PSK Is A Fragile Mode

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PSK Is A Fragile Mode

Dick Boley (N3HKN) on January 21, 2004
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PSK Is A Fragile Mode

The popularity of PSK is born from a simplicity of implementation and ease of operation. Hams that have almost any kind of a computer can get on PSK. Most of the needed software is free and the ease of cobbling an interface allows those with a fear of solder to give it a try. As more and more Hams find themselves victims of restrictive regulations of various sorts, PSK enables communication around the world with modest power (less than 50 watts usually) and small antennas.

However, PSK is fragile. Unless you own a receiver with extensive filtering (xtal or DSP) in the AGC loop strong signals can significantly harm a contact with a weak station. Even with the best receivers a close-in strong signal will kill the weaker contact. With PSK the rule of only using the amount of power needed to make a contact is of paramount importance. Stations with large beams on 20 meters (the most popular PSK venue) can run 50 watts and make life very difficult for those less fortunate. I suspect that there are even some who run linears just to insure that they make contacts anytime they feel the need. Seems simpler, and cheaper, to just call the other station on the phone.

The other area where PSK is fragile is the over-modulated signal. A mildly distorted signal is usually occupying about twice to three times the needed bandwidth. But if the overdriven PSK signal is exceptionally strong (muscle stations) then we can sometimes see artifact signals all over the bandwidth of the receiver. This is the worst case and often renders the bandwidth almost useless.

Remedies are simple. Hams who are over-modulated and distorted should be told that they have a problem. However, it seems that many either do not understand the PSK mode, and therefore fail to see the problem, or they are afraid of insulting the other Ham. In either case the problem persists. I have worked with other Hams over the air many time as we found the proper level of audio to clean up the signal. However, some are totally ignorant of the function of the controls and after several minutes of discussion they simply are afraid to touch anything. Their signals remain a problem. Hams must provide others with offensive signals a valid report so that they can make corrections.

Overly strong signals and highly distorted PSK signals are a problem for a mode that naturally operates with low power and is thus vulnerable to mistakes of others. Fortunately, the vast majority of signals are very good. However, unless we make the Ham with the offending signal aware of a problem it might become worse as higher power and higher distortion take their toll on the fragile PSK signals.

Dick N3HKN

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PSK Is A Fragile Mode

by VK2TUI on January 21, 2004 Mail this to a friend!

Hi Dick very good article and I think you highlight the problem of the overdriven PSK signal quite effectively. The big problem I believe is in the signal reporting regime where most reports are of the nature RST and this is not appropriate for this mode of operation. I feel the RSQ method is far better and should be pushed as a standard so that a meaning full signal report will indicate to the transmitting station the quality of the transmission,
R = Readability i.e percentage of good print out R5 = 95% to 100% error free. R1 = 5% to 25% only error free
S = Signal strength...S9 = Very strong trace and S1 = Barely percetible trace
Q = Bandwidth or Quality where Q9 = Clean Narrow Signal approx 60Hz and Q1 = Filling Entire Waterfall and needs fixing.

By using a meaningfull reporting system one would expect the receiving party of a crap Q report to go away and fix it.

Details of the RSQ method of reporting can be found at www.psb-info.net.

PSK31 is a terrific way to work the world with only a minimum of power. My station runs about 10 watts mostly on 14.070 and 21.070 and when band conditions are good one can work everything you hear.

The message is you dont need heaps of power and keep the signal clean. Don't overdrive and no ALC.

73's Alan VK2TUI

PSK Is A Fragile Mode

by AG4GM on January 21, 2004 Mail this to a friend!

I have also found the PSB reporting system to be quite effective. From my experience, though, not many people are familiar with it. I was introduced to it by a fellow ham on one of my first 20m PSK contacts. More information can be found at http://www.psb-info.net. There is also information there about the RSQ reporting system.

PSK Is A Fragile Mode

by K4EQ on January 21, 2004 Mail this to a friend!

I agree with AG4GM on the PSB reporting system. It makes a lot of sense. Giving an RST report has never made sense to me on PSK. When there's multiple PSK stations on the band, I've never been able to tell which of the many signals is pushing my needle anyway. --Dale, K4EQ

RE: PSK Is A Fragile Mode

by N3HKN on January 21, 2004 Mail this to a friend!

If I may add a note - I find that the any reporting system to be flawed by the the unknown calibration of S meters and the application of preamps. As an example I can have no preamp on my Icom-746, or one preamp, or TWO preamps!.

Quality reports can be as simple as telling the other Ham that their signal is wide. Some have no idea how to properly adjust their rigs and interfaces. Some are actually afraid to touch anything!

IMD reports must also be tempered. Unless the signal is quite strong noise causes a false IMD reading. So you have to be careful in this respect also.

Fortunatly, on the 746 I can insert audio from the PC on the back panel and bypass the compressor. Others are not so fortunate and may mistakenly leave the darn thing on.

