8. CALIBRATION PROCEDURE

 

8.1 AUDIO

 

All adjustments are located on the control C/B

 

a) Select INT 1kHz and monitor the audio modulation  output on a true r.m.s. voltmeter., Adjust P306 (1kHz LEVEL) for a reading of 1.00V r.m.s.

 

Select 0.00% AM and monitor pin 1 of U305 with a DVM. Adjust P301 (DAC

OFFSET) for a reading of O.OOmV.

 

Monitor pin 7 of U307 with the DVM. Select RF OFF and adjust P304 (DAC OFFSET) for a reading of -10.0mV0.5mV.

 

Select SYNTH RATE at 1.00kHz and 99.9% AM.       Adjust P201 (SYNTH LEVEL) for an audio modulation level reading of 1.00V r.m.s.

 

b) Select EXT MOD and feed in a 1.00V r.m.s. 1kHz sine wave to the modulation input BNC. Set the front panel modulation level control full clockwise.

 

Monitor pin 14 of U404 with the DVM.  Adjust P405 (DETECTOR CAL) for a reading of 1.10V + 0.05V. Remove the external signal and adjust P406 (DETECTOR OFFSET) for O.OOV at pin 7 of U403.

 

Re-connect the external signal and adjust P407 (METER CAL) for FSD on the front panel meter.

 

c) Connect the INT 1kHz audio modulation signal to the SINAD input.

 

Adjust P402 (NOTCH ADJ) for minimum 1kHz signal at test point X401, typically 40mV pk-pk.

 

Remove the SINAD input and adjust P404 (SINAD OFFSET)for O.OOmV at pin 6 of

U407.

 

Feed in a standard 25% distorted 1kHz signal to the SINAD input.

 

Adjust P403 (SINAD CAL) for a front panel meter reading of 12dB. Re-check

P404 adjustment as above.

 

d) Connect a +12V d.c. source (+24V for option) to the power supply and monitor the source voltage with a DVM.

 

With +12.0V input, adjust P401 (BATTERY  CAL) so the front panel battery level indication is on the red/black marker.

 

8.2 SYNTHESIZER

 

a) Select 1GHz and monitor the RF output on a frequency counter referenced from a frequency standard.

 

Adjust P101 (FREQ TUNE HS1) for a reading of 1GHz + 100Hz. Fine tune the frequency using the back panel control.

b) Monitor the FM loop tuning voltage on socket X301 with a DVM.

 

Select 512.0MHz and adjust the core of L301 for reading of -1.0V +0.2V on the DVM.

 

8.3 SPECTRAL PURITY

 

a) Select 512MHz and monitor the RF output on a spectrum analyser, scan width

1MHz per div.

 

Adjust P401 (OFFSET ADJUST} located in section HS4 on the synthesizer C/B

for minimum amplitude of the 1.25MHz reference sidebands, typically -65dBc.

 

b) Select 256MHz and +7dBm. Monitor pin 3 of U4 on the range divider with a

DVM.

 

Adjust P2 (FILTER TUNE) for a reading of 1.0V +0.1V. Check the harmonic content is < -25dBc.

8.4 RF LEVEL CALIBRATION

 

a) Select 100MHz and +13.0dBm.  Monitor the RF output on a power meter. Adjust

P303 (RF LEVEL CAL) on the control C/8 for a reading of +13.0dBm.

 

Select -2.0dBm and adjust P2 (DETECTOR BIAS) on the output amplifier C/8 for a reading of -2.0d8m.               Re-check the +13.0dBm setting.

 

b) Select 10.0MHz and +13.0d8m.              Adjust P300 (IF LEVEL) on the range divider

C/B for a reading of +13.0dBm.

 

8.5 AM CALIBRATION

 

a) Allow the unit to warm up for 30 minutes before making adjustments.

 

Select lOOMHz, +6.9dBm and 80% AM INT 1kHz. Monitor the RF output on a mod analyser.

 

Adjust P302 (AM CAL) on the control C/8 for a reading of 80.0%.

 

b) Select -2.9dBm and adjust P1 (AF SHAPER) on the output amplifier C/B for minimum modulation distortion, typically 1%.

 

Check the difference between 80% AM at +6.9dBm and -2.9dBm is less' than 1.0% AM.  If not, slightly re-adjust P2 (DETECTOR BIAS) and re-check the RF level calibration.

 

8.6 FM CALIBRATION

 

a) Select INT 1kHz, 99.9kHz FM and monitor pin 1 of U307 (on the control C/B)

with a true r.m.s. voltmeter.

 

Adjust P305 (FM CAL) for a reading of 1.00V r.m.s.

 

Monitor pin 1 of U209 on the synthesizer C/B with a DVM.              Select MOD OFF and note the d.c. offset.

 

Deselect MOD OFF and adjust P202 (OFFSET ADJUST HS2) for the same d.c. offset as above.

 

b) Select lOOMH, OdBm, INT 1kHz, 99.9kHz deviation.

 

Monitor the RF output on a mod analyser.              Adjust P201 (FM CAL, HS2)

for a reading of 99.9kHz.

 

Change the deviation setting to 5.0kHz and adjust P203 (10kHz ADJUST HS2)

for a mod analyser reading of 5.0kHz.