Simple DIY Active Antenna for Crystal-Clear Reception

Tired of static on your AM or shortwave radio? Do you struggle to hear distant stations? There is a simple fix. You can build a special antenna that makes radio signals much stronger. This guide shows you how to build a DIY active antenna. It is a fun project that can give you crystal-clear reception.

https://vu3dxr.in/simple-diy-active-antenna-for-crystal-clear-reception/

 

DIY AM Transmitter Circuits from VU3DXR.in: A Complete Collection

The VU3DXR.in blog has become a treasure trove for amateur radio enthusiasts and electronics hobbyists seeking practical DIY AM transmitter circuits. This comprehensive guide covers the extensive collection of AM transmitter designs available on the platform, ranging from simple beginner circuits to more advanced QRP transmitters.

Complete List of AM Transmitter Circuits

Based on the comprehensive AM transmitter collection available on VU3DXR.in, here are all the available AM transmitter circuits:

1. Simple Series Modulated AM QRP HF Transmitter

The Simple Series Modulated AM QRP HF Transmitter represents an excellent starting point for beginners. This low-power design uses series modulation to achieve AM transmission and is specifically designed for QRP (low-power) operation. The circuit supports both 3.9 MHz and 7.2 MHz operation with different inductor configurations.

Key Features:

• Multi-band operation (3.9 MHz and 7.2 MHz)
• Uses BD139 power transistor with heat sink requirements
• Simple construction with minimal components
• Ideal for QRP enthusiasts

2. Series Modulated AM Transmitter

The Series Modulated AM Transmitter provides a more detailed exploration of series modulation principles. This circuit uses a crystal-controlled oscillator that produces square wave outputs rich in harmonics, making it suitable for experimental broadcasting applications.

Notable Characteristics:

• Crystal-controlled frequency generation
• Square wave output with harmonic content
• Requires potentiometer adjustment for proper modulation
• Educational value for understanding AM principles

3. Simple Two-Stage Transistor One Watt AM Transmitter

The Simple Two-Stage Transistor One Watt AM Transmitter delivers approximately one watt of output power using common transistors. This design offers flexibility in transistor selection and provides good performance for amateur radio applications.

Power Output with Different Transistors:

• BD139: 1.2 watts at 12V
• C2314: 2 watts at 12V
• BLY88C: 2.3 watts at 12V
• 2N2219: 1.3 watts at 12V
• SL100: 1.1 watts at 12V
• 2N3553: 1.8 watts at 12V

4. 7MHz CW/AM QRP Transmitter

The 7MHz CW/AM QRP Transmitter offers dual-mode operation, supporting both Continuous Wave (CW) and AM modes. This versatile design includes proper antenna tuning networks and switching capabilities for mode selection.

Dual-Mode Features:

• Crystal-controlled 7MHz operation
• Switchable between CW and AM modes
• Antenna tuning network included
• Suitable for both Morse code and voice operation

5. Micro Power AM Transmitter

The Micro Power AM Transmitter is designed for short-range transmission and experimental use. Based on a Techlib.com design, this compact circuit uses a 2N2222 transistor differential amplifier for clean series modulation.

Specifications:

• Power output: Up to 100 milliwatts
• Maximum antenna length: 3 meters
• FCC Part 15 compliant operation
• 1811 ferrite core inductor with center tap
• Crystal oscillator for frequency accuracy

6. Steve Quest AM Transmitter

The Steve Quest AM Transmitter is a popular design among hobbyists that teaches basic radio principles. This circuit operates on 12V DC and uses a 7MHz crystal for frequency stability.

Circuit Components:

• 7MHz crystal (CR1) for frequency reference
• 2N2222 transistor (Q3) for oscillation
• BD139 transistor (Q2) for amplification
• 6V 500mA power transformer for modulation
• Specific winding instructions for transformers and inductors

7. Class C AM Transmitter

The Class C AM Transmitter represents a high-efficiency, solid-state transmitter design that is popular among amateur radio enthusiasts. Class C AM transmitters rule the amateur radio world. These solid-state transmitters are known for their simplicity, affordability, and efficiency compared to other types of transmitters.

Key Characteristics:

• High-efficiency operation
• Solid-state design
• Popular among amateur radio enthusiasts
• Cost-effective construction
• Suitable for higher power applications

Supporting Circuits and Resources

Audio Processing Circuits

The VU3DXR.in blog also features numerous supporting circuits essential for AM transmitter operation:

• Microphone Preamplifiers: Various designs for different microphone types
• Audio Compressors: Using LM1458 and TL071 operational amplifiers
• Audio Transformers: Guidelines for selecting and using modulation transformers

Related Transmitter Projects

Beyond AM transmitters, the blog includes complementary projects:

• 90MHz Crystal Controlled FM Transmitter
• Simple CW Transmitter Using 74HC240 Buffer IC
• 80M CW Transmitter from Scratch

Construction and Component Guidelines

Transistor Selection and Heat Management

Most circuits emphasize proper heat sinking, particularly for power amplifier stages. The BD139 transistor appears frequently across designs and requires adequate thermal management to prevent thermal runaway.

Transformer and Inductor Specifications

The circuits provide specific winding instructions for transformers and inductors, often using standard ferrite cores like T50-2 and specific wire gauges for optimal performance.

Crystal Selection and Frequency Control

Crystal-controlled oscillators are preferred across most designs for frequency stability. The circuits support various crystal frequencies depending on the intended operating band.

Safety and Legal Considerations

Amateur Radio Licensing

All transmitter circuits require proper amateur radio licensing for legal operation. The designs emphasize low-power operation suitable for amateur radio use while maintaining compliance with local regulations.

