Category Archives: HF home made transceiver
IF/AF unit
This unit includes the following:
- intermediate frequency IF amplification – MC1350
- optional crystal filter
- RX product detector – SA612
- AF preamplifier – LM837
- RX MUTE and sidetone input circuitry
- AF final amplifier – SA58631
- Fast IF 134kHz Automatic Gain Control scheme – SA612,LM837
- Optional AF filter board
MIC amplifier, DSB, CW modulator unit – SSBGEN
In order to form DSB/CW modulation on TX, a SSBGEN board is used.
It consists of the following parts:
- Microphone preamplifier and TX audio amplifier – TL082
- Switched input: LINE IN or MIC (MUX 4053)
- DSB modulator – SA612
- CW drive level and form circuit – ½ of MCP4631 dual digi pot
- SSB drive level (mic level) – ½ of MCP4631 dual digi pot
BAND PASS FILTERS
Six band pass filters were built to cover 10-80m bands on RX. Schematic utilizes Skywork solutions AS169 PHEMT GaAs SPDT switches, used in modern wirelless equipments. In order to perform individually “fine tune” a variable coil inductors are used. The module fully meets project CLICKLESS concept as there aren’t any mechanical switching components. MCP23008 serial controlled I/O expander is used to engage needed filter. The board has a provision for two optional filters.
The board
Filters spectrum analyzer plots:
Custom made control knobs
Three types control knobs are used in this project:
MAIN dial knob – for VFO frequency tune
ENCODER knobs – various functions
DUAL CONCENTRIC knobs – AF/RF gain control
FACE PANEL MOLD PLASTICS OR ALUMINUM MACHINED
To bring more professional and stylish appearance we decided to design custom front panel especially for this project.
Next question was: Injection plastic mold or machined aluminum
First, we made one prototype of machined aluminum in order to test if everything in design is right on the place
Then we start building (ordered) our face panel plastic injection mould. It is known that this was pain process and it took almost 3 months to build it .. after three revisions here it is now ready to “SHOOT” our plastic panels
We made some samples of all three materials available: Glass filled polyamide (black colored), Glass filled polypropylene (grey colored), ABS plastics (white colored)
MOSFET LINEAR POWER AMPLIFIER 50 WATTS
Final 50W amplifier is designed using 4pcs. QFET N-MOS FAIRCHILD FQP13N10 transistor. The module consist of three stages: predriver with MITSUBISHI RD00HVS1, driver in push-pull configuration (2xRD06HVF1) and final unit utilizing 4pcs. (2 by 2 push-pull in parallel) FQP13N10 transistors in easy to mount TO-220 case.
Main reason we chose such a general purpose switching MOSFET’s is that they are cheap and is in current production so can be delivered anytime from a trusty supplier.
Input matching and especially Ciss (~400pF) compensation is performed by input transformer TR2, ferrite beads B1-B4 which are strung over leaded ballast resistors R7,R16,R26,R39. This group of components increases input drive signal for frequencies over 10MHz and swamps input energy for low frequencies where the overall gain is more than sufficient.
Bias voltage for all transistors is provided by voltage regulator 78L05 (U1) and BC327-40 (T10) which is in good contact with final transistor heatsink in order to perform needed temperature compensation.
LOW PASS FILTER BLOCK 3.5-30MHz
This board consist of the following modules:
5 chebyshev type low pass filters to cover all bands
High voltage (210V) scheme
Antenna RX/TX switching
SWR directional coupler and measurement of Vfwd/Vref
Optional LPF (160m) connector
This module ensures clear harmonic output of the linear amplifier, also fits the components for antenna RX/TX switching. Following the “click-less” conception, there are no mechanical relays in the circuit. After long searching for suitable power switching component I found VISHAY high voltage rectifier diode S07J that met all the requirements for reverse voltage capacity, reverse recovery time, forward current and reverse voltage. So S07J were used in the project to ensure good switching of TX power to the antenna via proper LPF and also reliable isolation between each other low pass filters not selected for this band portion.
High voltage generated from input signal polarizes unused switching diodes in reverse direction ceasing the chance for signal leak. Same votage is used in RX/TX switch for completely disconnecting receiver front end on transmit.
Block interconnection diagram
My homebrew HF transceiver consist of the following printed circuit boards:
- Front Panel assembly – plastic front panel, control knobs, FSTN display and keyboards, control board
- Mother board – fits all connectors on the rear panel, power supply, I/O controller (second CPU) intended to be a chassis for all RF boards and options, as long as “cable harness” and board interconnections.
- IF/AF Board – IF and audio circuitry, IF AGC 134kHz. Second narrow band crystal filter (option). AF filter (option)
- RF mixer board – RX/TX switching, receiver front end, first RX mixer, TX mixer, first roofing crystal filter, ALC circuit. Noise blanker (option)
- Band pass filters – Front end filters 160-10m (160m option)
- SSB GEN board – forms both CW and SSB signals, microphone amplifier, compressor unit (option)
- LO board – local oscillators, side tone and beep tone oscillator. First oscillator and BFO oscillator.
- Compressor unit (option)
- Automatic antenna tuner (option).
- Transverter/RX antenna board (option).
- Power amplifier assembly – consist of two boards PA50W and LPF nested directly onto the rear panel
Crystal filter 9MHz 2.7kHz
One of the most important modules in the home made HF transceiver project is the crystal filter. It is made of individual quartz crystals with matched parameters – Fser. (+/- 15Hz), Lm and Q factor > 100 000. A large quantity of 9MHz oscillator crystals were purchased to extract only few to fit those requirements. Three type of quartz filters are used in this project – main (roofing) filter, narrow filter for SSB or CW modes and noise filter. All the filters are internally impedance matched to 50 ohm input/output circuitry and individually aligned.
Here is information about first – wide 2.7kHz SSB filter:
Filter type Chebyshev 8 pole
Center frequency 9MHz
Bandwith at -6db 2.7kHz
shape factor -6/-60db 1.75
IN/OUT impedance 50ohm
Band pass ripple <1db
Stop band attenuation >80db
VNA plot
Circuit diagram. Chebyshev 8 pole ladder type crystal filter
Custom multicolor backlit FSTN LCD for HF QRP transceiver project
In order to fulfill all the requirements to show different modes and parameters we decided to make our own liquid crystal display.
It is designed and built on the well proved – FSTN technology with high visibility and contrast.
Technical data:
LCD type FSTN
Mode positive
Poarizer type transflective
View direction 12h
Connect type pin
Glass thickness 1.1mm
Working Voltage 3/5V
Multiplex level 32/5
Operating temp 0 – 50C
Storage temp
Content Digits/Symbols
Measures 114.3 x 27.94mm
num of symbols 149
backlight type LED multicolor
It was firstly designed with 5 multiplex lines but soon after receiving first samples it turned out that this is not suitable as there is no driver chips on the market with 5 multiplex lines so we redesign the LCD with 40/4 so the most common Phillips chip can drive it.
