PSK operators tend to hang out at certain frequencies on the bands. Some of the frequencies are dependent on the location of the station, due to local regulations or QRM. Here are the most common:

Almost all of these are the transceiver settings for USB operation, so most PSK signals are within the 3 kHz above these frequencies. (80M operation tends to be both above and below 3580, and there's always W1AW's code practice to avoid at 3581.5) By convention, BPSK is symmetric, you can also operate in LSB mode - just set your transceiver 3 kHz above these frequencies. (If you operate QPSK you'll have to use the "invert" setting in your software.)

Back in the early days of PSK31, the suggested operating frequencies all ended in ".150 kHz". This was at a time when tuning was done using the transceiver. Now that all PSK software is "click and tune", this level of detail is unnecessary. In fact, you only need to set your transceiver "near" the above frequencies, where "near" is defined as within a few hundred Hertz - you'll be able to tune in most of the activity with your software. But don't forget to tune around a bit when the waterfall is very active, as some stations may be operating outside of the "normal" range when there are a lot of stations on the air.

When you are operating USB, your actual transmitted frequency (the actual frequency of your PSK signal) will be equal to the sum of your transceiver setting plus the audio offset displayed in your software. Some people prefer to quote this as a sum, as in "14070 + 1200" for a transceiver set at 14070 kHz and a 1200 Hz offset. Others will state this as the sum itself, 14071.2 kHz. Both of these are exactly the same, as would be someone working the same station with a transceiver set at 14069.5 kHz and an audio offset of 1700 Hz. Note that if you are using LSB, you have to subtract the audio offset from the transceiver frequency. For the exact same operating frequency as above, an LSB station may be set at 14073 with an audio offset of 1800 Hz, which could also be quoted as "14073 -1800".

Many thanks to W3HF for the bulk of this page. The comment about W1AW came from K8IJ.

So what is PSK31 all about? This page is not intended as a complete tutorial covering all facets of PSK. It's an overview of PSK, enough for you to understand the terminology and concepts, and give you a head start towards further research.

What is PSK?

PSK stands for Phase Shift Keying. In the context of amateur radio, it describes a family of operating modes (each of which has a slight variation in the signaling parameters) that are used for on-the-air keyboard-to-keyboard contacts.

Where did PSK31 come from?

Phase Shift Keying has been around as a digital modulation scheme in the commercial and military worlds for many decades. Hams (notably SP6VRC) realized in the late 1990s that computer technology, including the ubiquitous sound card, had progressed to the point where simple software could be used to modulate a PSK signal at an audio IF, which could then be upconverted to RF and transmitted using a conventional SSB transmitter. (The receive process is the reverse - the SSB receiver downconverts the incoming PSK signal to the audio IF, and the computer/soundcard demodulates it.)

Peter Martinez (G3PLX) established signaling parameters (bit rates, coding schemes, etc.) and called his product PSK31. This included two variants: BPSK31 and QPSK31. Binary PSK transmits one bit at a time, using one of two possible phase states. Quaternary (or Quadrature) PSK sends two bits at a time, using one of four possible phase states. Both send the same number of phase transitions per second, so QPSK can send twice as many bits as BPSK. Martinez used this extra capacity to include a rate-1/2 convolutional code to improve its efficiency. He selected 31.25 baud (31.25 phase transitions per second, rounded down to 31 for use in the name) as a reasonable rate that allowed text to be sent at approx. 50 wpm and could also be easily derived from the 8 kHz. sampling rate common in DSP systems (like a computer sound card).

Others have developed extensions of the PSK31 concept to enhance its capability for specific applications. For example, if you want higher text speeds, you could try PSK63 and PSK125. For operation at lower signal-to-noise ratios, there is PSK10. All of these, and even the original QPSK31 variant, are much less common on the air than BPSK31.

How does PSK work?

The generation of a PSK31 signal can best be described in the following sequence of four steps. Actual implementations may not follow precisely this sequence, but the result is the same.