I adjust my levels as follows. I set my RF Level to MAXIMUM, or at least more than I expect to use. That gets that control out of the picture. I then simply use the audio level control on the PC to set my power. Some Hams seem to set their output power with the RF Level control and thus overdrive/ALC the rig. Set it higher then your target power (usually set to more than 50 watts). Adjust the RF power with the PC audio. Obviously avoid creating ALC since that also indicates clipping/distorting of the fragile signal.

Dick N3HKN

RE: PSK Is A Fragile Mode

by K5DVW on January 21, 2004 Mail this to a friend!

The issue seems to be with people using the mode who have no concept of basic radio fundementals. I most often give an IMD number in my report and I ask whoever I'm chatting with to give me my IMD. This should be as common as exchanging RST, which I agree means nothing on PSK. I'm astonished that seemingly over half the people I ask to give me an IMD reading dont know how, or dont know what IMD is. Or if I give them a high IMD and point out that it's high or they are wide, they dont know what to do about it. That's the REAL problem, education!

Many operators are under the mistaken impression that the system works like CW or SSB, you just hook it up to the computer and go and there's no need to think about anything. They fail to realize its not an "appliance operator" mode like everything else, and it takes some effort to understand and set up correctly.

EVERY TIME I operate PSK I go thru a tune up procedure to verify my transmit levels, ALC, sound card output setting, etc. This should be mandatory for anyone running PSK. I guess it's easier to be lazy.

RE: PSK Is A Fragile Mode

by KA2UUP on January 21, 2004 Mail this to a friend!

Agree with N3HKN!

I normally used a SM-220 monitor scope to check on quality. However, later I have bee using the PSKMeter accessory. Even with full drive on my ICOM-746, the automatic level adjustment will bring the power down to about 30 watts.

I do not understand why would somebody use a linear amp for PSK31, when the mode's attractiveness is really the low power it needs to communicate. To each his own, I guess. However, I have barged in QSOs a couple of times on hams who occupy the whole waterfall and have gotten flamed.

The RSQ reporting system makes sense. Some of us are willing to work to hwlp others adjust their system for a clean signal. Some hams must learn to use the constructive criticism to better your skill, don't take it as an offense.

73 and good luck the Bert @ KA2UUP

PSK Is A Fragile Mode

by WA4ET on January 21, 2004 Mail this to a friend!

Having been what one might can a muscle station, not by design, but by ignorance, well maybe that’s not being fair to myself, but by lack of ability to see what the signal looks like while transmitting.

I have dabbled in PSK for some time, it wasn’t until I worked a station in 6 land that I ran into this problem. He was kind enough to explain there was a problem, but I did understand what he meant, so he emailed me pictures of my signal, broad as the Grand Canyon. It was at that point I understood the problem, but also realized, there was no way for me to know this information. Most ops have no way to check out there signal, and without feedback, there is no way to correct it.

I would guess that most of the perfect signals you see, are by accident, or by a dedicated PSK station that has worked this problem out, and never futz with it. SO be kind and help those that cant, so should a say SEE themselves, as not everyone wants to be a band hog.

I can also say, one of the biggist problems when operating PSK are the canned BRAG files, although some certainly have there place, alot of PSK ops do not use them with discretion. Having been on a few DXpeditions in my time, and operated PSK,, the last thing I want to listen to is abt their computer,pet dog, and the color of the most recently purchased car. HOw abt 59 and thank you very much, and let me go onto the next Ham that might need my location for that mode

Regards

DAvid

PSK Is A Fragile Mode

by K0RGR on January 21, 2004 Mail this to a friend!

I have found that best receive performance on PSK and most digital modes is to turn off the AGC on my IC-746 and use the RF Gain control to adjust the sensitivity. That helps to eliminate the problem of strong signals swamping out the weaker ones.

PSK Is A Fragile Mode

by K0RFD on January 21, 2004 Mail this to a friend!

Good post. I have carefully and courteously told a few operators that they were wide (usually not until they splatter harmomics across the entire passband), and each time this news was NOT received in a defensive manner by the other operator. We all have to look out for each other on PSK, and most ops seem to recognize this and take the news about a too-high IMD in a very positive and gracious spirit.

Another "threat" is that PSK frequencies are not formally recognized in the ARRL's Band Plans. If one goes to the The "Considerate Operator's Frequency Guide" on the ARRL website, http://www.arrl.org/FandES/field/regulations/conop.html one sees nothing about PSK or other low-power, low-bandwidth data modes. PSK is just lumped with "Data". Whenever a Pactor station fires up in your passband automatically without listening, there goes all of PSK until it is done. I assume that these stations are supposed to operate where the bandplan says "automatically controlled data stations" -- but they operate in the PSK area ALL THE TIME, especially on 40 meters.

