Hopefully this discussion is not too far off-topic. But state-of-the-art receiver design certainly does seem related to the K3. :=)
On Tue, 2009-02-24 at 19:50, Eric Scace K3NA wrote: > At the W1KM contesting site, we routinely see signals of +5 dBm or > louder on/near 40m from SWBC stations (using a single Yagi). We also > have two modest-power local AM stations (1 to 5 kW, a few miles away) > just below 1500 kHz that show up even a bit stronger than that on our > 160m antennas. +5 dBm is S9+78 dB. Definitely pinning the S-meter! > Without taking into consideration signals from our own multi-multi > transmitters, a receiver is already faced with >>130 dB range between > weak signals on 160m in mid-afternoon arriving from Europe and these > other signal sources. > > WD3Q, a contester in Washington DC, has much stronger AM BC stations to > deal with, including a 50 kW station on 1500 kHz. > > Wide-open receiver front ends attached to an A/D converter are not yet > viable for these locations. Even with direct sampling of the RF signal with an ADC you would still want bandpass filters in the front end. For best performance, each one should be just wide enough to cover a ham band, as they are in the K3. > -- Eric K3NA > > on 09 Feb 24 20:44 N8LP said the following: > > You may be right, Al. I think the improvements may be incremental, and > > distributed among various aspects of the design, not just the ADC. For > > instance, ultra-low jitter clock sources, faster FPGAs with improved IP > > cores, etc. I think most hams would be thrilled with an improvement to 130dB > > BDR, along with getting rid of phase distortion, ringing and other anomalies > > in the xtal filters and other analog components. Unless you live near a > > shortwave broadcast station, or have a high power ham nearby on the same > > band, you're not likely to need 130dB BDR anyway. Even in those cases, > > having 200dB BDR probably wouldn't help unless there is a LOT of improvement > > in transmitter spurious emissions, distortion and phase noise. > > > > The highest signals I have seen here, during Field Day when there were > > several stations operating within a few miles of me, were <120dB above the > > noise floor. Of course, it's very important not to use any more front end > > gain than necessary for the band/conditions. Thermal noise in a 500 Hz bandwidth is about -147 dBm. Assuming band noise on a quiet band is, let's say, 12 dB above that, the noise floor is -135 dBm. If Eric is seeing +5 dBm interference, that implies you need 140 dB of blocking dynamic range. Admittedly that does seem pretty close to a worst-case situation. > > > > 73, > > Larry N8LP Al N1AL ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
