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Adding A Driver / Amplifier for Increased Output Power

Addition o an RF power stage that you can use to extend your communications range. This part of the transmitter is arranged for class-A linear service.

Although it is not necessary to use a linear amplifier for CW or FM amplification, there are some advantages : (1) a linear amplifier produces a lower level of harmonic currents; (2) it is easier to drive when a low-power stage is used to excite it. (3) the keyed waveform of the overall transmitter is less clicky than when using a class C amplifier after the keyed stage.

The Output power from Q2 is approximately 1 watt. This level of power will enable you to work DX when band conditions are good.

(source : W1FB Design Notebook)

150 mW CW Transmitter Circuit

A Schematic diagram of A 150 mW CW transmitter, Fixed value capacitors are disc ceramic , 50 V or greater , Resistors are 1/4 or 1/2 watt carbon film or carbon composition, C1 and C2 are feedback capacitors , C3 is a 10-100 pF ceramic or mica compression trimmer.

A two circuit phone jack is used for J1 and an RCA phono connector or SO-239 coax connector may be used for J2, L1 is a 2.3 uH toroidal inductor. Use 24 turns of no. 26 enamel, wire on an Amidon T37-6 toroid core or other brand. L2 has three turns of no. 26 enamel, wire wound over the +12 V end of the L1 winding.

Q1 is a 2N4400 or 2N4401 or equivalent transistor . A 2N2222A may be substituted, but will deliver less output power . Y1 is a fundamental crystal, 30 pF load capacitance.

(source : W1FB Design Notebook)

A Strobe flasher for bike indicator

Simple circuitry allows the project to be built at low cost in a lightweight, compact

package that can be secured to the bicycle or the rider's belt.

The light from this circuit uses a xenon tube to generate a bright flash that can be

seen from a great distance - but is not intense enough to destroy a driver's night vision.

Circuit

Parts Lists

Build your own this low cost analog capacitance meter

When a capacitor is connected to a constant-voltage source through a resistor, the charge on the capacitor increases exponentially. If the source supplies a constant current, however the charge on the capacitor increases linearly. This linear charging principle is used here in the design of capacitance meter which will measure values outside the range of most such meters.

By using a constant-current source, the meter determines the time it takes to match the charge on the unknown capacitor to a known reference voltage. The meter has five full scale range o 1, 10, 100, 1000, and 10,000 uF.on the 1-uF scale , values as small as 0.01 uF can be read easily.

The Circuit

Power Supply

Parts List

PCB Layout

Component Layout

Prototype:

source : Electronic Experimenters Handbook 1980 edition

Zero Energy Device Example

“Free-Energy Devices” or “Zero-Point Energy Devices” are the names applied to systems which appear to produce a higher output power than their input power.

There is a strong tendency for people to state that such a system is not possible since it contravenes the Law of Conservation of Energy. It doesn’t. If it did, and any such system was shown to work, then the “Law” would have to be modified to include the newly observed fact. No such change is necessary, it merely depends on your point of view.

For example, consider a crystal set radio receiver:

Fig 1 . Crystal Set

Looking at this in isolation, we appear to have a free-energy system which contradicts the Law of Conservation of Energy. It doesn’t, of course, but if you do not view the whole picture, you see a device which has only passive components and yet which (when the coil is of the correct size) causes the headphones to generate vibrations which reproduce recognisable speech and music.

This looks like a system which has no energy input and yet which produces an energy output. Considered in isolation, this would be a serious problem for the Law of Conservation of Energy, but when examined from a common sense point of view, it is no problem at all.

The whole picture is:

Fig 2. Crystal Set whole Picture

Power is supplied to a nearby transmitter which generates radio waves which in turn, induce a small voltage in the aerial of the crystal set, which in turn, powers the headphones. The power in the headphones is far, far less than the power taken to drive the transmitter.

There is most definitely, no conflict with the Law of Conservation of Energy. However, there is a quantity called the “Coefficient Of Performance” or “COP” for short. This is defined as the amount of power coming out of a system, divided by the amount of power that the operator has to put into that system to make it work. In the example above, while the efficiency of the crystal set radio is well below 100%, the COP is greater than 1.