While nobody "owns" a frequency, bandplans provide a nice agreed-to way of mitigating the impact of one operating mode on another. Because of the fragile, low-power nature of PSK, and also because of the real benefits it provides in the form of packing LOTS of QSOs into a small space (not to mention its popularity), it should be recognized in the Band Plans. And I don't think that PSK ought to be alone in being recognized. Because the digital modes are all quite different, an operator in one mode often can't tell that there's something going on in another mode on the same frequency. Time to at least introduce a little formality into the most common modes.

And I agree with the poster who mentioned inane "brag files", hihi. While I DO care about what kind of rig and antenna someone uses, I have never yet been able to tell the difference between a PSK station running on a Pentium 100 and one running on a Pentium 4 umpteen jillion gigaherz. Or between cat and dog owners either, for that matter. Who cares? It's 31 baud for cryin' out loud, it takes 10 minutes just to read one of those brag files! I love learning about people and having a real conversation. If the conversation comes around to what kind of computers we run (or about cats and dogs), by all means tell me. But don't program it all into a button then walk away while it sends. That's not conversation.

RE: PSK Is A Fragile Mode

by M0CMQ on January 21, 2004 Mail this to a friend!

Hi Darrin K5DVW
I've just joined e.HAM.net and have been very interested in this forum about PSK.
May I asked a question or two... re: the tune up procedure for PSK, some chapter and verse would be good for me as a comparative newcomer to PSK.
Problem just now...I'm using a KENWOOD TS 570D with Digipan 1.7, a soundcard and a RigblasterPlus. Doing
well until last Saturday when I discovered that I wasn't transmitting in this mode PSK (CW is ok).
I've done all the basic tests and checks without any good results.
Any ideas please.
Yes I'm checking with Bartg ( British Data group) and
with West Mountain Radio ( makers of RigblasterPlus).
73 de
Mark M0CMQ.

PSK Is A Fragile Mode

by ON4MGY on January 21, 2004 Mail this to a friend!

Hi,
when I'm running PSK31 I'm using only 3 to 5 Watts to work all over the world. The biggest problem with PSK is that some people don't know or don't want to know that they should turn the speech-processor OFF. When everybody should do that life would be a lot easier for the PSK-operators.
73
ON4MGY Nic

PSK Is A Fragile Mode

by K2WH on January 21, 2004 Mail this to a friend!

You very lightly touched on the use of narrow band filters without any detail and you failed to address the issue on how to make sure your PSK signal is above reproach. I wonder what you are doing to make sure YOUR signal is good? You did not mention what methods you use.

A very strong signal in the typical 2khz PSK window will make other weaker signals disappear. However, switching in a narrow filter and retuning your rig to eliminate the offending signal is a way to make sure the strong signal is not in your passband. I almost always use a 50hz filter. I call CQ in that filter and only receive in that filter. There is no need except for "it looks pretty", to receive the entire 2-3khz segment of the band.

Secondly (and I have said it before), the only foolproof way to adjust your audio level into the transmitter to ensure a pure PSK signal is a SCOPE. Scopes are available many places and are relatively cheap. I use and old Kenwood SM-220 monitor scope that will work with any transmitter. It just goes in the coax line and will display a perfect egg shaped PSK signal when your transmitter is adjusted properly.

K2WH

PSK Is A Fragile Mode

by K4JRB on January 21, 2004 Mail this to a friend!

Hams are not timid. If someone is distorting there will be plenty reporting this to the offending station.

PSK is no more fragile than satellite communications.
As with any operation the least amount of power should be used to make the QSO.

Dave K4JRB

PSK Is A Fragile Mode

by VE3WMB on January 21, 2004 Mail this to a friend!

As a couple response postings have mentioned, the fragility of PSK31 is compounded by the fact that most operators cannot see the signal that they are producing. However, there is a simple rule that helps to ensure that you are not overdriving.

I call it the 50% rule.

Reduce your rig RF output level to 50% .(ie if your rig puts out 100W then set it to output 50W). Remember PSk31 is >75% duty cycle .. this will also help your rig live longer.

Adjust the level control on your soundcard interface (if you have a control) so that when the windows slider for TX level is about 50% of the way up your rig output on PSK31 is peaking at about 50% of the power level you have set (ie should be no more than 25W in this example).

Fine tune the Tx slider so that there is no ALC indication (ie increase until you have ALC indication, then back it off)

You should now have a pretty clean signal. Remember, you must repeat this before every session and any time you change bands.

Many of the signal quality problems result from driving the soundcard at too high a level. Above 50% output most soundcards become non-linear quite quickly.

So, if you follow the simple rule of not setting your TX controls above 50%, you can pretty much guarantee that you won't be one of the problem stations and you will still make lots of contacts.

