"Fractenna" wrote in message
...

I am confused: are you saying that my comments contain errors? If so, what
is
incorrect?:-)

Yes; OSU masters students in antennas are very good. I have one working
for me
right now.

73,
Chip N1IR


No, Chip.

I do not see any errors in your comments.

What I was saying was that building such a system as originally described is
a daunting task. There are many problems to overcome, one of which is
getting an antenna to work over a 25: 1 bandwidth with reasonably constant
performance. Another is that the pattern of the array will change
tremendously over the same bandwidth, but this can be "fixed" by using only
part of the array at higher frequencies.

Maybe that is why it was "broke up"? Also keep in mind the reputation of
news outlets as to technical accuracy.


My Maser's wasn't so much in antennas (although I did do a bunch of research
to identify the problems and propose solutions), but more at the systems
level to show how digital signal processing can be used to solve previously
"impossible" problems. I recall that at the time the experts in Radio
Astronomy thought the idea wouldn't work at all.
--
Jim
N8EE--

to email directly, send to my call sign at arrl dot net

What I was saying was that building such a system as originally described is
a daunting task. There are many problems to overcome, one of which is
getting an antenna to work over a 25: 1 bandwidth with reasonably constant
performance.

That's do-able.

Another is that the pattern of the array will change
tremendously over the same bandwidth, but this can be "fixed" by using only
part of the array at higher frequencies.


Yes. Actually not an element problem, but a problem with fixed height above
ground; ground characertistics; mutual coupling; and element spacing--I am sure
you know this; others might not.

Maybe that is why it was "broke up"? Also keep in mind the reputation of
news outlets as to technical accuracy.


My Maser's wasn't so much in antennas (although I did do a bunch of research
to identify the problems and propose solutions), but more at the systems
level to show how digital signal processing can be used to solve previously
"impossible" problems. I recall that at the time the experts in Radio
Astronomy thought the idea wouldn't work at all.

They were wrong; you and Bernard Steinberg (at Valley Forge/UPenn) showed
otherwise:-) BTW, I read your thesis about 10 years ago.Nice work. Others
might also like to know that a synopsis isup on the NAAPO site.

I think the Euro folks are too jazzed by the computational technology end and
have lost sight of the overall goal. That is my personal opinion.

73,
Chip N1IR

Some more "Trivia" for you and other interested parties....

The actual idea was conceived by Dr. Robert S. Dixon W8ERD, who at the time
was Assitant Director of the Ohio State RadioObservatory (Big Ear) and
Director of the Academic Computer Center. I was working there as a Graduate
Research Assistant (official title) and Chief Engineer (unofficial title)
and had not yet decided on a thesis topic. He was wondering if it would be
possible to digitize the signals at each antenna element in an array and
then, through digital signal processing, form all possible beams in all
directions simultaneously. And the rest is history, as the saying goes.

Also, I had previously read the book Imperial Earth by Arthur C. Clark,
where he describes a space based array that could look in all directions
simultaneously. He called it "Argus", and I thought that we should use the
same name for our system. My prototype, however, was called a Radio Camera
since the basic idea was to form a picture of the RF environment, and the
name Argus is now being used for the present system at OSU (not to be
confused with the system that uses satellite TV dishes at many locations).

You'll get a laugh out of this... My original system used a PDP-11/40 with
a whopping 10 MB of hard disk. I had the whole thing to myself as exclusive
user. Even at that it was too slow (even with a 10 kHz signal bandwidth),
so I collected the raw data and processed it off-line. I used weather radio
stations at 162.55 MHz as my sources since they all run the same power and
same antennas. Any differences in signal would be due to propagation and
distance.

The basic idea of Argus is to be able to look in all directions at the same
time, thereby increasing the chance of detecting transient signals. Big Ear
had detetected some transients (the most famous being the WOW! signal)
mainly from the direction of the galactic poles, but considering that it
would take Big Ear several years to survey the entire sky the detection of
such transient signals is pure luck. An Argus system, however, can survey
the entire sky (by this I mean what is visible from a given location---you
would need one in space to see everything) in one day, theoreticaly.

--
Jim
N8EE

You'll get a laugh out of this... My original system used a PDP-11/40 with
a whopping 10 MB of hard disk.

I still have my PDP10 programming manual. Jeez, I --AM-- OLD!:-)

Yes; Bob had a great idea.

I suspect it will take 30 years (from now) to do this properly, get all the
birdies out; get a nice patch of land in Arizona or Utah; build the
system;find ET's; and so on.

Pioneering doesn't seem like that to contemporaries. We all need lasik!

73,
Chip N1IR

Even more trivia:
My work at the Big Ear under W8JK years before N8EE's work involved the
first digital recording of radio astronomy signals including time
information. (Slave labor, AKA graduate students, were used previously to
digitize the strip charts used.) The recording medium was punched paper
tape and the (very off-line) processor was an IBM 1620 (or something like
it - it was a true decimal machine intended originally for accounting - some
arithmetic operations involved table look up!). It took several orders of
magnitude improvement in computational power and in ancillary equipment to
arrive at what Jim was able to do. I delight in that progress.
Pertinent to this group, is the admonition that one still needs to
understand the analog part of any such information gathering system even
while digital power increases. At least within my remaining lifetime, the
antenna(s), transmission line(s), and "first stage" will remain the province
of analog engineering. This group will have plenty to discuss before it is
supplanted with an A to D converter!
73 Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:
"JLB" wrote in message
...
Some more "Trivia" for you and other interested parties....

