Amateur Radio Info & Exams - Operations 3

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Amateur Radio Info & Exams - Operations 3 - Digital Modes

Didn't we cover Digital modes on the Tech paper? Yes, but this section deals with modes most often used on HF, MF, and LF, although there is no reason they can't be used on VHF and up.

In at least some cases the recommended digital portion in the bandplan is 70 to 100 kHz above the start of the band, for example, 3570-3600 kHz, or 14.070 to 14.100 MHz. On 40 metres it is 7.080 to 7.125 MHz.

There has been a change in the function of the computer in digital systems. Early Amateur packet systems required a Terminal Node Controller which took commands and text from an often pre-PC home computer (Commodore 64, MicroBee, etc), and assembled data packets, as well as generating and decoding audio tones. Some contained mailboxes, so could operate without a PC being left on. The BayCom modem system used driver software within the DOS PC to assemble to packets, and to tell the modem to send either a high or low tone. Now the PC (Linux, Windows, BSD, etc) uses an internal or external sound-card to generate tones sent directly to the radio, and to decode them.

"Soundcard" is a somewhat archaic term, from the days when a "Sound Blaster" or similar card was inserted into a 486 or similar PC. Later devices include them on the motherboard, and when additional ones are needed, these are available as low-cost USB devices (a few dollars online). The latter allows you to use the inbuilt one for the normal human facing functions, and the USB for radio facing ones.

RTTY

Often pronounced "ritty", this stands for Radio-Teletype, and originally used electro-mechanical teletype machines, with radio replacing the telegraph / telex lines. These were used by the military, diplomatic organisations, between ships, and by news agencies. You may have seen them in the film "Good Morning, Vietnam". TELEX was a wire based system using the same machines, where each business using one had a number, similar to a telephone number, such as Dick Smith's AA20036.

The original version directly keyed the transmitter to shift between two frequencies for mark and space. The modern version uses audio frequency shift keying, although for SSB this is has the same effect. RTTY usually uses Lower Sideband - LSB.

On HF the shift is usually 170 Hz. At LF is often half this, and there are certainly systems which use greater shifts. Speed is 45.45, 50, 75, or 100 baud, so fairly slow. Higher bit rates can be used on electronic systems. Baudot code, a 5 bit system, rather than ASCII, is often used. As 5 bits only gives 2⁵, or 32 characters, barely enough for upper-case characters, one of these is a "number shift" allowing the bit patterns to double-up as numbers and punctuation, a second "letter shift" character returning to letters.

RTTY is somewhat like voice or Morse, in that a station can communicate with more that one station, and take part in round-table conversations and nets. Material such as radio club news can be broadcast to many Amateurs. It is also possible for a non-ham to decode signals.

While the use of a PC, or "glass terminal" is common, restoration of electro-mechanical gear is also part of the hobby for some. As well as these very heavy machines, there are the SAGEM units which use a dot matrix printer, based on the 6800 processor. They should still be a two person lift. Many machines, modern and ancient, include a paper-tape reader, with a row of fine tractor sprocket holes, and 5 rows of holes, being the data. These allow a message to be prepared ahead of transmission, or for incoming messages to be stored for re-transmission. This also makes sending complex art made from alpha-numeric characters, or heading text as below, possible.

RRRR TTTTT TTTTT Y Y R R T T Y Y RRRR T T Y R R T T Y R R T T Y

PACTOR

A development of RTTY was AMTOR (AMateur Teleprinting Over Radio), and this was further developed with Packet Radio concepts to form PACTOR. It uses rapid switching between transmit and receive for error checking and retransmission if necessary. Its uses include inter-continental forwarding of packet messages.

While it is possible to listen in, only two stations can actively communicate at one time.

Pactor has reached its 4th iteration. You can read more at: Wikipedia: PACTOR

VARA & Winlink

VARA is a proprietary data transfer method used on HF radio. Along with PACTOR, it is used as the modulation and protocol for "Winlink", a radio to email system used by hams and yacht sailors.

The various protocols used for Winlink divide data into packets, and can operate on HF or VHF.

WINMOR, which can be used with a soundcard, has now been removed from Winlink operations.