Michael

P.S. Keep an eye on that ALC, on some rigs you will find that you need to slightly re-tweak your soundcard TX level if you transmit
a higher or lower audio tone so if you tune around using software with a Panoramic display, such as Digipan, you might find that your drive is sometimes a bit too high.

RE: PSK Is A Fragile Mode

by WA3KYY on January 21, 2004 Mail this to a friend!

There is now a device you can get as a kit that automatically adjusts your signal for optimum IMD and thus a proper PSK signal. It samples your RF output and feeds that back to a small program on your PC that adjusts your audio drive. Do a search on PSKMeter to find out more information.

73,
Mike

RE: PSK Is A Fragile Mode

by WA5ZNU on January 21, 2004 Mail this to a friend!

>the only foolproof way to adjust your audio level into the transmitter to ensure a pure PSK signal is a SCOPE.

Actually, as another ham noted above, the PSKMeter accessory is a smaller/cheaper/easier way to check your output levels.

You hook it up to a T in your transmission line and run a serial port to your computer. It displays your IMD, tells you if you are over- or under-driving, and will even adjust the computer audio gain for you automagically. It's a lot cheaper and smaller than a scope, and can be taken hfpacking with you, and operates off a 9v battery. I built my kit in a couple of hours.

The Windows software is great, but for Linux use I wrote my own software for it. See
http://www.ssiserver.com/info/pskmeter/ for the PSKMeter and Windows softare and http://wa5znu.org/pskmeter for Linux (and probably MacOS X too if someone recompiles it).

There's a review of it here: http://www.eham.net/reviews/detail/3347

73,
Leigh.

RE: PSK Is A Fragile Mode

by K2WH on January 21, 2004 Mail this to a friend!

by WA5ZNU on January 21, 2004

>the only foolproof way to adjust your audio level into the transmitter to ensure a pure PSK signal is a SCOPE.

Actually, as another ham noted above, the PSKMeter accessory is a smaller/cheaper/easier way to check your output levels.

You hook it up to a T in your transmission line and run a serial port to your computer. It displays your IMD, tells you if you are over- or under-driving, and will even adjust the computer audio gain for you automagically. It's a lot cheaper and smaller than a scope, and can be taken hfpacking with you, and operates off a 9v battery. I built my kit in a couple of hours.

The Windows software is great, but for Linux use I wrote my own software for it. See
http://www.ssiserver.com/info/pskmeter/ for the PSKMeter and Windows softare and http://wa5znu.org/pskmeter for Linux (and probably MacOS X too if someone recompiles it).

There's a review of it here: http://www.eham.net/reviews/detail/3347

73,
Leigh.

While this is true, the use of a station monitor or scope allows one to add a vital piece of test equipment to ones station that is more than just a PSK monitor. Yes, a scope is more expensive, but for me, the CRT scope is the way to go. A computer is not required.

PSK Is A Fragile Mode

by W5EEX on January 21, 2004 Mail this to a friend!

I strongly agree with the adoption of the RSQ reporting approach. I often watch PSK QSO's and see one ham giving a 589 or 599 signal report to the other, and I wonder what he must be using for a receiver that enables him to pick just ONE PSK signal out of the receiver's passband and call it 599...?? I use several modern technology receivers and none of them give me the capability to differentiate just one 60Hz wide signal out of the 2.5Khz receive bandwidth. I have seen some PSK signals that are almost the entire width of the waterfall display....I guess those are 599 signals...but not ones I would be proud of....hi hi.
73,
W5EEX

PSK Is A Fragile Mode

by N4CW on January 21, 2004 Mail this to a friend!

Lots of emphasis has been placed on adjacent signal overloading, and that makes a lot of sense. However, I feel that there's easily-obtained relief from good audio filtering.
PSK31 decoding is done via the sound card, and it won't do better than what's put in to decode. IMHO, a good audio filter is essential to minimizing the influence of nearby loud signals, even with good i.f. filtering.
Let me suggest using an outboard DSP or SCAF filter to handle the audio. Specifically, I use BOTH: a Timewave DSP-59+ and an Idiom Press SCAF-1. The Timewave in bandpass mode is excellent, and the SCAF-1 also functions very well as a variable low-pass filter. I have also successfully used the original SCAF high/low filter, but they're no longer in production. The audio filter skirts on the Timewave are superior to the SCAF filters, but is more complex.
I find the audio filters a NECESSITY on my IC-706 MkIIG with 1.9 kHz internal filtering. And, I've also used them with my FT-1000MP, even with the 250 Hz tandem filters and found them useful there, too.
Of course, there's nothing that you nor anybody else can do about Pactor interference....that's a whole 'nother can of worms.
73,
Bert, N4CW

RE: PSK Is A Fragile Mode

by N6CRR on January 21, 2004 Mail this to a friend!

Great thread.

I am in listen mode right now on PSK31, got the interface on order. I do see lots of good signls and some not so good on the waterfall display.

