Category Archives: Digital Communications in Amateur Radio articles

Digital Communications in Amateur Radio series of articles written for Amateur Radio newsletters.

Digital Communications in Amateur Radio: Conversational Digital Modes (PSK, RTTY, MFSK, Olivia)

This article appeared in the The Wood County Amateur Radio Club newsletter CQ Chatter February 2017 edition.

Read the rest of the series in the Digital Communications in Amateur Radio articles category.


Got a new rig for Christmas? How about working digital? The most popular digital modes in ham radio are conversational modes (keyboard-to-keyboard). Best way to describe these is the instant messaging or text messaging of ham radio digital modes. One station sends a message to another station. The other station does the same in return. Conversations can be about anything – the weather, where that person lives, traveling, or life stores – for as long as you want. These modes include (in order of popularity): PSK, RTTY, MFSK, and Olivia. All, except Olivia, are available on the W1AW digital operating schedule. Others will pop up on the bands from time-to-time too or you may choose to play around with a buddy using other modes.

For the popular flavors of these digital modes, I performed a transmit time test. The text was one paragraph of “Lorem Ipsum” with 83 words consisting of 569 characters. I recorded how long it took to transmit the message in minutes and seconds to compare the speed of each flavor. The results were close between equivalent modes. PSK-31 and RTTY-45, for example, took about 2 minutes. This indicates that the advantage is not necessarily in speed but which mode works better in a situation. Popular HF frequencies are also listed. There is a lack of consensus on some of the exact frequencies. It won’t be uncommon to hear these modes in other portions of the data sub-bands. Different flavors tend to operate on the same frequency to stir up activity.

Commonalities among conversational modes include the RSID (Reed-Solomon Identification) tones which universally identify a digital signal at the beginning and, occasionally, the end of a transmission. RSIDs are more popular on rarer and wider modes like PSK-63, MFSK, Olivia, and other rare modes. An RSID tone is about 170 Hz so announcing your PSK-31 signal at 31 Hz will interfere with other conversations.

It is common to give a signal report using the IARU RSQ reporting system. Like the RST system of “59,” RSQ adds an additional number “599.” These numbers stand for:

Readability (percentage of good text received):

  • 5: 95+%, perfectly readable.
  • 4: 80%, little to no difficulty.
  • 3: 40%, considerable difficulty and many missed characters.
  • 2: 20%, occasional words distinguishable.
  • 1: 0%, unreadable.

Strength (measure how strong the signal trace is on the waterfall, there are only 5):

  • 9: Very strong trace.
  • 7: Strong trace.
  • 5: Moderate trace.
  • 3: Weak trace.
  • 1: Barely visible trace.

Quality (measure of unwanted artifacts in the signal: pops, clicks, splattering, harmonics, and unwanted modulation):

  • 9: Clean signal.
  • 7: One barely visible sidebar pair.
  • 5: One clearly visible sidebar pair.
  • 3: Multiple visible sidebar pairs.
  • 1: Splattering over much of the spectrum.

Also brush up on CW shorthand as these are used in exchanges. Commonly used abbreviations: btu (back to you), k (any station may transmit), kn (specific station only may transmit), sk (done transmitting, clear), pse (please), de (this is).

Reminder: review the first two articles in the series for information that will be omitted here including some modes operate your transceiver at 100% duty cycle, use upper sideband (USB), and don’t drive the transmitter with too much audio as the signal will be wider than intended.

PSK

PSK-31 is the most widely used HF digital mode. It’s popular because of its narrow signal. PSK was at the forefront of the digital sound card revolution in 2000. It was discovered that ordinary sound cards and computers had enough power to become digital-to-analog converters. Peter – G3PLX created PSK-31 to perform well with weak signals and operate at a narrow bandwidth. In a perfect world, within 3 kHz you could potentially have nearly 100 individual QSOs happening at once.

PSK stands for Phase Shift Keying, the modulation method used to generate the signal. It’s a common mistake to believe that 31 stands for the amount of bandwidth the signal occupies. It does occupy 31 Hz, however 31 stands for the bit rate of 31.25. There are other flavors of PSK: PSK-63, PSK-125, and PSK-250 each less likely to be seen on the bands than the previous.

It might be observed that software applications may have BPSK and QPSK in their list of operating modes. BPSK stands for Binary Phase Shift Keying and QPSK Quaternary Phase Shift Keying. The differences between these two are significant. When people refer to PSK, 99% of the time they are referring to BPSK. QPSK is a better choice under adverse conditions because it adds a significant amount of error correction ensuring nearly 100% copy of the transmission during signal fade or interference. However, both stations need to be on frequency, within 4 Hz, for error correction to work correctly. It takes a lot more work for two stations to be in sync with each other using QPSK.

