User's Manual

Table Of Contents

EX7100 Technical Manual - Module Descriptions

7.7.3 Alignment

Module Re-tuning

The main Receiver module should not require any adjustment when being re-channelled.

The Receiver Front-End module Type 8018 requires adjustment of the receiver bandpass

filters.

Note: There are three variants of the Front-End module, one covering 138-148MHz, one

covering 147-162MHz, and the other 159-174MHz.

The front-end bandpass filter requires adjustment when the receiver frequency is being

changed by more than 250kHz from the filter’s previous centre frequency.

1. 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 0dBm and span of 4MHz/div.

3. Set the RF output of the analyser’s tracking generator level to -40dBm and feed it into

test socket SK101 on the Receiver Front-End module.

4. Using a suitable hex tuning tool, gradually adjust the Front-End bandpass filter, to

“walk” the filter response along, until it is centred on the desired receive frequency.

(The filter is made up of five tuneable inductors inside an aluminium block; access is

made through the five small holes in the block.) Tune the filter starting from the

centre inductor and working outwards. This procedure may need to be repeated a

number of times. Be careful not to bottom the cores at either end of travel as the

cores will break.

5. Remove the can lid from the Front-End. Adjust FL101 for maximum signal. Note that

FL101 consists of two filters.

6. Set the span of the spectrum analyser to 2MHz/div. Repeat the adjustment of the

controls above and also CV101, CV102 and CV103 for maximum gain and sharpest

response at the desired receive frequency. Check that the filter response is >34dB

down at ±5MHz from centre frequency.

7. Disconnect the analyser. Reconnect the Duplexer to SK101 and the Receiver Module

to SK102.

8. Set the new receive frequency from the front panel per Section 3.

9. Check that the VCO Loop Volts (TP401) measured on the receiver main board (or

from the front panel) is within the limits, 4 to 5 Volts. If necessary, reset the loop volts

to 5 volts by adjusting the VCO trimmer capacitor.