[Elecraft] K3 Dual Receive Surprise

[Stephen W. Kercel]

Dave:

I had not thought of that. but you make a good point. It is kind of like 
optical interferometry, where the receiving electronics is inherently 
too slow to capture the instantaneous vibrations of either light wave, 
but can easily detect an interference pattern resulting from the 
interaction of the two light waves.

73,

Steve
AA4AK


Dave Gilbert wrote:
>
>
> It is not unusual for me to hear some sort of multipath propagation on 
> 20m late in the afternoon here in Arizona when beaming to Japan 
> (single receiver and 4 element yagi with a good F/B ratio).  The 
> disparity in arrival time is often enough to make signals totally 
> unreadable at CW speeds of roughly 25 WPM.  The middle of a character 
> or even a word sometimes just sounds like a continuous carrier.  This 
> might go on for an hour or more until one of the paths disappears.  I 
> have on two occasions this winter even heard three different arrival 
> times for the same signal, which was very weird and I wish I had 
> recorded it.  Given the differences in path length necessary to 
> generate that kind of delay I make no claim regarding the cause ... 
> only that I have clearly heard it several times. 
>
> In any case, if such delays are enough to blur 25 WPM CW, they would 
> be enough to be easily noticed in static crashes.  Of course, that 
> still requires some sort of polarity disparity to create the effect 
> observed by Mr. Zilmer.
>
> 73,
> Dave   AB7E
>
>
>
> Stephen W. Kercel wrote:
>
> Recall that radio waves move at 3 x 10^8 meters per second. If you look
> at multi path propagation at HF radio waves over intercontinental
> distances, and suppose that your two receivers were responding to two
> different signals taking two different paths, the differences in time of
> arrival of the different signals would be 1/10000 second or less.
>
> ... the delay is many orders of magnitude too short for your internal 
> cognitive processes to
> detect the difference in arrival time of RF wave fronts.