Having not transmitted yet, I really appreciate the info.

Cheers

Rules of thumb:

by KF6IIU on January 21, 2004 Mail this to a friend!

- For audio level, I look at my ALC meter. If the ALC meter moves at all, I am overdriving the rig. I've always gotten good signal cleanliness reports.

- As others have noted, NEVER use speech compression.

- PSK is no good against polar flutter. I've worked Western Europe from here in California, but I've never been able to decode a signal from further east than about Austria.

RE: PSK Is A Fragile Mode

by W2AEW on January 21, 2004 Mail this to a friend!

Many good posts have been made regarding how to carefully setup your PSK signal. If you have a scope, use it! If you don't the next best thing is to make sure that you have NO ALC indicated.

Another good suggestion is to control your power output by the AUDIO level, NOT by the RF POWER control. Leave the RF power at max, and cut down the audio drive (via mic-gain, sound-card output, etc.) until you have only 5-10W out. This will ensure that the rig is not being overdriven. However, be SURE to check this EACH time you move in offset frequency! Because the sound-card, interface, SSB-audio chain frequency response will likely not be FLAT, and the drive level WILL change as you move your TX/RX offset frequency.

On the receive side, narrow filters will really help pick out the desired signal from adjacent big signals. Unfortunately, some rigs don't allow you to use the CW filters while in SSB mode. However, if your rig has 2 VFOs, you can get around this! Simply operate split. Use one VFO in SSB mode for transmitting, and the second VFO for RX in CW mode. For the RX VFO, you'll have to adjust your VFO frequency (or RIT) by an amount equal to your CW sidetone - so that your tx and rx audio frequencies line up. I wrote a letter to Hints&Kinks in QST describing this method last year. I have a copy that you can read on this website:

http://www.qsl.net/w2aew/psk31filterhk.html

Happy PSK-ing!

RE: PSK Is A Fragile Mode

by N3HKN on January 21, 2004 Mail this to a friend!

I totally agree with W2AEW. DO NOT set your power with the RF power control or whatever its label. Leave it at max or at least comfortably above your target power level. If you use the power control to set power output you stand a good chance of causing ALC to come into play and distortion results. One other note on xmit. Your output level will be different in the middle of the passband versus the ends. Thus if you set your xmit power WITH THE AUDIO LEVEL (interface or PC) at the top end, you may overdrive if you QSY to the middle segment. My Icom-746 has bad IMD even without ALC with more than 65-70 watts out. I have a feeling that Kenwoods can do better.

It was mentioned that a good audio filter will help. Actually it only helps your ears and the display. it DOES NOT help the reduced sensitivity if the AGC is reacting to s strong signal and your target signal is weak. This would only be true if the audio filter also derived an AGC voltage for the preamp and other stages.

The best solution to minimizing the reduction in receiver gain due to strong nearby signals is to have one of the better receivers with IF DSP (not audio).

I have tried using no AGC and riding the RF gain control. It works but the control is awkward to use on the packed panel of my Icom-746. This raises a question - for those who have used narrow filters (DSP or xtal) on PSK what has been your experience? Can you reliably copy a PSK signal with a 50hz filter or does it take something wider. Is 250hz a good choice. I can simulate a crummy filter with the passband controls on the 746 but the best I can really do is around 7oohz wide with very sloppy slopes. However, it is better than nothing.

Dick N3HKN

PSK Is A Fragile Mode

by AG4RC on January 22, 2004 Mail this to a friend!

I use an Autek QF-1A audio filter between my Kenwood TS-130SE and my computer...

...Makes working digi modes (PSK31, RTTY, MFSK,,,) a breeze!

73 - Peter

PSK Is A Fragile Mode

by N7XB on January 22, 2004 Mail this to a friend!

All good points being made. However, when trading IMD reports, remember to just send a carrier with no text. The other guy should be able to get a good reading for you.

As to those brag files. I love 'em. It takes me 2:22 to microwave a cup of tea, which is what I do when you send me those interminable brag files, like:

"BEEN A HAM SINCE WORLD WAR I. STILL CAN'T FIND THE CAPS LOCK KEY ON MY KEYBOARD. RIG HERE IS A YAESU FT-1000MP MARK V RUNNING TEN WATTS TO A FIVE ELEMENT BEAM UP 100 FEET. PC IS A HEWLETT-PACKARD PENTIUM III CENTRAL PROCESSING UNIT RUNNING AT 500 MEGAHERTZ WITH 128 MEGABYTES RANDOM ACCESS MEMORY AND A SIXTY GIGABYTE HARD DRIVE. SOFTWARE IS MICROSOFT WINDOWS VERSION 98 MILLENIUM EDITION, DIGIPAN VERSION 1.6, QUICKEN DELUXE AND FREECELL. SHACK RUNNING ON ALTERNATING CURRENT GENERATED BY HYDROELECTRIC DAM IN THE NEXT STATE . . ."

