On Tue, 6 Jul 2010 16:16:29 +0000, The Smiths wrote: >Now, this has become an argument.
That happens when some of the people talking don't know what they're talking about. Tom (JI), Tom (RC), Paul, Joe, and Guy know what they're talking about. They not only have the experience, they understand the physics. There is more to this than some folks understand. I urge them to go back and study my most early in this thread. Pete asks, >Isn't the whole point of diversity reception in the K3 >that the receivers **are** synchronized to the same clock? That puts them on VERY nearly the same frequency, but the RF inputs to the two RXs are from different antennas. Think about what W8JI has said, which is absolutely correct -- that is, to be effective in DIVERSITY mode, antennas must be widely separated. WHY? Because MOST fading is the result of cancellations between a direct wave and a reflected wave arriving at some particular point. This is EXACTLY the same as picket- fencing on VHF and UHF that we hear when we or the other station is mobile, or when there is a reflection from an airplane completing the path. When the signal peaks, the two delay between the two signals are some multiple of wavelengths so that they are precisely in phase AT THAT FREQUENCY. At some other frequency, they will be some degree of out of phase, and for some delay they will be 180 degrees out of phase. That fading is periodic, and is wavelength and frequency dependent. That's why it's fast at VHF/UHF, and MUCH slower on 160M -- indeed, that's what we're hearing when there's LONG, DEEP QSB on 160M. Diversity helps this by having two RXs listening to two antenna that are SPATIALLY separated from each other, so that when the null is at one antenna, the peak is more likely to be at the other (or, with less separation, the null is not so deep). But it is the TIME DIFFERENCE between these antennas, plus the delay in the feedlines of the two antennas, that produces the time offset between the two signals. And that time offset produces a phase difference that depends on the time and frequency. It is the relation of the time and frequency to phase shift that produces the ROTATION that several guys have talked about. That's the swimmy sound you hear in the headphones in diversity mode with widely separated antennas. 73, Jim Brown K9YC ______________________________________________________________ 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