1. Each individual keyboard character is encoded into a string of bits. This is done using a lookup table that implements what Peter Martinez called a Varicode, which is a variable-length coding scheme. Martinez examined the English language and the frequency of appearance of all the characters, and used shorter bit sequences for the most common characters and longer ones for the less-common ones. (Note that this is exactly what Samuel F. B. Morse did approximately 160 years earlier to develop the code that now bears his name.) Unlike RTTY (and Morse), Martinez included both upper-case and lower-case letters, and the lower-case ones get shorter codes because they are more common in written text. He also defined the possibility of "extensions" to the Varicode to cover additional character sets, like for non-English languages. Details of the Varicode can be found here.

2. PSK31 is defined to operate at 31 baud, which corresponds to 31 bps for BPSK. If the operator is not typing fast enough to create a stream of characters that generates bits at this rate, "fill bits" are inserted.

3. The 31 bps stream is then used to PSK-modulate an audio "carrier". (Technically PSK31 uses Differential PSK, where the "difference" between successive bits defines the transmitted phase. [For logic levels, if the two bits are the same, the difference is zero. If the two bits are different, the difference is one.] This allows for a simpler receiver, as it need not establish a phase reference other than the immediately previous bit.) The signal generated is then a carrier whose phase "shifts" 180 degrees when the next bit is the same as the previous bit, and doesn't shift at all when the next bit is different from the previous bit. (This may seem backwards compared to the definition, but it forces phase transitions even when the bit sequence is continuous "fill" bits, allowing the receiver to stay in synch.)

4. The final step is an amplitude modulation that reduces the amplitude to zero at the phase transitions. (The amplitude is not reduced if the phase is not shifted.) This has two benefits: First this serves as a timing reference for the receiver providing an easy way to determine when the transmitted signal is "shifting", and, secondly, the instantaneous phase shifts produce many harmonics; reducing the amplitude to zero at precisely that instant suppresses these sidebands.

Reception of the PSK31 waveform follows these steps in reverse:

1. The amplitude modulation is recovered to determine the timing reference.

2. The phase of the signal is sampled based on this reference and the phase shift sequence is recovered.

3. The fill bits are removed.

4. The remaining bits are translated into text using the Varicode lookup table.

How is PSK31 generated by an amateur radio station?

The classic PSK hardware configuration is a computer with sound card, an SSB transceiver and an interface between the two (for audio signals and sometimes the Push-To-Talk or PTT). The computer generates the PSK signal as an audio signal - effectively the audio serves as the first IF of the transmitter chain. The output of the computer sound card then feeds an SSB transmitter which is used only as an upconverter - the audio signal is simply translated to the RF spectrum. The translated frequency is equal to the sum of the transmitter frequency plus the "audio IF" for USB, and the transmitter frequency minus the "audio IF" for LSB.

PTT can be enabled in multiple ways, depending on how your interface is configured. Some radios can use their internal VOX functions, especially when using the MIC input. (This is not often available with DATA inputs.) Some interfaces receive "trigger" signals via a conventional serial port, or a USB port, and perform the level conversion necessary to "close" a PTT switch, either in the MIC jack or on a DATA jack. Some interfaces have internal VOX-type circuits, so the software doesn't have to do anything special, but the interface closes the PTT switch itself. And some software/interface combinations use CAT commands, the same type of signals used for computer control of the radio. Examples of these can be found on the PSK Hardware/Software page elsewhere on this web site.

What is the Audio Offset?

"Audio Offset" is another tem for the audio frequency at which the PSK signal is generated. It's called this because it's the "offset" between your transmitter dial frequency and the actual frequency at which your PSK signal appears in the RF spectrum. Additional information on this can be found on the PSK Frequencies page elsewhere on this web site.

So what's different about QPSK31?