DE-9 Connectors

These have been removed from the exam, as modems are being replaced with software and soundcard based systems, or USB devices. However, some equipment you come across may use them. You may wish to skip down to PSK31.

Line drawings of standard density 9 and 25 pin connectors on a yellow background.

The smaller connector is the DE-9 D-subminiature connector used for serial communications, for some modems, or at the PC end of the cable. The modem may use this, or the larger DB-25 connector, as used on dial-up or leased-line comms equipment. The larger connector, invented in 1952, was adopted in the 1960s RS-232 standard. The pinout for RS-232 over the 9 pin is defined in the 1990 standard, TIA-574. Lines include ground(s), transmit data, receiver data, optional flow control lines, and modem control lines. Older high end transceivers had these for computer control, or an interface which used an adaptor with serial at the PC end.
Note that the letter defines the shell size, with "DB-9" being a common error.
Some radios use USB connections which may be converted to RS-232 within the radio, including for programming.
These connectors, and versions with different numbers of pins are or were used for many things, including PC VGA (using high density DE-15HD) and other video connections, old external drives, printers, joysticks (DA-15 on PCs), barcode readers, and multiple industrial uses. There are male and female; and either can be mounted to a panel, or cable mounted with a backshell. When panel mounted there are usually nuts where the circles are on the drawing are, which accept 4-40 UNC screws, to stabilise the connectors. On the DE-9 these are spaced ~25 mm; and on the DB-25 it is ~53 mm. The nuts are 3/16" AF, but you can use a 5 mm driver or spanner.
A standard for the connector series is Mil Standard 24308.

In many cases you buy the connectors, and chassis mounting nuts or back-shells separately. While Jaycar may sell connectors and grey backshell sets for A$2 each, Element 14 have bags of 5 for under A$3 tax paid. E14's backshells are coded with letters, DE, DA, DB, etc, and are available in colour plastic (with nice jack-screws), metalised plastic, and for the big bucks, metal. These connectors have the pins in the connector, with solder buckets on te rear of each pin. There are also crimp pins which are inserted into housings, insulation displacement for ribbon cable (requiring a press), and PCB mount. Hobbyists often keep a small stash of these in their parts drawers. Beware the 23 pin version - these can "contaminate" stocks of 25 pin units. Ditto DE-19s and other 19 pin units.

RS-232

This is also off the exam, but may be useful if setting up older Packet "Terminal Node Controllers" or Pactor gear.

You can read about the RS-232 standard on Wikipedia: RS-232. Some terms date from the era of simple terminals connected to more centralised computers, as well as to modems or similar equipment. The connection of pins 2 and 3 requires close attention, as while they are used for TxD and RxD, the data transmit and receive lines, this varies between 25 and 9 pin connectors; however, each TxD connects to the other device's RxD. Signal ground is also needed. A range of control lines may also be used. RTS and CTS are cross-connected, or are occasionally looped back at each end. See: Wikipedia: Serial port, especially the Pinouts section.

Computers and terminals are termed "data terminal equipment", or DTE; and modems and the like "data communications equipment", or DCE.

The Null Modem is another useful cable if you like playing with old PCs, or things like MicroBees, or both at once. You can use one as computer as the terminal for the other.

You may be able to use cables supplied with the device, or perhaps buy them; or you can make them by soldering, or using crimp systems. In most cases the back-shells can be retrofitted to connectors without removing the cable, as they are in often 2-part, or fold open. Coloured units may remain available. In a return to past ideology, cards remain available for retrofitting to desktop PCs, but with modern buses. At one time these were included on motherboards. Some motherboards may included them, needing just a ribbon cable with a connector on a slot cover.

The alternative is a USB to Serial cable or module. These may be a few 10s of dollars if you need one today; a few dollars if you can order one from eBay or AliExpress in China. These use FTDI or clone chips - this search provides various boards to use in prototyping, retrofitting, etc. Be aware that some do true RS-232, some TTL (discussed below).

Speed / baudrate, as well as the number of data bits (such as 5, 6, 7, or 8), use of a parity bit (or not), and of stop bits are amongst the parameters you need to get right. "9600 7N1" is an example.

