PSK31 is a 'RAVE:'
To speak of it any other way, or in any manner other than; It' s a rave, would be understating its presence and impact on the world of ham radio communications. PSK31 is sweeping through the SWL and Amateur Radio ranks like a brushfire. Not since the early days of FM repeaters has any mode inspired so much interest in HAM radio and short wave radio monitoring than PSK31.
If you have a short-wave receiver that supports single-sideband reception, and a PC (486/100 MHz or faster) running Windows 95, 98, or XP, equipped with a Creative Labs' compatible (SB16 or later) sound card, then you have the ingredients to receive PSK31.
At figure one, I' ve drawn a very simple and basic interface diagram that makes receiving PSK31 easy for anyone with the two basic items I' ve listed above. You' ll need the FREE software which I' ll talk about later in the text, but first, I need to explain what PSK31 is.
FIGURE 1
What is PSK31?
As the name implies, PSK (phase shift keying) modulates the phase of a carrier, and the number ''31'' references the actual bandwidth (31 Hz) occupied by the PSK31 signal.
The software that implements PSK31 with a Windows PC and soundcard is a program written and developed by Peter Martinez G3PLX. Two of the most significant features that make this the ideal mode for digital communications is the extremely narrow band width, and the fact that it is highly immune to noise and QRM.
Up front, phase modulation has more advantages than (morse code), CW. CW uses amplitude (On/Off) keying. In a noisy or distorted propagation environment, the amplitude of a signal will shift and vary much more than the phase of a signal. When compared to CW, PSK31 is a much more resourceful, and robust operating mode.
The baud rate used by PSK31 is 31.25 baud. This is fast enough to handle most operators manual typing capabilities, a speed of about 50 words per minute. It is intended as a means of keyboard to keyboard communication between two or more operators (oh happy day, we' re talking to each other again), using a very small amount of frequency spectrum.
By comparing the small bandwidth of PSK31 and measuring its gain against a CW filter of 500 Hz; 10 * log (500/31) dB = 12 dB, quickly reveals that a CW transmitter must put out 15 to 18 times more power than a PSK31 transmitter, just to achieve the same signal to noise ratio at the receiving station. This is the reason the PSK31 operating mode has gained so much popularity in such a very short period.
The end result is that a PSK31 station can operate with reduced power and smaller antenna installations. As an example; My 20 meter, 14.073 MHz, antenna, is located in the attic of my garage (about 14 feet above ground), and my DX70H runs around 35 watts output.
Now comes the real tease, just for the DX hounds among us. In the last three months, I' ve work over 75 countries, and each morning I spot a new one that I have not yet worked. It gets better! For some reason' I think it' s because PSK31 is so much fun' , I' m finding more DX stations on PSK31 than I' ve ever encountered on SSB and other modes combined. At any given moment, day or night, it appears that 20 meters is always open.
Twenty meters is not the only band that has PSK31 activity, but it is a good place to start when you first begin operating PSK31.
AND, IT' S ALMOST FREE:
When the prospective PSK31 user discovers PSK31 for the first time, a look of both extreme pleasure, and amazed disbelief appears on their face. WOW, we' ve just discovered a mode that is so much fun, yet, it' s almost FREE! After a few days of operating PSK31, the internet becomes obscured in the mist of all the fun we' re having ' doing' PSK31.
Yes, there are a large number of PSK31 programs that support the PC, LINUX, and the MAC. We' ll also cover them later in this article.
KUDOS ARE DUE THE AUTHORS OF PSK:
Before I get into interfacing our HF transceivers and the sound cards, I would be remiss if I didn' t give credit to the author(s) of PSK.
Here, in his words is the background and the PSK31 philosophy, of and by Peter Martinez G3PLX.
PSK31 is the result of my belief that the present batch of "data" modes have left a gap in amateur radio operating, the gap that was previously filled by AMTOR or even traditional RTTY, in which two or more operators chat to each other on an open channel. Modes such as packet radio, Pactor, and others, are highly complex, are unsuited to multi-way conversations, and in particular, the long block lengths introduce an unacceptable delay in the processing of text such that even normal conversation is unpleasant and quick-break question/answer sessions are impossible.
