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- Written by: Jari Ojala
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Radio amateur station OH8LQ has four rotating masts, three 42 m high and one 30 m high. The masts can be used together or separately at the same time.
Mast 1
5 el 15 m yagi stack
4 el 10 m yagi
5 el 20 m yagi
160 m dipole
Mast 2
80 dipole
Mast 3
16 o 16 2 m yagi
6 el 6 m yagi
5 o 5 10 m yagi
5 o 5 15 m yagi
5 o 5 20 m yagi
2 o 2 40 m shorty yagi
Mast 4
2 o 2 40 m shorty yagi
160 m guy wire slopers
80 m 4 SQ system
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- Written by: Jari Ojala
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3 kW linear amplifier with four ART1K6 LDMOS fets
The purpose of the project is to build a linear LDMOS amplifier for HF bands 160-10 m. The amplifier must withstand a continuous power of 1.5 kw. Because of reliability, I have ended up using several separate amplifier modules. Implemented with four modules, only less than 400 W of power is taken from one module. It is possible to get a power of more than 1 kw from each module, so the amplifier will not be overloaded in any situation.
The amp does not have WARC bands, maybe I will add them in the future?
Circuit boards of the RF part
Drilling holes in copper plate
Fets soldered in a cooling plate
Two RF modules with a heatsink
Each module is tested separately
Heat sink datasheet
Four modules with cooling plates and combiner and divider
RF amplifier unit and power switches
Control board
UI at rear panel
Simulation vs. real world
Diplexer looks good!
Why diplexer? The diplexer directs the desired signal to the antenna, but harmonics to the dummy load (the so called harmonic load). In the LDMOS amplifier (push-pull), the third harmonic can be only 10-12 dB weaker than the useful signal, This means if you drive 1.5 kW antenna, and 150 W go to dummy load!
20 m Diplexer
More diplexers....
Testing a diplexer with network analyzer
Output without diplexer
With diplexer.... 3rd harmonic -50 dB@ 2 kW...
Dummy load spectrum
6-band HF diplexer
Test at 1,5 kW per band
160 m
80m
40 m without filter and with filter
20 m
15 m
10 m
Need more attenuation for 3rd harmonics at low band.
WaveNode SWR sensor added inside of amplifier
Installed Diplexers
Thermal cam tests
Diplexer and harmonic load
Harmonic load
Effiency
9 kW 50 V three-phase power supply ESP120
Power connectors
Power switch
Arduino controller on board
TFT-touchscreen UI
TRX-relay board
Almost ready to use
Added handles, weights approx. 40 kg
The amplifier was in real operation for the first time at the WPX CW 2023 contest. No problems found.
Three phase power supply
Three-phase power supply from three Huawei R4850G2 power supplies connected in parallel. Maximum power about 9 kW.Why three power sources when one or two would be enough? In three phase system, loading one phase would cause a so-called bias load to the power grid.
DC output connectors and D15 connector CAN bus for control
Linear + power :)
TO BE CONTINUE....