RE: PSK Is A Fragile Mode

by N3HKN on January 22, 2004 Mail this to a friend!

AG4RC,
I have experimented with audio bandwidth, IF bandwidth and noise reduction DSP. I really cannot see any difference in their decoding ability using Moe Wheatly's dll in various programs. I have also used Moe's PSK signal/noise generator and find that all of the programs that I have tried are very close in performance. My conclusion is that reducing the bandwidth at the audio or IF level does not seem to help decoding.

I use Warbler and have macros that will automatically set my Icom-746 passband controls to minimum bandwidth and automatically center the selected PSK signal in the now narrow passband. Poor Ham's xtal filter. As has been said many times this helps to remove the effect of stronger signals de-sensitizing the receiver via AGC. Audio filters inboard to the rig(DSP) and outboard (SCAF) do not seem to make a difference in the ability to decode the signal. I thought that by reducing the amount of "stuff" that the sound card has to process would help but can't see any. To-date I have not seen anything that helps decoding.

Dick N3HKN

PSK Is A Fragile Mode

by K2JX on January 22, 2004 Mail this to a friend!

The easy way to determine if your PSK signal is distorted, overdriven etc...Just listen to it with another rcvr if possible. In the old days of separate transmitters-receivers one could listen to his signal (any mode) BEFORE going on the air.
If your signal sounds poor to your ears, I doubt you would want to put it on the air ! I listen to my PSK signal while adjusting the sliders in the Windows sound card program. I adjust the "Vol" slider for best audio and RF output before the ALC kicks in. With a bit of practice PSK tune up is quick and easy.
73, Jack K2JX

RE: PSK Is A Fragile Mode

by K2WH on January 22, 2004 Mail this to a friend!

I have absolutely no problem copying a PSK signal with the filter set at 50hz. No problem at all. It makes the band dead quiet and you only receive the one signal you want. There is simply no reason to receive the entire 3khz segment.

K2WH

PSK Is A Fragile Mode

by WA7NCL on January 22, 2004 Mail this to a friend!

I agree with K2WH. PSK is not "fragile". Its just the way we are using our radios is a lashup.

Firstly, using the 3Khz waterfall and complaining about the AGC being captured is the same problem that hams had on AM and SSB before Xtal filters were widely available. The RX is not allowing "single signal" reception so of course you have inter signal interference. The answer to the problem is to have a DSP reciever like the TS870, IC756 etc and use the very narrow CW filters for RX when the band is crowded. With "single siganl" RX you can use the AGC because it is only operating on the signal you are RXing at the time.

I have a TS870 and this works quite well. The result is not "fragile". I can RX weak signals very close to strong ones. It also has the benefit of increasing signal to noise ratio because the bandwidth is minimized.

Making everybody try to adjust their power so somebody doesn't have an AGC problem is just a bandaid. Bottom line here is RX design needs to be brought up to modern times or accept the limitations of the older equipment.

Secondly, I agree on transitted signal quality. You need to do whatever is required to make the transmitter completely linear. This usually requires the use of no ALC compression. Usually this is just as simple as just making sure the ALC level on the rig is not showing any indication or just on the verge of indicating. If you do this you will get good IMD reports assuming you are running a reasonablely modern radio.

With proper attention to RX and TX, PSK is the CW of the 21st Century!

RE: PSK Is A Fragile Mode

by W4EF on January 22, 2004 Mail this to a friend!

WA7NCL wrote:

>I have a TS870 and this works quite well. The result >is not "fragile". I can RX weak signals very close to >strong ones. It also has the benefit of increasing >signal to noise ratio because the bandwidth is >minimized.

Not really. Although the audible SNR will improve, the SNR of demodulated signal won't change much since its set by the matched filter in the sound card. The real benefit of the IF filtering in the radio is as you mention, improved dynamic range.

>Making everybody try to adjust their power so >somebody doesn't have an AGC problem is just a >bandaid. Bottom line here is RX design needs to be >brought up to modern times or accept the limitations >of the older equipment.

I agree, but receiver design isn't the whole story. Although most modern receivers are a bit lacking in close-in dynamic range performance (the Ten-Tec Orion and Elecraft K2 non-withstanding), most of them do include the provision for a narrow CW IF filter. The sound card has plenty of dynamic range, so the real key is to keep strong adjacent signals out of the receiver passband where they can pump the AGC or generate IMD products that can mask the weak desired signal. DSP filters are a nice follow-on because they have linear phase performance which allows you to tighten up around the PSK carrier more than you can with an unequalized crystal filter.