The move to automated unattended message forwarding has left a gap in the person-to-person communication field, and PSK31 is an attempt to remedy this situation with a simple but efficient code structure coupled with the narrowest possible bandwidth, and with only enough error-correction to match typical typing-error rates, and with no time-consuming synchronization, changeover, and ARQ processes.
The 31 baud BPSK modulation system used in PSK31 was introduced by SP9VRC in his SLOWBPSK program.
Instead of the traditional frequency-shift keying, the information is transmitted by patterns of polarity-reversals (sometimes called 180-degree phase shifts).
This process can be thought of as equivalent to sending information by swapping-over the two wires to the antenna, although, of course, the keying is more usually done back in the audio input into the transceiver. A well-designed PSK system will give better results than the conventional FSK systems that amateurs have been using for years, and is potentially capable of operation in much narrower bandwidths than FSK. The 31 baud data rate was chosen so that the system will handle hand-sent typed text easily.
There is a problem with PSK keying which doesn't show up with FSK, and that is the effect of key-clicks.
We can get away with hard FSK keying at moderate baud rates without generating too much splatter, but polarity reversals are equivalent to simultaneous switching-off of one transmitter and switching-on of another one in anti-phase: the result being key-clicks that are TWICE AS BAD as on-off keying, all other things being equal.
So if we use computer logic to key a BPSK modulator such as an exclusive-or gate, at 31 baud, the emission would be extremely broad. In fact it would be about 3 times the baudrate wide at 10dB down, 5 times at 14dB down, 7 times at 17dB down, and so on (the squarewave Fourier series in fact).
The solution is to filter the output, or to shape the envelope amplitude of each bit which amounts to the same thing. In PSK31, a cosine shape is used. To see what this does to the waveform and the spectrum, consider transmitting a sequence of continuous polarity-reversals at 31 baud. With cosine shaping, the envelope ends up looking like full-wave rectified 31Hz AC. This not only looks like a two-tone test signal, it IS a two-tone test signal, and the spectrum consists of two pure tones at +/-15Hz from the center, and no splatter. Like the two-tone and unlike FSK, however, if we pass this through a transmitter, we get inter-modulation products if it is not linear, so we DO need to be careful not to overdrive the audio.
However, even the worst linear will give third-order products of 25dB at +/-47Hz (3 times the baud rate wide) and fifth-order products of 35dB at +/-78Hz (5 times the baud rate wide), a considerable improvement over the hard-keying case. If we infinitely overdrive the linear, we are back to the same levels as the hard-keyed system.
There is a similar line of reasoning on the receive side. The equivalent to "hard-keying" on the receive side is a BPSK receiver which opens a gate at the start of a bit, collects and stores all the received signal and noise during the bit, and then "snaps" the gate shut at the end. This process gives rise to the receive-side equivalent of key-clicks, namely side-lobes on the receiver pass band. So, although this "integrate-and-dump" method is 100% efficient in the task of sorting out signal from noise, it will only reject signals by 10dB at 3 times the baud rate wide and so on, the same spurious rejection figures that we got as spurious emission figures for the transmit side.
The PSK31 receiver overcomes this by filtering the receive signal, or by what amounts to the same thing, shaping the envelope of the received bit. The shape is more complex than the cosine shape used in the transmitter: if we used a cosine in the receiver we end up with some signal from one received bit "spreading" into the next bit, an inevitable result of cascading two filters which are each already "spread" by one bit.
The more complex shape in the receiver overcomes this by shaping 4 bits at a time and compensating for this inter-symbol interference, but the end result is a pass band that is at least 64dB down at +/-31 Hz and beyond, and doesn't introduce any inter-symbol interference when receiving a cosine-shaped transmission.
