JUMA TX136 and TX500 Frequency Fine Tuning instruction   Last update 2009-12-05 OH7SV

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.

The instructions
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 PWR button.
4. Set reference oscillator according to the counter reading with UP/DOWN buttons
5. Push OPER button to save the setting