The real problem is transmitter linearity. If you look at the IMD performance of most modern transceivers, they are aweful. This is the achilles heal of PSK which does make it "fragile". The fact that you have to back off your transmitter so far to get good IMD performance negates the benefit of the improved link performance that PSK should be able to deliver. With CW (assuming I have a good receiver), I can get right next to a guy who is S9+40dB and pull out a signal at the noise floor. You just can't do that with PSK31 because the guys IMD sidebands will be too large. Even if he has them down -50dBc, that is still around S8. Based on the IMD performance of most modern rigs, I think you'd be hard pressed to get -50dB IM performance on a PSK31 signal. The counter argument to that is hey don't run any power on PSK31, but to me that is the big joke. You say PSK31 is the CW of the 21 century, but the dirty little secret is that it's so dirty you can only run 15 watts. I can run 1500 with CW and not bother the guy next to me. If I drop my power from 1500 watts to 15 watts, I have just reduced my communication range by a factor of 10. Wow, what an improvment in communications capability (NOT)!! PSK31 is also sensitive to multipath distortion. I don't know why people aren't giving MFSK16 more attention. It's constant envelope so you can rull your exciter Class C (or even Class E for that matter) without having to worry about IMD sidebands (there are none). MFSK16 is also more robust in a multipath environment, so its a better choice for an ionospheric channel, especially on polar paths that have lots of flutter.

>If you do this you will get good IMD reports assuming >you are running a reasonablely modern radio.

Good is a relative term. Modern rigs have lousy IMD characteristics. Just look at the ARRL test reports. The FT-1000MP Mark V in Class A mode is a notable exception. Most of the rest are hideous. You'll never get the close spaced dynamic range capability of CW until this problem is solved, and without good closed spaced dynamic range capability you'll be restricted to draconian power limitations which will necessarily limit the usefullness of PSK31 in an ionospheric propagation environment where it is common to have nearby signals that are 100dB stronger than the weak DX stations you want to work.

Don't get me wrong, I think PSK31 is a cool mode, but it has some real limitations that many people fail to acknowledge. Just because a computer is involved, doesn't make it better than CW. You have to look at the complete picture of the ionospheric channel, and the available hardware so that you are doing a true apples to apples comparison. On this basis, I think CW is still a better mode. When someone works their 300th country and 40th CQ zone on 160 meters with PSK31, then feel free to serve me a plate of crow.

73 de Mike, W4EF...........................

RE: PSK Is A Fragile Mode

by AA4PB on January 22, 2004 Mail this to a friend!

I use the 50Hz IF DSP filter on my 756PRO all the time. It works great. With MixW I can create a macro that will automatically change between the narrow and wide filters while retuning the radio to keep the desired signal centered in the narrow filter. It's the best of both worlds - full spectrum display to see all the signals on the band and then narrow the IF filter around the one you want to copy with a single "click".

Using the narrow filter improves the S/N ratio that you are listening to in the speaker but inside the PSK31 program there is already a narrow filter so the S/N ratio does not improve any at that point. The main purpose of the narrow filter is to keep strong unwanted signals outside of the IF passband and away from the AGC. Any signal in the passband can push the AGC up, decreasing the receiver sensitivity and causing the desired weak signal to disappear.

A better way of reporting RST, and adjusting your

by KD7KGX on January 23, 2004 Mail this to a friend!

I looked at the www.psb-info.net website, and quite frankly both methods of signal reporting are more subjective than objective. I prefer the method that was described in QST a few years ago... I wish I recalled the author's name (he described his system in a letter to the editor) so I could give him full credit for what I believe is the best PSK reporting system I've ever heard of... and I use it everytime I give a report and also provide an explanation of what I'm doing so the other ham can understand it.

The RST report works fine, if we objectively break each component (Readability, Signal strength, and Tone quality) into regions.

For 'R', simply provide the quintile that indicates quality of print, with '1' being 0-20%, '2' - 21%-40%, etc. Print quality of 85% would be '5', and print quality of 50% would be '3'.

For 'S' I use my S-meter signal indication. I know this can vary somewhat from rig to rig, but a strong signal on one rig is a strong signal on another rig at the same QTH. If I report an S-4 signal then it is moderately strong and the other op will understand this, and evaluate his signal quality (strength over the noise floor) by looking at both 'R' and 'S' (a noisy band might result in a 349 or 449 while a quiet band may give a 549) My choice of rig (Ten-Tec Omni VI) lets me switch in extremely narrow filters to prevent other signals from affecting the AGC and affecting the reported #s.

For 'T' I use the percentile of signal strength, with an IMD of -30 being assigned as 100%, similarly to the way 'R' is handled. '1' is from 1-3, '2' is from 4-6, etc. An IMD of -17 would be '5' and an IMD of -28 or better would be a '9'.

Therefore, a very clean signal with 100% copy, S-5 on my meter, and with an IMD of -26 would result in an RST of 558. A splattery signal that was very strong with an S-7 level and an IMD of -8 would be 573.

