Tuning instructions for AP 2000 UHF 1. Tuning of the synthesizer circuit A. synthesizer oscillator Connect a high input resistance DC-voltmeter to TP 1 on print board B 56. By tuning coils L1 and L2 to max., a reading of approx. 1,7 V should be obtained. The coil L3 is later used for frequency adjustment. B. Phase locked loop If the set contains more than one channel, turn the channel selector to a channel with frequency in the middle of the used band. Check the channel code with a voltmeter on points 1, 2, ..........64, 128 on print board B 17. Computation of the channel code is contained in the technical description of the synthesizer circuit. Note that there are three types of VCO's corresponding to the following Rx-frequencies 406-432 MHz,432-450.NHz,450-47Q MHz check that the right type is used for the desired fre- quency range. The marking is noted on the VCQ-diagram. Set the trimmers C24, C30 and C35 to the center position and then connect a counter to point 5 (coaxcable). The VCO should now be set to about the right frequency (with C4). Connect a DC-voltmeter to TP 1 and tune C 24 to maxi- mum reading ( about 1 VDC ). Move the voltmeter to point 2 on the VCO print board and an oscilloscope ( sensitivity 1 V/div.) to testpoint TP 1 on the logic print ( print board B 17 ) Adjust the VCO trimmer until the loop goes in lock. The loop is in lock when a stable 25 kHz ripple sawtooth is appearing on the scope, and the voltage on the voltmeter increases while turning the VCO trimmer clockwise. Adjust the VCO so that the loop voltage is 3 V. This loop voltage corresponds to mm. 25 (20) kHz ripple on TP 1. Now when the loop is in lock a slight tuning of C 24 should be done to control that the voltage on TP 1 still is maximum. For multichannel sets, turn the channel selector to the lowest and highest frequency and check that the loop still goes in lock. Considering a set with the max. possible band- width 2 MHz, the loop voltage shall lie between .2 and 4 V going from the lowest channel to the highest in such a man- ner that increasing voltage corresponds to increasing fre- quency. C. Rx-freguency. Select the mid-frequency channel and connect a 500 MHz coun- ter to the VCO-output point 5. The reading will be Rx-fre- quency + 21,4 MHz and for fine tuning of the Rx-frequency, use C 39 on synthesizer mixer print board B 56. ------------------------------- 2. Tuning of the receiver. A. 21,4 MHz and 455 kHz IF ( print board B0l ). Connect a 21,4 MHz sweep generator (a lo,7 MHz sweep gene- rator normally contains sufficient second harmonics to be used on 21,4 MHz to point TP 2 on the RF and mixer print board B 48 and the (DC) probe on point TP 1 on the IF print board B 01. Adjust L 6 (print B 48) and L 1 (print B 01) for minimum ripple. L 2 is tuned to max. amplitude while L 3 is tuned to best possible symmetry. Use the lowest possible in- put level to prevent limiting in the mixer. Connect the pro- be to the AF output from the detector (a suitable point is pin 1 on the ampl. print B 09) and adjust L 4 in the IF to max. discriminator slope and the best linearity. B. RF amplifier and mixer (print board B 48) With the voltmeter on TP 1 (print board B 48) the capaci- tors B 43 - C 35, B 48 - C 10 and C 11 are adjusted to max. deflection (approx. 2 V DC). With the signal generator con- nected to the receiver input, C 20, L1, L2, L3 and L4 are now tuned to give optimum sensitivity. C. AF-amplifier, squelch and key circuit (print board B 09). Adjust the output level for the handset earpiece to 60 mV with potmeter R 31. (3,5 kHz dev., 1 kHz modulation ).