Our thanks and with credits to Peter Martinez, G3PLX for PSK31.Contact Information:
Peter Martinez G3PLX
High Blakebank Farm
Underbarrow Kendal
Cumbria LA8 8BN
United Kingdom
THE QUICK BROWN ' VOX'
For this discussion, we will NOT consider using the VOX (voice operated relay) circuits in our transceiver to control PSK31 changeover from transmit to receive and vice versa. Especially since most of us have a spare or extra serial comport(s) that we can use to do the same thing, and without having the transceiver hiccup a transmitted signal every time the sound card burps. As you will soon see, there is an easier way to handle the push-to-talk (PTT) function in PSK31.
ATTENUATOR; YES OR NO:
Yes, we should consider the use of some level of attenuation either into the sound card or out of the sound card into the transceiver. I think the easiest way to approach this is to understand first that modern day transceivers are designed for inputs into the transceiver for SSB, FM, AFSK, RTTY, and in some cases, SSTV. We should maintain the levels similar to those we normally use when using a microphone.
Since many transceivers that we will be using are beyond ten (10) years since their purchase, some of us will be using the microphone port for our PSK31 input. If this is the case, and you plan to drive the microphone with your sound card (LINE OUT), then the level from the sound card should be comparable to the output level of your microphone.
But I've already said that haven' t I? YES, I have, but I want to stress a point. In this case, we will need to employ padding of about 40 DB. I refer to these attenuators as ' pads.' This term comes from a time when we referred to it as ' padding the signal down.' For the new HAM, padding down of a signal can reference either audio or radio frequencies (AF / RF).
To keep it simple, I' ve drawn an attenuator ' pad' at figure two. Again, it is a device that is simple to build since it employs only two resistors. Unless your sound card is a slam-dunk' n, speaker popper, you should be able to get by with quarter watt sized resistors.
Figure 2
While many sound blaster compatible sound cards have the capability to be set for high or low level outputs, they are almost always providing outputs which are much to high for the input level to the microphone port of our transceiver.
If you cannot use the sound card ' Control Panel (settings)' in Windows (or your WINPSK, or other software) to decrease the output level of your sound card to meet the level requirements of your microphone input, then you are about to construct the resistive attenuator shown at figure two to reduce the LINE OUT level to your transceiver MIC port. The idea is to keep your signal at a low enough level to have a clean PSK31 signal on the air.
With PSK31, the first thing I do is set my transceiver for normal single side-band (SSB) operation. I turn off any speech processing and after I have the microphone level properly set for PSK31, I don' t change this setting again.
All future levels are set into and out of the sound card using the volume and wav controls built into the sound card ' control panel' software. In DigiPan II, these controls are easily accessed from the task bar at the top of the screen. Simply click on ' configure' and use the ' Transmit Drive' (Photo B), command to properly drive the transceiver so that no ALC action is observed. This is how I avoid causing phase distortion or overdriving the inputs of my transceiver.
While we' re discussing sound card I/O levels, in case of feedback (usually "motorboating"), which may be caused by the common ground of the soundcard input and output, ' MUTE' the ' line in' ON THE "VOLUME CONTROL" panel under Windows or in WINPSK or digiPan configure/transmit/check ' Mute' . This change will stop the sound in your PC speakers, but it may also stop the motor-boating of your PSK31 transmit signal.
Let me say it again, in another way, so the message is well understood. The Microphone and Line inputs on the Volume Control panel, controls the SOUND to the speakers (not the spectral display) and muting these inputs will render no sound (receive) from the computer speakers, but the transceiver speaker can still be used to audibly monitor the PSK31 signal if you so desire.
If you are using the external speaker jack for receive audio to the sound card, then a 3.5 MM plug and two-jack splitter may be required to feed both an external speaker and the sound card. This is because the internal transceiver speaker will be muted by the closed-circuit (opened) jack.
LET' S GET BUSY:
If you are taking the constant level output of audio from your transceiver and driving the sound card, then you can rest assured you need to be very critical of levels into the sound card. Read your transceiver manual as it should tell what the levels are at the various inputs and output jacks.
READY, SET, PSK31:
The following is a list of frequencies (in kHz) where you may find more PSK31 activity are:
18100.150
21080.150
24920.150
28120.150
Because I am most familiar with WINPSK 2.12 PSK31 software, I will use it as a reference during my explanation for setting up the transceiver and sound card levels.