The best thing about this method of signal reporting is that, once having it explained and then receiving the RST, the operator knows EXACTLY what his signal looks like at the other end.

Re someone's comments about how the operator cannot judge his signal without external monitoring or feedback, I say "Hogwash!" EVERY operator can tune his signal to have an IMD of -20 or better, which would GREATLY clean up the PSK bands, without assistance from a monitor scope or other ham. Every rig has an ALC light to show when modulation approaches 100%. Just turn off speech processing, set the mic gain to about 25% of full value, and use the soundcard volume control to turn DOWN the volume until the ALC light barely flickers while you transmit.

Once this is set, it will remain valid AT ONE FREQUENCY OFFSET IN YOUR WATERFALL but if you change the audio frequency of your signal to your rig by moving up and down the band on the waterfall you will want to monitor your ALC visually and re-adjust as necessary for subsequent QSOs.

Finally, we should recognize that PSK31 is a clever hack, but really only works well under decent band conditions. What the world needs is a 100 Hz-wide digital mode that is immune to phase shifting (like MFSK) and transmits data at a rate of PSK63 or faster. I much prefer PSK63 for ragchewing, and MFSK for DX-ing. I encourage all of you who have tried PSK and who like it, but who have never bothered to try other modes, to experiment with them. There are better modes out there!

RE: A better way of reporting RST, and adjusting y

by KF4HEY on January 23, 2004 Mail this to a friend!

To KD7KGX and others looking for other simple and robust digital modes: why not try Throb in MixW or the new experimental version called ThrobX. ThrobX is an 11 tone version and is more robust than Throb and somewhat easier to tune. Go to http://www.lsear.freeserve.co.uk/page3.html and download Throbx2.zip and give it a try around 14.078MHz.

I will be happy to set up a sked with anyone wishing to try this mode.

73, Mike KF4HEY

PSK Is A Fragile Mode

by N7MJW on January 24, 2004 Mail this to a friend!

Here is what I discovered with PSK, MFSK, etc.

The soundcard is a huge offender in creating harmoics all over the band. When driving with more than the absolute minimum on the soundcard, it throws harmonics all over the band.

I've noticed this when monitoring on a seperate pc and receiver and watching on the waterfall. While turning the transmitter soundcard up, the harmonics come up. This is while running minimum power on the transmitter. You will not see this on your ALC.

Always check for proper impediances on soundcards, microphones etc. Line levels should be 600 Ohms, but consumer manufacturs dont seem to understand this.

I was blessed by having a very linear transmitter. With a clean signal from the soundcard, i could push it all the way to its max of 150 watts. I actually never could get the transmitter to distort the signal.

The $20 soundcard this mode is advertised to require, is really quite innacurate. Those soundcards were meant and designed to drive a pair of speakers or headphones in a cheap and non-percise way. The design critera was "it doesnt sound bad in the speakers". We are asking WAY too much for them. Our approach to soundcards should be an external, high end device that we treat like a percision PC controled DSP box.

As for strong signals ruining things for everybody. Well, if the signal is clean its not their fault. That strong signal may be necessary to be copied by a station with marginal equipment, etc. The fault here really likes in using a SSB filter to look at a 3 Khz chunk of spectrum, and copy multiple stations simultaniously. Using a properly configured receiver will resolve this, but then you cant look at all those conversations at once!

I was able to use the CW filters in my transceiver by switching out he 1Khz tone used for CW keying with an audio line. Gave me the CW filter. Another way is to rig a switch to the filter control lines, and send the appropiate voltages to the diode swithces. Problem is, in some cases (mine) the IF is shifted around when switching modes. Look at your radio schematic.

RE: PSK Is A Fragile Mode

by WR8D on January 24, 2004 Mail this to a friend!

Guys please disable the cw id's you're running with your psk programs. Those things splatter all over the segment just about as bad as a station thats running to much mic gain. You have no need to let that thing go off after you clear with another station. It honestly does cause a lot of qrm there.

73
John WR8D

PSK Is A Fragile Mode

by KC4ZGP on February 20, 2004 Mail this to a friend!

Good Afternoon All.

Ah a forum I can actually enjoy. Since meeting PSK31 almost two years ago, I gave up on the other modes. I lost track of the paddle and microphone. Does anyone need a good used T.N.C.?

I use digipan and the only way I know to give a signal report is to tell them what the waterfall looks like,

I push fifty watts to my copper tubing loop. That statement might have sounded familiar to some folks.

I'll see you folks on 14.070/PSK this weekend.

73

Kraus

RE: PSK Is A Fragile Mode

by GI7KMC on November 5, 2004 Mail this to a friend!

A comment was made about disabling CW id. I think sending the cw id at the end of every transmition is over kill but don't forget that in some countries ,like the UK, the licence requires a cw id to be sent every 30mins if not using cw or voice.

Jonathan

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