Antenna Handbook

2-Element Yagi Array Antenna Calculator: A Complete Guide (2025 Edition)



Yagi-Uda antennas—commonly known as Yagi antennas—have long been a preferred choice for applications ranging from ham radio and amateur television to Wi-Fi and satellite communication. Among the simplest yet most effective designs is the 2-element Yagi array, consisting of a driven element and a reflector or director. This configuration is popular due to its balance between simplicity, gain, and directionality.

In this article, we will explore everything you need to know about the 2-element Yagi array antenna calculator: how it works, the physics behind it, the math involved, and how to use an online calculator to design your own high-performance antenna.

Table of Contents

  1. What is a Yagi-Uda Antenna?

  2. Components of a 2-Element Yagi Array

  3. Why Use a 2-Element Yagi?

  4. Key Parameters in Yagi Design

  5. Mathematical Formulas for a 2-Element Yagi

  6. How the 2-Element Yagi Calculator Works

  7. Step-by-Step Example Calculation

  8. Applications of 2-Element Yagi Antennas

  9. Benefits and Limitations

  10. Top Online Yagi Antenna Calculators

  11. Final Tips and Best Practices

1. What is a Yagi-Uda Antenna?

A Yagi-Uda antenna, or simply a Yagi antenna, is a directional antenna system made up of:

  • A driven element (typically a half-wave dipole)

  • One or more passive elements, which include:

    • A reflector (placed behind the driven element)

    • One or more directors (placed in front of the driven element)

Yagi antennas are widely used for their ability to focus signal energy in one direction, offering high gain and directivity.

2. Components of a 2-Element Yagi Array

The 2-element Yagi is the most basic configuration and includes:

  • Driven Element: The active radiator, typically a λ/2 dipole.

  • Reflector or Director: A passive element that alters the radiation pattern.

Two types of 2-element Yagis can exist:

  • Driven + Reflector: More common, provides modest gain with a wide beamwidth.

  • Driven + Director: Offers slightly higher gain but can be more difficult to tune.

3. Why Use a 2-Element Yagi?

While more elements can yield higher gain, a 2-element Yagi has several advantages:

  • Simple to build and tune

  • Improved forward gain (~4–5 dBi)

  • Reduced back lobe radiation

  • Compact size, ideal for portable or small-scale applications

These characteristics make the 2-element Yagi ideal for:

  • Field day amateur radio setups

  • Direction-finding (DF) antennas

  • Wireless communication experiments

4. Key Parameters in Yagi Design

When designing a 2-element Yagi antenna, you need to consider several key parameters:

Parameter Description
Frequency (MHz) Operating frequency of the antenna
Wavelength (λ) Derived from frequency (λ = c / f)
Element Lengths Physical lengths of the driven and passive elements
Spacing Distance between the driven element and the reflector or director
Impedance Matching Ensuring the antenna feeds correctly into a 50-ohm or 75-ohm system
Boom Length Total length of the boom holding the elements

5. Mathematical Formulas for a 2-Element Yagi

📏 Wavelength Calculation

λ=cf\lambda = \frac{c}{f}

  • Where:

    • λ\lambda = wavelength (in meters)

    • cc = speed of light (approximately 3 × 10⁸ m/s)

    • ff = frequency in Hz

🔧 Driven Element Length

Ldriven=λ2L_{\text{driven}} = \frac{\lambda}{2}

Or slightly less (approx. 0.47λ) due to end effects.

🔧 Reflector Length

Lreflector≈0.55λL_{\text{reflector}} \approx 0.55 \lambda

Slightly longer than the driven element.

🔧 Director Length

Ldirector≈0.45λL_{\text{director}} \approx 0.45 \lambda

Slightly shorter than the driven element.

📐 Spacing Between Elements

  • Typical spacing: 0.15λ to 0.25λ for reflector-driven

  • 0.1λ to 0.2λ for driven-director setup

6. How the 2-Element Yagi Calculator Works

A 2-Element Yagi Antenna Calculator automates the calculations based on input frequency and desired configuration. Here’s what it typically does:

  1. Accepts operating frequency (in MHz) as input.

  2. Computes wavelength (λ).

  3. Calculates element lengths based on Yagi design formulas.

  4. Provides optimal spacing between the elements.

  5. (Advanced calculators) may simulate gain, front-to-back ratio, and impedance.