First we' ll set the soundcard output level to approximately one third to half-scale (click the speaker symbol on the Windows taskbar). Connect a dummy load to the transceiver antenna output and click on the software ' TX' menu button.Next, let' s make sure we have our transceiver set for USB (Upper side-band) operation, and the AGC set for Slow (recovery). We' re now set to begin our on-the-air (dummy-load) setup.
Using your favorite watt meter and dummy load connected to the output of your transceiver, click on the PSK software ' TX' menu button and adjust the Speaker volume slider on the Windows taskbar tray for an output power reading of about one third to one half the power you would normally see when operating CW. DO NOT operate your transceiver at more than half its maximum power level rating!
Once you have the power level set, type a few characters and watch the power meter. As you type, the text you are sending should cause the meter pointer to have a slight jitter. If you have the LINE OUT/MIC IN level set properly, you should see the power move slightly upwards. At no time should you see the power level go above 50% or your transceiver' s rated power output. If it does go higher, simply turn the Transmit Drive level down, using the ' SETTINGS, /transmit Level Icon in WINPSK 2.12.
SOFTWARE, SOFTWARE, EVERYWHERE:
There' s plenty of software to help you get on the air with PSK31. You can choose the one you like best and of course some of your decisions will be based on the particular operating system for your computer. Be sure you read the PSK31 software user' s manual or the ' help' files that relate to the software you plan to use. OR... read our PSK31 HandBook resident on our 2008 CD ROM.
In the next few paragraphs, I' ll name a couple of software packages for PSK31 operation. Before I go there, I' d like to point out that so much of this software is FREE, however, the software writer and author's cannot live by bread alone; He/she must have peanut-butter, and peanut-butter cost money! Which ever software you finally choose, remember the author of that software package dedicated his or her time to making your hobby more fun. If you like the software, send the author a small donation as a sign of your appreciation for their contribution to making your hobby fun and exciting. By sending a small contribution to the software author's, you are also encouraging them to extend additional effort to add more features and updates for your future enjoyment.WINPSK uses digital signal processing (DSP) to do all these features and then decode the resulting PSK31 sounds into characters on the receive screen. The display shown at photo A, is how a typical PSK software spectrum (panoramic waterfall) window appears.
A bright yellow bar with the diamond-shaped cursor in it is a PSK31 station. To the left and right of the station select cursor, are other PSK31 stations. Some appear weaker and others will display brighter, which indicates stronger signals. Although some signals in the display appear weak, they will still print perfect copy.
The most recent receive signals are displayed at the top of the PSK software waterfall display. To the right of the cursor, is another PSK31 station that is almost too weak to copy.
To tune and receive any of these stations, it is only necessary to point to the station signal with the mouse and click! The diamond-shaped cursor will jump immediately to the center of the station signal and the text from the station will begin to appear on screen in the receive window.
During an idle moment, you can read the IMD of the selected station on the lower feature bar in most PSK software programs. The IMD reading of the station displayed in photo ' A' is minus 23.5. A good signal and ideal IMD is between minus (-)22 and -32.
Other sections of the software screen are devoted to buttons to control the functions of program, and select keys for the activation of a large number macros. The ' text' button on the task bar enables the operator to choose any number of text files to send, including the familiar ' BRAG.TXT' that all us ole RTTY ops are familiar with.
Just a word to the wise; In order for the program to provide a panoramic display with point-and-click tuning of stations, it is necessary for our transceiver' s to provide both panoramic reception and transmission. The receive band pass should be capable of receiving a large number of PSK31 stations at one time. So far, all the transceivers I've operated or interfaced, have this capability.WinPSK: 2.14 (or above)
There is a new version of WinPSK by Moe AE4JY. It adds two interesting features, the first is a new user interface that favors the disabled ham who cannot use a mouse, but through the use of the function keys and Macros, it' s a snap to use. The second one that Moe has produced has a PskCORE DLL that is available in binary along with instructions. You can go to Moe' s page at: http://www.qsl.net/ae4jy/
I keep a copy of the Moe' s user manual in .pdf format and his technical supplement close by. It is a must, plus a real pleasure to read. Here you can learn both implementation details and the theory and operation of PSK31.
