Dick Green WC1M
On Mon, Jun 21, 2021 at 12:28 PM, Jim Brown wrote:
Back to fundamentals -- Diversity is NOT about low noise, it is about dealing with Selective Fading -- cancellation of the same signal that arrives at our antennas via different paths, and thus drift in and outTrue. But in addition to dealing with Selective Fading, Diversity can help contesters with the zero-beat pileup problem brought on by packet spots.
In big pileups where the loudest stations have the exact same pitch and signal strength (because they all clicked on the same packet spot), it can be nearly impossible to pick out any one signal. It all sounds like mush. But sometimes a signal will arrive with polarity that's different from the bulk of the other stations, and if your two Diversity antennas have different polarity, that station will be louder on the antenna with matching polarity and will appear to be spatially separated from the other stations in the stereo soundstage.
For example, say you feed the VFO with a yagi into your left ear and the VFO with a vertical into your right year. Since the yagi has higher gain, most stations will be louder in your left year (you'll hear them in the right ear, too, but they'll be weaker.) But if a station's signal arrives with vertical polarity, it'll be louder than the rest of the stations in the right ear. In practice, the station will usually "float" around in the soundstage, seemingly moving in space, which makes it distinguishable from the stations that are strongest on the yagi. Rather than distinguishing the station by pitch or signal strength, you can distinguish it by the position in the sound field. The polarity can change back to predominantly horizontal at any moment, but all you need is for the polarity difference to last long enough to pick out the call or a decent portion of it.
I use Diversity on one of my K3s with a full-size 2-el 40m yagi and a 4-square.The beam is on the Main antenna and the 4-square is on the Aux (RX) antenna. The combination is killer in pileups. In addition to helping with zero-beat pileups, I can switch the direction of the 4-square to instantly amplify stations calling off the back or sides of the beam (and I can safely switch direction while transmitting!) While I'm sure Jim is correct that Diversity is not about noise mitigation, it always seems to me that I can copy stations better with Diversity when the bands are noisy.
73, Dick WC1M