"Chuck Harris" <cfharris@...> writes:
If the OP's description of the set point being 2-3 dBm,
is accurate, you can do nothing else but use a 50 ohm
probe to make the connection.
dBm is totally undefined at the arbitrary high impedances
of FET probes.
dBm is totally undefined at the arbitrary impedances of something
like the Andrew Zonenberg probes.
dBm is totally undefined at the arbitrary impedance of using
a resister in series with the center lead of a coax cable...
The only way the high impedance route could work is if the OP,
or the MFR, used dBm in an imprecise way, and really meant something
else. If the MFR did that, he likely would have the sort of probe
he intended listed in the necessary calibration equipment table for
the instrument.
Ok, fair enough. I had assumed 2-3 dBm meant into a 50ohm load presented
by whatever is downstream of this. If it's 2-3 dBm when you load it
externally with 50 ohms, then yes of course you'll want to load it. It
does seem a little odd to ask you to change the circuit behavior when
probing though, which is what will happen if you load it down by an
external 50 ohms. But, admittedly, I haven't seen this sort of test
point much so maybe I'm just not familiar with the typical procedure
here.
Minor nit: passive probes like the Zonenberg probes aren't "arbitrary
impedance". They're designed for specific division ratios into a 50 ohm
input, so they have a very well-defined impedance, at least over the
specified bandwidth.
Matt
