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PA3FWM's software defined radio (SDR) page documents his extensive hardware and software development efforts between 2004 and 2009. Initial experiments utilized a direct conversion receiver with 90-degree phase difference, feeding a PC soundcard at 48 kHz sample rate, covering 24 kHz of spectrum around a 7080.5 kHz local oscillator. This setup, similar to AC50G's QEX 2002 article, allowed for basic I/Q signal processing to distinguish signals above and below the LO frequency. Limitations included fixed crystal frequencies, 16-bit dynamic range, and narrow bandwidth. Subsequent hardware iterations aimed for enhanced performance, incorporating external 24-bit ADCs with 192 kHz sample rates, connected via 10 Mbit/s Ethernet. A **MC145170-based PLL** and programmable octave divider provided a 58 kHz to 30 MHz tuning range. The **Tayloe mixer** was employed, with differential outputs feeding a PCM1804 ADC. An ATmega32 microcontroller handled serial data conversion to Ethernet frames, though without CRC calculation due to processing constraints. Later designs integrated AD7760 2.5 Msamples/second ADCs and a Xilinx Spartan-3 FPGA, enabling direct reception of 0-1 MHz spectrum and eventually 2.5 MHz bandwidth across the shortwave spectrum. Software was refactored to use an initial 8192 non-windowed FFT for efficient high-bandwidth processing. The project culminated in a two-way QSO on 21 MHz using the developed hardware and software, demonstrating transmit capabilities with a D/A converter. The system exhibited a 2.5 MHz wide spectrum display and a zoomed 19 kHz display, capturing signals like ionospheric chirp sounders and RTTY contest activity. Challenges included noise leakage from digital circuitry and cooling for high-power dissipation components.

Restoring vintage amateur radio gear often presents challenges with accurate dial calibration due to the non-linear characteristics of analog tuning capacitors. This resource details the construction of a 100 kHz crystal calibrator, a crucial tool for precisely setting the frequency of older rigs lacking digital readouts. The design cleverly circumvents the scarcity and cost of 100 kHz crystals by utilizing a readily available 8 MHz microprocessor crystal, such as a _HC49U_ type, in conjunction with common _CMOS ICs_ like the 74HCT00 quad NAND gate and 74HCT393 dual 4-bit binary ripple counter. The circuit employs a two-stage frequency division process: the 8 MHz crystal oscillator output is first divided by 16 to yield 500 kHz, then further divided by 5 to achieve the desired 100 kHz output. A 5.1-volt Zener diode, _1N4733A_, regulates the power supply for the HCT series logic. The article also provides a modification to produce a 50 kHz calibrator by altering the counter reset logic. Installation involves feeding the output to the receiver front end, ensuring it's post-TR relay to prevent RF damage, and incorporating an ON/OFF switch for the 12V supply line.

This simple 30m QRSS beacon is built entirely out of junkbox parts, the only component purchased specifically for this project was the 10,140kHz crystal. Hans Summers' 30m QRSS beacon project emphasizes simplicity and low cost, built almost entirely from reused parts. Key components include a 10,140kHz crystal, a 2N3904 transistor from a broken DVD player, and an ordinary LED used for frequency shift. The oscillator is stabilized in a polystyrene box, with power amplification driven by recycled copper PCB. Output power peaks at 360mW, and a custom 50-ohm dummy load manages heat. Though aesthetically unconventional, the beacon works effectively, fulfilling the project's low cost aim.

A DIY project details the construction of a modular QRP CW transceiver specifically designed for the **20-meter band**. The design is segmented into three distinct modules—VFO, Receiver, and Transmitter—allowing for phased construction and independent testing. The VFO circuit, capable of operating as a conversion VFO or a free oscillator, provides a frequency span of approximately _70 KHz_ (2.433 to 2.510 MHz) with a 4V pp output level, utilizing a Colpitts FET oscillator and buffer. The receiver employs a classic superheterodyne architecture with MOSFETs in the front end and mixer for improved overload immunity, incorporating a 4-crystal ladder filter with a 600 Hz bandpass and an LM386 audio power amplifier delivering about 1W into an 8-ohm load. The transmitter section uses frequency conversion with an NE602 mixer to achieve 14 MHz operation, featuring a power broadband stage capable of 4-5W output into a dummy load, and includes a double Pi filter for signal cleanliness. The resource provides detailed component lists, tuning instructions for each module, and 1:1 scale PCB layouts for single-sided boards.

