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Graphical view of limits and specifications

As with other measurements, the actual limits depend on many factors, namely,

class, type, system and power level. Figure 13 gives example limits for EGSM900

MS and Normal BTS at high power.

Practical measurements

Spectrum due to modulation and wideband noise measurements are both difficult

and time consuming if made precisely as the ETSI and ANSI type approval

specifications require. It is normal to perform some subset of the defined

measurement set in most applications for time and/or cost reasons.

At wide offsets such as 600 kHz and above, these measurements require high

dynamic range—this has historically been expensive. They also require a large

amount of processing power if they are to be done rapidly. In some applications

the complete suite of spectrum due to modulation and wideband noise measure-

ments are only performed on a sample basis.

Historically, standard spectrum analyzers have been used, and when provided with

an appropriate gate signal this method works well. However, this time-consuming

technique requires a series of separate measurements and frequent re-tuning. The

VSA-series transmitter tester provides two techniques for overcoming this prob-

lem.

First, with a wide bandwidth sampler, it is possible to perform many of the close-in

measurements up to 600 kHz, using DSP techniques—essentially FFTs. This

means that several measurements can be performed on the same sample set,

which results in a significant speed improvement.

A further speed improvement can be achieved by measuring over a greater portion

of the burst. The standards define that these measurements should be performed

over the 50%–90% portion of the burst. However, for practical speed improvement,

it is quite reasonable to measure over 10%–90% portion of the burst.

960 962

Freq (MHz)

= 942.5923 925

0.5 dBc

Power

(dBc)

fc + 100 kHz

+ 200 kHz

+ 250 kHz

+ 400 kHz

+ 600 kHz

+ 1200 kHz

+ 1800 kHz

+ 6000 kHz

–80 dBc

Band edge + 2 MHz

–30 dBc

–33 dBc

–60 dBc

–70 dBc

–73 dBc

–75 dBc

–80 dBc

Example: E-GSM900, normal BTS, middle channel, high output power

Referenced to power in 30 kHz RBW

(approx 8 dB less than power in 300 kHz RBW)

RBW = 30 kHz RBW = 100 kHz

Channels:

B, M, T. Signal carrier

Hopping:

Off

RBW:

30 kHz and 100 kHz

VBW:

=RBW

Detection:

Gated over 50%–90% of burst

Zero span (≤ 1800 kHz offsets)

Average

Filter:

5-pole sync tuned

Notes:

For low O/P power levels

further conditions apply (limits

are less demanding).

Figure 13. Spectrum due to modulation and wideband noise, normal BTS, limits

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 35 36

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