Input Example:

  • Frequency: 144 MHz (2-meter band)

Output Example:

  • Wavelength (λ): 2.08 m

  • Driven Element Length: ~0.98 m

  • Reflector Length: ~1.05 m

  • Spacing: ~0.3 m

7. Step-by-Step Example: Designing a 2-Element Yagi for 144 MHz

Let’s walk through a full example.

Step 1: Determine Wavelength

λ=3×108144×106=2.08 meters\lambda = \frac{3 \times 10^8}{144 \times 10^6} = 2.08 \text{ meters}

Step 2: Driven Element Length

Ldriven=0.475×λ=0.988 metersL_{\text{driven}} = 0.475 \times \lambda = 0.988 \text{ meters}

Step 3: Reflector Length

Lreflector=0.55×λ=1.144 metersL_{\text{reflector}} = 0.55 \times \lambda = 1.144 \text{ meters}

Step 4: Element Spacing

Spacing=0.2×λ=0.416 meters\text{Spacing} = 0.2 \times \lambda = 0.416 \text{ meters}

Now you have all dimensions needed to construct a functional 2-element Yagi for the 2-meter amateur band.

8. Applications of 2-Element Yagi Antennas

Yagi antennas are used in a variety of real-world applications. A 2-element version is especially useful in:

  • Ham radio (VHF/UHF)

  • Wi-Fi (2.4 GHz directional boosting)

  • Digital TV reception

  • RFID reader antennas

  • Satellite communication (e.g., weather satellite downlink)

  • Directional jamming or detection systems

  • Emergency services and mobile command setups

9. Benefits and Limitations

✅ Benefits:

  • Simple to build, even for beginners

  • Lightweight and compact

  • Provides meaningful gain (~4–5 dBi)

  • Improves signal-to-noise ratio in one direction

❌ Limitations:

  • Less gain than multi-element Yagis

  • Narrower bandwidth than log-periodic antennas

  • Requires precise spacing and tuning for best performance

10. Top Online Yagi Antenna Calculators

If you're designing your own 2-element Yagi, here are some excellent free tools:

  1. K7MEM Yagi Calculator

  2. Yagi Calculator by VK5DJ

    • Windows application with modeling features

  3. MMANA-GAL

    • Free antenna modeling software for simulating radiation patterns

  4. Ham Radio Secrets Yagi Calculator

    • Simple HTML tool with straightforward frequency-to-length conversion

11. Final Tips and Best Practices

🧰 Building Tips:

  • Use aluminum tubing for lightweight and durable elements.

  • Mount elements on a non-conductive boom (e.g., PVC or fiberglass).

  • Ensure all connections are well-soldered or crimped to minimize loss.

🧪 Testing and Tuning:

  • Use an SWR meter or antenna analyzer to tune for lowest VSWR.

  • Adjust spacing and element lengths slightly if performance is suboptimal.

  • Test in an open area away from buildings and metal objects.

🌐 Using with a Transceiver:

  • Match impedance with a balun or gamma match to prevent mismatch losses.

  • Ensure proper grounding and lightning protection if mounting outdoors.

Conclusion: Design Smarter with a 2-Element Yagi Array Calculator

The 2-element Yagi antenna is a compact and powerful design that strikes an excellent balance between performance and simplicity. Whether you’re an amateur radio operator, a Wi-Fi hobbyist, or a field engineer, a 2-element Yagi array antenna calculator can save you time and ensure a high-performance result.

By using simple math and the right tools, anyone can build a reliable directional antenna tuned to their desired frequency. With modest effort and low cost, a 2-element Yagi can greatly enhance signal clarity, range, and overall communication quality.


read also 3 Element Yagi Calculator


2-Element Yagi Antenna Calculator

2-Element Yagi Antenna Calculator

Enter the operating frequency in MHz:

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Best Broadband Plans for Work From Home in Tokyo, Japan (2025 Guide)

With the rise of teleworking and hybrid jobs, having fast, reliable, and affordable broadband is essential—especially in a bustling city like Tokyo. Whether you're a remote worker, freelancer, digital nomad, or running a home office, this guide will help you find the best broadband plans for work from home in Tokyo, Japan in 2025.

