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