The QPSK31 format transmits two bits per phase state, and transmits one of four phase states each time. (If you think about it, there are four possible combinations of two bits, and each of these combinations is assigned a unique phase.) This allows twice as many bits to be sent in the same period of time (and bandwidth) as with BPSK. Martinez coupled this with a rate-1/2, constraint length 5 convolutional code to improve the power efficiency of the modulation (defined as the signal-to-noise ratio required to deliver a specified bit-error-rate, or BER).

This adds a step in the transmission process - generation of the coded bitstream - after the insertion of fill bits. It also adds a corresponding step in the receive process. After the bits are recovered from the phase transition, a Viterbi decoder removes the redundancy inserted by the code, corrects bit errors (up to a point) and recovers the original bit stream for translation of the Varicode.

One interesting note is that while the BPSK31 signal is phase-symmetric, QPSK31 is not. This means that if you are using BPSK, it doesn't matter if you are using USB or LSB - the signal is the same. If you are using QPSK, both stations must be using the same sideband, or one must use the "invert" function in their software.

Videos

Randy, K7AGE, has produced numerous ham radio videos for You Tube. Four of these are an introduction to PSK31:

How to Receive PSK31

Soundcard Interfacing

Sample of Activity on 20 Meters

PSK31 Operating

Many thanks to Steve, W3HF, for this page.

The following is the Ø7Ø Club policy statement reqarding callsigns and their use within the Ø7Ø Club program. While this FAQ attempts to address most of the common issues an Ø7Ø Club Member may come up against, it is not all-inclusive by any means. To avoid misunderstandings and/or disappointments, it is always best to send an email to Jay, N3DQU, and ask for the official Ø7Ø Club policy regarding your special callsign question BEFORE your expected operation is to take place.

Q1: Who can be an Ø7Ø Club Member?

A1: Any amateur radio operator licensed to operate on the HF bands who has made 50 (fifty) different PSK31 contacts on the HF bands (160M - 6M).

Q2: What about a Club station?

A2: Amateur radio clubs can become members too, if the 50 contacts were made using the club callsign.

Q3. What is the Alpha List?

A3: The Alpha List is an alpha-numerical list of active Club members (individuals and clubs) listed by callsign. Even though we list members by their callsigns, it is the individual (or club) that is the member. The current Alpha List is always available on this web site.

Q4: Suppose I get a new callsign? What happens then?

A4: Notify the Club of your callsign change and we'll update the Alpha List. Contacts made under both your old and new callsigns will count for your endorsements.

Q5: Suppose I get a special event callsign. Or what if I use an "alternate" callsign, like a temporary special prefix? Do these count?

A5: You can count all contacts you make under all of these situations, IF the callsign was assigned to you personally. But if it's a club special event station, and you were just the operator, they won't count. Just notify us of the special callsigns and effective dates so we can update our records and give credit to anyone who worked you.

Q6: If I let someone else use my station, can I count the contacts they make towards my endorsements?

A6: If you are an individual member, then only contacts made when YOU are the control operator count. But if the member is a club, then anyone can be the control op and the club gets credit.

Q7: Can I count contacts I make if I'm operating a club station, like at Field Day?

A7: Only contacts made by you (as the control op) operating a station licensed to you count towards your Ø7Ø awards.

Q8: Suppose I operate from another country? Can I count contacts I make there?

A8: As long as you meet the other requirements (that you are the control operator and the station is licensed to you personally), then any contacts you make anywhere will count, provided you were operating legally and in accordance with privileges granted to you by the licensing authority.

Q9: What about "automatic" reciprocal licenses that are defined by treaty, like the US and Canada (e.g. W3HF/VE3), or CEPT (F/N3DQU) or IARP?

A9: As long as you meet the other requirements (that you are the control operator and the station is licensed to you personally), then any contact you make anywhere will count, provided you were operating legally and in accordance with privileges granted to you by the licensing authority.

Q10: What about reciprocal licenses that DON'T include my callsign, like W3HF operating as ZF2HF?

