User's Manual

22 Carrier Frequency Offset Adjustment (Newer Reciters) © Tait Electronics Limited 2005
Carrier Frequency Offset Adjustment
(Newer Reciters)
The TCXO (temperature compensated crystal oscillator) provides a reference
frequency from which all other RF frequencies are derived. Reciters with
hardware version 00.03 and above have a voltage-controlled TCXO, with a pot
for adjusting the reference frequency to remove any carrier frequency offset.
The Carrier Freq Offset Adjustment wizard provides assistance with this
procedure.
Tait recommends that the reciter TCXO is recalibrated after 3 months service
and that annual checks are made thereafter in order to compensate for
frequency drift. Recalibration ensures that the SDB (signal displacement
bandwidth) is within 250 Hz.
The TCXO has a frequency stability of 0.5ppm (parts per million)
corresponding to 250Hz at a carrier frequency of 500MHz. Tait recommends
that the TCXO is calibrated to within 0.1ppm.
Equipment ■ Torx 10 screwdriver (to remove the reciter cover)
■ Tuning tool
■ Frequency counter
■ RF attenuator (only required if you are using a PA)
Important: The accuracy of the calibrated TCXO frequency is only
as good as the accuracy of the frequency counter.
Setup
You need direct access to the TCXO circuitry on the reciter RF board. This
involves removing the reciter RF cover.
Important: The reciter contains devices that are susceptible to
damage from static charges. You must handle these devices
according to the recommended ESD precautions.
To adjust the carrier frequency
1. Remove the reciter from the subrack.
2. Remove the M3 Torx screws securing the reciter RF cover to the heatsink
and to the front and rear panels. (The RF side of the reciter can be identified
by the two BNC connectors on that side of the reciter’s rear.) Lift off the
RF cover.
3. Connect the Calibration Kit to the reciter (see “Connecting to a Reciter
Outside the Subrack” on page 5).
4. Select the Reciter Calibration tab, and double-click Carrier Freq Offset
Adjustment. The Carrier Freq Offset Adjustment wizard appears.
1
2
3
4
1 Reciter 3 RF Attenuator pad (optional)
2 PA (optional) 4 Frequency counter