3.6 Dynamic Range
Dynamic range has many definitions, but one common definition in spectrum analysis is 2/3(TOI
– DANL). A typical number for 1 GHz, -10 dBm reference level (10 dB attenuator), would be: TOI=
+21 dBm, DANL = -150 dBm (1 Hz RBW). Dynamic range, 2/3 (TOI – DANL) = 114 dB, and would
be mostly a function of RBW and frequency.
3.7 Protecting the RF Input
The SM200 and SM435 front end have ESD protection, but ESD damage is still possible. Signals
above +20 dBm peak (not RMS) can also cause damage. Some common events which may lead
to front end damage include:
1) Applying more than +20 dBm peak power, such as an antenna exposed to a radar pulse.
2) ESD from a passive antenna, either from discharge to an antenna element, or from
connecting a large antenna or cable which has built up a static charge.
For any application which may expose the SM200 to front end damage, including connecting to
active or passive antennas, a coaxial limiter is recommended to protect the input.
A limiter will protect against overpowering the input, typically raising the damage level above 2
watts, as well as offering additional protection against ESD. It will also offer some protection
against the energy spike you get when connecting to equipment with a DC or static voltage
present. The energy may significantly exceed +20 dBm for several microseconds.
Generally, the performance at low input signal levels is just the insertion loss of the limiter, but at
high signal levels there will be some nonlinearity and the resulting intermodulation products. A
typical limiter will have an IP3 around +30 dBm, so for input signals below -20 dBm there should
be little to no effect on SM200 linearity.
If it is a passive antenna mounted using a long coaxial cable, it may be building up a significant
static charge until it is connected. For this reason, it might make the most sense to keep the limiter
connected to the antenna rather than the SM200 / SM435. A DC block is probably not necessary
for passive antennas in most cases.
3.8 Power Management
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