Category Archives: HF home made transceiver
RX MIXER
RX MIXER standard is ADE-1 diode ring mixer. Here described is optional high dynamic range H-mode mixer.
The schematic and original H-mode mixer concept has been designed by Colin Horrabin G3SBI and further developed by Martein Bakker PA3AKE.
PCB component side
RF MIXER
RF MIXER board does all RX/TX signals on IF and operation frequencies.
On receive the signal comes on CX3 coaxial connector, then passes (or not) through input attenuator R10,R13,R14, then via switches come to BPF board. IF TRAP circuitry consists of L1, C7, C38. Then signal passes through U3 (ERA6SM) RX preamplifier (operator switchable). RX MIXER is on additional subboard and sits over RF MIXER board. 9MHz diplexer follows and then IF amplifier – U12 (ERA6SM). After some switching and attenuation signal comes to the first crystal filter – 2.7kHz then to CX6 coaxial connector and IF/AF board.
On transmit the signal from SSB GEN board through CX7 connector passes through crystal filter and after TX/RX switch to a pin diode D1 attenuator. It is driven by ALC circuitry performed by U16 and T4.
U11 is TX mixer which is fine balanced by R62 and impedance matched by L10,L18 wide band transformers. Output mixed signals are further filtered by BPF board and amplified by U3 and U9. Output attenuator R4,R5,R6 is following then via CX4 signal goes to linear amplifier PA55W board.
Component side PCB
Component side values
IF/AF unit
This unit includes the following:
- intermediate frequency IF amplification – MC1350
- optional crystal filter (4 pole variable crystal Johnson type filter)
- RX product detector – SA612
- AF preamplifier – MC33079DG
- RX MUTE and sidetone input circuitry
- AF final amplifier – SA58631
- Fast IF 134kHz Automatic Gain Control scheme – SA612,MC33079DG
- Optional AF filter board
PCB component side
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
PCB component side
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.
PCB component side (bottom)
PCB top
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 NXP PD85004, driver in push-pull configuration (2xPD85004) 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, inductors L3, L7, L8, L9, swamp 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 MPSA13 (T11) which is in good contact with final transistor heatsink in order to perform needed temperature compensation.
In order to minimize voltage drop power supply input and current sensor are also on this board – C58,C59, D1, ZXCT1081E5
PCB component side:
PCB component side (references)
LOW PASS FILTER BLOCK 3.5-30MHz
This board consist of the following modules:
5 sub PCB with low pass filters chebyshev type for all HF bands. There is place where to be nested one optional LPF subboard (for 160m)
High voltage (210V) scheme (voltage tripler)
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” concept, there are no mechanical relays in the circuit. After long searching for suitable power switching component I found VISHAY high voltage rectifier diode S07J (S07M) 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.
PCB layout
Component side (bottom) values:
Component side (bottom) reference names
Top – connector side:
Picture of the ready board with filter subboards on it:
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
