In PA Unit can be used MOSFETs: SD2933, SD2943, SD4933, VRF2933 . With up to 900-1400W PEP output power.
Unlike previous versions PA Unit for DN-600, this version have additional stabilizing BIAS integrated, increased transformers size. Changed diagram and PCB topology.
With those changes, possible to obtain up to 1400W on all bands 1,5-35MHz.
PA Unit previous version, description and photo, you can find on author website => www.qsl.net/ut2fw
- Model: PA Unit 4x VRF2933 Rev. 2015
- Frequency range: 1.5-30MHz
- RF power output: 1200W typical, 1300W max.
- Modes Supported: FM, CW, SSB and others.
- RF power input: 16-18W typical, 20W max.
- Supply: 50-54VDC / 32-35A
- Board dimensions: 186 x 135 mm
In the KIT you get a Board PA Unit 4x VRF2933 (transistors included) + copper plate. Not included heat sink.
The circuit uses dual feedback system for better linearity. The main emphasis in the scheme - is an addition to improve reliability for PA.
PA input is protected by resistor attenuator. Also, АТТ is optimizing input for input VSWR. Elements are protected circuit for РА if input power is too high.
Trimmer you can adjust protection drop value (configured to 20W - R10).
Protection scheme is with the "sticky" status, i.e. transistor key state is holding until you will connect ESC contact with the ground or OFF/ON the main +12V voltage for the protection board.
The temperature control is separated for BIAS and for fans from two thermistors. BIAS - trimmer R28, fans - trimmer R72.
Fans turns changing smoothly in dependence on temperature. In TX mode - fans is turning on full turns. For this PA - has been used three cooling fans.
The fans is turned on simultaneously.
Protection against an overheat is established on 50-70 degrees Celsius of heat sink (configured to 60 degrees - R75).
BIAS voltage are adjusted for each MOSFET (R24, R25, R26, R27) separately and stabilized by, in this case, can by in range +12-15V.
LED-IN, LED-FAN, ТХ indicators are on PA front panel.
ALC negative voltage towards - trimmer R67.
The amplifier runs of +50V and with 1200W. With +52-54V - the power increased up to 10-15%. With 45-48V – the power decreased up to 5-10%.
For board control, does not necessary external voltage +TX. To control output switching, just short the ground pin and pedal pin.
PA Unit schematic in a qualitative form will be included on CD.
The power measurement was measured with following set (the set photo is located below).
Heat sink + Copper plate + PA Unit + LPF600.
Power unit + 50V RSP-1500-48.
In the photo below you see a PA Unit 4x VRF2933 mounted on a heat sink, which is used in the amplifier DN-600.
The area of the heat sink for DN-600 is insufficient for power 1200W.
For 1200W apply heat sink with dimensions not less 200 x 200mm.