Dale, The bandwidth can make a difference - the noise is broadband while the signal is narrowband. If the bandwidth of the receiver input is wide, then a preselector will make a difference because it decreases the total noise that the receiver is handling.
Note that many(most) tuners will not produce that pre-selector effect. Only those with a resonant circuit will do that. Most common T-network of L-network tuners create either a high pass or a low pass filter. 73, Don W3FPR On 3/29/2011 9:55 AM, Dale Parfitt wrote: > I believe I understood all of your comment Ron. > But as our noise floor at HF is limited by external noise (atmospheric, > manmade and galactic) I don't understand how efficiency, within reason, > comes into play for a receive antenna. Certainly, for signals above the > noise floor, adding in 3 or 10 of attenuation makes no difference in the S/N > ratio, and since the preselector cannot discriminate between signal and > noise, I still don't understand the mechanism of how a preselector improves > S/N unless its BW is better than the BW of the receiver- and I can't imagine > that situation either. > One of my best low band antennas is a rotatable half sized Flag whose gain > runs around 30dB below my sloper. > > Dale W4OP > >> The antenna tuner acts as a pre-selector so to speak, by making the sytem >> of >> the antenna, the transmission line, and the radio, resonant, and matched >> impedence. >> >> All of this adds up to minimize losses in a couple of ways. The impedence >> matching means that the xmission line and antenna are as close to the >> input >> impedence of the radio (nominally 50 Ohms these days). If it is not at 50 >> Ohms then you do not get maximum power in to the rig based on simple >> simple >> Ohms law power. >> >> A highly simplified way of explaining resonance part of "a resonant >> antenna" >> is the act of making sure all of the current is in phase with the voltage >> so >> that when the power does get to the reciever, that it is in a useable form >> to drive things. It is somewhat the reverse or inverse of a good spring >> and >> shock absorber system on a car....if you have things wrong, and drive >> along >> a rough road with bumps spaced jsut right relative to how fast, then all >> heck breaks loose; maximim power transferred, and that is a resonant >> system. >> If things are not resonant, well, you get a smooth ride in your car, or in >> the case of your radio, poor reception (and transmission). >> >> -ron WT5RZ >> >> -- >> View this message in context: >> http://elecraft.365791.n2.nabble.com/A-comment-about-Receiving-tp6216105p6217679.html >> Sent from the Elecraft mailing list archive at Nabble.com. >> ______________________________________________________________ >> 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 > > -------------------------------------------------------------------------------- > > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 9.0.894 / Virus Database: 271.1.1/3536 - Release Date: 03/28/11 > 14:34:00 > > ______________________________________________________________ > 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 > ______________________________________________________________ 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