This is because the owner of the crystal radio set does not have to supply any power at all to make it work, and yet it outputs power in the form of sound. As the input power from the user, needed to make it work is zero, and the COP value is calculated by dividing the output power by this zero input power, the COP is actually infinity.

Efficiency and COP are two different things. Efficiency can never exceed 100% and almost never gets anywhere near 100% due to the losses suffered by any practical system.

Reference :https://www.free-energy-info.com/

Loop Amplifier

Sharpening the loop

Many years ago, the Q-multiplier was a popular add-on accessory for a communications receiver. These devices were sold as Heathkits, and many construction projects could be found in magazines and amateur radio books.

The Q-multiplier has the effect of seeming to greatly increase the sensitivity of a receiver, as well as greatly reducing the bandwidth of the front end. Thus it allows better reception of some stations because of increased sensitivity and narrowed bandwidth.

A Q-multiplier is an active electronic circuit placed at the antenna input of a receiver. It is essentially an Armstrong oscillator, as shown in Fig. 15-11, that does not quite oscillate. These circuits have a tuned circuit (L1/C1) at the input of an amplifier stage and a feedback coupling loop (L3). The degree of feedback is controlled by the coupling between L1 and L3. The coupling is varied by varying both how close the two coils are and their relative orientation with respect to each other.

Certain other circuits use a series potentiometer in the L3 side that controls the amount of feedback. The Q-multiplier is adjusted to the point that the circuit is just on the verge of oscillating, but not quite. As the feedback is backed away from the threshold of oscillation, but not too far, the narrowing of bandwidth occurs, as does the increase in sensitivity. It takes some skill to operate a Q-multiplier, but it is easy to use once you get the hang of it and is a terrific accessory for any loop antenna.

Loop amplifier

Figure 15-12 shows the circuit for a practical loop amplifier that can be used with either shielded or unshielded loop antennas. It is based on junction field effect transistors (JFET) connected in cascade. The standard common-drain configuration is used for each transistor, so the signals are taken from the source terminals. The drain terminals are connected together and powered from the
12-V dc power supply.

A 2.2- F bypass capacitor is used to put the drain terminals of Q1 and Q2 at ground potential for ac signals while keeping the dc voltage from being shorted out. The two output signals are applied to the primary of a center-tapped transformer, the center tap of which is grounded.

To keep the dc on the source terminals from being shorted through the transformer winding, a pair of blocking capacitors (C4, C5) is used. The input signals are applied to the gate terminals of Q1 and Q2 through dc blocking capacitors C2 and C3. A pair of diodes (D1, D2) is used to keep high-amplitude noise transients from affecting the operation of the amplifier. These diodes are connected back to back in order to snub out both polarities of signal.

Tuning capacitor C1 is used in lieu of the capacitor in the loop and is used to resonate the loop to a specific frequency. Its value can be found from the equation given earlier. The transistors used for the push-pull amplifier (Q1, Q2) can be nearly any general-purpose JFET device (MPF-102, MPF-104, etc.). A practical approach for many people is to use transistors from service replacement lines, such as the NTE-312 and NTE-316 devices.

Wideband Active Loop Antenna for Shortwave band general purpose receivers

Active Wide band Loop Antenna for 10-30 MHz Band shortwave band you can construct in your home as Do It Yourself Project (Source article : Elektor Electronics Magazine).

Parts List :

PCB Design and component place :

Loop Antenna is a good indoor antenna alternative for a long wire antenna.

Active Wideband Loop Antenna for 10–30 MHz Shortwave Band – DIY Home Construction Guide

The Active Wideband Loop Antenna is one of the most effective receiving antennas for the 10–30 MHz shortwave spectrum. Unlike long wire antennas that require large outdoor space, this compact loop antenna can be built at home as a DIY project while delivering excellent performance for shortwave listening (SWL), amateur radio, SDR receivers, and HF monitoring.

Originally inspired by classic designs published in Elektor Electronics Magazine, this modernized version is optimized for today’s receivers and offers low noise, wide bandwidth, and high signal-to-noise ratio.