📡 Why You Need High-Quality Broadband for Remote Work

Living in Tokyo gives you access to some of the most advanced internet infrastructure in the world, but not all plans are created equal. Here’s why choosing the right provider matters:

  • Speed: To handle video calls, large file transfers, and multiple devices.

  • Latency: Especially important for video conferencing and cloud collaboration.

  • Stability: Frequent disconnections can disrupt your workflow.

  • Support: Reliable customer service is a must when issues arise.

🏆 Top Broadband Providers in Tokyo (2025)

Here are the top broadband providers suitable for remote work in Tokyo, based on speed, reliability, coverage, and customer reviews.

1. NTT FLET’S Hikari (フレッツ光)

Overview: NTT East’s FLET’S Hikari is Japan’s most widely used fiber-optic network. Most other ISPs like So-net and OCN operate on this backbone. It offers high reliability and city-wide coverage in Tokyo.

🧾 Available Plans (via ISP partners like OCN, So-net):

  • Plan: FLET’S Hikari Next Family Type

    • Speed: Up to 1 Gbps

    • Price: ¥5,500 – ¥6,600/month (with ISP + line fee)

    • Setup Fee: Around ¥8800 – ¥22,000 (often waived in promotions)

Pros:

  • Broad coverage throughout Tokyo

  • Highly stable and fast connection

  • Can choose from many partner ISPs

Cons:

  • Complex setup (you pay for the line + ISP separately)

  • Requires Japanese language proficiency for support

2. au Hikari (KDDI)

Overview: Operated by KDDI, au Hikari is another popular fiber service, known for excellent performance in Tokyo's residential areas.

🧾 Available Plans:

  • Plan: au Hikari Home 1 Gbps

    • Speed: Up to 1 Gbps

    • Price: ~¥5,200/month (with promotions)

    • Optional ISP Bundling: @nifty, BIGLOBE, So-net

    • Discounts: Up to ¥1,100/month off for au mobile users

Pros:

  • Excellent for detached homes and family use

  • Bundling discounts with au mobile

  • High-speed and stable connection

Cons:

  • Limited coverage in certain apartment buildings

  • Requires long-term contracts for best prices

3. SoftBank Hikari

Overview: SoftBank Hikari is ideal for those using SoftBank or Y!mobile mobile phones. It runs on NTT's fiber network but includes SoftBank's own backend systems and customer support.

🧾 Plans:

  • Plan: SoftBank Hikari 1 Gbps

    • Speed: Up to 1 Gbps

    • Price: ~¥5,720/month (after discounts)

    • Mobile Set Discount: Up to ¥1,100 off/month

Pros:

  • Simple setup, good for SoftBank users

  • Good upload/download symmetry

  • Optional Wi-Fi 6 router rental

Cons:

  • Less optimal for non-SoftBank mobile users

  • Can be less reliable in crowded areas during peak hours

4. NURO Hikari (by Sony)

Overview: NURO Hikari is one of the fastest residential broadband options in Japan, offering 2 Gbps speeds. It’s ideal for power users, content creators, and tech-heavy households.

🧾 Plans:

  • Plan: NURO Hikari G2V

    • Speed: Up to 2 Gbps (download), 1 Gbps (upload)

    • Price: ~¥5,200/month

    • Contract: 2-year required for discounts

    • Setup Fee: ¥44,000 (often 100% discounted)

Pros:

  • Ultra-fast speeds

  • Flat-rate, includes ISP + line in one bill

  • Good customer satisfaction for performance

Cons:

  • Installation can take 2–4 weeks

  • Limited availability in some Tokyo apartments

5. Docomo Hikari

Overview: Powered by NTT, Docomo Hikari is a bundled internet service for Docomo mobile users. It's convenient and offers extra value through smartphone plan discounts.

