++++++++++++++++++++++++++++++ See also K1_Design_Comments +++++++++++++++++++++++++++ Date: Sun, 12 Aug 2001 07:30:13 -0700 From: pqd Subject: Re: [Elecraft] K1 / K2 Sensitivity >Does receiver sensitivity equal or directly/indirectly correlate to MDS ? Sure. MDS = Minimum Discernible Signal (3db increase above noise floor). >What is the MDS for the K1 ? ARRL's review reports MDS on 7MHz and 14MHz as -129 dBm (w/500Hz filter) The spec for the K2 w/ Pre-Amp on is -135dBm and -130dBm off (700Hz filter), as you quote. There was a posting by Wayne recently describing the differences in K2/K1 Rx design. You might search the archives and present it to your friend. Again, as you state the article mentioned the K1 power consumption as a factor in Rx design. Best, the pqdevice k2 0x8a8 - ----- Original Message ----- From: "Goody" To: Sent: Saturday, August 11, 2001 22:40 Subject: [Elecraft] K1 / K2 Sensitivity > A friend of mine was comparing the receiver sensivity of another friend's K1 > and K2 by switching back and forth between each rig listening to weak > signals. He noticed the K2 was much more sensitive than the K1 and was > dismayed by the K1's performance. I reassured him that the K1 doesn't have > a bad receiver design and attempted to dig up some specs. So, here's some > questions I had. > > The receiver sensitivity for the K1 and K2 (both) is listed as 0.15 uV, > which is about -123 dBmW. Minimum Discernable Signal for the K2 is listed > as -130 dBm, though. I can't find an MDS spec for the K1. > > Does receiver sensitivity equal or directly/indirectly correlate to MDS ? > What is the MDS for the K1 ? > > It's my understanding that the K1 receiver sensitivity is very good for a > rig of its class. Its weakness is strong adjacent signals due to the NE602 > frontend. Attempts to yield a better receiver most likely would have > resulted in a much higher power consumption. Correct ? > > Thanks and 72 > Goody > K3NG > ++++++++++++++++++++++++++ Date: Sun, 12 Aug 2001 08:29:58 -0700 From: lhlousek Subject: Re: [Elecraft] K1 / K2 Sensitivity Hi Goody, The K2 is awesome and the K1 is a little less awesome due to being optimised for small size, low current drain, and lower cost. Bottom line is the K1 has more internally generated noise than the K2. When listening to a sig you are hearing a combination of signal, "atmospheric noise", and noise generated internally to the radio. Usually, the lower the band the greater the atmospheric noise and it is much greater when a band is open. Often, on lower bands, the atmospheric noise is much greater than the internally generated noise so the internally generated noise becomes insignificant. How this sounds is also affected by the width and shape of the filters. Radios can generate internal noise at stages before and after the IF filters. Noise generated before is affected by the IF filter selection. Noise generated after is not affected by the IF filters but will be affected by down-stream filters including audio and DSP filters. e.g. The K2 employs a filter after the IF amp to greatly reduce it's contribution to the internally generated noise. MDS is a measurement of the internally generated noise (including theoretical MDS) of a radio. It assumes that a signal would have to be at least that big to be discernable. This is done with an instrument that responds to all sound coming out of the radio, much of which is in the passband, so the measured value is dependent on the width and shape of the IF passband. A wider passband will yielder a higher (worse) MDS. For different width passbands of the same shape MDS is roughly proportional to the SQRT of the width. Published MDS numbers usually list the filter bandwidth with which the measurement was done. Recent ARRL tests use the closest internal filter to 500Hz. Older tests do not and there is a considerable difference in the width and shape of the filters in the radios tested so this should be taken into consideration when comparing MDS numbers. Employing down-stream filters can greatly improve MDS. ARRL test are performed with any switchable down-stream filters turned off. The human ear is different from the instrument used to measure MDS in that it can discriminate frequency and responds to sounds as a function of their frequency... like a spectrum analyzer. So although an MDS measurement performed at 500Hz bandwidth may indicate that a given signal is below the noise level, the ear can still copy the signal because it can detect the signal using a much narrower bandwidth. Strictly speaking, there really is no such thing as detecting signals below the noise level. That happens only when the method of measuring the noise level is different from the way the signal is detected. Measuring MDS at a 500 Hz bandwidth but copying by ear is just one example of this. Had the MDS measurement been performed at the same effective bandwidth that the human ear can discriminate it would have shown the signal to be above the noise. Lou W7DZN ++++++++++++++++++++