Why Use an Active Loop Antenna?

Traditional wire antennas often suffer from high noise pickup, especially in urban environments. An active loop antenna solves this problem by using a small magnetic loop combined with a low-noise RF amplifier.

Compact size – ideal for apartments
Excellent noise rejection
Wide frequency coverage (10–30 MHz)
Directional properties reduce interference
Perfect for SDR and portable receivers

This antenna is designed primarily for receiving, not transmitting.

Frequency Coverage: 10–30 MHz Explained

The 10–30 MHz HF spectrum covers a wide range of important radio services:

International shortwave broadcast stations
Amateur radio bands (20m, 17m, 15m, 12m, 10m)
Utility and maritime communications
Military and aviation monitoring
Time signal stations (WWV, CHU)

A wideband loop antenna allows you to monitor all these frequencies without retuning coils or switching antennas.

How an Active Loop Antenna Works

The antenna consists of two main sections:

1. Magnetic Loop Element

A loop of wire responds primarily to the magnetic component of radio waves, which makes it inherently resistant to electric-field noise generated by household electronics.

2. Wideband Low-Noise Amplifier

The amplifier buffers the loop, providing:

Impedance matching
Flat frequency response
High dynamic range
Low intermodulation distortion

This design ensures consistent performance across the entire 10–30 MHz range.

Advantages Over Long Wire Antennas

Feature	Active Loop Antenna	Long Wire Antenna
Size	Compact	Large
Noise Immunity	Excellent	Poor
Urban Use	Ideal	Problematic
Bandwidth	Wide	Variable

DIY Construction Overview

This project is suitable for beginners with basic soldering skills. All components are inexpensive and widely available online.

Loop Dimensions

Loop diameter: 0.8 – 1 meter
Wire: insulated copper wire or coax shield
Mounting: PVC pipe or fiberglass support

Larger loops improve sensitivity but are not mandatory.

Electronic Circuit Description

The amplifier uses a wideband RF transistor or JFET configured as a low-noise buffer. The design prioritizes stability and flat gain across HF frequencies.

High input impedance
50Ω output matching
Powered via 9–12V DC or bias-T

The amplifier can be housed in a small waterproof enclosure near the loop.

Component List (DIY Friendly)

Insulated copper wire (1–1.5 mm)
Wideband RF transistor (2N5109 / J310 / BF245)
Resistors (metal film recommended)
Capacitors (ceramic + electrolytic)
PCB or prototyping board
BNC or SO-239 connector
9–12V DC power supply
Plastic enclosure

🛒 Recommended Components (Affiliate Links)

Using quality components improves reliability and noise performance.

RF Transistor J310 / 2N5109
Amazon | Shopee | Tokopedia
Coaxial Cable RG-58
Amazon | Shopee | Tokopedia
SDR Receiver (RTL-SDR / Airspy)
Amazon | Shopee | Tokopedia

Installation Tips

Install outdoors or near a window
Rotate loop to null interference
Keep amplifier close to loop
Use quality coaxial cable

Performance Expectations

When properly built, this antenna delivers:

Strong reception across 10–30 MHz
Reduced urban noise
Stable operation with SDR receivers
Excellent DX capability

Many users report better results than long wire antennas in noisy environments.

Is This Antenna Legal?

Yes. This antenna is receive-only and does not transmit RF energy. It complies with radio regulations worldwide.

Conclusion

The Active Wideband Loop Antenna for 10–30 MHz is one of the most practical DIY antennas for modern shortwave listening. With compact size, low noise, and wide coverage, it is ideal for home construction and urban environments.

Inspired by classic Elektor designs and updated for modern receivers, this project offers excellent performance.

DIY SWR meter

DIY SWR Meter: Build Your Own Standing Wave Ratio Meter at Home

Standing Wave Ratio (SWR) is one of the most important parameters in radio frequency (RF) systems. Whether you are a ham radio operator, CB radio user, or RF electronics hobbyist, understanding and measuring SWR is essential for protecting your transmitter and maximizing antenna performance.

