[digitalradio] Re: 10 Tips for the PSK31 Digital Mode
--- In digitalradio@yahoogroups.com, Ed Hekman [EMAIL PROTECTED] wrote: I made a similar modification to an IC-735 to use the 250Hz CW filter in SSB mode although that was a bit more complicated. Let me know if you would like me to send the instructions. Hey Ed. I now have the IC-735 and it has the FL-63 250hz filter installed. I'd love to know how to make it work on SSB! Thanks for heads-up. Coincidence that I got the 735 in trade for some computer work! Vy 73, de Frank, K2NCC
[digitalradio] Re: 10 Tips for the PSK31 Digital Mode
--- In digitalradio@yahoogroups.com, Rein Couperus [EMAIL PROTECTED] wrote: First thing to do of course is make sure THERE ARE NO STRONGER ONES. This can be done various ways. Typically, I use the variable bandwidth tuning and IF shift to avoid strong signals. But, that's rare to need to do so. I am rarely unable to decode a trace, even with a much stronger signal close by. we used so-called X-tal filters to filter out signals... This worked perfectly. Since hams started tuning with clicking a mouse instead of turning a frequency dial this became impossible. I can appreciate the old-school guys. They had to work hard to get where they are. I am using an old rig that has no DSP and would say it does a better job than most modern rigs. However, don't be so bent on mouse-clicks. Evolve or die, I say. I love big knobs as much as the next guy, but I also like to expand my knowledge beyond the box. 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. AGC appears to do nothing for weak signals. AGC is for leveling sound but doesn't appear to increase it. Have you ever used AGC and saw a weak signal get stronger? I haven't. When I notch out everything but a weak trace, then turn on the AGC, the trace doesn't intensify, but fades. Another reason I used RF ATT and just bumped up the volume. That way I can see the whole pass band and get very little splatter. But, again, this is on a single rig. Everyone can feel free to send me your radios so that I may conduct further tests! 8) Just using an RF attenuator because there is a strong alien signal within your passband is the WRONG weapon against this. When I use AGC, it gives more to the stronger signals. Unless I'm working that strong signal, I leave AGC off. When I use RF ATT, it balances all the signals out to a softer level. When I work a very weak station, I leave RF ATT off. I have reconsidered the constant use of my RF ATT. I've done further experimenting since this article (almost two months old) and found that there are times that a very weak signal fades right off the waterfall when I use RF ATT. But it's nearly always a TX that I can't copy very well anyway, so I think the benefits could swing either way. Moreover, NO RX IS LINEAR, so it will produce mixing products which will hit your weak signal. Keep in mind I'm a new ham, with little technical expertise in this hobby beyond my two years of study and HF operation. I don't always know why something does what it does, but experience and the ability to recreate results is what drives my proclamations. I'm always willing to be educated, but I may squirm a bit until I get it. ... if you want to really take advantage of the small bandwidth why add all that bad stuff on the RX side? By all that bad stuff, do you mean the RF ATT and AGC recommendations? Hardly seems to be as massive an issue as suggested. RF ATT may need more consideration, true, yet it still works nicely in 90% of my traces, so I think little harm is done. To make copy more difficult? That does not seem to be a major case here. If you're in a room full of people, all speaking very loudly, you might not be able to hear the guy right next to you. Drop the room (and the guy's) volume down 40db, and imagine how clearly you will hear him then. I don't think adding AGC will increase his volume, but of you put walls around him (notching) or eliminate 80% of the voices (VBT), it'll be even better. Come on, with CW there was an operator who did the decoding. You cannot expect a computer to be as efficient as that. This seems only vaguely related, so I'm guessing you're a hard-core CW fan? Your rig, if younger than a decade or so, IS a computer. So why not help the poor DSP and filter out noise That's assuming one has a DSP filter. I use IF Shift, Notch and VBT. Again, on a different rig, I might get different results. This is a fairly stupid advice, and if you follow it you will miss about 50% of the fun. 'Fairly stupid advice' is a trolling expression and not the best way to get a diplomatic response. I doubt 50% is a fair number either, but anyway. I welcome corrections and will change my mind based upon new information. I appreciate your advice and hope to hear more. You appear to be more technically savvy with the radios, so maybe you'll offer some sort of test for us to try. I'd love to compare numbers and to learn more. Keep in mind, the article isn't meant for as a bible of PSK. It's just sharing what I've learned in the last year, which is constantly evolving. The majority of the article still stands on it's merit. Frank, K2NCC
Re: [digitalradio] Re: 10 Tips for the PSK31 Digital Mode
