Re: K2: Various Receive Problems
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This is an update to a post I made in Nov 2008. I've received a fair number
of off-board emails over the past 1-1/2 yrs asking me about the problem and solution, so I figure I'll post the solution and save others from some embarrassment. My original problem was described as follows: >>2. On receive, stations are either there or not there. >>In this case, if I hear a signal, I hear it at the same volume as I tune across the signal's bandwidth. The perceived signal strength simply does not change. >>Along with this, there is no interference from adjacent signals. I'm always hearing the strongest station and only the strongest station at whatever spot that my VFO is tuned to. >>3. As I tune across a CW station's signal, there is no change in audio frequency. Well, it's embarrassing to admit it publicly, but both of those problems turned out to be user error (really really dumb user error). I did not understand the differences between digital tuning (like the K2 and K3) and analog tuning. More specifically: With digital tuning, each incremental shift of the VFO jumps the tuning by the set amount -- from one frequency instantaneously to the next frequency without sweeping through the frequencies in-between. Thus, for example, if you have the rate set to 1KHz and are at 7035.00, a slight move of the VFO to the right (clockwise) will result in your jumping to 7036.00 without having heard any of the frequencies in-between. Compare that with analog tuning where you sweep through the frequencies so that you hear all of them -- briefly, but you hear all of them. In other words, tuning in a digital world is like tuning a television or tuning a VHF FM mobile rig -- you're jumping from one frequency to another, you're not sweeping through the frequencies between them. For example, assume there are two CW signals out there: a strong signal centered at about 7036 and a weaker signal centered at about 7035, each with a bandwidth of about 2.4KHz. That means that the weak signal extends from about 7033.8 to about 7036.2, and the strong signal extends from about 7034.8 to about about 7037.2. If you're tuning with a 1KHz RATE, you probably won't hear anything at 7033.10. Turn the VFO slightly and you're at 7034.10 where you'll hear only the weak signal since you're already within its bandwidth but not within the bandwidth of the strong signal. Tune again (to 7035.10) and you'll only hear the strong signal because it will overwhelm the weak signal. Tune again (to 7036.10) and you're again hearing the strong signal. Tune again (to 7037.10) and you're again hearing only the strong signal, especially because you're outside the bandwidth of the weak signal). Tune again (to 7038.10) and you won't hear anything. Thus, it winds up sounding just like what I had described in my original post. Note that in the example above, you've only listened to 6 specific frequencies (7033.1, 7034.1, 7035.1, 7036.1, 7037.1 and 7038.1). You have no idea what's happening at any of the frequencies in between. You haven't listened to them or swept through them. You have completely jumped over them. And just to make matters worse, the brain tries to interpret the sounds at those spots as being identical volume. As does the AGC. The effect doesn't appear to happen with a tuning rate of 10Hz because you're going in such small increments that your brain interprets it as continuous sweep tuning. As you tune from low to high, you'll hear the weak signal start to come in and rise in volume, then you'll hear the strong signal start to come in, then you'll hear the strong signal overwhelm the weak signal, then nothing but strong signal, and then you'll hear the strong signal start to "fade" out as you tune past it. Compare that with tuning at a 1KHz rate where things seem to magically appear and disappear. When I first started working with the K2, I had never before experienced digital tuning (at least not on an HF rig) and thus I was expecting something along the lines of what I was used to in my old Swan 350 and in my FT-897 -- that tuning was sweeping through frequencies rather than jumping from frequency to frequency. In my expectations, the RATE on the K2 was setting how fast I swept through the frequencies rather setting how much I jumped between frequencies. ***** Hope this helps Jon KB1QBZ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Just one of many differences between analog and digital radios.
Since radios' frequency generation schemes have become more accurate, most casual SSB operators will settle on half or integer kHz frequencies. I have the coarse adjustment on my K3 set for 1/2 kHz steps, which makes it possible to scan a band with the tuning know very quickly. Except during contests, almost all signals will be perfectly tuned as I scan across. It is an observed fact that those who tune to these settings want their rigs to be exactly on those frequencies. Many of us have decades of analog radio use before we laid hands on a radio with digital features. With a little research in the reflector archives there is a steady stream of posts asking whether some artifact of digital processing is normal. Half-century old artifacts of analog processing are considered "normal". The K2 is a half-way-ish merge between a pure analog radio and the K3. My K2 became more digital when I added the DSP option. We already have radios that go digital immediately after RF amplification, almost at the very front end and whose functions are accomplished in a program running on a PC. The Flex transceivers are an example of that. There has been a lot of energy spent making a digital radio behave analog, because for the most part "intuitive" is also analog. If you analyze the K3 in detail, you will find many more digital "isms" that have been specifically designed/disguised to mimmick analog behavior, some of which are debatably not needed, but whose analog-reflective presence would simply be a stumbling block to most operators' now unconscious and instinctive expectations of how a radio functions. One item of such technical interest in the K3 is the RF gain, which really only provides an advice number to the main K3 CPU, which is combined with other considerations to control the gain of an 8 MHz IF amplifier just ahead of the 2nd mixer driving the digital to analog converter. The only real control of RF gain in the RX is the PRE and ATT controls, which don't directly control a circuit either. Not having an RF gain control likely would have been a human factors nightmare, however valid that tactic may have been technically. Enjoy the digital journey and 73, Guy. On Sun, Jul 11, 2010 at 9:13 AM, Jon Perelstein <[hidden email]> wrote: > This is an update to a post I made in Nov 2008. I've received a fair number > of off-board emails over the past 1-1/2 yrs asking me about the problem and > solution, so I figure I'll post the solution and save others from some > embarrassment. > > My original problem was described as follows: > > >>>2. On receive, stations are either there or not there. > >>>In this case, if I hear a signal, I hear it at the same volume as I tune > across the signal's bandwidth. The perceived signal strength simply does > not change. > >>>Along with this, there is no interference from adjacent signals. I'm > always hearing the strongest station and only the strongest station at > whatever spot that my VFO is tuned to. > >>>3. As I tune across a CW station's signal, there is no change in audio > frequency. Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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