Boonton 4530 Peak Power Meter User Manual - Manual (Page 155)

Boonton Electronics Chapter 5
4530 Series RF Power Meter Making Measurements
5-13
5.6.6 Measuring HDTV. Both of the common HDTV formats (8-VSB and COFDM) are very similar to CDMA in
many respects. They are both spread-spectrum formats, usually occupying a 6MHz television channel. The
modulated signal appears very much like random noise in the time domain, with a fairly high peak-to-average
ratio (sometimes called “crest factor”). There is no periodicity, and it is not very helpful to use a triggered
measurement such as Pulse Mode. It is a simple matter to measure average power and peak-to-average ratio
in Modulated Mode (default settings with a longer filter are usually fine), but this doesn’t tell the whole story.
A Statistical Mode measurement taken over several seconds is a much better choice, and can be used to
display the probability of occurence of all power levels in the sample population.
Meas Mode: Statistical
Frequency: 0.283 GHz (or whatever operating frequency is in use)
Stat Mode: 1 - CDF
Terminal Count: 10 Msamples
Marker Mode:
Vertical (set markers to measure power at a percent probability)
Marker1 Pos: 0.1% (returns power level exceeded by 0.1% of all samples)
Marker2 Pos: 0.001% (returns power level exceeded by 0.001% of all samples)
Query Cmnd: FETCh1:ARRay:AMEAsure:POWer? (returns array of statistical measurements)
Statistical measurements include long term average power, minimum and maximum instantaneous powers,
peak-to-average ratio, power at each marker, percent at each marker, and total number of samples.
The video bandwidth of the 4530 Series power meters with a Boonton 575xx peak power sensors is just wide
enough to cover a 6MHz channel. For HTDV formats using more than 6MHz of spectrum space, the 573xx
series sensors should be used.
5.7 MEASUREMENT ACCURACY
The 4530 Series includes a precision internal RF reference calibrator that is traceable to the National Institute for
Standards and Technology (NIST). When the instrument is maintained according to the factory recommended one
year calibration cycle, the calibrator enables you to make highly precise measurements of CW and modulated signals.
The error analyses in this chapter assumes that the power meter is being maintained correctly and is within its valid
calibration period.
Measurement uncertainties are attributable to the instrument, calibrator, sensor, and impedance mismatch between the
sensor and the device under test (DUT). Individual independent contributions from each of these sources are com-
bined mathematically to quantify the upper error bound and probable error. The probable error is obtained by combin-
ing the linear (percent) sources on a root-sum-of-squares (RSS) basis. RSS uncertainty calculations also take into
account the statistical shape of the expected error distribution.
Note that uncertainty figures for individual components may be provided given in either percent or dB. The following
formulas may be used to convert between the two units:
U
%
= (10 (UdB/10) - 1)
0 100
and U
dB
= 10
0 Log
10
(1 + (U
%
/ 100))
Section 5.7.1 outlines all the parameters that contribute to the power measurement uncertainty followed by a discus-
sion on the method and calculations used to express the uncertainty.
Section 5.7.2 continues discussing each of the uncertainty terms in more detail while presenting some of their values.
Section 5.7.3 provides Power Measurement Uncertainty calculation examples for both CW and Peak Power sensors
with complete Uncertainty Budgets.