Some stations may request an IMD (Inter-Modulation Distortion) report. This metric can only be observed while the other station is in transmit mode but no text is being sent; idle in other words. The station might type a message saying they’re looking for an IMD report and leave it idle for 10, 15 seconds, or more. There will be a measurement on screen in negative dB; lower the negative number the better. Readings in the -25dB to -30dB rage are considered very good, -20dB or greater is considered bad. A bad reading is usually caused by driving the transmitter with too much audio.

Transmit test: PSK-31: 1:58, PSK-63: 1:00
Frequencies: 3580 kHz, 7070 kHz, 10140 kHz, 14070 kHz, 21070 kHz, 28120 kHz.

RTTY

After six decades of use by hams RTTY, known as Radioteletype, is still a very popular mode for contesting and DXing on the low bands. RTTY has a long history and HF digital operators are very comfortable with it. Many transceivers also have RTTY built in. This mode works better in decoding large pileups than other modes. RTTY is efficient in that it works at a speed of about 60 words per minute – which is about the fastest one person can type. Other modes are typically much slower.

RTTY is based off the Baudot digital code which represents each character as a series of bits for telephone or radio communication. W1AW will refer to RTTY as Baudot on their operating schedule. Looking at a RTTY signal on a waterfall, the 1’s and 0’s are represented by twin tones for the mark (1) and space (0) tones. The two data streams are separated by the shift or space between them. When people refer to RTTY, they will most commonly refer to RTTY-45 (baud) but 75 can be seen as well. Inverted RTTY flips the mark and space data streams.

Transmit test: RTTY-45: 1:53, RTTY-75: 1:09.
Frequencies: 3580-3600 kHz, 7040-7100 kHz, 14080-14099 kHz, 21080-21100 kHz, 28080-28100 kHz.

MFSK

Multi-Frequency Shift Keying, known as MFSK, is “super-RTTY” which uses multiple tones instead of the two used in RTTY. The most popular is MFSK-16 using 16 tones. MFSK was developed as a flexible point-to-point solution to combat multipath propagation problems. It is very good at detecting noise and reducing transmit errors with error correction all while utilizing low bandwidth. MFSK is slow to decode so be patient!

An exciting addition to some MFSK flavors is the ability to send small images. MFSK-16 can send images but not MFSK-8. A 320×256 sized color image took 4:26 using MFSK-16. It’s unlike Slow Scan TV where the software will size the image and overlay a template. The image needs to be fully prepared before it can be transmitted.

Transmit test: MFSK-16: 1:45, MFSK-8: 2:48.
Frequencies: 7072 kHz, 14072-14076 kHz.

Olivia

MFSK is good in poor band conditions but Olivia offers even better performance. Developed by Pawel – SP9VRC it is named after his daughter Olivia. It is called the JT65 of conversational modes because it’s incredibly slow but unlike JT65, it’s not a structured exchange.

There are different combinations of bandwidth and number of tones used, such as 500/16 is 500 Hz with 16 tones. Fldigi reverses these numbers for some odd reason and will read “Olivia 16 – 500.” Locking on to an Olivia signal may take 15 seconds. If the software is not decoding after that time, the bandwidth might be correct but the number of tones maybe wrong. For this reason, a call for “CQ” may take a minute or longer so stations can lock on and return a call. Be patient!

Olivia is great for poor band conditions because a trace may not be seen on the waterfall but a signal might be decoded! One example I share is a buddy of mine and I tried operating Olivia. We established contact and had strong traces on the waterfall using only 1.5 watts. We decided to compare it to sideband voice. We couldn’t contact each other on sideband until we were nearly up to 100 watts!

Transmit test: Olivia 500/16: 4:56, Olivia 500/8: 3:20.
Frequencies: 1835-1838 kHz, 3583.25 kHz, 3577 kHz, 7035-7038 kHz, 10141-10144 kHz, 14072-14075.65 kHz, 14106.5 kHz, 18102.65 kHz, 21072 kHz, 24922 kHz, 28122 kHz.

Software

I love and recommend software applications that are capable of operating multiple modes (multimode) using one application. This keeps the clutter down of installing multiple applications for each mode. The two I use are Digital Master 780 (DM780) as part of the Ham Radio Deluxe suite (http://ham-radio-deluxe.com/). This package is not free and only available on Windows. If that is out of your budget, then I recommend Fldigi (http://www.w1hkj.com/). It’s free, open source, and cross platform available on Windows, Mac, and Linux including Raspberry Pi. Both of these support many different modes and are constantly being updated and with newer modes.

MixW (http://mixw.net) and MultiPSK (http://f6cte.free.fr/index_anglais.htm) are alternatives and support most modes. There are specific mode applications like DigiPan (http://www.digipan.net/) for PSK and MMTTY (http://hamsoft.ca/pages/mmtty.php) for RTTY. Both are no longer maintained but are reported to work well with later versions of Windows. Other programs have known issues with versions of Windows later than Vista. Keep that in mind when trying older programs.