Presents a QRP AM/CW transmitter project specifically designed for the 10-meter band, utilizing a crystal oscillator and a collector-modulated AM oscillator. The design employs a 2N2219(A) transistor in a Colpitts configuration, generating 100 to 350 mW of RF output power depending on the 9-18 Volt supply voltage and modulation depth. Frequency stability is maintained by a 28 MHz crystal, with fine-tuning possible via a Ct1 trimmer capacitor for approximately 1 kHz adjustment. The resource details the RF oscillator stage, implemented with a 2N2219 NPN transistor, emphasizing frequency stability and low power dissipation. It also covers the amplitude modulation stage, managed by a 2N2905 PNP transistor, which impresses audio information onto the carrier. Selective components (C3, C4, C7, C5) enhance voice frequencies within a +/- 5 kHz bandwidth, and modulation depth is controlled by R2 and R3. The project includes a 3-element L-type narrow bandpass filter (Ct3, L3, C10) to suppress harmonics and ensure a clean output signal. The project provides a complete schematic diagram, a comprehensive parts list including specific capacitor, resistor, and inductor values, and construction notes for the coils (L1, L2, L3). It also offers practical advice on enclosure requirements, suggesting an all-metal case or a PVC box with graphite paint for RF shielding. Operational parameters such as current draw (27mA@9V to 45mA@16V) and input impedance (50 Ohms) are specified, alongside guidance on antenna matching and the importance of a valid amateur radio license for 10-meter band operation.

This page describes an cheap RF signal source, a portable micro beacon, using a low cost temperature controlled crystal oscillator

A simple low-power broadcast-type circuit, using a crystal oscillator integrated circuit and an a collector modulated AM oscillator

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The Kenwood TS-870S HF transceiver features two state-of-the-art 24-bit 20 MIPS DSP chips, providing over 100dB out-of-passband attenuation and CW bandwidth adjustable to 50 Hz. It operates across 160-10 meters with 100 watts output, incorporating digital filtering, a beat canceller, and 100 memory channels. The radio also includes a transmit equalizer, RX antenna input, and a K1 Logic Keyer, enhancing signal processing and operational flexibility for amateur radio operators. Advanced capabilities include IF stage DSP, dual noise reduction, and an auto notch filter, all contributing to superior signal reception and clarity. The TS-870S offers a variable AGC, voice equalizer, and an RS-232C port for computer control, with Windows™ software supplied. Its built-in automatic antenna tuner functions on all bands for both transmit and receive modes, streamlining station setup and operation. Available accessories such as the DRU-3A digital recording unit, SO-2 high stability crystal oscillator, and VS-2 voice synthesizer option further extend the transceiver's utility. The unit requires 13.8 VDC at 20.5 Amps and is supplied with an MC-43S hand microphone, making it a comprehensive station component.

Quartslab has over 30 years of experience in supplying quartz crystals to the international communications market. Our product range includes the supply of quartz crystals in the frequency range 1.5 to 225 MHz in all popular holder types as well as crystal oscillators in DIL8 and DIL14 packages.

A simple transmitter built into a small cat-food tin! It consists of a single 2N2222 crystal oscillator and runs about 100mw output, depending on the supplied voltage

Unlike older radios, the 706 uses only one crystal oscillator (called the Master Oscillator). All other frequencies in the radio (L.O., 3-4 I.F. stages, VFO, and CW-offset) are computer-derived from the Master Oscillator. This makes it relatively simple to frequency-align the radio, so that it agrees with the Frequency Display in all modes.

Clarifies the intricate process of calibrating the _Elecraft K2_ dial, addressing common user challenges and lively discussions on the Elecraft reflector. Wilhelm, W3FPR, dissects the K2's PLL synthesizer design, chosen for its low phase noise, kit-friendly duplication, and cost-effective components. The resource emphasizes the critical role of the 4000.000 kHz reference oscillator's accuracy during CAL PLL, CAL FIL, and CAL FCTR functions, noting its dependence on temperature and crystal stability for optimal performance. Explaining the K2's frequency display, the document reveals it relies on microprocessor-driven look-up tables generated by CAL PLL for VFO values and CAL FIL for BFO values. In SSB and RTTY, these combine, while CW and CWr modes also factor in the sidetone pitch. The author details inherent limitations, such as the 10 Hz increment resolution of the dial and varying PLL step sizes—from 3 Hz on 160 meters to 10 Hz on 10 meters. BFO increments range from 20 to 35 Hz, collectively limiting practical dial accuracy to within **20 Hz** with diligent effort, or **30 Hz** for a slightly less demanding task. The guide outlines a four-step calibration procedure: setting the reference oscillator, running CAL PLL, running CAL FIL, and setting all BFOs. It highlights the _N6KR Method_ as a particularly easy and accurate approach, requiring only the K2 and a known frequency source like WWV for zero-beating, eliminating the need for external test equipment.

Learn how to build a VHF 144MHz transverter connected to an LMR SDR radio using easily accessible components. The transverter works by mixing the 144Mhz input frequency with a 116 MHz local oscillator frequency. Explore the challenges of finding a 116 MHz crystal and the solution of using a programmable Si5351A oscillator. Follow the provided schematic for the RX and TX sections. The transverter design is still a work in progress, with ongoing trials to achieve optimal results.

Recently, at the Ballarat Hamfest, the author acquired an old Marine transceiver for just $10, charmed by its sturdy construction and waterproofing. Made by Findlay Communications in Sydney, this crystal-controlled transceiver had been dormant but was reinvigorated with minor fixes. A manual was sourced, and further repairs were made, including an ingenious crystal oscillator replacement using an Si5351a controlled by an Arduino. The refurbished radio, complete with a fresh coat of paint and added customizations, is now operational for 160m AM and 30m SSB. A successful and cost-effective restoration.

