User's Manual

TB8100 Calibration Kit User’s Manual Carrier Frequency Offset Adjustment (Older Reciters) 21
Carrier Frequency Offset Adjustment
(Older Reciters)
The carrier frequency is derived from a reference frequency generated by the
reciter’s TCXO (temperature compensated crystal oscillator). The reference
frequency can drift over time, causing an offset to the carrier frequency. When
you connect to a reciter with hardware version 00.02 or earlier, the Calibration
Kit provides the following procedure that enables you to adjust the carrier
frequency and remove the offset.
Reciters are delivered from the factory with a 0 offset. Carry out the following
procedure if you suspect that the base station is transmitting off-frequency.
(Off-frequency is defined as being outside the range of -1 to +1 ppm.) It is a
good idea to calibrate the TCXO every few years. Exactly how often you do
this will depend on the harshness of the conditions in which the base station is
operating.
Ideally, you should calibrate the TCXO at a room temperature of 25 +/- 5
degrees Celsius. Complete the calibration as quickly as possible since extended
transmission times increase temperature, which makes the calibration less
accurate.
Equipment ■ 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
To adjust the carrier frequency
1. Ensure that the Calibration Kit PC is connected to the reciter (see
“Connecting to a Reciter via the Control Panel” on page 7).
2. Select the Reciter Calibration tab, and double-click Carrier Freq Offset
Adjustment. The Carrier Freq Offset Adjustment Wizard appears.
3. Attach an appropriate load and frequency counter (or a test set) to the exciter
or PA output, and then click Next. (This instructs the setup to transmit.)
4. Using the slider, adjust the TCXO pot until the actual frequency is exactly
the same as the selected frequency value. Click Coarse to roughly (and
quickly) adjust the output frequency, and then click Fine to fine-tune it.
When you have finished, click Finish. (The setup now stops transmitting.)
When you have finished, the icon on the Reciter Calibration tab indicates
that this task is complete.
1
2
3
4
1 Reciter 3 RF Attenuator pad (optional)
2 PA (optional) 4 Frequency counter