Two way Radio BJ-550 UHF Power Amplifier, Power Set Level 10-80W, 1.2-1.9 V. AM, SSB Modulation Mode


Two way Radio BJ-550 UHF Power Amplifier, Power Set Level 10-80W, 1.2-1.9 V. AM, SSB Modulation Mode


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UHF 400-470MHz Full Band FM/AM/SSB Walkie Talkie Power Amplifier 10W-80W Power Level Selectable VSWR Display 13.8V 15A Input




Mode Color Type Blink Function
Power measurement Green Bar-graph No Measurement output power, 10W increments
Power setting display Green Bar-graph Yes Indicates actual power limit (10,20……70,80Watt)
SWR measurement Green Dot No* Shows VSWR
Error indicator Red Dot(s) No Indicate error condition

*Blinks on under/over range

Push buttons function

Name Function
RX LNA Toggles operation of receiver pre-amplifier(LNA)
TX PA Toggles operation of transmit power amplifier
SSB ON Toggles SSB mode
SET POWER Displays/changes transmit power limit
SHOW SWR Enables SWR display

Turning amplifier on and off

Transmit power amplifier and receiver preamplifier functions are independent on each other . They can be toggled on/offby pressing respective pushbuttons : RX LNA and TX PA . When function is enabled , LED associated with pushbutton is lit .

Amplifier is completely off , when both LEDs are dark .

Changing power level

Transmit power amplifier is equipped with Automatic Level Control loop (ALC).Preset power is adjustable is 8 steps:10W, 20W 30W,40W,50W,60W,70W,80W.Firstpress of SET POWER button enters power setting mode. Multi-function display barblinks, showing preset power level. First press of SET POWER button, doesn’tchange the level, but displays actual setting.Subsequent       pressing of SET POWERbutton change power setting. Amplifier exits power setting mode ifSET POWERbutton is not pressed again within 2 seconds.

Automatic Level Control is of saturated nonlinear type, only suitable for FMmodulation. While using amplifier with AM/SSB modulations, set ALC threshold tomaximum power (50W), then adjust transceiver power to yield appropriate powerdisplayed on bar-graph. For AM modulation, carrier power should not exceed 10-15w,to accommodate modulation peaks withoutdistortion.

In case of SSB modulation, observe bar-graph which is ofPEP type, keeping 50WLED lit only occasionally.

Turning SSB mode on/off

The SSB ON button toggles SSB mode on/off, actual state indicated by associatedLED. When SSB mode is enabled, carrier sensing algorithm, time delays, powermeter bar behaviour are changed to address modulation properties. There is no

difference in power amplifier biasing itself, since this modern design is inherentlylinear, unlike elder bipolar transistor based designs.

Using external PTT input

The external PTT (“external keying”) mini jack socket is located on the rear panel. Itallows the TX mode to be enabled by shorting the center conductor of the plug to theouter conductor (to ground). First, enable the TX PA function, by pressing the TX PAbutton. The associated LED will light up. Upon the first shorting of the external PTT,the amplifier enters external PTT mode of operation. The associated LED will startblinking.

In external PTT mode, the amplifier no longer reacts to the RF input signal from thetransceiver. Instead, it goes into TX mode every time the external PTT signal hasbeen applied. Once the SSB mode is enabled, the TX/RX transition delays remainshort. Power meter operates in the PEP mode.

The amplifier remains in the external PTT mode, until the TX PA button is pressed orthe DC power is removed.

Measuring VSWR

This useful function allows to accurately measure amplifier load VSWR.To enableVSWR measurement, press SHOW SWRbutton while transmitting. This mode willpersist as long as amplifier is in transmit mode. Display returns to normal operation

(power measurement) after releasing transceiver PTT button.

Actual VSWR is represented as single”moving dot”. Lowest reading is 1.20, belowthis value respective LED starts blinking, indicating underrange. Highest reading is1.90, crossing 2.00 will cause respective LED blinking, indicating overrange.

Built in VSWR meter is of good quality, compensating for detector nonlinearities,what makes measurement result fairly independent on output power. It also offersexceptional directivity, with residual VSWR reading in order of 1.10.

Error Signalling

To signal error in amplifier operation, multi-function display bar LEDs change colorto red. Appearance of any error denies power amplifier transmit operation.

Error LED Meaning Amplifier reaction
High SWR Excessive VSWR (over 2.1) detected. Typically caused by

faulty antenna.

Deny transmitting, resume

after PTT release

OVER DRIVE Excessive input power(>7Watt) Deny transmitting, resume after PTT release
DC VOLTAGE DC supply voltage out of permissible range (10.5V to 14.8V) Deny transmitting, resume

after PTT release and voltage


HIGH TEMP Chassis temperature over 60℃ Deny transmitting, resume

after cooling down

PA FAIL Amplifier electrical failure Deny transmitting, resume

after PTT release

Specifications: Power amplifier
Parameter Min Typ. Max Remarks
Frequency range 400MHZ 470MHZ
Maximum output power 75W 80W 85W ALC limited
Input power range 0.7W 7W Between carrier detect and overdrive thresholds
Input power for full output 3W 5W Frequency dependent
Bypass power 50W
Harmonics suppression 63dBc
Modulation AM,FM,SSB
Circuit type Twin MOSFET, PUSH-PULL

Specification: Receiver preamplifier

In-band gain 13dB 15dB 15.5dB 400-470MHZ
Noise figure 2.4dB 3dB

Specification: General

DC Supply voltage 10.5V 12.6V 14.8V Operation at low end of range may not yield specified maximum power
Transmit supply current 12A 13A Transmitting at maximum power. Frequency dependent
Standby supply current 20mA All functions OFF
35mA TX功enable
80mA RX LNA enable
88mA TX PA & RX LNA enable
RF connector N-Type connector
Size 50H*125W*210L mm


Each Package Contains:

1× Power Amplifier 80U

1× Power Cable

1× RF Connection Cable

1× User Manual

Weight 1.5 kg
Dimensions 300 × 400 × 150 cm


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