Now that the K4 has exact knowledge of its gains and losses through the preamps, attenuators, splitters, bandpass filters and so forth, could this enable an alternate way of visualizing the receiver's range? This alternate measurement would be quite useful in setting the controls optimally for any situation.
Imagine a scale -- I suppose it would be in dBm -- showing the K4's total dynamic range. Say it's 100 dB in total. The lowest point is the minimum discernable signal (MDS); the highest point is the damage level, or if that's a bit too frightening, call it the maximum ADC level or something else to denote it as a Level Not To Be Exceeded. Since the K4 will know not only what the noise floor of the band you're listening to is, but the absolute value of that level in dBm, the scale can be annotated with a dynamic marker to show where the band noise falls in that 100 dB range. I'm calling it 'dynamic' because it'll vary a few dB as band noise does, but it will sit at a calibrated level, relatively motionless on the scale as Wayne described the S-meter doing. As the operator kicks in more gain by turning on preamps or turning up the RF Gain, the scale shifts downward by the same amount. For instance, if the scale was showing -120 to -20 dBm -- a 100 dB range -- and then the operator turns on a 10 dB preamp, the scale must change to -130 to -30 dBm, because the preamp has made the receiver more sensitive while also reducing the max permissible level. Conversely, if the operator turned on 10 dB of attenuation, then the scale would shift upward to -110 to -10 dBm, indicating clearly that sensitivity is being sacrificed for greater large signal handling capability. The noise floor, being a relative constant, would move closer to the bottom of the window, or rather, the window would move relative to the noise floor in such a way as to place it 10 dB closer to the bottom end. So actually, as I'm thinking about this, the meter wouldn't move at all. It's the noise marker that would float higher and lower within the window as you varied the controls, just as on an S-meter. I guess what I'm describing here is more or less an S-meter calibrated in dBm! But perhaps the best reason for looking at the receiver this way would be to tune the controls precisely for a given noise floor. Twenty meters, with its -120 dBm noise floor, will require one combination of preamps and/or attenuators. On 80 meters, if the noise is, say, -100 dBm, the operator knows (because he can see the graphic) exactly how much attenuation is acceptable while still keeping the band noise marker in the operating range. It would behoove the operator to keep the noise floor marker near the bottom to 1) give him the maximum dynamic range under those conditions, and 2) to avoid becoming "my K4 is noisy" guy. Presumably, as each K4 goes through RF calibration at the factory it will know exactly the gain of each preamp, attenuator, filter, and splitter in its path. The scale could be custom for each individual unit, although I wouldn't want to start any "my K4 is more sensitive than yours" wars. I leave it to the programmers to decide on the specific eye candy of such a readout. I for one would find this type of meter fun and useful in getting a mental picture of where in dynamic range space the receiver is sitting. Can anybody see any flaws in this idea? I can foresee at least one. I don't know how the front end of the K4 will work, but if it is constantly moving the receiver range in response to what it hears, that is, in response to the total amount of power incident on its antenna port, then perhaps that might pose a real challenge to giving this type of feedback to the user. I don't know. Al W6LX ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