There is no difference between an RF gain control and AGC. AGC is just Auotmatic Gain control instead of manual gain control. The only way to copy a weak signal adjacent to a strong one is to prevent the strong signal from affecting the AGC, and the only way to do that is by using a narrrow filter or notch filter (at IF, not audio) to attenuate the strong signal. You can use a wide (SSB) filter to see all the stations in the passband, and then use Passband Tuning or IF Shift, or a narrow filter (at IF, not audio!) to narrow in on the station you want to work if it is one of the weaker ones. You do not need to do anything for the strong signal unless it is overloading your front end and then you can switch in attenuation and switch it out again when you are finished. Many people have experienced a weak PSK31 signal disappearing or waterfall darkening when a strong signal comes on. This is because the strong signal is reducing the gain (and therefore the noise background), just the same as if you manually reduced the gain, and generally the only cure for this is using narrow filtering. Some receivers, designed specifically for PSK31, such as our latest PSK-20, do not use AGC, but distribute gain in such as way that it can copy weak signals adjacent to strong ones, without distorting the last IF stage or detector, but few transceivers can do this. A dual-loop AGC system may help and some high-end transceivers have this. 73, Skip KH6TY
RE: [digitalradio] Re: 10 Tips for the PSK31 Digital Mode
One more consideration is AGC recovery time. Slow AGC and static crashes are not a good combo in many of the digital modes. No AGC or Fast AGC will make a difference in that situation. This may not apply to PSK-31 as much as more complex digital modes, but a point worth considering. DSP filtering of signals above and below the signal you are trying to copy are also a great help; if your rig will allow that narrow of a passband. David KD4NUE -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of kh6ty Sent: Wednesday, March 12, 2008 4:13 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] Re: 10 Tips for the PSK31 Digital Mode There is no difference between an RF gain control and AGC. AGC is just Auotmatic Gain control instead of manual gain control. The only way to copy a weak signal adjacent to a strong one is to prevent the strong signal from affecting the AGC, and the only way to do that is by using a narrrow filter or notch filter (at IF, not audio) to attenuate the strong signal. You can use a wide (SSB) filter to see all the stations in the passband, and then use Passband Tuning or IF Shift, or a narrow filter (at IF, not audio!) to narrow in on the station you want to work if it is one of the weaker ones. You do not need to do anything for the strong signal unless it is overloading your front end and then you can switch in attenuation and switch it out again when you are finished. Many people have experienced a weak PSK31 signal disappearing or waterfall darkening when a strong signal comes on. This is because the strong signal is reducing the gain (and therefore the noise background), just the same as if you manually reduced the gain, and generally the only cure for this is using narrow filtering. Some receivers, designed specifically for PSK31, such as our latest PSK-20, do not use AGC, but distribute gain in such as way that it can copy weak signals adjacent to strong ones, without distorting the last IF stage or detector, but few transceivers can do this. A dual-loop AGC system may help and some high-end transceivers have this. 73, Skip KH6TY
Re: [digitalradio] Re: 10 Tips for the PSK31 Digital Mode
Skip - Original Message - From: David Little [EMAIL PROTECTED] To: digitalradio@yahoogroups.com Sent: Wednesday, March 12, 2008 4:25 PM Subject: RE: [digitalradio] Re: 10 Tips for the PSK31 Digital Mode One more consideration is AGC recovery time. Slow AGC and static crashes are not a good combo in many of the digital modes. No AGC or Fast AGC will make a difference in that situation. This may not apply to PSK-31 as much as more complex digital modes, but a point worth considering. DSP filtering of signals above and below the signal you are trying to copy are also a great help; if your rig will allow that narrow of a passband. David KD4NUE You never want to use Fast AGC on PSK31, because the receiver will attempt to follow the PSK31 signal and cause distortion. Always use the slowest AGC setting you have, or no AGC at all. BTW, to accurately measure IMD, reduce your RF gain until the IMD reading stops falling and report that as the IMD reading. The reason for this is that the receiver must amplify linearly for PSK31 and if a signal is strong enough to distort the RF amplifier or IF amplifers, you get a false (usually poorer) IMD reading. Also, IMD is the measure of the first set of unwanted sidebands and if the signal to noise ratio is poor, the software will be measuring the noise at the same point as unwanted sidebands and reporting a poor IMD. It is better just to look for unwanted sidebands and report if you see any or not. The caveat is that the unwanted sidebands may be so far down in the noise you cannot see them, even though they are there, but as far as you, or a station with the same reception as yours, it does not matter, as the unwanted sidebands are not going to bother an adjacent station. Still, the best practice is to always transmit with a linear, clean, signal so your unwanted sidebands do not QRM any adjacent station, either near to you or somewhere else 73, Skip KH6TY .
