[digitalradio] 10 Tips for the PSK31 Digital Mode
http://www.arrl.org/news/features/2008/03/11/10007?nc=1 10 Tips for the PSK31 Digital Mode By Frank Ravenswood, K2NCC [EMAIL PROTECTED] March 11, 2008 There's more to going over the waterfall than just having a good barrel. An example of a Waterfall display. [photo by Frank Ravenswood, K2NCC] Use the center of your waterfall (see definitions of italicized terms below) display. Testing will show that your transmit (TX) and receive (RX) will be strongest there. Don’t blindly use a 1000 Hz tone or strictly follow the VFO “set it and forget it” concept. You can easily lose 20% or more of your power on each edge of your passband. Passband centering of the signal will give the best results of both RX and TX. There's no need to have the waterfall streaking bright red. Set your rig's volume to a low level (less than 25% of maximum) and adjust your waterfall and sound card levels for good contrast. Do not overdrive your sound card! Get the background noise and the transmit trace well defined and separate. Keep in mind that how your waterfall looks does not impact decoding, but it is harder to work it if you can’t see it. Use UPPER CASE characters sparingly. Lower case text in PSK31 varicode transmits fewer bits of data. You'll increase transmit speed and improve the likelihood of proper decoding on the other end by using lower case text as much as possible. (For example, the difference between a lowercase “e” (11) and an uppercase “E” (1110111) is three times more bits.) Enable your RF attenuation and increase the volume. This can help keep a strong signal from wiping out the weaker ones. Attenuation will probably be around 20 dB, but by dropping the noise level, the signal readability may improve. AGC (Automatic Gain Control) does nothing for a weak signal; it only levels the louder ones. Use your digital mode’s software, or a program like Spectrogram, to see what your noise level is with the radio off. This will give you an idea of how “clean” your sound card is. Typically, onboard (built-in) sound hardware (as found in most “mainstream” computers like Dell or HP) does not have a signal-to-noise ratio as good as an inexpensive (less than $50) separate sound card. When purchasing a sound card, look for one with a signal-to-noise ratio over 100 dBA. [A-weighted decibels; a scale of sound “loudness’ used in acoustics that simulates the response of human hearing. — Ed.] [Many onboard sound interfaces, while not optimum for high fidelity stereo sound, perform well for many amateur applications. For a technical review of various sound cards see J. Taylor, K1RFD, “Computer Sound Cards for Amateur Radio,” QST, May 2007, pp 63 — 70. — Ed.] Consider dual monitors (most modern video cards have two jacks). This allows you to have the waterfall or spectrum display on one screen and your logger, text window, etc on the other. It makes a huge difference in speed and ease-of-use when you don't have to swap between screens or use smaller windows for your contact. When transmitting, keep your ALC reading as close to zero as possible. This will help keep your signal clean and your IMD at an acceptable level (-20 dB or better is ideal). Your power output will drop, but there's no need to overload the transmit level. PSK31 uses an 80% duty cycle. Even with a full duty cycle rig, it still needs to dissipate heat! Besides, 20 W more makes little difference. Output of around 50 W is enough to work the world, and your fellow operators will appreciate the courtesy. Also be sure your voice processor is not enabled when using digital modes. Ask for an RSQ (readability, strength, quality) report. When in a contact, send just a tone and ask for your IMD and a report on how your trace looks. This will give you a better idea of what adjustments may be needed. There are hundreds of digital modes. To get started or to learn more about the most common ones, refer to the list of digital mode references at the end of this article. Bonus Tip: Try 30 meters PSK31. It’s a robust band, offering the best of 20 meters and 40 meters. Only digital modes and CW are permitted and contesting is not allowed. Be sure to operate within your privileges. PSK31 can typically be found around 10.140 MHz. Definitions of Terms: AGC (automatic gain control): The ability to reduce signal strength on-the-fly, giving you more level audio reception on stronger stations. ALC (automatic level control): A voltage adjustment or reading, indicating your transmit signal levels. ALC is designed to control voice and carrier signal levels, not digital modes. Typically for digital modes, if the ALC meter moves, then the microphone gain is too high. Signal-to-noise ratio (S/N): A comparison of the signal levels to the relative noise level. Ideally, a perfect signal would have no noise, but realistically, you’ll want an S/N ratio well within the tolerances of the mode you’re using. PSK31 tolerates about a 10