The software applications are similar in setup and operation. Exact labeling might be different from application to application. I am going to reference Fldigi, though not going in-depth with settings, it should get you started. Install Fldigi with the default options. A configuration wizard will appear the first time the application is started. Fill out all your station information. Select the sound card interface (USB Audio Codec for SignaLink). If the transceiver is using something other than the SignaLink for keying, select the appropriate radio and COM port for TX control.

There are many parts to the Fldigi window. Standard menu options are seen like “File,” “Op Mode,” “Configure,” etc where operating modes or Fldigi configuration can be changed. Below that is Radio Control and Logging. When using internal logging, you’ll want the frequency to be correct. Rig control will help greately to automatically log the correct frequency as you change the VFO. Below that is the tan box where received messages will be displayed as well as transmitted messages will be copied here. The blue box is the transmit window where messages are composed for transmitting. If you have a white box to the left of the transmit and receive panes, this is the signal browser. This will display all conversations taking place, using the same mode, on the same frequency at once! Below the transmit text box is a line of colored buttons which are macros. Macros are pre-populated and commonly exchanged texts so you don’t have to keep typing them (right-click the button to edit). Below that is the frequency scale in Hz and waterfall. Below the waterfall are the waterfall controls. The line below that are the status messages and readings. To the right of the waterfall are two vertical white and a gray bars which indicate the strength of the decoded digital signal and squelch setting.

Tune your radio to one of the PSK frequencies to get setup. 20 meters is better during the day and 40 at night. The waterfall should start turning blue and yellow. If it is black, check the audio paths between the radio and computer, verify the audio input is set correctly in the Fldigi setup. Radios with a main and sub-band often cause confusion as to which band sends audio to the computer. If there is blue and yellow but a lot of black on the waterfall, check and disable radio filtering. Pro tip: the waterfall is a great educational place to visualize the filtering changes of the radio.

Now from the menu select “Op Mode,” “PSK”, then “BPSK-31.” To select a digital signal on the waterfall, simply click on the waterfall and the cursor will move to that location. Signals under the cursor will be displayed in the receive pane. It’s important to move the cursor on screen and do not adjust the radios VFO. Once a strong PSK signal is selected, you’ll notice the white squelch bar fills with green. The green needs to be above the light gray squelch slider to break squelch and decode. This is the first place to look if the cursor is over a signal but it is not decoding. Having the squelch set too high will miss decoding weaker signals and having the squelch too low will produce a lot of garbage text in the receive window. If a specific signal is strong but not decoding, the signal could also be multipathing, thus confusing the program. Watch conversations a good while to make sure you understand how the program works and for conversation syntax. Many programs have a “Signal Browser” or “Signal Sweeper” (DM780) which will decode multiple conversations at one time! In Fldigi, this can be broken out in a separate window under the “View” menu option.

Someone calling CQ will send CQ two-three times. I am K8JTK and Steve – W8HF will be the other station in these examples.

CQ CQ CQ de K8JTK K8JTK K8JTK
CQ CQ CQ de K8JTK K8JTK K8JTK

Repetition is good for weaker stations that might miss a letter or two. A responding station may respond with: K8JTK K8JTK de W8HF W8HF pse kn.

The two stations might begin the exchange using macros. These are good conversation starters. Macro messages typically include age of the operator, when they were licensed, radio and antenna, digital software program (Fldigi), computer operating system, physical location, etc, etc. This macro is called the “Brag” macro because you brag about your station. Beware though, for slower modes like Olivia, it can take a LONG time to send the same macro that takes seconds using PSK. The two stations could conclude the exchange or go back and forth typing out messages using the keyboard.

When receiving a message from another station, the responding station can begin typing a response in the blue transmit window even before the other station has finished transmitting. Always begin with something like “W8HF de K8JTK” so the other station knows you are responding to them, then continue with your message. If you’re conversing with a station and they don’t respond back after your message, they may have lost your signal, their program crashed, or became distracted. I typically wait 30 seconds – 1 minute and try a quick call back to the other station: W8HF W8HF W8HF de K8JTK K8JTK K8JTK, did I lose you? W8HF de K8JTK pse kn. I’ll try this 2-3 times and if they don’t return, I’ll log the QSO and move on.

End of transmissions should conclude with something like “btu Steve W8HF de K8JTK pse kn” noting the station is turning it back over to the other station. Concluding the conversation will end with something like: thx for QSO Steve, 73, W8HF de K8JTK sk. Other stations will end with a similar macro that includes their QSL information or when they upload their logs.

To transmit CQ, find an open space on the waterfall and click to bring the cursor to that spot. Tones will be generated in the same place as the cursor on the waterfall during transmission. Tune up on frequency and call CQ using the “CQ” macro. Some macros start and/or stop transmitting on their own. The “T/R” button under the waterfall is your best friend to start or stop transmitting. Some of the macros have the sequence “^r” at the end. This is an Fldigi command to change from transmit mode to receive mode aka transmission complete. This can be typed in manually at the end of messages too. PSK Reporter (http://pskreporter.info/) can be used just like JT65 to see how far you’re reaching.