Just as D-connectors don't have to be RS232, RS-232 does not have to use these connectors: Many handhelds are programmed using a 3-wire system, via the typically 3.5 mm speaker-microphone terminal. CAT (Computer Aided Transceiver) uses an 8 pin mini-DIN. GPS / GNSS devices may send NMEA "sentences" over a 2 wire interface. Surplus GARMIN "hockey puck" devices turn up at little cost at times, with more modern units using USB (there are also antennas in this format, requiring a separate Receiver). The former case may be an example of TTL (+5 volt and 0 volt) interface. RS-232 standard specifies voltages of +3 to +15 for Logic 0, and -3 to -15 for Logic 1. A MAX232 or similar IC converts these levels.

TTL RS-232 can also be used to send data from a GNSS module within an APRS tracking device to the processor and modem IC, without a PC. The device in the yellow case on Wikipedia: APRS is an example.

Note that the BayCom packet modem of the early 1990s very much operated outside the standard, using data lines to harvest power, and control lines for data.

PSK31

This is a narrow bandwidth mode which can function with very low received signal levels. The software includes a waterfall display, which allows you to see where in the band segment there are signals. It uses Phase Shift Keying at 31 baud. It uses a PC with a sound-card, and a radio in the SSB mode, or related "data" mode. Use is from MF to UHF.

A basic HF radio, and a modest wire or other antenna is all that is needed to "work the world".

You can read more at: Wikipedia: PSK31, bpsk31.com, and RSGB: PSK31

The shift can be 180 degrees (binary phase shift keying (BPSK) or 90 degrees (quadrature phase shift keying (QPSK)). It is this use of phase shifting which differentiates it from RTTY, and from FT8 and the like, discussed below.

Waterfall displays

Just as water in a waterfall flows vertically over time, the information on the screen flows vertically, frequency is displayed horizontally, increasing left to right, and the colour or brightness (intensity) of the display indicates the strength of the signal. A simple signal, such as "QRSS" Morse can be seen in the waterfall as an on-and-off vertical line.

Things like harmonics of oscillators in low quality switch-mode power supplies (smaller Jaycar 13.8 volt ones are poor) which vary in frequency as the supply heats up may be seen as a diagonal trace. I understand that PSK31 appears as two closely spaced lines. Additional lines can be the result of over-modulation.

You can see many Signal Identification Wiki, linked to below.

It is possible to use tones to display a callsign in the waterfall.

WSJT-X

This stands for Weak Signal by Joe Taylor, with version 2.7 supporting FST4, FT4, FT8, JT4, JT9, JT65, Q65, MSK144, WSPR, FST4W, and Echo. These modes use AFSK (audio frequency shift keying), typically with the radio set to USB.

These mode utilise a PC's soundcard, and software. There are Windows and Linux versions, with the latter also running on the RaspberryPi. There is also a MacOS version. These are free and open source.

The documentation and download site: WSJT-X on sourceforge.io or sorceforge.net. You can also search WSJT-X on GitHub.

FT8

Of the modes above, FT8 is the likely most popular, especially on HF. It uses very narrow bandwidth, with multiple stations able to operate within the passband of a radio set to USB. Stations take 15 second turns to transmit or listen. These blocks, and the multiple narrow transmissions appear on this FT8 page: Wikipedia: FT8. Clicking the 40 metre band image shows the alternation between stations.

Apparently to respond to a station you select a frequency which is free during the timeslot in which that station does not transmit, although this can be automatic, just click a callsign, and the system will attempt to make a contact.

The benefit of this mode is that it allows a station in a noisy city location to make contacts around the world, which would be very difficult using voice, while using a modest radio, and simple wire antenna.

A popular frequency range is 14.074 MHz to 14.077 MHz, a little over 70 kHz above the bottom of 20 metres, an effective DX band.

The software includes frequencies in other bands, and can set the radio to these, if set up appropriately.

As an aside, there is a special mode for DXpeditions, which can handle a large number of contacts rapidly. The DX station in the "Fox", and others are the "Hounds". Apparently the software in this mode allows the Fox's software to control the transmit frequencies of the Hounds' radios, via the "Computer Aided Transceiver" protocol. This freaks out operators who haven't "Read The Fine Manual".

