectors and various number versions of USB like 2.0, 3.0 &Etc 

So, USB has become an agreement to not have a standard.  Just like RS-232 you need to specify which flavors of USB cable you want.  This allows retailers to sell cables without specifying the connector and instead specifying what models of phones they fit.  Of course this is accompanied by a price 10X higher than what you would pay for the generic cable.

Operation - Starting at the correct time.

After using time.is web page on my cell phone, I started getting signal reports.
It's also important to start on an even minute, which I may have done by accident.
The time to send one frame is just under 2 minutes.
"Press the button 2 seconds after the start of an even minute.

It turns out that the time shown on my WIN7 desktop computer was off by 1.8 seconds and my LG-VS988T cell phone does not display seconds on the clock.
The desktop clock was fixed by using Dimension4 software.  Now the desktop computer agrees with the UltraLink WWVB receiver and time.is web page.
I added the ClockSync app to the cell phone but unless you root your android phone it can NOT set the system clock.  But it does have a seconds display.  This is because the Android system forbids apps from changing the system time or date, probably because if you could do that, then you could keep trying the demo version by setting the clock back to when you loaded the app.
home page - Vimeo: ClockSync assisted (Rootless) mode - this only works when the cell phone is off by 30 seconds or more.  It can NOT set the phone's clock to fractions of a second.
Need to find a GPS app that displays seconds or use time.is.
I've added the time.is web page as an icon on my cell phone making it easy to call up.

Reports

-------------------------------------------------------
reports in the first hour of operation

DX10: N6GCE - 7 MHz - 200mW

Distance (km) Call Spots count Last seen
652 KD7OFU 1 2018-06-22 18:58
646 W7OWO 12 2018-06-22 17:02 to 20:26
246 KM6I 2 2018-06-22 18:06 to 18:26
174 KK6ZIZ 7 2018-06-22 17:02 to 18:20
173 KP4MD 4 2018-06-22 17:02 to 18:26
155 KPH 20 2018-06-22 17:02 to 20:14
153 SWL-CM98DN 1 2018-06-22 17:04
Average distance: 220 km
------------------------------------------------------

Maps & Graphs

160m  (26 June 2018)
Only my friend K2HZO can here me

80m
WSPR Map 80meters
                  WSPRlite N6GCE

WSPR Map
                  80meters WSPRlite N6GCE
40m
WSPR Map 40meters
                    WSPRlite N6GCE
WSPR 40m
                    DX10 Graph
30m

20m (27 June 2018)
Heard immediatly by K7QXY
WSPR Map 20 meters
                    WSPRlite N6GCE

WSPR 20m
                    DX10 Graph

10m (29 June 2018)
WSPRlite 10 meter
                    map
sorted by S/N (notice all contacts late at night
timestamp date & time rx_call rx_grid snr freq power_dbm drift distance azimuth
1530823680 7/5/2018 20:48 WA6JRW DM14he -7 28126189 23 0 774 138
1530823440 7/5/2018 20:44 WA6JRW DM14he -9 28126188 23 0 774 138
1530827880 7/5/2018 21:58 WA6JRW DM14he -11 28126184 23 0 774 138
1530823200 7/5/2018 20:40 WA6JRW DM14he -11 28126188 23 0 774 138
1530817560 7/5/2018 19:06 KA7OEI DN40ao -14 28126112 23 0 947 79
1530798000 7/5/2018 13:40 KA7OEI DN40ao -18 28126113 23 1 947 79
1530822600 7/5/2018 20:30 KA7OEI DN40ao -19 28126112 23 0 947 79
1530822240 7/5/2018 20:24 KA7OEI DN40ao -19 28126112 23 0 947 79
1530815640 7/5/2018 18:34 WA6JRW DM14he -19 28126180 23 0 774 138
1530819000 7/5/2018 19:30 KA7OEI DN40ao -20 28126113 23 0 947 79
1530823440 7/5/2018 20:44 KA7OEI DN40ao -21 28126112 23 0 947 79
1530818640 7/5/2018 19:24 WA6JRW DM14he -21 28126184 23 0 774 138
1530816360 7/5/2018 18:46 WA6JRW DM14he -21 28126180 23 0 774 138
1530813000 7/5/2018 17:50 KA7OEI DN40ao -21 28126107 23 0 947 79
1530822360 7/5/2018 20:26 KA7OEI DN40ao -22 28126112 23 0 947 79
1530818520 7/5/2018 19:22 WA6JRW DM14he -22 28126184 23 0 774 138
1530821160 7/5/2018 20:06 KA7OEI DN40ao -23 28126113 23 0 947 79
1530813120 7/5/2018 17:52 KA7OEI DN40ao -23 28126106 23 0 947 79
1530828720 7/5/2018 22:12 WA6JRW DM14he -25 28126185 23 0 774 138
1530821040 7/5/2018 20:04 KA7OEI DN40ao -25 28126113 23 0 947 79
1530820680 7/5/2018 19:58 WA6JRW DM14he -25 28126186 23 0 774 138
1530816480 7/5/2018 18:48 WA6JRW DM14he -25 28126180 23 -1 774 138
1530827880 7/5/2018 21:58 WB6B DM14nf -26 28126100 23 0 800 135
1530820680 7/5/2018 19:58 KA7OEI DN40ao -29 28126114 23 0 947 79