A10: As long as you meet the other requirements (that you are the control operator and the station is licensed to you personally), then any contact you make anywhere will count. Since this is a case where you might not be recognized as an Ø7Ø member, you must notify the Ø7Ø Club of your alternate callsign and the effective dates.

Q11: I want to get a separate Ø7Ø Club membership for my alternate callsign. Can I do this?

A11: If you are assigned a separate and distinct callsign for reciprocal operation, you can choose to request a separate Ø7Ø Club membership for that call once you have made the required 50 PSK31 contacts using that call. Note that in this case you must keep your contacts separate between your two calls - you can't combine them for endorsement purposes.

Q12: What about LONP? Can I count a contact with F/N3DQU or ZF2HF (operated by W3HF) as contacts instead of working their home calls?

A12: You can count ANY PSK31 contact you make with another member for your own LONP credit. If his reciprocal license includes his home call (e.g. F/N3DQU), then all you have to do is list it on your contact list. If the other station is using a special event call, a special prefix, or a reciprocal license that doesn't include his home call, then you can only count those contacts AFTER the other station has notified the Ø7Ø Club of the callsigns. NOTE: It is the responsibility of the member operating under a recriprocal callsign to notify the Ø7Ø Club of the details of the operation so that members can be given credit for the contacts.

Q13: I contacted the same person twice, once at his home QTH and once when he was operating in a foreign country using his reciprocal callsign. I notice that he has a separate Ø7Ø Club membership for his reciprocal call. Can I count this as two separate LONP contacts?

A13: Yes. Since he has two separate Club memberships you can contact each of them and count them separately.

Q14: I plan to be outside of my country during the TDW contest. Can I operate in the TDW using a reciprocal license?

A14: Yes. Since you are an Ø7Ø Club member you can operate in the TDW using any callsign that is personally assigned to you. But you might have to take one extra step depending on your reciprocal callsign. For the contest to be fair, it is imperative that all members know the callsigns of all other members that can be contacted for credit. For this purpose, the Club publishes what is called the "Final Multiplier List" approximately three days prior to the start of the contest. This "Final Multiplier List" is in fact the official list of all stations that may be counted for multiplier credit during the TDW. So, if you will be using a callsign during the contest that is different from the one listed in the Ø7Ø Club's Alpha List, you must notify the Ø7Ø Club at least five days prior to the start of the contest so that your alternate callsign can be listed in place of your permanent one. If you don't do this you can't participate in the TDW and contacts made with you may not be counted for contest credit. More information on the Three Day Weekend (TDW) is available on this web site.

Q15: If I hold two calls personally assigned to me, and both calls are listed as Ø7Ø Club members on the Alpha List, can I have a friend operate under one call in the TDW while I operate the other?

A15: No. Except for the special case where a club station is listed as an Ø7Ø Club member, you must be the control operator at the time the contacts are made to count for TDW credit. You may, however, operate the TDW under one of the callsigns, then travel to the location where you are licensed under your alternate callsign and operate the TDW from there. In this case, multipliers are counted separately for each station and separate contest entries submitted.



Q16: There is no more room on my membership certificate for endorsements. What do I do now?

A16: Send a request to the Ø7Ø Club Manager for an Endorsement Page.



Q17: What if I lose my Ø7Ø Club membership certificate? Can I get a new one?

A17: At the discretion of Ø7Ø management, a membership certificate may be reissued for loss only. The new certificate will be reissued under the original callsign, membership number and issue date. A request for endorsements to repopulate the reissued certificate may also be made and we will try our best to fulfill your request, but there is no guarantee that all past endorsements will be available.



Q18: If I change my callsign, can I get a new Ø7Ø Club membership certificate with my new callsign on it?

A18: No. A membership certificate may be reissued for loss only (see above). However, a request may be made for an Endorsement Page showing the new callsign.



Q19: What if I lose my Endorsement Page? Can I get a new one?

A19: Yes. However, there is no guarantee that all past endorsements will be available to repopulate your new Endorsement Page.


(Many thanks to W3HF for his work on this page.)