Chapter 5 5-15
Making GSM Cable and Antenna Measurements
Making Loss/Gain Measurements
made. For example:
• If making a passband-ripple measurement, the spectrum
analyzer requires a narrow span and typically < 10 dB per
vertical division to get more resolution on the display.
• If making a stop-band attenuation measurement, the spectrum
analyzer requires a wide span and a narrow RBW filter.
NOTE Having adjusted the control settings, do not alter them during the
course of the measurement.
To obtain a faster sweep, change the coupling from normal spectrum
analyzer mode to stimulus response mode by pressing the
Sweep
front panel key and Swp Coupling SR SA menu key until SR is
underlined. Note that the limitation on sweep speed is typically
determined by the device and care must be taken to allow the device
sufficient time to respond to the signal being passed through it. If
the auto stimulus-response-mode sweep is too fast, slow it down
until no changes in amplitude occur on the trace.
2. Establish a 0 dB reference trace for normalizing the measured data.
Normalization removes any frequency-response errors introduced by
the components of the test setup before making the measurement. It
is performed by removing the device and measuring a ‘thru’ from the
source directly to the receiver. This establishes a 0 dB reference
trace which is stored in the spectrum analyzer and then used to
normalize the measured data:
a. Remove the BPF and connect the tracking generator output
directly to the spectrum analyzer input, as shown in Figure 5-8,
using the same test cables to be used when making the
measurement. Use a thru adaptor to connect the test cables if
necessary.
b. Press the
View/Trace front panel key.
c. Press the
More menu key.
d. Press the
Normalize menu key, Store Ref (1 - 3) and normalize On.
This procedure automatically subtracts the measured ‘thru’ level
from an ideal ‘thru’ (a flat reference line) and stores it. This
reference is then used to normalize the measured signal where:
normalized signal = measured signal – error
With the device disconnected, the displayed trace is then flat, or
normalized.
The normalized trace can be moved to a different position on the
display by pressing the
Norm Ref Posn menu key. This may be useful
if the device to be tested has positive gain, such as an amplifier.
To Next Page
Loading...
Need help?
General
