User's Manual

Table Of Contents

EX7100 Technical Manual - Module Descriptions

7.4.3 Alignment

Re-tuning Of the Transmitter Module

If the frequency of the Transmitter 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 Transmit frequency via the front panel as per Section 3.

2. Remove the bottom cover and refer to Figure 7.12 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 7.12 below. (It will be necessary to remove the screw in the aluminium block

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

Figure 7.12: Location of Loop Volts adjustment CV101

Adjustment of the transmitter bandpass filter

1. With the bottom cover removed, disconnect PL103 (to PA Module) and remove the

“Tx RF out” SMB lead from socket PL107. Connect the RF input of a Spectrum

Analyser with Tracking Generator or scalar network analyser to socket PL107.

2. Set the analyser’s tracking generator output to –10dBm. Feed the tracking generator

output into SK303.

3. Apply power to the terminal. Turn the Transmitter off by setting the terminal’s

operating mode to ‘On-Demand’. (Refer to Section 3 for details).

4. Adjust the two helicals within the output filter to achieve a suitable flat passband at

the desired frequency. The passband should be approximately 5.0 MHz wide and flat

within +/- 2.0 dB across that band.

Note: The Duplexer module must also be adjusted to suit the new centre frequency

(refer to Section 7.10.3 for tuning details). Failure to adjust the Duplexer module at

this point may result in damage to the PA module