Operating instructions

RF Technology PA501 Page 9

3 Field Alignment Procedures 3.1 Output Power Level

3 Field Alignment Procedures (Rev 05/9151)

Section 3.1 below describes how to adjust the PA501 amplifier for a particular output

power level. Section 3.2 broadly describes how to align the PA501 matching circuits.

This second procedure should not be necessary except after repair of a damaged unit,

and requires specialised equipment. It should not be undertaken without appropriate

tools and equipment.

3.1 Output Power Level

1. Set the unit up on a bench with the standard test equipment listed in table 2.

2. Set VR136 and VR137 both fully counter-clockwise.

3. Set the exciter to the desired operating frequency.

4. Adjust VR136 to set the output power on the meter to the level at which you want

the RFO LED to indicate (allowing for load attenuation). Note that the meter should

be calibrated to read the power at the connector of the power amplifier, not at the

end of any cables or attenuators.

5. Adjust VR137 until the RFO LED just goes out.

6. Adjust VR136 for the desired output power.

3.2 Tuning Procedure

Adjustment of the matching circuits is carried out with the aim of:

• ensuring that the specified power of 100 Watts is available

• balancing the load reasonably equally between the power transistors, and

• obtaining acceptable efficiency in the power transistors.

Note that the factory alignment procedure is complicated, but allows a given unit to

operate across a full 450-512MHz band, without further adjustment. Alignment without

appropriate equipment can leave the amplifier unstable or otherwise unable to meet

specification.

The procedure calls for detection of the output power while sweeping the test frequency,

preferably by means of a calibrated network analyser or spectrum analyser. If this is not

possible, a rough approximation may be possible by observing the output of the unit’s

own ALC detector circuit with a swept stimulus.

____________________

At some frequencies a continuous power level of 120W is possible.