On 11/9/2013 10:42 AM, ve6dc wrote:
I am new to the idea of diversity receive and wonder if this is mainly used on the lower bands, 160, 80 and 40 meters or all amateur radio bands.
It's most useful when there is QSB, or when signals are arriving at different vertical angles or when there is selective fading. Much QSB is the result of multiple copies of signals that arrive by slightly different paths, and are thus a bit out of time (and phase) by virtue of slightly different travel times. The result is heard as "picket fencing" with short VHF/UHF wavelengths, very slow QSB with the 200X longer wavelengths on 160M. When the two arrivals are nearly equal and close to 180 out of phase, they cancel, often by as much as 20 dB, and when in phase, add by as much as 6 dB.
With diversity RX, the concept for this sort of fading is to have antennas separated by some significant fraction of a wavelength, so that when the arrivals are cancelling at one, there will be addition (or at least less cancellation) at the other. For the other situation of high angle vs low angle paths, using a vertical antenna that favors low angles and another antenna (Beverage or low horizontal dipole) that favors high angles.
An excellent place to study these the propagation concepts is the ON4UN Low Band DXing book. The fading caused by cancellation of multiple arrivals is not widely understood by hams on the HF bands and 160M, but it is VERY well understood by many audio professionals working in live sound.
73, Jim K9YC ______________________________________________________________ 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