WSJT (Wiki)

A package of Weak Signal (WS) digital modes.
WSJT Home Page by K1JT - includes a sub page for WSPR -

Chirp

Although chirp transmitters are intended for measuring H.F. propagation they do have a MSK like mode where a short message is sent over and over again and the transmitter sweeps from 2 to 30 Mhz.  If there's a path somewhere in that range the message gets through.

 Automatic Link Establishment (Wiki: ALE)

This really is not a mode, but rather a protocol for linking HF radios automatically.  Each radio in a net periodically polls the other radios in the net and keeps track of what frequencies work for which radios in the net at different times of day.

Digital Voice (eHam, ARRL)

The military uses Continuously Variable Slope Delta (CVSD) as a method of converting voice into a digital signal.  This is the signal that is sent over the wires of the TA-1042 Digital field phone.  For use in the KY-57, KY-58, or KYV-2 Secure Voice Module the CVSD data is enciphered prior to sending and then descrambled at the receiving end.  This is a symetric system with the same key used for both sending and receiving.

I started looking into what it would take to make a digital voice interface to work with the military radios that have "wide band" capability, i.e. the VHF and UHF radios.  The CVSD chips used in the early military voice encryption units are now obsolete.  There was some amateur radio work done using the AD73311 CODEC, but it has a 16 bit word output with a framing pulse.  This makes it very hard to send over the air without also using some type of VOCODER chip to reduce the bandwidth.  By using a CVSD type of codec the output is just a single bit data stream with no framing required, making it relativity easy to send and receive.

I recently saw a nice distinction made between voice scrambling and voice encryption.  The implication was that scrambling involves mixing up the audio and sending that audio, whereas enciphering implies using a digital data stream to carry the voice message.  From what I've read it's possible to reconstruct any mixed audio scheme, but very much more difficult to break a digital cipher.

The  KY-38 came out during the latter part of the Vietnam era and worked with the PRC-77, so probably used a digital enciphering method rather than an analog scrambling method, but this is all speculation since not much has been published about it.

Frequency Hopping (Wiki)

One way to make direction finding difficult is to have the transmitter change frequency frequently.  Note that the hopping itself may not provide any security since a simple crystal radio that had a wide band input would detect all the transmissions.  This is the case no matter in what order the frequencies are changed.  So voice encryption is needed in addition to the hopping and that's what is done in the COMSEC part of the SINCGARS radios, externally with a KY-57 for the early radio and internally in the later radio.

Spread Spectrum

Although Frequency Hopping is a form of spread spectrum, the term is used more often to describe what is called a direct sequence (Wiki).  This is where the data signal is mixed with a spreading signal with a data rate considerably higher than the data signal rate so the the final signal that's transmitted has a bandwidth larger than what would be used for just the data.  For example the C band satellite television system spreads the normal 4.5 MHz video signal out to 36 MHz thus adding process gain to the system allowing much lower transmitter power in the satellite.  The Magnavox Procom hand held radios have a very long range for a low power radio because of the spread spectrum signal. The GPS satellites use spread spectrum and the signal falling on the Earth is so weak that it is below the background noise level.

The Black Box uses pulse modulation but it's transmitted spectrum looks very much like spread spectrum.  I assume that there's a receiver optimized to receive this signal. But none of the receivers I know about will receive the signal.