Logging is fairly straight forward. RTTY and Olivia are logged as their respective mode only. BPSK is logged as PSK31, PSK63, etc. QPSK31, MFSK8, and MFSK16 are all logged as listed. If an RSQ was exchanged, log it accordingly. IMDs for either station can be recorded in the comments for future reference.

One idiosyncrasy with Fldigi: the position of the cursor in the transmit pane is critical. Fldigi will remain idle during transmission until the cursor is moved further down or moved to the end of the message. Many people are confused by this behavior and other programs don’t seem to follow this convention. For example if you had a sentence with “this that” and positioned the cursor after “this,” characters before the cursor will be transmitted until the point of the cursor was reached. The word “this” would be transmitted then Fldigi will remain idle in transmit mode until the cursor is moved. When moved, “that” will be transmitted until the program reaches the cursor again. Position the cursor at the end of the message during transmit and all will be well.

That’s it. These conversational modes are very open and very free form. Contesting will have a structure but casual operating is very informal. This outline can lead to operating other modes like Contestia, Thor, Throb, MT63, or Hell. Yes “Hell,” short for Hellschreiber, is a facsimile based mode where there is a reason everything is printed twice.

Find out more information:
“PSK31: A New Radio-Teletype Mode” by G3PLX: http://www.arrl.org/files/file/Technology/tis/info/pdf/x9907003.pdf
“Get on the Air with HF Digital” book: https://www.arrl.org/shop/Get-on-the-Air-with-HF-Digital
“RTTY/PSK31 for Radio Amateurs” book: https://www.arrl.org/shop/RTTY-PSK31-for-Radio-Amateurs-2nd-Edition/
“Nifty E-Z Guide to PSK31 Operation” book: https://www.arrl.org/shop/Nifty-E-Z-Guide-to-PSK31-Operation/
“How to get started with PSK-31 Ham Radio” by K7AGE on YouTube: https://www.youtube.com/playlist?list=PL8D7C6EBD6E2081E2

Digital Communications in Amateur Radio: JT65 and JT9

This article appeared in the The Wood County Amateur Radio Club newsletter CQ Chatter August 2016 edition.

Read the rest of the series in the Digital Communications in Amateur Radio articles category.


My favorite digital mode has to be the “JTs” otherwise known as JT65 and JT9. Many have equated them to watching paint dry. Others call it the musical mode. I call it my ADD mode. Whatever you call ’em, JT65 has become one of the most popular digital modes second only to PSK. I call it my ADD mode because I can browse the web, watch TV, or write this article during the 7-minute exchange. But you better pay attention because it can still keep you on your toes!

JT65 and JT9 began with Nobel Prize Winner Dr. Joe Taylor – K1JT. One of Dr. Taylor’s passions was weak signal communications and moonbounce (EME). A signal is sent toward the moon at about 1.5 kW on VHF using large directional antenna arrays. The signal is reflected off the moon and received by an equally powerful station with large arrays. After the signal makes the 500,000 mile round trip, there wasn’t much left. CW was the only effective mode. In 2001, K1JT came up with JT65 which allowed hams to make Earth-Moon-Earth contacts with 150 W and 11-element beam antennas. Still not exactly easy but it made EME a possibility for many more hams. Years later it was discovered that JT65 works great on the HF bands too. It allows stations to make contacts without high power or gain antennas. This is perfect for hams that cannot have large or visible antennas. Over time, JT9 was added specifically for the LF, MF, and HF bands (“Work the World with JT65 and JT9”).

It’s not my intention to dive into the technicals of any mode but to give hams practical operating information. When talking about JT65 almost all information applies to JT9 as well. Both are highly time-synchronized. The computer’s clock must be as accurate as possible and within 2 seconds of other stations. One minute transmit and receive sequences are utilized. Transmitting happens within a one-minute window then the roles are reversed for the following minute. Stations begin transmitting 1 second after the beginning of the minute and stop 47.7 seconds later. In the remaining 11.3 seconds applications decode received signals, display them on screen, and receiving stations get their message ready to transmit. The total exchange takes about 7 minutes. More if the message is lost or not decoded. Being such a robust protocol doesn’t leave room for long messages meaning it’s not a conversational mode. The maximum message length is 13 characters with the intent of limiting the exchange to call signs and signal reports. Below is an actual exchange. The first column is the time, second is the exchange, third is the exchange translation. Exchange beings at 01:00 UTC and completes at 01:07. In messages with two call signs, the receiving station is to the left and the transmitting station to the right.

