Nino, That was kind of my thought...interesting about the Chip64 decoder...I will have to study the mode more.
In my post I did day that it was a 100 mile path but did not stipulate that is was all over land. Also, unless you live in an area where the ground conductivity changes a large amount over 100 miles...as in transmitting from the coast to inland, you won't generally see all that much change as the ground conductivity is gradual...except as the above case and some places in Colorado, California and Germany that I know about. Thus I normally tend to disregard loss due to ground loss/attenuation. Also, you might be thinking that the first hop of three hops ia 33 miles, the second 66 miles and the third 100 miles. Not necesarly so and generally not. The First hop might be anywhere from 10-15 miles to 35 miles, the next hop more or less than 66 miles and the third hop more or less than 100 miles. When the signal "hits the ground" it spladders as my old PhD in physics Elmer used to say...he maintained that it created another set of groundwaves and that groundwaves from the various hops could mix with the skywave signals and cause even worse signals that you describe Nino. REalize that this was in the 60's and his observations were from the 30's and 40's when little was really known about the ionosphere. Also there are hops between the F1 and F2 layer during the day so in fact you might have 3-6 hops before you receive the signal with only 2 being skywave hops. Very complex. The key to overcoming all this has got to be a way to know exactly which signal is the "real" signal. There is a "system" that originally used an atomic clock to track signals and today uses a GPS clock. I can't say much more about that system. (Because I don't know much more about it.) IMHO, the PSK modes have dealt adequately with the noise problem but the problems caused by the ionospheric have yet to be adequately addresses. Thanks for your input Nino. 73 All and CUL, Walt/K5YFW Nino Porcino (IZ8BLY) wrote: > > > Walt/K5YFW wrote: > > > if you may be receiving 1, 2 and 3 hop signals. How does this affect BPSK > > and QPSK signals from for example PSK31/63/125? > > the 3 different signals will sum at the receiver, but, having each one a > different phase, the sum is destructive with the result that they tend to > cancel. If the paths are stable you notice a drop in the signal strength but > if paths are unstable (as it is often the case) one signal may win over the > others and the phase of the PSK decoder will wander back and forth. The > clock recovery is also problematic because of the unstability of the > reference. > > Among the possible solutions to multipath there is the spread spectrum > modulation (as in Chip64) where the symbols at the receiver aren't expected > at a precise timing, but are decoded in a "clockless" manner. In Chip64 > signal scope you can actually see the signal trace wandering left and rigth > due to path hopping or see the ghosted trace of the secondary path. > > Nino/IZ8BLY > >
