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

Oh my goodness! No bias! Wow.
Both Jim's and Richard's observations are the sort of things that need to be
told to budding engineers.
I tell quite a few stories in class. After all, engineers kill people
with their mistakes in wholesale lots. Stories, since well before writing,
have been the way to communicate the important "stuff." The black box story
needs to be told. I effect some of Jim's story with the (apparently) simple
lab job of connecting N CMOS inverters in a ring - and then "playing."
(Fortunately, we have very high bandwidth scopes in each workstation so that
clues to what is going on can be seen. Thanks to a generous grant from a
company formally known as HP, we can see spectrum too.)

Many thanks for your contributions.
73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Richard Clark" wrote in message
...
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