0100 CQ K8JTK EN91
I’m calling CQ from grid square EN91.

0101 K8JTK K5ND EM12
K5ND is returning my CQ from grid square EM12.

0102 K5ND K8JTK -01
I reply to K5ND with his signal report of -1 db (RST Sent).

0103 K8JTK K5ND R-05
K5ND responds with my signal report of -5 db (RST “R”eceived).

0104 K5ND K8JTK RRR
I respond with “roger-roger-roger.”

0105 K8JTK K5ND 73
K5ND responds with best wishes.

0106 K5ND K8JTK 73
I respond with best wishes.

Differences between JT65 & JT9 are bandwidth and signal reports. JT65 takes up just under 180 Hz and about 16 Hz for JT9. JT9 is much better for spectrum efficiency and uses less power due to narrower bandwidth. The JT65 sub-band can often be seen with multiple overlapping signals and they usually decode correctly. JT9 can have ten-times the signals but decoding of overlapping signals is much less likely to happen. Signal reports range from -1 to -30 db signal-to-noise in JT65. The lowest I’ve seen is -27. They are capped at a -1 db upper limit to keep somewhat consistent with EME reports. JT9 is extended to give more accurate signal reports with a range from -50 to +49 db. The limits I’ve seen are -27 and +15. Propagation is comparable between the two modes. JT65 is the overwhelming favorite of operators.

JT65 & JT9 have their own sub-bands. Below is a listing of those frequencies. JT9 is typically 2 kHz above the JT65 frequency. USB is the mode regardless of band.

JT65 JT9
1838 1838
3576 3578
7076 7078
10138 10140
14076 14078
18102 18104
21076 21078
24917 24919
28076 28078
50276 50278

Software is available on all major platforms. Ham Radio Deluxe is expected to include JT65 in the very near future.

Windows:
JT65-HF (http://jt65-hf.sourceforge.net/). It’s very reliable and I’ve only noticed one issue where free hand text doesn’t always transmit. This is the old standard but no longer in development.

JT65-HF-HB9HQX-Edition (http://jt65hfhb9hqxedi.sourceforge.net/). This is the replacement for the above. It’s built on the same code-base so look and feel are similar. The developer has implemented many new useful features. I recommend using this one for newcomers.

Windows/Mac/Linux:
WSJT-X (http://physics.princeton.edu/pulsar/k1jt/wsjtx.html). Software released by K1JT. This seems to give the most accurate signal reports. It’s the only program that currently implements JT9. WSJT-X is the program that I use.

WSJT-X Conversation
WSJT-X application showing QSO with XE1SAX

Application setup is fairly straight forward. In the setup, enter your call sign and grid square. If you don’t know your grid square, check QRZ or enter your address on: http://www.levinecentral.com/ham/grid_square.php. Choose the correct sound input/output devices. Configure Rig Control/PTT if needed. Rig Control is not required but helpful when using the internal logging methods.

Before starting any of the applications, ALWAYS sync your computer’s clock with the Internet. In Windows, go to the Control Panel, Date and Time, Internet Time tab, Change settings, click Update now. Most Linux distributions need to invoke ‘ntpdate.’ One feature of the HB9HQX version is automatic time syncing every 15 minutes.

All programs have the same general layout and operate in the same manner. They have a waterfall showing signals received and display markers indicating active transmit and receive windows. These can be moved by clicking on the waterfall.

Conversational buttons and boxes are often labeled Calling CQ and Answering CQ. These buttons automatically generate text during the conversation (following the standard exchange format). Free Text/Message is for free hand text. Other buttons will enable and disable transmitting. Halt will interrupt the transmission midway through. Even/odd indicates which minute you will transmit (only applies to calling CQ). It has no effect when answering a CQ because the software will transmit in the next minute.

The Signal Decoding window is the most important because this is where all conversation exchanges are displayed. A couple labels are seen: UTC – time the signal was decoded, Sync – measurement of the sync signal — higher the better, DT – time difference between decoded station and yours — should be less than 2 seconds, DF – frequency deviation above or below the center point in Hz, and finally the Exchange or Message text. Colors are frequently used to distinguish items of importance. Green is a station calling CQ, red is a message/exchange intended for your station (contains your call sign), gray is exchanges between other stations.

Luckily the software takes care of much of the exchange. It generates response messages by double-clicking a received line. Stations that don’t follow the standard format can easily confuse the software. This is where it will keep you on your toes. If you’re not careful you can end up sending a message twice or not properly advancing to the next message in the exchange. The software does not automatically advance the conversation for you. If things go off the rails, use the appropriate conversational button to get things back on track.

