Block Diagram Theory of Operation

Block Diagram 2

To speed up the operation during frequency changes, a Sum Loop pretune line is provided by the A26 Step Loop A assembly and drives the A25 Sum Loop assembly. This pretunes the VCO in the A25 Sum Loop assembly to allow it to lock more quickly as the A26 Step Loop A and A27 DAC/Upconverter assemblies change frequencies.

The diagnostics procedures check the A26 Step Loop A assembly at various frequencies but can only verify operation during static (non-hopped) operations. If the instrument meets its specifications during static operation but fails during frequency hopping, it may be that the A25 Sum Loop or A26 Step Loop A assemblies are slow to lock-up to the correct new frequency. The error might appear as a high phase or frequency error at the beginning of a new frequency hop, or the instrument may occasionally lose lock during a frequency hop. These might be symptoms of a mis-adjusted A25 Sum Loop or possibly a faulty A26 Step Loop A or A25 Sum Loop assembly.

A25 Sum Loop

This assembly contains the circuity to add together the CW signal from the A26 Step Loop A assembly and the modulated signal from the A27 DAC/Upconverter assembly. A pretune line is provided from the A26 Step Loop A assembly to speed up the ability of the A25 Sum Loop A assembly to phase lock. The output from this assembly is a 0.3 GMSK modulated signal at 500 to 1000 MHz, depending on the frequency that was selected.

The A25 Sum Loop assembly is adjusted to match the tuning characteristics of the A26 Step Loop A assembly. Whenever either of these two assemblies are changed, it is necessary to re-adjust the A25 Sum Loop assembly using the procedures in chapter 7.

The diagnostic program checks the A25 Sum Loop assembly at various frequencies but can only verify operation during static (non-hopped) operations. Measurements are made to determine if the A25 Sum Loop assembly can phase lock and that RF power is available on the output. If the instrument meets its specifications during static operation but fails during frequency hopping, refer to the previous discussion about the A26 Step Loop A assembly.

A13 Output

The main purpose of this assembly is to provide the ability to translate the RF signal from the A25 Sum Loop assembly to different frequency bands and to amplify the RF level. For frequencies between 500 MHz and 1000 MHz, the path through the A13 Output assembly is “straight through” and the RF frequency remains constant. A “divide by 2” is used to create output frequencies from 250 MHz to 500 MHz. For frequencies below 250 MHz, a heterodyne section is used to mix the frequencies down to the desired output frequency.

In addition to frequency translation and level correction, the A13 Output assembly provides AM modulation capabilities. The connections into and out of the A13 Output assembly are shown on Block Diagram 2.

The diagnostic procedures verify the tracking filters, ALC loop controls and, DAC values, and measure RF output power at various frequency and power settings.

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Agilent Technologies 8922 manual A25 Sum Loop, A13 Output

8922 specifications

Agilent Technologies 8922 is a versatile and robust mobile communication test set, designed to fulfill the demanding requirements of wireless device manufacturers and service providers. Primarily focused on mobile radio communications, the 8922 provides a comprehensive solution for testing a wide array of signaling standards and technologies, making it essential in the rapidly evolving telecommunications landscape.

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