In this in-depth guide, you will learn how to build a DIY SWR meter at home using inexpensive components. This project is inspired by classic RF measurement concepts popularized in publications such as Elektor Electronics Magazine, rewritten here as an original, practical, and beginner-friendly tutorial.

This article is optimized for SEO, Google AdSense monetization, and affiliate revenue, making it ideal for electronics blogs, ham radio websites, and DIY project portals.

What Is an SWR Meter?

An SWR meter measures how efficiently radio frequency power is transferred from a transmitter to an antenna. When the antenna impedance does not match the transmitter output (typically 50 ohms), part of the RF energy is reflected back toward the transmitter.

The Standing Wave Ratio is defined as:

SWR = (Forward Power + Reflected Power) / (Forward Power − Reflected Power)

A low SWR indicates good impedance matching, while a high SWR means power loss, signal distortion, and potential damage to the transmitter’s output stage.

Why Every Radio Operator Needs an SWR Meter

Protects transmitter final amplifier
Improves antenna efficiency
Reduces RF power loss
Improves communication range
Essential for antenna tuning

Commercial SWR meters can be expensive. Fortunately, a DIY SWR meter can deliver excellent performance at a fraction of the cost.

How a DIY SWR Meter Works

The core of an SWR meter is a directional coupler. It samples:

Forward RF power (from transmitter to antenna)
Reflected RF power (from antenna back to transmitter)

By rectifying these RF signals using diodes and measuring their relative levels, the SWR can be determined accurately.

This design works best for:

HF amateur radio bands
CB radio (27 MHz)
Low VHF frequencies

DIY SWR Meter Circuit Overview

The circuit consists of:

Directional coupler transformer
Germanium or Schottky diodes
Analog panel meter (microamp type)
Calibration potentiometers
RF connectors (SO-239 or BNC)

This passive design requires no external power supply, making it highly reliable and portable.

Component List (Bill of Materials)

📦 Core Components

Toroidal ferrite core (FT-50-43 or equivalent)
Enamel copper wire (0.5 mm)
Germanium diodes (OA90 / 1N34) or Schottky (BAT85)
Analog panel meter (100 µA or 200 µA)
Potentiometers (2 × 10kΩ)
Resistors (carbon film)
Ceramic capacitors (100 pF – 1 nF)

📦 Mechanical Parts

Metal enclosure (RF shielding)
SO-239 or BNC connectors (input/output)
Knobs and scale plate

🛒 Recommended Parts

Using quality RF components improves accuracy and durability.

Ferrite Toroid FT-50-43
👉 Amazon | Shopee | Tokopedia
Germanium Diode 1N34 / OA90
👉 Amazon | Shopee | Tokopedia
Analog Panel Meter 100µA
👉 Amazon | Shopee | Tokopedia

Building the Directional Coupler

Wind the toroidal transformer carefully:

Primary: 10 turns bifilar winding
Secondary: 2–3 turns sensing coil

Keep leads short and symmetrical to maintain RF balance. This step determines measurement accuracy.

Detector and Meter Circuit

The RF voltage from the coupler is rectified using germanium or Schottky diodes. These diodes are chosen for their low forward voltage drop, allowing accurate detection at low power levels.

Each detector feeds the meter through a calibration potentiometer, enabling precise SWR adjustment.

Calibration Procedure

Connect transmitter → SWR meter → dummy load
Set transmitter to low power
Adjust forward calibration control to full scale
Switch to reflected mode
Read SWR from scale

Once calibrated, the meter can be used for antenna tuning and system diagnostics.

Expected Performance

Accurate SWR readings from 1:1 to 5:1
Usable from HF to low VHF
No power supply required
Portable and rugged

Common Mistakes to Avoid

Using silicon diodes instead of germanium
Poor enclosure grounding
Long unshielded wiring
High transmitter power during calibration

Conclusion

Building a DIY SWR meter is a rewarding project that deepens your understanding of RF systems while saving money. Inspired by classic Elektor-style designs, this project offers professional-level performance using simple, accessible components.