The actual idea was conceived by Dr. Robert S. Dixon W8ERD, who at the
time
was Assitant Director of the Ohio State RadioObservatory (Big Ear) and
Director of the Academic Computer Center. I was working there as a
Graduate
Research Assistant (official title) and Chief Engineer (unofficial title)
and had not yet decided on a thesis topic. He was wondering if it would
be
possible to digitize the signals at each antenna element in an array and
then, through digital signal processing, form all possible beams in all
directions simultaneously. And the rest is history, as the saying goes.

snip
--
Jim
N8EE

Chip wrote:
"I still have my PDP 10 programming manual."

As I recall from circa 1970, the Digital Equipment tiny-biny was the
programmable data processor, PDP 8. I remember Schlumberger having in
its Houston Headquarters a PDP 10, The PDP 10 was a rather large number
cruncher which could be used for scientific purposes as well as for
business applications. I think they ran both FORTRAN and COBOL.

My employer tried Raytheon 704`s for minicomputers, then switched to
Digital Equipment VAX machines. They worked well.

Best regards, Richard Harrison, KB5WZI

while digital power increases. At least within my remaining lifetime, the
antenna(s), transmission line(s), and "first stage" will remain the province
of analog engineering. This group will have plenty to discuss before it is
supplanted with an A to D converter!
73 Mac N8TT

Mac,

These days, good analog RF folks are worth their weight in platinum. I like to
maintain a library of older RF books just to keep the younger guys on their
toes:-)

73,
Chip N1IR


73,
Chip N1IR

Chip:
Amen. An objective of most who teach in the area is to nurture students
who are able to discern when it is analog time and when it is digital time.
The allure of digital has to be mollified. Occasionally one has a student
who's eyes light up when he or she is exposed to the art of analog after
seeing the science of same. Many more students are appalled.

It has been one of the pleasures of my life to collaborate with a
wonderful colleague (and extra class radio amateur) as a catalyst and teller
of stories while he puts down some of the accumulated analog wisdom
reinforced by his analysis, insight, and exposition. No doubt some was
acquired in this group. Look for his encyclopedic book from CRC to be
available within about a month.
73 Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Fractenna" wrote in message
...

while digital power increases. At least within my remaining lifetime,
the
antenna(s), transmission line(s), and "first stage" will remain the
province
of analog engineering. This group will have plenty to discuss before it
is
supplanted with an A to D converter!
73 Mac N8TT

Mac,

These days, good analog RF folks are worth their weight in platinum. I
like to
maintain a library of older RF books just to keep the younger guys on
their
toes:-)

73,
Chip N1IR


73,
Chip N1IR

One of the concepts that I have had trouble getting 'younger' engineers to
understand is that a digital signal IS analog! Just because you are
running at "only 10 MHz" doesn't mean that you can have 4 inch pigtales.
The actual signal bandwidth would extend up to 50 MHzor even more, and you
have to treat it like a VHF/UHF RF signal or the bits are going to get lost.
Digital is Digital only in the purely logical sense (pun very much intended,
by the way).

As for digital signal processing is concerned, just because you have
digitized the signal doesn't mean that you have eliminated all of the analog
problems. I can think of only three ways that DSP is better...1)no cross
talk in signal paths, and 2) lossless signal duplication (think of an analog
power splitter), and 3) you can do things easily that previously were just a
glimmer in an analog engineers eye (such as multiple simultaneous beams from
an antenna array?)

--
Jim
N8EE

to email directly, send to my call sign at arrl dot net

On Fri, 24 Sep 2004 14:42:54 -0400, "JLB"
wrote:

As for digital signal processing is concerned, just because you have
digitized the signal doesn't mean that you have eliminated all of the analog
problems.

Hi Guys,

This reminds me of the problems I had teaching the digital types
Shannon's law for BER.

When I designed the black box for the 757/767, all of my digitized
readings (taken from 600 leads) was passed over to a specialized tape
recorder (25 hour capacity).

Problem was that this digital signal was fed into the recording head
without any bias. Many may be unaware of the advances in audio tape
recording BW that came by the addition of bias, and more, that it
reduced the head's tendency to erase its own stored signal. In
essence, with no bias, you were recording data with two strikes
against you. This was not the hallmark design for a data sensitive
product. Worse yet, was this digital mentality had recorder
specifications that allowed for a S+N/N of 2.

What were the comments I heard in response? "This is not HiFi, it's
digital data, on/off."

Within weeks I was drawn into their simulator lab to view a simulated
cockpit of an KLM aircraft that was being used to display flight
recorder data that was rather -um- noisy (much too much for KLM's
engineers to make sense of it). I watched that plane hit the ground
several times as they struggled to recover digital bits lost in analog
noise.

Several (many) years later I was called to consult on the TWA flight
800 data - more noise that lead to hints of missile strikes. The
panel's best spin on the topic was that it was old data printed
through the new data (even though the difference in time would not
correlate to the two data sets overlapping). We reported it as
exploding gas tanks, Tehran reported it was revenge for our shooting
down one of their civil aircraft during the first Gulf War. Like the
first attack on the Twin Towers, government and the media shrugged off
correlations.

73's
Richard Clark, KB7QHC