The Free Text field can be used for noting your power, antenna, or sending holiday greetings. These messages are often in place of the 73’s and will not show up in red because no call signs are included. You may see “30W DPL” (I’m running 30 watts into a di-pole antenna), “50W LOOP” (I’m running 50 watts into a loop antenna), “THX 4 NM” (we’ve worked before, thanks for the contact using a new mode from previous contacts), “THX 4NB” (we’ve worked before, thanks for the contact on a new band), “SRY/SRI NO DECODE” (I see a signal on the waterfall but it did not decode) you’ll see this one but it’s not commonly used, “MERRY XMAS” –you get the idea. It’s only 13 characters. Be careful not to baffle the user and you have to be quick. There are some I’ve received that I still have no idea what they mean.

In the JT’s it’s ether a clean decode or nothing at all. No in between. When I see a signal on the waterfall and the message doesn’t decode, I always send my last message again. Some stations will not transmit in the following minute. Other stations (wrongly) move on in the conversation. Then I have to use free hand text to send “SIG RPT?” or similar because I didn’t receive my signal report. At minimum, I make sure RSTs (reliability – strength – tone) have been exchanged and won’t log the contact until “RRR” has been sent/received. Some QSLs I received go as far to log the DF frequency. I’ve only logged the center frequency.

After you feel comfortable monitoring activity, double-click a green “CQ.” The Generated Text field will update with your call sign, their call sign, and your grid square. You’re off! Also, refer back to article two for station/DSP/audio setup. I’ve seen some of the worst over modulated signals on JT65. JT users are really good about uploading spots to PSK Reporter (https://www.pskreporter.info/pskmap.html). You can use it as a ‘reverse beacon’ network to see where your signal is propagating.

PSK Reporter Spots
PSK Reporter application showing received stations worldwide

It’s a lot to take in but an extremely fun mode to work. Find out more information:

Amateur Logic.TV on JT65: https://youtu.be/L7e5NbqhbVU?t=28m10s

QST article: http://www.arrl.org/files/file/Get%20on%20the%20Air%20with%20HF%20Digital/FORD%20JT.pdf

PowerPoint introduction: http://www.arrl.org/files/file/Get%20on%20the%20Air%20with%20HF%20Digital/Getting%20Started%20with%20JT65%20on%20the%20HF%20Bands.pps

“Work the World with JT65 and JT9” book: http://www.arrl.org/shop/Work-the-World-with-JT65-and-JT9/

Digital Communications in Amateur Radio: Station Setup

This article appeared in the The Wood County Amateur Radio Club newsletter CQ Chatter May 2016 edition.

Read the rest of the series in the Digital Communications in Amateur Radio articles category.


This time in our quest to get on the air with digital, I’ll discuss station setup. For most of this article, it will be related to HF and sideband operation. I’ll talk about FM near the end.

For a Ham Radio digital setup, three things are needed: a radio, computer, and an interface to connect the two.

First the radio. Theoretically, any radio can be put into digital service. Two things are important to consider: frequency stability and switching speed. Frequency stability is critical to digital operations because drift is deadly. Tube and older radios tend to drift in frequency as they warm up. For a mode such as PSK, drifting a few hertz puts you into someone else’s conversation. Switching speed and fast turnaround times are needed. The switching speed of older radios can be hard on relays. Solid-state radios manufactured in the last two decades are recommended. Radios that cover HF/VHF/UHF all mode – open up even more operating possibilities.

icom_ic-7000_(accessory_&_data_ports)
ICOM IC-7000 rear view showing data and accessory ports.

Most radios are designed with digital modes in mind. Radios with an “accessory port” or “data port” built in are ready to go, though not plug-and-play. The data port is the recommended way to connect an interface to the radio. These ports have pins for keying, transmit audio, and received audio. The audio pins have fixed audio levels and do not change based on the volume setting of the radio. If the radio doesn’t have accessory or data ports, microphone and audio out can be used. It’s not an ideal situation but it will work. An important thing to keep in mind, some radios mix various audio inputs. An example is an external mic connected to the accessory port maybe mixed with audio coming into the data port. This means audio generated by the computer will mix with ambient noise picked up from the microphone. You don’t want this because you’ll interfere with other digital exchanges. It’s important to know your radio and how it operates in different configurations. Test with a buddy or Elmer first before jumping in.

CAT (Computer Aided Transceiver) ports on the radio including RS232 (serial port) and CI-V are useful when creating your own interface. Audio cables between your radio and computer would provide transmit and receive audio but these won’t key the radio. CAT ports provide a lot of functionally including the ability to change settings in the radio, update memory channels, change frequency, etc. Keying the radio via CAT is universally supported in applications. A configuration example would be using the soundcard for audio in/out to the audio out/mic-in on the radio. A separate cable between the computer and radio provides CAT commands, usually via a COM port.

