From a brief look at the referenced web site, it looks like the author
did a decent job of making a low impedance probe. It should work quite
well if carefully constructed.

But it's actually a lot easier to make a good 50 - 1000 ohm probe (which
the web site describes) than a 10 meg probe. A 10 meg, 10X probe is a
lot more useful for most everyday measurements, which is why it's
universally used on scopes up to several hundred MHz. At least as
important as the high resistance is the relatively low capacitance it
presents to the measured circuit. (A good low Z probe has considerably
less capacitance yet, so it's a better choice at really high
frequencies. It's also fine for probing in 50 ohm environments.)

Making a good 10 meg probe is quite an art as well as a science. If you
ever disassemble an old Tek probe, one of the first things you'll notice
is the coax. It's specially made with a resistive center conductor to
damp reflections, and lossy dielectric to reduce piezoelectric and
triboelectric effects. (If you don't know what these are, connect a
piece of regular RG-58 to your scope input, turn the sensitivity up, and
flex it or rap it with a mallet.) Another tough problem is "hook", a
nonlinear property of many capacitors, dielectrics like PC board
material, and even resistors. This creates funny, hook-shaped step
responses (which is how it got its name), that are difficult or
impossible to compensate. You probably won't see hook at 50 ohm levels,
but it's pervasive in high impedance environments. The little circuit
board in the scope compensation box is likely a specially-made low-hook
expoxy glass formulation, or an inherently low-hook dielectric like
polysulfone. And both the capacitors and resistors were carefully chosen
and specified for low hook and other nonlinear properties.

A cheap or homebrew 10 meg probe is fine if you don't really care if
what you see on the scope looks like the real signal. Or if the
amplitude of a sine wave is really what the scope says it is. But if you
do, you need a decent probe.

Roy Lewallen, W7EL

Symon wrote:
Steve,
I don't like to disagree with the other folks on here, but IMO you can
make a bloody good probe yourself. You'll also learn a lot more than
just going out and buying one. Try this link for starters.
http://www.emcesd.com/1ghzprob.htm
HTH, Symsx.

(Swells8044) wrote in message ...

I was given a BK1570a scope but I need probes can these be homebrewed?Im a
newby to scopes so this is a learn as you go project.Any help is appreciated.
Steve