🧾 Plans:

  • Plan: Docomo Hikari 1 Gbps

    • Speed: Up to 1 Gbps

    • Price: ¥5,720/month (with discounts)

    • Bundle Discount: Up to ¥1,100 off Docomo smartphone plan

Pros:

  • Convenient for Docomo users

  • Uses FLET’S Hikari backbone (stable and fast)

  • Good support channels in English

Cons:

  • Speeds and support may vary by ISP partner

  • Not a good deal unless you have a Docomo mobile

📊 Broadband Plan Comparison Chart (2025)

Provider Speed Price (approx) Contract Required Notable Features
NTT FLET’S + ISP 1 Gbps ¥5,500–¥6,600 Optional Choose from many ISPs
au Hikari 1 Gbps ~¥5,200 Yes (2-year) Mobile bundling discounts
SoftBank Hikari 1 Gbps ~¥5,720 Yes SoftBank mobile discounts
NURO Hikari 2 Gbps / 1 Gbps ~¥5,200 Yes (2-year) Very high speeds
Docomo Hikari 1 Gbps ~¥5,720 Yes Best with Docomo smartphone

🔍 How to Choose the Right Plan for Your Work-From-Home Needs

👤 Solo Remote Workers

  • Recommended: SoftBank Hikari or FLET’S with OCN/So-net

  • Why: Affordable and reliable, with good upload speeds for Zoom calls

👪 Families or Roommates

  • Recommended: au Hikari or Docomo Hikari

  • Why: Bundling discounts, stable during high use

🎥 Content Creators / Heavy Users

  • Recommended: NURO Hikari

  • Why: 2 Gbps download makes uploads, editing, and live streams seamless

🏙 Apartment Dwellers

  • Recommended: FLET’S Hikari (Mansion Type) or SoftBank Hikari

  • Why: Both are widely available in Tokyo’s apartments

🧠 FAQs: Work-From-Home Broadband in Tokyo

Q: What is the minimum speed I need for working from home?
A: At least 100 Mbps download / 30 Mbps upload. For multiple devices, aim for 300+ Mbps.

Q: Can I get an English-speaking ISP in Tokyo?
A: Some providers like SoftBank, NTT East, and Sakura Fiber offer limited English support. Consider using a service like GTN or Sakura for expats.

Q: Is installation fast in Tokyo?
A: Installation usually takes 1–3 weeks. NURO Hikari may take longer due to dual-stage installation.

Q: Are there data caps on Japanese broadband?
A: No. Most broadband plans in Japan are truly unlimited.

📍 Steps to Get Broadband Set Up in Tokyo

  1. Check Address Availability: Use the provider’s online checker with your Japanese address.

  2. Apply Online: Applications often require a Japanese phone number and sometimes a My Number card or residence card.

  3. Schedule Installation: Technicians usually visit within 2–4 weeks.

  4. Receive Equipment: Most providers ship a Wi-Fi router or ONT (Optical Network Terminal).

  5. Connect and Confirm: Ensure your upload/download speeds meet expectations.

🧾 Final Recommendation: Best Overall Plan for Remote Workers

🏆 NURO Hikari is the best all-around choice if available at your address. With 2 Gbps download speed, low pricing, and unlimited data, it's ideal for remote workers, video editors, and tech-savvy users.

For most users:

  • Best Value: au Hikari

  • Best for Expats or English Support: SoftBank Hikari

  • Most Flexible: FLET’S Hikari with So-net or OCN

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Best Broadband Plans for Home Use in Sydney – May 2025

Best Broadband Plans for Home Use in Sydney – May 2025



In Sydney, selecting the right broadband plan can be a daunting task given the plethora of options available. Whether you're working from home, streaming high-definition content, or gaming online, it's crucial to choose a plan that aligns with your usage patterns and budget. This guide explores the top broadband plans in Sydney as of May 2025, highlighting key features, pricing, and provider comparisons to help you make an informed decision.

