--- 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
