Category Archives: Modules

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



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:



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.


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.



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.

img_3916  img_3917

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


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