User's Manual

PINEAPPLE TECHNOLOGY, INC.

VTX2KW-A Operating and Service Manual

Page 43

VIII — ADJUSTMENTS AND TUNING

The VTX2KWA is basically a broadband transmitter with a few frequency selective sub-assemblies which

comply with FCC Type Certiﬁcation requirements. A list of these sub-assemblies are listed below and fol-

lowed by general instructions where applicable:

A. MODULATOR Instructions for making adjustments to the modulator are included in the Manufac-

turer’s Instruction Manual

B. BPV2KW Band Pass ﬁlter comes adjusted to the channel as purchased. To change frequency would

require a tuning adjustment to the ﬁlter. To perform this adjustment it is necessary to use a NET-

WORK ANALYZER and a signal generator with necessary I/O Adaptors to connect to the ﬁlter. The

Technician performing this adjustment should be skilled in tuning Band Pass Filters. If the target

frequency is outside of the tuning range of the ﬁlter, it becomes necessary to purchase a new ﬁlter.

Replacement ﬁlters and service is available from Pineapple Technology Inc.

C. V600LDV2 POWER AMPLIFIER MODULE: The V600LDV2 has three areas where adjustments

may be necessary over time or in the event of a frequency change. These areas are:

1. Bias adjustments: The LDMOS FET devices used in these pallet ampliﬁers are set to 500ma/

device side or a total of 1 amp/device. This adjustment can be made on the bench by ﬁrst termi-

nating the input and output with 50 ohm terminations. Apply 31 volts DC to the PA using a power

supply that can provide a minimum of 15 amps. Note: a cooling fan will be necessary to cool the

ampliﬁer during this adjustment.

To adjust biases it is best to turn all the bias adjust resistors CCW or to minimum on the pallet

being adjusted. Using a clamp on DC AMP Meter connected to the DC Feed terminal located on

the DC ISOLATION AND CURRENT MONITOR BOARD measure the current levels. The ﬁrst

resistor is increased to 500ma indicated on the Amp meter. Repeat this adjustment for each addi-

tional resistor for reading of 1.0 A, 1.5 A, and 2.0 A. This will indicate that each device half is set

to 500 ma.

This concludes the bias adjustment procedure. This adjustment should be made at all time when

a device has to be replaced. Normal bias ranges from 1.5 amps to 2.3 amps per pallet as indi-

cated on the ADP500/1000. DO NOT USE THE ADP500/1000 CURRENT READINGS FOR

MAKING BIAS ADJUSTMENTS.

2. PA PALLET RF circuit tuning: These circuits are Broadband and Fixed tuned providing no

adjustments. Any turning at this level is performed by the factory.

3. GAIN & PHASE MATCHING: Each V600LDV2 must be gain and phase matched to each unit

in the system. This is accomplished by maintaining tight manufacturing tolerances on devices,

cables, and component selection. No adjustment are required at this level and should not be

attempted in the ﬁeld