Re: [digitalradio] 10 Tips for the PSK31 Digital Mode
Enable your RF attenuation and increase the volume. This can help keep a strong signal from wiping out the weaker ones. Attenuation will probably be around 20 dB, but by dropping the noise level, the signal readability may improve. AGC (Automatic Gain Control) does nothing for a weak signal; it only levels the louder ones. This is a fairly stupid advice, and if you follow it you will miss about 50% of the fun. First thing to do of course is make sure THERE ARE NO STRONGER ONES. In the good old days of CW (an ancient digital mode which was heavily used by older generation hams) we used so-called X-tal filters to filter out signals on a different frequency than the one we worked on. This worked perfectly. Since hams started tuning with clicking a mouse instead of turning a frequency dial this became impossible. QSB on a PSK signal can amount to 80 dB, and using (slow) AGC is a must if you want to copy the weak ones. It also helps to pull weak signals out of noise generated in later stages of the RX. Just using an RF attenuator because there is a strong alien signal within your passband is the WRONG weapon against this. Moreover, NO RX IS LINEAR,so it will produce mixing products which will hit your weak signal. if you want to really take advantage of the small bandwidth why add all that bad stuff on the RX side? To make copy more difficult? Come on, with CW there was an operator who did the decoding. You cannot expect a computer to be as efficient as that. So why not help the poor DSP and filter out noise and crap BEFORE it enters your sound card? 73, Rein EA/PA0R/P (sorry to hit on the same nail over and over...) -- http://pa0r.blogspirit.com Announce your digital presence via our Interactive Sked Page at http://www.obriensweb.com/sked Check our other Yahoo Groups http://groups.yahoo.com/group/dxlist/ http://groups.yahoo.com/group/contesting http://groups.yahoo.com/group/themixwgroup Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ * Your email settings: Individual Email | Traditional * To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) * To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [digitalradio] 10 Tips for the PSK31 Digital Mode
My comments were meant to be a bit provocative I am reacting to this subject now for the umpteenth time, and still people get the advice to use 2.5 kHz bandfilters on a 31 Hz wide signal. That way you will not get optimum performance from your RX. The ONLY point I wanted to make is that if you use a proper filter, matched to the mode, you will have a lot more fun and hear/work many more stations. The tradeoff is that you have to use a round knob instead of a computer mouse to tune the signal. And as this is the digital RADIO group I thought that a warning was appropriate :) Maybe I should advice to reread the articles about proper RX design by Ullrich Rhode in QST, maybe around 1970... that also tells you how large signals in your rx produce mixing products and desensing, and also why a properly designed AGC system will actually work. I am camping in EA at the moment, and 2 times during the day the pskmail servers I use are slowly QSB'ing from S0 - 20 dB to S9. The AGC easily fixes that (300 HZ filter on a FT897D, using PSK250). The APRS backbone on 10.149 kHz which would be fully inside the 2.5 kHz passband would make all operation impossible without a filter... (These guys relay 300 Bd APRS packets from 2meters to HF by the way, and I could read a book in the light of lamp connected to my antenna... :) The 'noise and crap' I was referring to is the stuff your RX adds to the signal by using non-linear circuits, before giving it to your SOUNDCARD DSP. So even if your rig doesn't have one, your computer does... And yes, I have visited several hams who could hear MORE than twice the stations after switching from a 2.5 kHz (panoramic) to 250 Hz filter. To answer some questions from Jose... Yes, I have worked in M/M and M/2 HP environments. Check CT9L, TS7N (2003), 5A7A(2005), ED8A(last November), all top 3 WW operations. For such activities we use K2's most of the time. And bandfilters on every TRX. And yes, at home I am using a TenTec ORION (100Hz for PSK31). 73, Rein EA/PA0R/P -Ursprüngliche Nachricht- Von: digitalradio@yahoogroups.com Gesendet: 12.03.08 21:36:18 An: digitalradio@yahoogroups.com Betreff: Re: [digitalradio] 10 Tips for the PSK31 Digital Mode Enable your RF attenuation and increase the volume. This can help keep a strong signal from wiping out the weaker ones. The same that was recommended to work CW ages ago, using manual gain control and no AGC. Attenuation will probably be around 20 dB, but by dropping the noise level, the signal readability may improve. 