In article , Paul Burridge
writes:

On Tue, 14 Oct 2003 15:30:54 GMT, Active8
wrote:

i don't usually have to bypass anything to shoot. you look for last
known good, first known bad, with your RF probe/scope/sniffer/whatever
and go from there. lift an input component leg, terminate an output,
check signal, if good, plug it back in. find the stage that's bad and
check transistor DC levels first.

Agreed. And that's what I'd do in practice.
I'm just curious, however as to what effect jumping RF from point A in
a circuit to point B with just a single wire has on the signal. IOW,
will the integrity of the signal be preserved by this quick and simple
expedient? The great and the good here seem to believe it shouldn't be
a problem up into VHF.

Paul, there seems to be some disagreement on the practical
aspects of breadboarding tests...if what you are doing is such.

First, there is always the possibility of "trouble" with "long leads"
at HF or higher. Without knowing more exact nature of a particular
circuit/system under development, it is IMPOSSIBLE for others to
predict what will happen. Too many variables to allow quick solution.

In the consideration of PRACTICAL bench work during development
(my assumption), AND of having a circuit board with a "good" (large,
inclusive) ground plane, it is quite probable that one would not
experience undue upset of a circuit/system under development
involving frequencies on up to UHF with "long leads" of up to 4 inches
length. That is my particular experience from longer than four
decades of working "on the bench" both at work and at home.

Others may wish to take exception to my statements and engage
in long, convoluted intellectual arguments about the whichness of
the what. That's okay with me. But, on the subject of ACTUAL
development, especially getting something DONE, all the jawing
about the whichness of the what isn't helping much. No time on
the bench. Trying out things may involve bypassing stages or
similar. Fine, sometimes that is the only way to discover what is
not quite right, troubleshoot, or just see alternate possibilites.

It's rather obvious that a single wire elevated above any ground
plane that may be an eighth of a wavelength long or so is NOT
going to be of the same impedance as the same wire laid down
next to the ground plane. But, will that matter? Depends. If the
load end has a low impedance near the source impedance value,
probably not. If the load end has a high impedance relative to
source, there might be some nasty effect. One has to THINK in
all cases, all situations, in terms relating to the particular project
in work. In development work with limited time available, one goes
ahead and tries something out...and looking, learning, discovering
what happens and getting a handle on the differences of the longish
jumper versus short-lead connection. Each and every project is
going to be different, unique, and none will have any ironclad rules
of "this is the one and only way to do it."

A case in point, mentioned in here befo Hans Summers' spectrum
analyzerS (plural). His first version was point-to-point using relatively
"ugly" (top foil of a PCB only, no etching) structure. That worked, but
no doubt he had some individual, spot problems here and there. For
the second version he went into modular style separation of basic
blocks connected with little coax cable assemblies. That modular
style can be considered the "best" for shielding, maintenance of Z
between stages (important for broadbandedness), and ability to
localize troubles should one module not behave. That's excellent, but
with a qualifier: It isn't practical unless one has a low-cost ready
source of coax cable assemblies and mating conntectors. Hans had
that from finding a local bargain in them. Already assembled, no extra
time required for those, quality control could be expected to be good,
not a lot of worry about open center contductors, and so forth. The end
result was neat, tidy, with less problems from construction compared
to the first. Development time could be concentrated on the interior
of each module and those characteristics rather than a lot of relatively
open hook-ups.

There's one rule that all have to keep in mind: Electroncs, fields, and
waves don't recognize "neat" or "pretty" or "approved ways." They
work with conductors, insulators, impedances, etc., on THEIR terms,
not humans. Everyone has to get acquainted with electrons, fields,
and waves' rules FIRST.

"Ugly" circuit board structures are just fine if the solder makes good
conductive intermetallic bonds, doesn't short out to other lines, doesn't
have a potential for near-future trouble from oxidation, coming loose, etc.
Neat it ain't, but electrons don't work on neat.

Sorry to get on the philosophical lecture pulpit. Other things locally
got me on a roll and I slipped in the butter...

Len Anderson
retired (from regular hours) electronic engineer person