Duty cycle is the amount of time the radio is generating RF. When operating SSB voice, the amount of RF the radio generates depends how loud your voice is at that moment. In CW, RF is generated with each dot and dash. In both cases, the radio is operating at less than 100% duty cycle due to pauses in between words and characters. Many digital modes operate the radio near 100% which causes a lot of heat. Heat causes components to fail. Radios are designed for SSB voice though some newer models are including 100% duty cycle. Operate the radio at a power setting of 50% or less (30% recommended) of the total output power. A 100 watt radio would be set between 30 and 50 watts. FM, by nature, is the exception because voice or digital over FM uses the same bandwidth. The typically longer key down times for digital will still generate more heat.

Radios have different operating modes: USB, LSB, FM, AM, RTTY, DATA, DIGITAL and possibly others. HF digital mostly uses Upper Sideband regardless of frequency. In most cases the USB setting is what you want. Some radios will not allow keying from a computer unless they’re in a ‘digital’ mode setting. Check your operating manual and, again, practice and test with a buddy first. Turn off all filters, blankers, attenuation and the like or set it to the least disruptive setting. Set transmit and receive bandwidths to the full SSB bandwidth allowed (2.8 kHz). No filtering and wide bandwidths have less of a chance to distort or modify the signal. Modification of the signal affects the ability to decode a signal. Filtering can be used but after practice and understanding how they affect decoding. Contests usually warrant filtering to keep loud adjacent signals from affecting the exchange.

The interface. It serves two main purposes: act as a modem and the device that keys the radio. It acts like a modem by taking modulated audio from the software application and sending to the radio for transmit and taking received audio from the radio and sending it to the application for demodulation. Nearly all computers and laptops in the last decade have on-board audio while older configurations utilize an addon soundcard. Most computers don’t have serial ports these days. If a serial port is needed for CAT, options such as a USB (Universal Serial Bus) to serial adapter, serial port addon cards, or cables manufactured with USB to serial adapters built in are available.

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RIGblaster interface–front view.

All-in-one interface solutions make the connection between the radio and computer easy. Solutions offer a built in sound card and fewer cables needed to make the connections. Offerings include products from West Mountain Radio, MFJ, MicroHAM, or RigExpert. These options free your on-board soundcard to listen to music or surf online minimizing the possibility of transmitting audio not suited for the airwaves. Adjustments on these interfaces are audio levels and speed (delay) at which the interfaces switches the radio from transmit to receive. Newer models include all functionality integrated into a single USB port requiring only one cable.

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SignaLink USB interface–front view.

The recommended solution for a radio without integrated USB audio is the Tigertronics SignaLink USB. Two cables are needed to make all connections. A USB cable connects the computer and SignaLink for the audio (soundcard) and a cable to the radio for audio and keying. The cable for the radio is specific to connector type or manufacturer. A list of cables is available and simple internal wiring diagram to match the cable to the radio.

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SignaLink USB interface–rear view.

Unterminated cables are available to create custom solutions. The SignaLink and cable are about $120 and available at all ham radio retailers. It is a simple VOX (“voice” operated switch) device. When sufficient audio is generated by the computer it keys the radio. It unkeys the radio when that audio has fallen below a threshold.

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SignaLink USB connection set up.

If you have an interface or are setting one up for the first time, I wrote a tutorial on configuring the interface in Windows. It shows setting default devices and audio levels. These settings help avoid splattering on the bands (taking up more bandwidth than intended) due to too much audio fed into the transmitter. Again, practice with a buddy or Elmer to verify optimal audio settings. Included is a section showing how to record digital transmissions and play them back for decoding at a later time (time shift) such as a net: http://www.k8jtk.org/2015/04/16/radio-interface-setup-for-getting-started-with-ham-radio-sound-card-digital-modes/

The computer. Aside from the requirements to make connections, most computers work fine for digital operation. Ones made within the last decade seem to work without issue. Some older ones tend to have issues. A computer with a 1.5 GHz CPU and 4GB of RAM is sufficient. As always, more is better. Windows is the operating system of choice for digital programs. Mac and Linux are well represented with a program or two less viable than their Windows counterparts. Let’s not forget portable devices like tablets and smartphones. Digital applications are available for those devices too. My operating has been on a Windows 7 64 bit desktop computer.

Up to this point I’ve talked about operating digital on HF and Sideband. What about Technicians who don’t have access to digital portions of the HF bands? All of these digital modes can be operated over FM so you Technicians can get in on the fun too. Won’t be able to transmit as far as an HF station but digital can be transmitted over simplex or even a net on a repeater using an HT! On HF, audio tones are generated by Audio Frequency Shift Keying (AFSK). Audio generated by the computer is converted into RF frequencies when transmitted. Only those frequencies in use at that time are transmitted by the radio. This allows hundreds of exchanges to take place on the same frequency. FM on the other hand occupies the full 10 to 15 kHz, even though the bandwidth of the audio generated by the computer is less. So it still stands only one transmitting station can have the frequency at a time. Yes, this defeats the purpose of narrow bandwidth modes. Someone wanting to learn and experiment with these modes may get bitten by the bug and lead to a license upgrade. I say let them have at it. That’s how I did it.