Military Designations

MIL-STD-188-110A/B/C  (Wiki, MARS) Interoperability And Performance Standards For Data Modems (Tactical Data Link: TADIL, Link 11)

110A-1991: 75bps through 2400bps coded and 4800bps with no FEC or interleaving
110B-2000: 9600bps coded in a 3Khz channel and
110C-2011: from 3Khz up to 24Khz in increments of 3Khz channels while providing user data rates up to 120,000bps coded hroughput with multiple HF Independent Sideband (ISB) channels.
STANAG 5066 Profile for HF Radio Data Communications (Data Link Protocol (DLP) (5066-ARQ))
MIL-STD-188-141B/C Interoperability and Performance Standards for Medium and High Frequency Radio Systems

STANAG (Wiki)

STANAG 4197 - Edition 1, Modulation and Coding Characteristics that must be Common to Assure Interoperability of 2400 b/s Linear Predictive Encoded Digital Speech Transmitted over HF Radio Facilities

FED-STD-1015 - Analog to Digital Conversion of Voice by 2400 bit/second Linear Predictive Coding (LPC)
STANAG 4198 Edition 1, Parameter and Coding Characteristics that must be Common to Assure Interoperability of 2400 b/s Linear Predictive encoded Digital Speech

STANAG 4203 - (Edition 3), Technical Standards for Single Channel HF Radio Equipment

STANAG 4285 - Characteristics of 1200/2400/3600 bit/s single tone MODEMs for HF radio links,
FED-STD-1052 Appendix B Telecommunications: HF Radio Modems (Data Link Protocol (DLP))

STANAG 4415 Characteristics of a Robust, Non-hopping, Serial-tone Modulator/Demodulator for Severely Degraded HF Radio Links

STANAG 4481 - Edition 1, Minimum Technical Standards for Naval HF Shore-to-Ship Broadcast System

STANAG 4529 - Characteristics of single tone MODEMs for HF radio links with 1240 Hz bandwidth

STANAG 4538 - (Edition 1) Technical Standards for an Automatic Radio Control System (ARCS) for HF Communication Links

STANAG 4539 C3 (Edition 1), Technical Standards for Non-hopping HF Communications Waveforms

STNAG 4591 - Edition 1, 600 b/s, 1200 b/s and 2400 b/s NATO Interoperable Narrow Band Voice Coder

STANAG 5065 MSK waveform

Link 11 MIL-STD-6011 (Wiki) -> Link 22 (Wiki)

U-229 AUDIO/DATA connector pin out.

DS-101 Smart Fill Devices (Wiki)
DS-102 Common Fill Devices
See Fill on the Crypto Machines web page

Other

There are a lot of digital modes in addition to those mentioned above.  Some are for transmitting text and some are for transmitting images.  For example see:
Worldwide Utility News (WUN) -

Harris 5710 & 5720

These are modems in a box that support many of the military data modes.
4365338 Technique for high rate digital transmission over a dynamic dispersive channel, Harris Corporation, Dec 21, 1982, 375/230, 375/254 -  referenced by 121 other patents - optimized for HF data - uses known preamble
4599732 Technique for acquiring timing and frequency synchronization for modem utilizing known (non-data) symbols as part of their normal transmitted data format, Harris Corporation,
Jul 8, 1986, 375/346, 375/367, 375/355 - referenced by 184 other patents - makes use of I & Q processing - preamble type known information is interleaved with the data so the receiver can dynamically re-equalize.

Related

The CV-89A/URA-8A is a Military tube type FSK converter with a CRT type tuning indicator.
The CV-483/URA-17 is a solid state FSK converter with a CRT type tuning indicator.
The Frederick 1203 FSK Demodulator
The Frederick 600A BER test set
Digitech also made a modular rack mount Digital Data Generator
MD-1142 Modem
Cryptographic Machines
Cryptography
Cryptographic patents
FS5000 cold war embassy secret coms 2-way HF radio set
PRC138 ALE capable HF manpack radio
Micom ALE capable HF vehicle radio
GRC-109 HF radio works with GRA-71 high speed Morse transmission (but not receive high speed Morse)

Test Equipment

In order to test any digital mode you need a test signal and a way to evaluate how it gets through the modulation - demodulation system.
Test equipment for early RTTY equipment was designed to test the mechanical RTTY machines and has special functions for them.  These machines were used in a current loop configuration where all the equipment was in series.  Included was a power supply of around 100 Volts and the current was adjusted for typically 60 ma and later 20 ma.
Digitech made a modular rack mount Digital Data Generator and analyzer

The Frederick 600A BER test set uses RS-232 levels rather than the older current loop type of interface.

When testing a communication path that will be used for encrypted messages the bandwidth of the test set needs to match that of the encrypted signal.  For testing both wire line and radio systems utilizing the VINSON protocol the F91120 test set is suitable.

Links

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page created 31 July 2001