Whether you are tuning an antenna, protecting your transmitter, or learning RF electronics, this home-built SWR meter is an essential tool for every radio enthusiast.

Extremely Low Frequency Reciever using Arduino

Using Arduino Uno and ADC module, this circuit can pick up ELF Signal

Car Radio Alarm Circuit

Car Lights Monitor

Bicycle Lights and Alarm

source : Elektor electronic

Car Fuse Monitor

Source : Elektor Electronic

Nicad Charger Circuit

Source : Elektor Electronic

Metal Pipe Detector Circuit

This circuit is useful for trace Metal Pipe Water and Gas.

Crystal Tester Circuit

The circuit is use for test Quartz Crystal from 1 MHz to 50 MHz, if the crystal X1 good enough, sinewave will appears on Emiter T1 BF494 , and rectified by D2 IN4148 , drive D1 IN4148 and will charge Capacitor C4 until enough voltage to turn on Transistor BC547 and make the LED 1 on. This circuit using 9 V battery for enough consumption , below is PCB you can design . ( Source : Elektor Summer circuit)

Wideband Spark Transmissions Signal Receiver

This is circuit for Fun, receive spark transmissions signal from switch on off light , motors, high voltage lightning , electric motors can detected by this receiver on short wave band.

AM SW Converter with NE602

If you have old AM radio , you can use this circuit to change to Short Wave Radio, and tune the Short Wave frequency and start listening Short Wave around the world. The AM SW short wave radio can works from 1.6 MHz until 10 MHz by C1 with various values. from 150 pF until 10 pF , or you can use Trimmer Capacitor from 0-200 pF. For Crystals X1 can use 34.545 MHZ overtone crystal.

As datasheet NE602 describe , the features of this IC :

* Low current consumption : typical 2.4 mA
* Excellent noise figure : < 4.7 dB typical at 45 MHz
* High Operating frequency
* Excellent gain : intercept and sensitivity
* Low external parts count ; suitable for crystal / ceramics filter

NE602 Pin Out :

Test Configuration for NE602 , look at Crystal on Pin 6.

Applications :
* Portable Radio
* Cellular Radio

Example for Cellular Radio Application :

* VHF Transceivers
* RF Data Links
* HF / VHF Frequency conversion
* Instrumentation frequency conversion
* Broadband LANs

Voice Memory Circuit Using Single Chip ISD1416 from Winbond

Voice IC recording system memory , ISD1416 from Winbond can use for many application such Answering Machine Phone, Talking Clocks also for private application such as in Public Services to tell People How To use Toilet, private toilet by record instruction for 2 minutes.

The Features of ISD1416 :

* Easy to use single chip voice record/playback solution
* High quality, natural voice/audio reproduction
* Push button interface
- Playback can be edge or level activated

* Single chip durations of 16 and 20 seconds
* Automatic power down mode
- Enters standby mode immediately following a record or playback cycle
- Standby current 0.5 uA (typical)
* Zero power message storage
- Eliminates battery backup circuits
* Fully addressable to handle multiple messages
* 100 year message retention (typical)
* 100,000 record cycles (typical)
* On-chip clock source
* No programmer or development system needed
* Single +5 volt power supply
* Available in die form, DIP, and SOIC packaging
* Industriall temperature (-40 Celcius degree to +85 Celcius degree) versions available

ISD 1400 Series Pinouts

Application Note example from datasheet ISD1416

For datasheet ISD1416 Please click here.

Simple Remote Control Tester

When your remote control TV problems , because not works well , you can use this circuit to check .

This circuit using BP103 which is photo transistor who will response to infra red spectrum when remote control TV problem.
Transistor BC548 will biases and turn LED D1 will flash when you test your remote by pressing the button and make sure the infra red of remote works well. Check it Out!

We have Generic Universal Tv Ir Remote Control Decoder Tester Infrared Remote Control Testing. with this tool you can answer the questions :

(1)How to confirm different TV remote controls can be compatible with each other?

(2)My TV remote control doesn't work, if you don't have the one I need,which model can take place of it?

Use this to test functionality of the remotes before listing them. Super easy to use and does exactly what it is supposed to..