20 dB MAY be too much...but it may help better than doing nothing. AGC (Automatic Gain Control) does nothing for a weak signal; it only levels the louder ones. Rein Couperus wrote: This is a fairly stupid advice, and if you follow it you will miss about 50% of the fun. I am afraid that such a phrase is too strong... First thing to do of course is make sure THERE ARE NO STRONGER ONES. How should that be physically accomplished ? Does that include the neighbor in the block, or is PSK meant only to be operated from desert places? And not only PSK, but include there CW, RTTY, SSB, whatever comes to your front end. Here, on 40 meters, things can get quite mixed up around 7070 (happily, there is no more Radio Tirana on 7065). In the good old days of CW (an ancient digital mode which was heavily used by older generation hams) we used so-called X-tal filters to filter out signals on a different frequency than the one we worked on. This worked perfectly. Since hams started tuning with clicking a mouse instead of turning a frequency dial this became impossible. No, there are still people who use those filters. I do ocassionally. All exagerations may entail surprises... QSB on a PSK signal can amount to 80 dB, and using (slow) AGC is a must if you want to copy the weak ones. If you do that, you will force the weaker signals to be incopiable. From THERE seems to arise your request to have only feeble signals near your passband. A good radio should have a larger dynamic margin, say, 100 dB. AGC should be able to level signals up to 120 dB... if the front end is not overloaded. A polyphase filter RX, using a quadrature sampling detector can achieve that, without AGC at all. It also helps to pull weak signals out of noise generated in later stages of the RX. Just using an RF attenuator because there is a strong alien signal within your passband is the WRONG weapon against this. Not necessarily so. Have you ever operated a multi operator multi transmitter station ? Maybe it looks against common sense, but that way you can achieve that your front end does not get overloaded. No stages on a linear receiver shoul be allowed to overload, ever. That was a fact when operating 80 meters in the ARRL International contest in 1999. The operator on 40 was using the BIG
Re: [digitalradio] 10 Tips for the PSK31 Digital Mode
Rein Couperus wrote: My comments were meant to be a bit provocative He! Well, you knew what you were doing The ONLY point I wanted to make is that if you use a proper filter, matched to the mode, you will have a lot more fun and hear/work many more stations. The tradeoff is that you have to use a round knob instead of a computer mouse to tune the signal. And as this is the digital RADIO group I thought that a warning was appropriate :) That is a tradeoff...selectivity for convenience...sadly, not everybody is aware of that FACT. Maybe I should advice to reread the articles about proper RX design by Ulrich Rhode in QST, maybe around 1970... that also tells you how large signals in your rx produce mixing products and desensing, and also why a properly designed AGC system will actually work. And Ham Radio in the 80's (there is a VERY GOOD article on digital military communications receivers in april 1985). Also I would recommend his book Communications Receivers. I am lucky I have been able to get a Ham Radio collection, a top notch magazine, indeed. I am camping in EA at the moment, and 2 times during the day the pskmail servers I use are slowly QSB'ing from S0 - 20 dB to S9. The AGC easily fixes that (300 HZ filter on a FT897D, using PSK250). The APRS backbone on 10.149 kHz which would be fully inside the 2.5 kHz passband would make all operation impossible without a filter... (These guys relay 300 Bd APRS packets from 2meters to HF by the way, and I could read a book in the light of lamp connected to my antenna... :) The 'noise and crap' I was referring to is the stuff your RX adds to the signal by using non-linear circuits, before giving it to your SOUNDCARD DSP. So even if your rig doesn't have one, your computer does... And yes, I have visited several hams who could hear MORE than twice the stations after switching from a 2.5 kHz (panoramic) to 250 Hz filter. To answer some questions from Jose... Yes, I have worked in M/M and M/2 HP environments. Check CT9L, TS7N (2003), 5A7A(2005), ED8A(last November), all top 3 WW operations. For such activities we use K2's most of the time. And bandfilters on every TRX. And yes, at home I am using a TenTec ORION (100Hz for PSK31). OK, those seem to be better radios than the older ones I mentioned, which is not surprising at all. Nevertheless, it is funny to experience what at times a toggle switch and two resistors do with not so top notch stuff. If you are living part time in Spain, I assume you understand spanish. So, Calderon said: En este mundo traidor, nada es verdad ni es mentira, todo será del color del cristal con que se mira. So, our experiences are certainly tainted (among other things) by the radios we use. I have used quite a few and not owned all of them...so far, I have not tried a K2 or an Orion... 73, Jose, CO2JA Linux User 91155