Then there is a Multi-Mode program appropriately called "HAMscope"
"HAMscope" supports several sound card digital modes. It now employs a waterfall type display. It also supports SSTV, RTTY, CW and Packet modes
.
LINUX
Amateur and PSK31 linux applications can be found at: ftp://metalab.unc.edu/pub/Linux/apps/ham/ There is a shareware program called Multimode by Chris N3JLY. It enables PSK31 operation for the Macintosh user. Go to: http://www.blackcatsystems.com/software/multimode.html
And' . Just in case I' ve not provided you with enough PSK31 fodder here in ' BUX Bitz, Bytez, and Baudz,' then have a look at: http://www.PacketRadio.com and read our PSK31 HandBook on our 2008 CD ROM,
HAM Radio FREEWARE Software for Sound Card applications. Sorry, we do not support soundcard program software. For soundcard software & program support, contact the software vendor or author.
by
G E "Buck" Rogers Sr; K4ABT
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As a final note: Many times, an over-driven interface with no attenuator or 40 db pad, can be construed as noisy or distorted on-the-air audio. In more than 85% of the soundcard or digital mode cases, the cure for this problem is to simply add a 40db pad as shown below. For the operator with sound card I/O, and a high-level SPEAKER OUT. Use a 40 db attenuator . $ 7.95 Order keyword = 40DBPAD
Solving hum problems in PC soundcards and Ham Transceivers
The typical ground loop hum problem often occurs when you connect your computer (PC) sound card to a transceiver which is connected to an AC outlet that is not connected to the same bond or ground as the PC.
Finding ground loops is not always easy; Once found, the solution may be effortless. Solving ground loop problems in typical HAM radio and PC sound card applications may be as simple as applying practical logic. If you have your transceiver and PC connected to different power outlet/circuits, you may be closer to the solution than you think.
Try connecting both the transceiver and PC to one "grounded" multi-outlet with a "third-wire ground" (bonded outlet), and then plug this multi-outlet into a grounded (bonded), wall AC outlet.
This usually solves eighty-five percent (85%) of all hum (ground-loop) problems, simply because you've created a star-point grounding scheme for both the PC and Amateur Radio transceiver. If this scheme does not cure the ills of the hum-loop, it could be that no bond or third-wire ground exists in your AC (utility) wall outlet.
Other Computer Soundcard Problems:
When, and if, the computer is connected to a separate power outlet which may or may not be connected to a common (same) bond as the transceiver supply, it can result in a potential difference between the PC and the transceiver. This is where many ground loops are formed, causing hum to be superimposed on the transmitted audio.
If the sound card audio ground is indeed connected to the AC (utility) ground, and a high pitched sound or squeal is heard on other receivers, then look for RF feedback (base rectification) at the input or output of the PC sound card. Often a ferrite bead placed around the lead, or a 47 ohm resistor in series with the audio line will act as a block to ingress or stray RF.
In some cases where the remedy mentioned above fails, the addition of a by-pass capacitor may be required. The value of the by-pass cap may be approximately .001 ufd to .01 uf. Under no circumstances will the by-pass cap be larger than .02 uf. A greater value than .02 uf may roll off in-band audio frequencies, and result in loss of audio output level.
If the by-pass cap is to be used, install it from the transmit audio line to the shield/ground. This is sometimes easiest achieved at the transceiver input connector (or jack).
Best audio to you and 73 de Buck Rogers; K4ABT
RASCAL SETUP & SUPPORT:
The RASCAL' , will not perform properly if the software and computer (PC) are not properly configured. Most problems encountered are usually due to PC and software setup. You should always read your software documentation. The WINPSK manual is also on the disk you received with your RASCAL' ,. Be absolutely sure that you have your software set up properly before connecting the RASCAL' ,. If the software and computer are not set up and configured properly, the RASCAL will not see the correct input, output and PTT control signal(s).
It is of the utmost importance that you read the documentation that comes with your software! See the Users Manual (PDF) file on the WINPSK disk that was sent with your RASCAL.