Re: [digitalradio] Re: 10 Tips for the PSK31 Digital Mode
kh6ty wrote: A dual-loop AGC system may help and some high-end transceivers have this. 73, Skip KH6TY Dual loop AGC is a two sided sword. I have come to find better, and not necessarily easier, to have low noise, low gain stages before the filters that will not overload so easily. The TS-520 I used in another contest in 1978 was deafened when a local station, 5 km away turned is beam towards Japan...and over me, on 15 meters. There was nothing I could do, again, in the middle of the contest, so I had to go back to 20, the next open band. His ground wave was desensing my front end so badly that it became useless to attempt to work the weak japanese signals while RF gain was pumped with his audio. And the attenuator did not solve that issue at all. Those are things you learn the hard way while contesting. Are you going to ask a competitor in the heat of a contest to lower his power because he is deafening you? 73, Jose
[digitalradio] Re: 10 Tips for the PSK31 Digital Mode
--- In digitalradio@yahoogroups.com, Rein Couperus [EMAIL PROTECTED] wrote: ... 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. While on the subject of filters, my current setup allows me to narrow my SSB signal down to 500 Hz. Maxed out, the pass band is about 2.7 kHz, (3.6 on CW Wide.) I have no optional filters installed, so I've been thinking of adding one or two (I think YK-88CN and YG-455CN). I like the idea of having a narrower VBT of 250 Hz (-6 dB) to 500 Hz (-60 dB) with the YG-455CN filter. BUT, it seems that's for the CW Narrow mode switch position. Will that do anything all all for SSB? It's a Kenwood hybrid (TS-830S). If a CW Narrow filter isn't going to help my digital modes RX, then is there some other filter I can add that will give the improvement you've stated above? I've heard of a YG-88S, but don't see any mention of it in the manual. Looks like http://www.qth.com/inrad/ has some in stock. Any suggestions? Well, other than buy a new radio! 8) Frank, K2NCC
Re: [digitalradio] Re: 10 Tips for the PSK31 Digital Mode
Frank, 500 Hz is already a nice improvement with respect to 2.5 kHz.. While on the subject of filters, my current setup allows me to narrow my SSB signal down to 500 Hz. Maxed out, the pass band is about 2.7 kHz, (3.6 on CW Wide.) I have no optional filters installed, so I've been thinking of adding one or two (I think YK-88CN and YG-455CN). I like the idea of having a narrower VBT of 250 Hz (-6 dB) to 500 Hz (-60 dB) with the YG-455CN filter. BUT, it seems that's for the CW Narrow mode switch position. Will that do anything all all for SSB? It depends... I don't know the 830 well enough to say. Anyway, the trick normally is to TX in SSB mode and RX in CW mode, and compensate any frequency difference with the RIT control or the CAT remote control. Most transceivers have this cross-mode possibility. Some other transceivers have an RTTY mode which can use a narrow filter, although that is mostly limited to min. 500 Hz. And some can receive RTTY but then only send FSK. In this respect the FT897D is ideal, it allows the use of all filters in all modes. (Which should be the normal case really, why should this be limited? It is set by the software anyway...). I have had bad luck at PI4TUE with the IC756 for instance. I bought a CW filter and found out that the set would not work cross-mode, not even from the memory bank! There the saviour was to shift the 'sweet spot' to 1500 Hz and use the internal DSP with 300 Hz BW. This happens inside the AGC loop, so it is o.k. If your set does not offer one of these possibilities and you don't want to consider buying a new radio you could always buy a K2 kit, which is a box containing 1300 parts. It only needs a bit of soldering, and is ideal for all digital modes :) 73, Rein EA/PA0R/P It's a Kenwood hybrid (TS-830S). If a CW Narrow filter isn't going to help my digital modes RX, then is there some other filter I can add that will give the improvement you've stated above? I've heard of a YG-88S, but don't see any mention of it in the manual. Looks like http://www.qth.com/inrad/ has some in stock. Any suggestions? Well, other than buy a new radio! 8) Frank, K2NCC -- 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/