Explore VK5DJ's experiments with the si5351a frequency synthesizer, a versatile device capable of generating frequencies from 8kHz to 200MHz. Learn how this I2C configurable clock generator can replace crystals and oscillators in various applications, providing stable and precise outputs. Discover how to program the si5351a for your own signal generator projects and repeater site setups. Utilize the affordable and efficient Adafruit module for reliable performance. Enhance your understanding of PLL/VCXO architectures and fractional dividers for frequency generation. Join the PDS Forum community in experimenting with this innovative technology.

Demonstrates the construction of an active loop converter specifically designed for the Low Frequency (LF) bands, addressing common localized noise interference in LF reception. The design integrates a sharply tuned circuit and a tuned loop antenna, utilizing the loop as the sole tuned inductive element. By applying positive feedback, the converter significantly increases the loop's effective Q, achieving factors between 1000 and 2000, which sharpens tuning and reduces noise. The circuit employs an _NE602_ mixer stage, feeding its output to an HF receiver, with a crystal-locked local oscillator at 4 MHz. A 20-turn, 0.8-meter square loop antenna with 500 uH inductance is detailed, connected via 2 meters of figure 8 flex cable. The converter offers three selectable frequency bands: 195-490 kHz, 150-220 kHz (including the New Zealand amateur band), and 128-160 kHz (covering the European amateur band). Performance measurements indicate an effective 3dB bandwidth of approximately 100 to 200 hertz at 200 kHz. The article provides insights into component selection, including an _LF353_ op-amp and a trifilar wound transformer on a ferrite core. Sensitivity figures are presented, showing 7.5 uV of converted output per 1 uV/meter signal strength into a 50-ohm load, or 37.5 uV into an _FRG7_ receiver, highlighting its capability to extract weak signals from noise.

The project details the construction of a GM3OXX OXO transmitter, designed to accommodate **FT-243 crystals** using 3D-printed FX-243 holders from John KC9ON. It presents specific frequency adjustments, noting a 7030 KHz HC-49/s crystal could be tuned from 7029.8 KHz to 7031.7 KHz with an internal 45pF trimmer capacitor. The build incorporates a modified keying circuit to prevent oscillator run-on key-up and includes a TX/RX switch for sidetone via a connected receiver, with the transmitter output routed to a dummy load on receive. Practical construction aspects are thoroughly covered, including the process of cutting a rectangular opening in a diecast enclosure for the FT-243 socket and the selection of a **low-pass filter** (LPF) based on the QRP Labs kit, derived from the W3NQN design. The author achieved approximately 800mW output power from a 14.75V supply, measured with an NM0S QRPoMeter, using a 16.5-ohm emitter resistor in the 2N3866 final stage. The article also touches upon the potential for frequency agility across the 40M band using multiple FX-243 units with various crystals. The narrative includes a brief diversion into Bob W3BBO's recent homebrew projects, such as his Ugly Weekender MK II transceiver, highlighting the enduring appeal of classic QRP designs. The author reflects on the personal satisfaction derived from building RF-generating equipment, irrespective of DX achievements, and shares experiences of making local contacts with the 800mW OXO transmitter on 40 meters.

Demonstrates the construction of 'The Virgin', a **direct-conversion receiver** specifically designed for the 40m amateur radio band. This project, completed in February 2016, features a fixed operating frequency determined by a crystal oscillator, requiring a physical crystal change to alter the reception frequency. The design incorporates two integrated circuits and a power regulator, emphasizing simplicity with a single control knob. The author details the initial design, subsequent modifications to the front end, and troubleshooting steps addressing common issues like audio motorboating and power supply instability. The resource presents the final design of the receiver, reflecting the author's first experience building such a unit between December 2015 and February 2016. It offers practical insights into basic circuit construction and the iterative process of refining a homebrew radio project. The content is particularly relevant for those interested in fundamental receiver principles and hands-on **QRP** transceiver building.

The W6PQL 23cm Beacon Project describes a **1296 MHz** beacon designed for microwave propagation studies and equipment testing, capable of 30 watts output. It utilizes a PIC 16F628A microcontroller to generate CW and FSK keying for a crystal oscillator, followed by a series of frequency doublers and triplers to reach the target frequency. The final power amplification stage employs a Mitsubishi M57762 module, providing a robust 10-watt RF output. The design emphasizes stability and reliability for continuous operation, with the microcontroller code, written in assembly, provided for customization of the beacon's callsign and message. Originally located in CM97am and aimed at 140 true, the beacon used four 4-foot Yagis stacked vertically for a total ERP of 3kW. The article includes schematics, parts lists, and construction notes to guide builders, along with antenna pattern measurements. Although the beacon itself is no longer in service as of August 2010, the detailed documentation remains a valuable reference for amateur radio operators interested in building similar **microwave** projects or understanding beacon operation.