OT Wullenweber Array

[charliedelta]

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The Wullenweber Array is a white elephant  by todays standards.
Arrays like these are being replaced by modern DSP DF arrays.
Modern DF arrays can fix a position from a single location. Modern
DF arrays measure the phase differences very accurately and can use
the phase difference to obtain directivity and azimuth. However
many of these Wullenweber arrays have been converted  as antennas
for use by modern DF DSP processing systems.

 The bigger the DF arrays diameter the greater the accuracy. With a
modern DSP DF array on a 8 meter diameter circle you can easily
achieve 1 degree of accuracy. Something like the Wullenweber array
fed with modern DSP processing can reduce that accuracy down to .1
degree accuracy. However reliable results from 1 to 30 mhz are
obtained using 50 meter diameter antennas using either crossed
loops or active short verticals. The DSP software alogorhythms used
are called MUSIC and ESPIRIT, its very interesting stuff.

http://www.monteriallc.com/almos/almos_hf_feat.htm
http://www.tcibr.com/spectrum-monitoring-hf.html
Rhode and Schwartz makes  some excellent equipment as well.

To keep this topic  Elecraft related, you can read here how to use
2 K2's as a phase locked receiver to do your own DSP directivity
experiments. With the advent of cheap SFDR radios we too will soon
be able to build  1 degree accurate DSP correlative arrays in our
backyards, assuming you have the space!

http://www.pa0sim.nl/index.htm

Craig
VK3HE
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[k6dgw]

[hidden email] wrote:
 > Modern DF arrays can fix a position from a single location. Modern
 > DF arrays measure the phase differences very accurately and can use
 > the phase difference to obtain directivity and azimuth.

One of the nice things about email reflectors like this one is that you
can learn a lot of useful things and also satisfy curiosity about some
things you have no use for.  Since Eric is allowing the Wullenweber
discussion to go on despite general non-relevance to anything Elecraft:

What is the difference between "directivity" and "azimuth," save
possibly that azimuth is referenced to some arbitrary zero direction
(like North) and directivity maybe isn't?  [teeny factoid: the US
military aircraft navigation system named TACAN uses a zero direction of
East -- always wondered why.  Maybe to confuse the enemy?]

How does one obtain a complete set of coordinates for the origin of a
received signal using only one passive receiving site (i.e. no
transponder for time delay measurement)?  I understand bearing (azimuth)
from the rx site ... how does one obtain distance?

I did think PA0SIM's phase coherent K2's was kind of cool.  I don't know
if the phase shifts are exactly the same across separate K2's, but I
guess whatever difference there was would be constant and could be
factored out?

Inquiring minds want to know.

73,

Fred K6DGW
Auburn CA CM98lw
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[Bill VanAlstyne W5WVO]

Fred Jensen wrote:

> How does one obtain a complete set of coordinates for the origin of a
> received signal using only one passive receiving site (i.e. no
> transponder for time delay measurement)?  I understand bearing
> (azimuth) from the rx site ... how does one obtain distance?

I would suppose you would have to plot the azimuth from two different array
sites (separated by hundreds or, preferably, thousands of miles) and
triangulate. Can't think of any way to do it from a single point on the
earth. You could approximate it by having some knowledge of how long the HF
skip distance appears to be over the path in question at the time the signal
is heard, but that sure wouldn't pinpoint it for you. Might put you in the
right (large-ish) country...

Bill W5WVO

>
> I did think PA0SIM's phase coherent K2's was kind of cool.  I don't
> know if the phase shifts are exactly the same across separate K2's,
> but I guess whatever difference there was would be constant and could
> be factored out?
>
> Inquiring minds want to know.
>
> 73,
>
> Fred K6DGW
> Auburn CA CM98lw
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[w6jd]

-------------- Original message --------------
From: Fred Jensen <[hidden email]>

> [hidden email] wrote:
> > Modern DF arrays can fix a position from a single location. Modern
> > DF arrays measure the phase differences very accurately and can use
> > the phase difference to obtain directivity and azimuth.
>
> How does one obtain a complete set of coordinates for the origin of a
> received signal using only one passive receiving site (i.e. no
> transponder for time delay measurement)? I understand bearing (azimuth)
> from the rx site ... how does one obtain distance?
>

Throughout the late '60s and up until June of this year Stanford University and SRI International were heavely involved in research and development of OTH-B (Over The Horizon Backscatter) radar systems. Actually Stanford got out of the business in 1970 when it was forced to drop its classified research, but I digress. During this period I developed signal processing and control software for SRI's OTH radar test bed. This was a bistatic system with the receive site located near Los Banos, California and the transmit site near Lost Hills, a separation of about 85 km. The receive antenna consisted of 256 vertical monopoles separated by 10 meters for a total length of 2.5 km, using analog beamforming to produce 32 independent sub-arrays. The full array provided azimuthal resolution of 0.25 deg at 10 MHz.
Which is the long way around of addressing the distance measuring question...no you cannot determine distance based on a single monostatic "look". We developed a number of techniques for distance determination. The radar waveform was swept-frequency CW ("Chirp").The waveform generators at the receive and transmit sites were synchronized with HP cesium clocks with the receive site's time delay offset to allow "range gating" of the received backscatter. By looking at the time delay of  the backscatter, distance to the echo could be determined. But, wait, just knowing time delay doesn't solve the equation, you need to know the propagation path and the height of the ionosphere to determine the path length and with a little geometry the ground distance to the echo. A separate backscatter sounding and vertical incidence sounding transmitter was used to determine the ionospheric layer structure and hence ground range from a given "slant range".
We also deployed "repeaters" at known time delays in the radar coverage area to provide "ground truth" and verify the accuracy of our ionospheric path determination.
So it was a sad day in June when the sites were "bulldozed", having spent a great deal of my professional life at one site or the other. The threat that OTH was designed to meet disappeared. The Air Force built a system in Maine based on our design, also one in Idaho which never went operational. The Navy still has an operational system on the East coast which looks into the Caribbean but that's about it for US OTH radar.
73,Doug W6JD
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