There are many probes on the market today, and it can be hard to
pick the best one. Since each TDR/VNA probe design
is different, you will have to do some research. Here are a few things you
should consider when choosing a probe.
Bandwidth
A probe's bandwidth is usually easy to identify. This factor is
basically how high a frequency a probe can read and pass on. Before purchasing
a probe, think about the frequencies you will be reading. Your probe should be
able to handle more than three times the frequency that you will typically be
reading.
Attenuation Ratio
Probes have different attenuation ratios, which determine how
the data they read is fed to you. Most will give you a fraction of the original
frequency. Your machine's scope reads this data and translate it to give you
exactly what the probe is finding. Higher attenuation ratios let you read
higher frequencies. However, the higher your ratio is, the more internal noise
you will get. For instance, a 100:1 probe gives you 100 times the internal
noise. This information might make you consider going with a lower probe.
However, that is not always a good idea. Lower probes lead to higher loadings
on a system.
Loading
Connecting anything to the item you are testing is going to
change the characteristics of a system. Like the ones on the Juno mission,
even the most advanced probes are subject to physics. Therefore, anytime you
use a probe, it affects your system, and more loading causes inaccurate
readings.
There are many probes available to help you read signals. To avoid messing up results, you need to consider the bandwidth, attenuation ratio, and loading a probe will provide. Understanding these aspects and how they affect your readings will help you choose the right probe.