NOTE, that some problems have been encountered using Windows ME and 2000 upgrades which sometime hold the comport RTS line "high." This can result in the PTT being activated when the DB9 is connected to the PC serial comport. There are several "patch" programs that may be of help to resolve this problem. Another source of patch fixes may be found at the microsoft support pages.
SPEECH COMPRESSION:
Be sure all speech compression is OFF. Observe the ALC indicator. Set the microphone gain to a level where there is little or no ALC indication on high peaks. Always insure that it is below the maximum ALC indication. Set the Windows volume control by double clicking the speaker icon (usually in the lower right desktop task bar), and set the wave volume as needed to drive your radio properly. You may also adjust the transmit level with the RASCAL internal Tx ' ' transmit level' ' control. Or' use the Tx Level and Rx Level setup under the WINPSK "SETTINGS" Icon. The final result of your sound card setting should be approximately mid-range or slightly higher, for the on-screen soundcard settings, and the RASCAL' , Tx audio level control.
One important item to remember; All adjustments to the soundcard will interact with other settings of the sound card. This is the nature of the soundcard and sound card driver (software).
VOX OPERATION:
If you prefer, or if you don' t have a spare serial comport available on your PC, the RASCAL' , has transmit audio to the microphone input when connected, setup, and software is set to "send" or "Transmit." By having the soundcard and RASCAL transmit audio active, you may use of the VOX circuits in your radio to activate transmit (PTT) control instead of relying on the PC serial port to control PTT for transmit/receive. If you have only a USB port, a USB to SERIAL converter is available at "www.BUXcommCo.com for $19.95.
Set all the microphone settings as described above. Activate VOX in your transceiver, and set the level, delay and anti-trip controls with the tones from the RASCAL/soundcard, as you would when using the microphone (voice) input. In most cases, I' ve found that normal VOX settings perform with the RASCAL and PC as both levels are set similar. WHEN OPERATING PSK31, SSTV, WSJT, AND OTHER SOUNDCARD DIGITAL MODES: UNDER NO CIRCUMSTANCES SHOULD THE POWER OUTPUT OF YOUR TRANSCEIVER EXCEED ONE-HALF THE TRANSCEIVER' S MAXIMUM RATED OUTPUT! FINAL' ' ..
Fine Tuning, or initial receive and transmit adjustments: Let' s make the initial adjustments to the RASCAL' interface. We can fine-tune the Volume Control for best operation with your PSK31 program, sound card, and radio. Here are the basic things to keep in mind: * The "Wave" slider controls the transmit level, in combination with the "Volume Control" slider. * The Volume Control slider controls both the level going to your computer speakers, (receive or transmit) and the overall transmit level. * The MIC, LINE IN, or AUXILLARY, controls the receive level. Notice that running the software Volume Control slider up and down will change the level of the receive audio going to your speakers, but it should not change the actual level of the recording (receive) stream.
Watch out for the "MUTE" boxes..... for if you mute the input you're using to receive PSK31, the audio will no longer be delivered to the speakers; however, it may still be sent to your PSK31 program. SOFTWARE SETUP FOR PSK31: Using a program like "WinPSK," enter your call sign using the "Settings" / "General Setup" menu. Here you can enter your call and other program setup items such as the serial Comport number and PTT (RTS) settings. Your call sign should now appear at the top of the WinPSK screen instead of the text,' "Call Sign Not Set".
You can do the soundcard level setup using the Tx and Rx levels shown under the "Settings" menu. Use the built in wave file player and recorder to get familiar with your sound card' s mixer settings and capability. The mixer control is used to set both the receive audio level to the PSK program as well as set the "coarse" level setting to your transmitter. If you are using the MIC input, you should use the radio' s mic gain for precise level adjustments..
It is also a very good idea to disable all the various Windows sounds if you have only one sound card, especially if you are using VOX PTT control. FYI, a good frequency to begin operating PSK31 is at: 20 mtrs @ 14.070 MHz USB
73 es I hope to QSO w/U on PSK31 soon,de Buck Rogers K4ABT s u p p o r t @buxcomm.com
