[Elecraft] Dual Receiver Tricks

[David Gilbert]

I agree that Ed misused the term "polarity" at the end of his post, but 
I'm pretty sure it was a slip of the pen (keyboard) because he has been 
doing this stuff for a long time.  I'm pretty certain he meant 
"polarization".  I know he has done some work (and written about it) 
using cross polarized antennas (orthogonal and spaced a bit apart fore 
and aft relative to the arriving signal) to measure both the degree and 
direction of ellipsoid arriving signals, and I remember that he took 
great pains to account for differences in the feedline delays.

When he's simply looking for the tilt angle and not the handedness of 
the ellipse, as he states below the two orthogonal antennas are in the 
same plane ... but if the arriving signal is circularly polarized the 
phase will indeed appear to be different between the two antennas.  If 
the arriving signal isn't particularly circular but simply has a 
polarization tilt, the phase difference would be small and the 
differences in amplitude would indicate the angle of tilt.

Be sure to correct me if I'm wrong here, Ed.  I'm doing my best to 
visualize this stuff.

I think Ed is telling me in in his post below the name of some software 
that allows him to compare the two signals, and presumably that is the 
case for both amplitude which he is using to get the tilt angle, and for 
phase, which I want to use to get arrival angle using two horizontal 
antennas one above the other or azimuth using two vertical antennas 
spaced laterally.  It will be interesting to see if that does the job.

As I once posted in the past, I have previously fed the audio from both 
K3 receivers while tuned to the same frequency in diversity mode ... 
with the signals coming from two different antennas, one above the other 
by a known distance ... into the sound card of my computer running a 
simple dual trace audio oscilloscope application.  By triggering on one 
of the signals while looking at the delay in the other signal I could 
get an approximate indication of the change in arrival angle over time, 
so I know the concept is valid.  To get a clean reading I used some 40m 
AM broadcast carriers during periods when there was no modulation, such 
as between programs.  The angle changed 10 to 15 degrees in fractions of 
a second, and if had been able to accurately know the delay difference 
between the two feedlines I would have been able to calculate the 
absolute arrival angles instead of just the changes.

To be honest, the software necessary to do all of this should be fairly 
straightforward.  I'm just not knowledgeable enough to code it myself.  
 From my perspective it should also be possible to do it inside the K3, 
K3s, or K4, but if that doesn't happen (and it appears that it won't) 
I'll try to figure out how to do it with a separate application.

As you say, all of this can be accomplished at RF as is done with the DX 
Engineering boxes ... but it can be done more simply at audio via 
software (at least for receive) since phase is preserved upon down 
converting.

73,
Dave  AB7E



On 6/26/2019 10:11 PM, Jim Brown wrote:
> Some words are being misunderstood and mis-used.
>
> Polarization describes the geometric orientation of the antenna and 
> the resulting EM field. Polarity is the positive or negative going 
> sense of voltage or current in a circuit (what for decades we 
> mistakenly called "in phase/out of phase).  Polarity has two values, 
> positive or reverse. We change the polarity by turning the wires over 
> in a circuit.
>
> Phase is a continuously valued function and is measured in degrees or 
> radians. The phase relationship between two signals has meaning only 
> for sine waves of the same frequency. The phase relationship between 
> antennas is a function of the distance between them, the frequency of 
> each signal they transmit or receive. Further, this phase relationship 
> is different for every angle from which a signal arrives or to which 
> it is transmitted. The phase relationship also includes the electrical 
> lengths of the transmission lines involved, and, of course, the 
> difference in phase increases in proportion to the frequency of the 
> signal.
>
> There's a tutorial discussion of these concepts in 
> http://k9yc.com/VE3DO.pdf in the context of how the DX Engineering 
> NCC-1 and NCC-2 work to steer the directivity of two spaced antennas. 
> The same laws of physics are at play in this discussion.
>
> 73, Jim K9YC
>
> On 6/26/2019 9:20 PM, Edward R Cole wrote:
>> I feed signals from two antenna that are orthogonally polarized (one 
>> is horz and other is Vert polarity, both pointed in the same 
>> direction and essentially in-phase).
>> I use the eme sw MAP-65 to process the output of both Rx and it 
>> resolves the angle of polarization and maxes signal strength in 
>> alignment with the actual angle of polarity.
>
>
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