🔍 Understanding Broadband Options in Sydney

Broadband services in Sydney are primarily delivered through the following technologies:

  • NBN (National Broadband Network): The government's initiative to provide high-speed internet across Australia. NBN plans are categorized based on speed tiers, with NBN 25, NBN 50, NBN 100, NBN 250, and NBN 1000 being the most common.

  • 5G Home Internet: A newer technology offering high-speed internet via 5G networks. Providers like TPG and Optus have introduced 5G home broadband plans in select areas.

  • Opticomm Fibre: An alternative fibre network available in certain Sydney suburbs, offering high-speed internet services.

🏆 Top Broadband Plans for Home Use in Sydney

1. Tangerine NBN 100 Plan

  • Speed: 100/20 Mbps

  • Price: AU$60.90/month for the first 6 months, then AU$85.90/month

  • Features: Unlimited data, no lock-in contract, optional home phone bundle for AU$10/month

  • Best For: Households with moderate to heavy internet usage, including streaming and online gaming.

2. Dodo NBN 100 Plan

  • Speed: 100/20 Mbps

  • Price: AU$73.90/month for the first 12 months, then AU$88.90/month

  • Features: Unlimited data, no setup fee, 30-day satisfaction guarantee

  • Best For: Budget-conscious users seeking reliable high-speed internet.

3. Swoop NBN 100 Plan

  • Speed: 100/20 Mbps

  • Price: AU$72/month (after applying code LOVE22 for AU$22 off for 6 months)

  • Features: Unlimited data, locally-based support, no congestion during peak hours

  • Best For: Users prioritizing customer support and consistent speeds during peak times.

4. Exetel NBN Superfast (NBN 250)

  • Speed: 220 Mbps typical evening speed

  • Price: AU$89/month for the first 6 months, then AU$104/month

  • Features: Unlimited data, 5 My Speed Boost Days per month, optional modem purchase for AU$170

  • Best For: Households with multiple users engaging in high-bandwidth activities like 4K streaming and online gaming.

5. TPG 5G Home Broadband Plus

  • Speed: 50 Mbps (approximate)

  • Price: AU$49.99/month for the first 6 months, then AU$59.99/month

  • Features: Unlimited data, no lock-in contract, 5G network coverage

  • Best For: Users in areas with strong 5G coverage seeking a wireless internet solution.

📊 Broadband Plan Comparison Table

Provider Plan Name Speed Price (First 6 Months) Price (Ongoing) Best For
Tangerine NBN 100 100/20 Mbps AU$60.90/month AU$85.90/month Moderate to heavy internet usage
Dodo NBN 100 100/20 Mbps AU$73.90/month AU$88.90/month Budget-conscious users
Swoop NBN 100 100/20 Mbps AU$72/month AU$72/month Consistent speeds during peak hours
Exetel NBN Superfast (250) 220 Mbps AU$89/month AU$104/month High-bandwidth households
TPG 5G Home Broadband 50 Mbps AU$49.99/month AU$59.99/month Areas with strong 5G coverage


💡 Tips for Choosing the Right Broadband Plan

  • Assess Your Usage: Determine your household's internet needs. For light browsing and social media, an NBN 25 or 50 plan may suffice. For streaming in 4K or online gaming, consider NBN 100 or higher.

  • Check Availability: Not all providers offer services in every area. Use the provider's address checker tool to confirm service availability at your location.

  • Consider Contract Terms: Some plans offer discounts for the first few months but may revert to higher prices afterward. Ensure you're comfortable with the ongoing costs.

  • Customer Support: Opt for providers with strong customer support, especially if you encounter technical issues.


📞 How to Switch Providers

Switching broadband providers in Sydney is relatively straightforward:

  1. Check Eligibility: Use the provider's address checker to confirm service availability.

  2. Compare Plans: Use comparison websites to find the best plan that suits your needs.

  3. Contact the New Provider: Once you've selected a plan, contact the new provider to initiate the switch. They will guide you through the process.

  4. Cancel Your Old Plan: After your new service is activated, cancel your old plan to avoid double billing.


🏁 Conclusion

Choosing the best broadband plan for home use in Sydney depends on your specific needs, budget, and location. The plans highlighted above offer a range of options to cater to different requirements. By assessing your usage patterns and considering the factors outlined in this guide, you can select a plan that provides reliable and high-speed internet connectivity for your household.

