User's Manual

Table Of Contents

EX7100 Technical Manual - Module Descriptions

7.8.3 Alignment

Re-tuning Of the Receiver Module

If the frequency of the Receiver module is to be changed by more than ±2.5 MHz from its

tuned frequency, the following checks or adjustments are required:

Checking the VCO Loop Voltage

1. Set the new Receive frequency via the front panel as per Section 3.

2. Remove the bottom cover and refer to Figure 7.25 below to identify the location of

the Loop Volts output feed-through capacitor in the local oscillator module. Check

with a digital multi-meter (DMM) that the VCO Loop Volts measurement is within the

range of 3 to 4 Volts DC.

If necessary, reset this by adjusting VCO trimmer capacitor CV101 as indicated in

Figure 7.25 below. (It will be necessary to remove the screw in the aluminium block

to access the trimmer. Always replace this screw after adjustment).

Figure 7.25: Location of Loop Volts adjustment CV101

Adjustment of the receiver bandpass filter

1. With the bottom cover removed, set terminal to ‘On-demand’ mode to ensure the

transmitter is turned off.

2. Remove the bottom cover as described in Section 6.1; disconnect the coaxes from

SK101 and SK102 on the Receiver Front-End module. Feed the output of SK102 to

the RF input of a scalar network analyser (or spectrum analyser with tracking

generator), with reference amplitude of -10dBm and span of 4MHz/div.

3. Set the RF output of the analyser’s tracking generator level to -50dBm and feed it into

socket SK101 on the Receiver Front-End module.

4. The filter is made up of a dual tuneable helical package (FL101) and triple tuneable

helical packages (FL102 and FL103) all within a tin can mounted on the PCB. Using

a suitable tuning tool, adjust FL102 and FL103 to “walk” the filter response along,

until it is centred on the desired receive frequency. Then tune FL101 for maximum

gain and sharpest response at the desired frequency.