This is to be expected. The engineers who work at the job all day, every
day, know and understand a lot more about the circuits they're designing
than someone to whom it's only a hobby.

And, considering the incredible time and effort that goes into the
design of each product, Tektronix and similar companies can't afford to
be making instruments that can be perfectly copied within days. I never
saw any conscious effort to obscure a design, but the normal process of
developing state-of-the-art equipment required use of techniques out of
the reach of amateurs or even most manufacturing companies. Let me give
you just a few examples.

1. Circuit board layout becomes critical for many high performance
circuits, and sometimes several iterations are required before all
problems are solved. There are also mechanical considerations such as
maintaining necessary air flow. In a product I worked on, we had to
solder the turns of a delay line together to reduce coupling from a CRT
deflection circuit. In another, the ground was broken in a critical
point to interrupt ground current flow.

2. Design techniques are used which aren't well known outside the
industry. For example, look at the schematic of the vertical amplifiers
in older Tek analog scopes. You'll find series RC combinations,
sometimes with a thermistor as the R, between the emitters of the
differential stage transistors. These served two functions. One was to
compensate for the delay line loss which increases as the square root of
frequency. The other is to compensate for thermals -- the fact that a
common-emitter stage gain changes as the transistor heats up in response
to a signal voltage change. This can usually be ignored in a time-domain
application, but can cause serious distortion of a voltage step or other
time-domain waveform. Changing the transistor type or sometimes even its
package type changes the compensation requirements.

3. Component selection and design are often critical, as is material
selection. As an example, some high impedance attenuators are built on
special circuit board material such as polysulfone, because of a
nonlinear property of FR4 and other materials called "hook" which causes
signal distortion.

4. Manufacturing techniques. The list of these is almost endless. It
becomes a major determining factor in circuit performance particularly
at very high frequencies, such as the 20 - 50 GHz sampling heads I
helped design.

I recall showing a photomicrograph of a new sampling head to a company
which was very sensitive to security, and telling the surprised
engineers that I'd be happy to give them a copy. I also told them
truthfully that even if I gave them the schematic and parts list, they
still wouldn't be able to build it. I'd guess that a competing company
with world-class engineers might be able to do so in about a year. There
were just too many special and selected components and manufacturing tricks.

So it's wishful thinking to believe that you can duplicate one of these
high-performance circuits by soldering parts together from a circuit
diagram. There's a very lot that goes into these products that most
people have no idea of.

Roy Lewallen, W7EL

J M Noeding wrote:
. . .
On the other hand one may experience that HP and Tek uses some extra
components which are difficult for the average constructor to explain
or understand the function for, and one may experience that even among
the amateurs somebody manage some technique which almost nobody else
can copy - not even very experienced persons, may I mention SM5BZR
Leif's techniques, it is many constructions, they may look so easy,
but one often need some more deeper understanding to succeed, what
say's G3SEK?

73
Jan-Martin
---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

my favorite commercial design "oops" was a pricey multi-port TTY
(teletype) i/o board for the then new Nova 4/X minicomputer (data
general). Worked great, as long as you only used video terminals
emulating a TTY on a current loop. Put on a _real_ teletype, and you
quickly fried the board, every time. No protection against counter-EMF.
After two board exchanges (in warranty, thankfully), we finally just
put in opto-isolators on our own TTY lines and it worked thereafter. ;-)

grins bobm
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************

On Fri, 15 Oct 2004 20:43:13 -0700, Tim Wescott
wrote:

Buy it, it's worth it.

I just have and it is. Especially since I got a brand new copy for
just over 5 quid! ($30 cover price)
Next target: "Experimental Methods...."
:-)

--

"What is now proved was once only imagin'd." - William Blake, 1793.