To this point, Stephen Cass – KB1WNR, Senior Editor for the IEEE magazine built a low power FM digital transmitter for just that reason, get more people interested in digital. It’s a great maker project or demonstration tool for digital. I also mention it because he used my instructions to get Fldigi running on the Raspberry Pi! http://spectrum.ieee.org/geek-life/hands-on/hands-on-a-ham-radio-for-makers

Next time, I’ll start covering specific digital modes, software, and operation.

Images: F8DZY, W3YJ, West Mountain Radio.

Digital Communications in Amateur Radio: Overview

This article appeared in the The Wood County Amateur Radio Club newsletter CQ Chatter February 2016 edition.

Read the rest of the series in the Digital Communications in Amateur Radio articles category.


When I was planning my HF station a few years ago, I knew I wanted to learn more about digital modes. I was familiar with some like Slow Scan TV and Craig – NM8W told me about JT65 a couple years ago. I didn’t understand HF – let alone HF digital. I was lost and had alot to learn.

Since I’ve been on the HF bands, the large majority of my contacts are some form of digital and I’m always exploring new ones. JT65 is my current mode of choice. The perception from many hams is digital modes are foreign and complicated to setup. It takes a little understanding.

In this series of articles, I will be discussing getting on the air with digital from your station. This article will give a general overview of digital communications. Future ones will discuss setting up your station, dive into operating specific modes, and using specific applications. Much of the information will be related to HF and sideband operation. Technicians – fear not, these can be operated on VHF/UHF sideband or even FM simplex with HTs. I’ll get into important distinctions between sideband and FM next time.

I’ve been using computers from a young age. I learned applications and started programming in middle school and continued through high school. I received my undergraduate degree in Information Systems. Through most of college, I was a Technician class licensee and didn’t know much about sideband. I didn’t use computers all that much in ham radio. Most of my activities were related to other things I knew how to do, like build websites. I wasn’t logging or controlling my radio since I was using HTs most of the time.

There were a couple FM digital nets on repeaters in Cleveland that got the ball rolling for me. Slow Scan TV was the first of these modes. It was really cool seeing still pictures come across my screen with a couple audio cables. Later, a digital net for NBEMS training was formed to practice passing messages and forms for emergency communications. That net exposed me to one of the most versatile programs for operating digital modes. After college, I got into D-STAR. That integrated IP (Internet Protocol) technology, which I studied in college, and continued my interest.

Let’s start by taking about digital communications. At a basic level, digital communications is a binary representation and transfer of data (1’s and 0’s). Data is encoded into some structure (protocol, format, rate) before it is transmitted. Digital communication is a very broad term and takes many forms.

Morse Code is the most basic form of digital. The signal is either on or off (1 or 0). The on/off keying creates a series of dots and dashes to make up letters, numbers, and symbols.

Digital voice (often referred to as “DV”) is a method of taking audio from a source (microphone) and digitizing (or encoding) it into a data stream. When decoded at the receiving end, the data stream is converted back into audio and played through a speaker. Voice formats include P25, D-STAR, DMR, FreeDV, and System Fusion. Many voice formats include the ability to transmit a small amount of text at the same time. This text stream is not very fast because voice takes higher priority and the majority of the bandwidth. Text is relegated to call sign, a banner message, or GPS coordinates; things that don’t take a lot of bandwidth.

Data formats exist to transmit text or binary data. Most text based formats are keyboard-to-keyboard or chat style exchanges. Binary exchanges can be files, pictures, or documents. Data format examples are D-STAR, MT-63, MFSFK, JT65/9, Olivia, Packet/APRS, PSK31, RTTY, and System Fusion. Some formats can carry voice (mentioned earlier) but most cannot (i.e. PSK31, RTTY).

Why digital communications? The widespread ownership of personal computing devices allows amateurs to develop and use these modes for communication purposes. Many digital modes are referred to as “sound card modes” because to operate many of them requires little more than a computer, sound card, and radio. In recent years, ‘personal computing devices’ has grown to include smartphones, tablets, and micro-computers because programs have been written to use these modes on those devices.

Digital transmissions can be faster and more reliable. Faster: more words per minute can be transmitted over digital modes. They can be more reliable over greater distances, poorer conditions, and contain error correction. Error correction is the encoding of redundant data into the transmission. When errors are encountered, the redundant information can help reconstruct lost data without retransmission. Error correction helps when noise or other undesirable characteristics are introduced to a receiver. If the signal is completely lost, interrupted, or falls to the noise, no level of error correction will decode the signal. Like most things in technology, each digital mode has its intended use, advantages, and disadvantages. Not all modes fit into all categories and may not be mutually exclusive to a single category.

Next time, I will discuss considerations for your station and the interfaces that go between your computer and radio. Please contact me with questions and ideas. It will let me know what readers are interested in and modes to cover.