JUMA TX136 and TX500
Frequency Fine Tuning instruction Last update 2009-12-05
The frequency accuracy of JUMA TX136 and TX500
is based on the reference crystal oscillator located on the main board (20 MHz in TX136 and 6 MHz in
TX500). The frequency fine tuning is not necessarily needed
because the typical actual frequency accuracy is better that ±5 Hz.
Note that the reference oscillator deviation impact is very small because the TX frequency
deviation is a fraction of the actual frequency and reference frequency.
E.g 136kHz/20MHz = 0.0068 which means that a 100 Hz deviation in the oscillator
corresponds 0.68 Hz deviation on the actual 136 kHz frequency.
The frequency fine tuning is done by software which calculates the frequency
correction for the DDS circuit. The correction is based on the actual measured
frequency of the reference crystal oscillator which is entered to the TX
in the Service mode.
1. Warm up the TX by keeping it on about half an our
2. Measure the reference oscillator frequency on main board at test point
(TP) with an accurate frequency counter
3. Go to the Service mode by switching on the TX with a very long push of
4. Set reference oscillator according to the counter reading with UP/DOWN
5. Push OPER button to save the setting