Power Output Limitations

Most circuits are designed for QRP operation, keeping power levels low to minimize interference and ensure safe operation for experimenters.

Antenna Considerations

Proper antenna design and impedance matching are emphasized across all circuits, with specific recommendations for antenna types and lengths.

Educational Value and Learning Progression

Beginner-Friendly Designs

The collection includes several circuits specifically designed for beginners, starting with simple series-modulated designs and progressing to more complex multi-stage transmitters.

Advanced Concepts

More sophisticated circuits introduce concepts like dual-mode operation, antenna tuning networks, and advanced modulation techniques.

Practical Construction Skills

The circuits emphasize hands-on construction skills, including PCB layout considerations, component selection, and testing procedures.

Conclusion

The VU3DXR.in blog represents one of the most comprehensive collections of DIY AM transmitter circuits available online. From simple micro-power transmitters to more sophisticated QRP designs, the collection offers something for every skill level and application.

The circuits range from educational beacon transmitters to practical amateur radio equipment, all while maintaining focus on safe, legal, and effective operation. Whether you're building your first transmitter or expanding your amateur radio capabilities, these designs provide solid foundations for successful projects.

The combination of detailed circuit descriptions, component specifications, and practical construction advice makes this collection particularly valuable for the amateur radio community. Each circuit is accompanied by clear explanations and safety guidelines, ensuring successful construction and operation.

For the complete collection and latest updates, visit the main VU3DXR.in website and explore the dedicated AM transmitter tag page for all available AM transmitter designs.

ATS20+ DSP Radio: Unpacking the Technical Details

 ATS20+ DSP Radio: Unpacking the Technical Details

The ATS20+ DSP Radio has been generating significant interest among radio enthusiasts, thanks to its impressive technical specifications and feature-rich design. For a detailed overview of the device, we recommend checking out the in-depth review on VU3DXR's blog.

One of the key features of the ATS20+ DSP Radio is its advanced DSP capabilities, which enable users to optimize their radio experience. According to VU3DXR's technical analysis, the device's DSP architecture provides a high degree of flexibility and customization, allowing users to tailor their radio setup to their specific needs.

The ATS20+ DSP Radio also boasts an impressive frequency range and sensitivity, making it well-suited for a variety of applications. For more information on the device's technical specifications and how to get the most out of them, refer to VU3DXR's guide on ATS20+ frequency range and sensitivity.

In addition to its technical capabilities, the ATS20+ DSP Radio also features a user-friendly interface and a range of operating modes. VU3DXR's article on ATS20+ operating modes provides a comprehensive overview of the device's capabilities and how to configure them.

For those looking to troubleshoot common issues or optimize their ATS20+ DSP Radio setup, VU3DXR's troubleshooting guide offers valuable insights and tips.

In conclusion, the ATS20+ DSP Radio is a powerful and versatile device that is well-suited for a variety of applications. For more information and in-depth technical analysis, we recommend exploring the resources available on VU3DXR's blog.

A Shortened Inverted L for 160 Metres

Despite the dreadful noise on top band caused by modern electronic gadgets and the difficulty in accommodating a necessarily large aerial in a small garden, I was keen to try to get on to top band. I experimented with some different ideas during 2009, some of which are shown on this page.

Eventually I settled on the design shown below. It is an Inverted L type aerial, shortened by the use of a loading coil. It uses a fibreglass telescopic fishing pole to allow it to be easily lowered out of sight when not in use.  Read more on Antennas page 2 here>

Shortened Base Loaded Top Band Antenna For Small Gardens
uses a fibreglass telescopic fishing pole to allow it to be easily lowered out of sight when not in use.

RF DIODE DETECTORS.

Simple diode detectors are not linear. There is a small forward voltage drop across the diode, and this voltage varies with diode current. Even if we allow for a fixed voltage drop across the diode, measurements will not be accurate at all power levels. At 1mA of diode current, the drop across a Schottky signal diode will be about 0.3V. At very low diode currents of around 1µA the drop will be much lower, typically about 0.1V.

This is not too much of a problem at higher power levels because an error of a fraction of a volt is quite a small percentage of a total peak voltage of several tens of volts. We can choose to ignore it or partially compensate by adding a fixed offset to the measured value. About O.6V for a silicon diode or O.3V for a Schottky signal diode such as 1N5711 or BAT 43 is close enough to be reasonably accurate. However, at very low power levels, the voltage drop is a significant fraction of the peak voltage and will lead to increasing errors as the peak voltage is reduced. For example, if the peak voltage is 500mV (+4dBm, or 2.5mW), a voltage drop of 0.2V across the detector diode would result in a measured peak voltage of just 300mV (0.46dBm, or 0.9mW). This problem gets even worse when the peak voltage input approaches 0.1-0.2V and the detector output voltage is close to zero.

 

There are a number of ways to improve the accuracy of a diode peak voltage detector. We could calibrate the meter by hand to eliminate errors at the lower end of the scale. This approach works well in practice but it is time consuming and requires unique calibration curves for individual diodes.

We could apply a small amount of forward bias to the diode which would reduce the voltage drop for RF signals or we could use a second identical diode as a reference to show us the required offset for a given level of current and diode temperature. It would be possible to apply all three methods to obtain the best possible accuracy but to keep things simple; I will adopt only the last method. Figure 3 shows how an opamp and a second diode can be arranged to compensate for the voltage drop of the detector diode. This circuit is due to KI6WX [2]. When used with a closely matched pair of 1N5711 diodes, this circuit will accurately track the input voltage down to a level of well below 0.1 V (-10dBm, or 100µW). If the circuit is to be used with a single-ended power supply, the opamp input and output voltage range must go all the way down to the negative supply rail. I used one half of an LM358. A CMOS input type like the CA3140 would be capable of even better performance.