Receiver
schematic:|
Page last updated: 12/09/2012 |
Single band HF SSB / CW super heterodyne receiver with AGC
Detailed here within is a simple crystal controlled receiver originally developed to operate on a single fixed frequency to monitor QRSS transmissions on the 40m amateur band, a little more sophisticated than the first two receivers detailed as AGC is employed with this design and again can be easily adapted to operate on any of the HF amateur bands by simply altering key component values.
Design concept:
The design concepts primary goals were as follows:
Small and compact design.
Simple, easy to set up and easy to replicate design.
Using easy to source readily available, economic components.
Good performance on today's crowded HF amateur bands.
Receiver description a single conversion super heterodyne reeiver.
The RF front end section comprising TR1,TR2,C31,C32, & C33 forming a three element Pi band pass filter impedance matched to both the antenna and first mixer IC2 (NE612). Although there is no RF pre-amplifier, the mixer IC2 does provide around 8db conversion of gain.
The receiver operating frequency is set by frequency of crystal Q7 (FQ7 = Frx + IF or FQ7 = Frx - IF). My receivers operating frequency is set to 7.0008MHz in order to monitor QRSS activity on the 40m amateur band, therefore (FQ7 = 7.0008 + 8.0000) 15.0008MHz. In reality the crystal used was 15MHz fine tuned to the correct frequency with its padding capacitor C36. Although it could be easily modified to cover a small section of a single amateur band i.e. the CW section, or for that matter part of the SSB section whilst still maintaining good frequency stability by adopting more aggressive VXO tuning of the crystal local oscillator.
The IF section comprising Q1, Q2, Q3, Q4, C1, C3, C4, C5, & C6 form a four pole crystal ladder filter, this is where the bulk of the receivers selectivity is achieved. Here as with the RF front end there is no amplification provided at IF, although again there is around 8db of gain provided by the product detector IC1. Sideband selection being achieved by appropriate adjustment of C9 the BFO/CIO crystal oscillator padding capacitor.
The AF section including AGC comprising of active devices IC3, IC5, and Q6 - IC3a first stage AF amplifier buffering the output of the product detector (IC1) and providing an initial 10db of gain, next IC3b, R6, R7, C18, & C19 forming an active filter, whilst D3, D4, IC3d, & D5 form the AGC detector, then IC3a & Q6 form the gain controlled amplifier. R2 provides manual volume control adjustment before the final stage the AF power amplifier IC5 capable of providing a more than adequate 500mW into an 8 ohm speaker.
The voltage regulator IC4, providing a stabilised 8volt supply to both IC1 & IC2, this improves the frequency stability of the receiver at less than 15Hz in the first 60 minutes after switch on. Please note bypass capacitors C14 & C15 are essential to eliminate any noise generated by the voltage regulator IC, furthermore chokes L8 & L9, and bypass capacitors C48 & 49 are essential to ensure no noise is introduced to the two mixers IC1 & IC2.
Receiver
PCB component placement / layout:
Original Files:
Further to the details of the pages above - the original CAD files created using EAGLE PCB Design software are included below, along with associated PDF files of both schematics and PCB layouts suitable for printing directly.
To use the original CAD files, they must be opened with EAGLE. Visit the CADsoft web site for more details, the software (including a freeware version), part libraries, tutorials, for EAGLE are available.
Receiver PCB component layout PDF
Receiver PCB bottom track layout PDF