Note that Technicians and Novices are NOT permitted to use FT8 in their CW-only segments on HF, nor elsewhere on HF, except as follows: It is permitted on 10 metres for both of these grades. The standard frequencies are 28.074 MHz for FT8, and 28.078 MHz for JS8Call*. For Technicians it works well on 6 metres (various frequencies). For Novices and Technicians in Region 2, 222.065 MHz is an option; unfortunately the recommended 23 cm frequency is outside the Novice allocation. The 2 metre segment starts at 144.174 MHz.

There is an FT8 Digital Mode Club, FT8DMC.

*JS8Call is a separate package, which builds on this system and others to provide an integrated messaging system. You can read more at: js8call.com

AREDN

AREDN stands for "Amateur Radio Emergency Data Network". It is a mesh network which uses modified Wi-Fi equipment to provide high speed data during emergencies and exercises.

You can read more at: AREDN Mesh

UI

These are "Unnumbered Information" packets, used for things such as beaconing and APRS. While they are a real and useful thing, the term appears in a couple of distractors (wrong answers).

Other comments

Off the exam, I understand that using DDS, Direct Digital Synthesis, it is possible to generate some of these modes directly, at RF.

Many radio have a "Digital" mode, in addition to the usual CW, USB, SSB, AM, FM, etc. You should consult the manual regarding its use.

I expect that audio DSP should be turned off when using many of these modes, although this is something which you can experiment with. While automatic notch filters will try to eliminate the tones, it is possible simple filtering may help old modems.

Fldigi

Also off the exam, but useful for practical communications, including in emergency communications support work, the Fldigi (Fast light digital) is an open source suite of programs which use the soundcard as a modem. It offers 20 modes, with many variants.

Identifying Signals

There are many more digital and narrowband image transmission modes. If you tune a radio with its speaker active across the data sections of the bands you will hear different patterns of tones. The Sig-ID Wiki has details and sound recordings of many of these. It included many non-amateur signals as well.

Visit: Amateur ralated signals list

Each has a page, examples being the four versions of Pactor, starting with PACTOR I . Meanwhile VARA is the perfect 1970s Sci-Fi "computer thinking" sound effect.

Relevant Questions

These are actual questions from the General exam pool.

G2E01 Which mode is normally used when sending an RTTY signal via AFSK with an SSB transmitter? A. USB B. DSB C. CW D. LSB

It is LSB, answer D.

G2E02 What is VARA? A. A low signal-to-noise digital mode used for EME (moonbounce) B. A digital protocol used with Winlink C. A radio direction finding system used on VHF and UHF D. A DX spotting system using a network of software defined radios

This is a digital protocol, used with Winlink, answer B.

G2E03 What symptoms may result from other signals interfering with a PACTOR or VARA transmission? A. Frequent retries or timeouts B. Long pauses in message transmission C. Failure to establish a connection between stations D. All of these choices are correct

All these problems can be caused by interfering signals, answer D.

G2E04 Which of the following is good practice when choosing a transmitting frequency to answer a station calling CQ using FT8? A. Always call on the station’s frequency B. Call on any frequency in the waterfall except the station’s frequency C. Find a clear frequency during the same time slot as the calling station D. Find a clear frequency during the alternate time slot to the calling station

You should find a clear frequency during the alternate time slot to the calling station's transmit one, answer D.

From the small amount of FT8 I have done at a friend's station, a free frequency may be selected automatically.

G2E05 What is the standard sideband used to generate a JT65, JT9, FT4, or FT8 digital signal when using AFSK? A. LSB B. USB C. DSB D. SSB

If the question is essentially "Which sideband?", then the answer must be one of the first two, and in this case it is USB, answer B.

G2E06 What is the most common frequency shift for RTTY emissions in the amateur HF bands? A. 85 Hz B. 170 Hz C. 425 Hz D. 850 Hz

The most common on HF is 170 Hz, answer B.

G2E07 Which of the following is a requirement when using the FT8 digital mode? A. A special hardware modem B. Computer time accurate within approximately 1 second C. Receiver attenuator set to -12 dB D. A vertically polarized antenna

This family of modes are often is based on a system of stations taking turns to send, according to a transmit / receive cycle, with 15 seconds being used for FT8. Thus an accurately set clock is required, answer B.

This can be achieved by using an internet time server (NTP) to set the time on the PC, or using a GPS based device.

G2E08 In what segment of the 20-meter band are most digital mode operations commonly found? A. At the bottom of the slow-scan TV segment, near 14.230 MHz B. At the top of the SSB phone segment, near 14.325 MHz C. In the middle of the CW segment, near 14.100 MHz D. Between 14.070 MHz and 14.100 MHz

This is in the digital segment, 14.070 to 14.100 MHz, answer D.

This has been modified from an answert indicating it is near 14.070, which while correct fails to indicate should be above the 14.070 point. The actual frequency has a dial frequency of 14.074, so the "band" extends a few kHz, to around 14.077 MHz. This is the width of a SSB signal.

Digital modes typically start 70 kHz above the lower edge of each HF band, at least in the pre-WARC bands. You can scroll down the HF bands here: ARRL Band-Plan, described thus: "A band plan refers to a voluntary division of a band to avoid interference between incompatible modes". The FT8 frequencies are well inside the General and Advanced area on those bands in which Extras have a additional spectrum. Presumably, the lowest 70 kHz is used for Morse.

G2E09 How do you join a contact between two stations using the PACTOR protocol? A. Send broadcast packets containing your call sign while in MONITOR mode B. Transmit a steady carrier until the PACTOR protocol times out and disconnects C. Joining an existing contact is not possible, PACTOR connections are limited to two stations D. Send a NAK code

PACTOR uses a station-to-station connection, needed to allow retransmission requests, so others cannot join into an existing connection, answer C, for Charlie.

G2E10 Which of the following is a way to establish contact with a digital messaging system gateway station? A. Send an email to the system control operator B. Send QRL in Morse code C. Respond when the station broadcasts its SSID D. Transmit a connect message on the station’s published frequency

The system's software contains commands which allow you to send connect messages to stations, presumably a string of characters including their and your callsigns, answer D.

G2E11 What is the primary purpose of an Amateur Radio Emergency Data Network (AREDN) mesh network? A. To provide FM repeater coverage in remote areas B. To provide real time propagation data by monitoring amateur radio transmissions worldwide C. To provide high-speed data services during an emergency or community event D. To provide DX spotting reports to aid contesters and DXers

This provides a data transfer service during emergencies or events, answer C.

G2E12 Which of the following describes Winlink? A. An amateur radio wireless network to send and receive email on the internet B. A form of Packet Radio C. A wireless network capable of both VHF and HF band operation D. All these choices are correct

It is all of these, answer D, for Delta.

G2E13 What is another name for a Winlink Remote Message Server? A. Terminal Node Controller B. Gateway C. RJ-45 D. Printer/Server

A gateway is the point at which the message transitions between the radio link and the Internet, answer B.

G2E14 What could be wrong if you cannot decode an RTTY or other FSK signal even though it is apparently tuned in properly? A. The mark and space frequencies may be reversed B. You may have selected the wrong baud rate C. You may be listening on the wrong sideband D. All of these choices are correct

Reversing frequencies or using the wrong sideband will prevent the signal being decoded, as will selecting the wrong baud rate, so all are correct, answer D.

G2E15 Which of the following is a common location for FT8? A. Anywhere in the voice portion of the band B. Anywhere in the CW portion of the band C. Approximately 14.074 MHz to 14.077 MHz D. Approximately 14.110 MHz to 14.113 MHz

14.074 MHz to 14.077 MHz gets the coconut, answer C.

As a form of data transmission, around 70 kHz (0.070 MHz) above the lower band edge. This bandwidth of 3 kHz fits within the pass-band of many transceivers, so multiple stations fit within the waterfall displayed on a user's PC. 14 MHz, or 20 metres is an effective band for long distance communications, so is the default band for such operations. If upgrading you may have already operated on other frequencies ending in 74.

Well done! You are now over a quarter of the way through the question pool.

On to: HF Propagation 1 - Sunspots & Usable Frequencies

You can find links to lots more on the Learning Material page.

Written by Julian Sortland, VK2YJS & AG6LE, June 2024.

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