For more detailed comparisons and to check the latest offers, visit Finder's Broadband Comparison and WhistleOut's NBN Plans.

Note: Prices and plan details are accurate as of May 2025 and may be subject to change. Always check with the provider for the most current information.

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Capacitor Network's

 Series

CT =  1/(1/(1/C1 + 1/C2 + 1/C3))

Series
CT = (C1 * C2)/(C1 + C2)

Parallel

CT = C1 + C2 + ....CN for 2 or more capacitors

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Voltage Divider

 


Formula for Voltage Divider :

Vout = Vin * (R2/R1+R2))

Where :

R1 and R2 can be a potentiometer 

reference :

[1] Formula's, Table, and Basic Circuit, Engineer's Mini-Notebook, Radio Shack 



                                   

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VHF Test Transmitter

 


If you want to be independent of the local radio stations for testing VHF receivers, you need a frequency modulated oscillator that covers the range of 89.5 to 108 MHz — but building such an oscillator using discrete components is not that easy. Maxim now has available a series of five integrated oscillator building blocks in the MAX260x series (see the May 2001 issue of Elektor Electronics), which cover the frequency range between 45 and 650 MHz. The only other thing you need is a suitable external coil, dimensioned for the midrange frequency. The MAX2606 covers the VHF band, although the frequency can only be varied by approximately ±3 MHz around the midrange frequency set by the coil L. The inductance values shown in the table can serve as starting points for further experimenting.The SMD coils of the Stettner 5503 series are suitable for such oscillators. In Germany, they are available from Bürklin (Buerklin.com) , with values between 12 nH and 1200 nH. You can thus directly put together any desired value using two suitable coils. If you want to wind your own coils, try using 8 to 14 turns of 0.5-mm diameter silver-plated copper wire on a 5-mm mandrel. You can make fine adjustments to the inductance of the coil by slightly spreading or compressing the coil. The circuit draws power from a 9-V battery. The BC238C stabilises the voltage to approximately 4 V. Although the MAX2606 can work with a supply voltage between +2.7 V and +5.5 V, a stabilised voltage improves the frequency stability of the free-running oscillator. The supply voltage connection Vcc (pin 5) and the TUNE voltage (pin 3) must be decoupled by 1-nF capacitors located as close as possible to the IC pins. The tuning voltage TUNE on pin 3 may lie between +0.4 V and +2.4 V. A symmetric output is provided by the OUT+ and OUT– pins. In the simplest case, the output can be used in a single-ended configuration. Pull-up resistors are connected to each of the outputs for this purpose. You can use a capacitor to tap off the radio signal from either one of
these resistors. Several milliwatts of power are available. At the audio input, a signal amplitude of 10 to 20 mV is enough to generate the standard VHF frequency deviation of ±40 kHz.
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Three Component Oscillator

 


At first glance, this circuit appears to be just a primitive microphone amplifier. Why then is the title of this article
‘Three-component Oscillator’? The answer is very simple:
the microphone is not intended to pick up speech; instead, it is placed so close to the loudspeaker that massive positive feedback occurs. Here we intentionally exploit an effect that is assiduously avoided in public-address systems — the positive feedback results in a terribly loud whistle. The loudspeaker is connected directly to the 12-V supply voltage and the power transistor, so it must be able to handle a power of at least 1.5 W, and it should have an impedance of 8 to 16 Ω. An outstanding candidate can be cannibalised
from an old television set or discarded speaker box. The microphone should be a carbon-powder type from an old-fashioned telephone handset. If you place a switch in series with the power supply, this sound generator can also be used as an effective doorbell or siren. Surprisingly enough, the circuit can also be used as a simple microphone amplifier — hardly hi-fi, of course, but still usable.

source : P. Lay - Elektor Circuit Collections 
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Tags:

2.5-GHz Signal Source

 


More and more communications systems are operating in the 2.4-GHz ISM (Industrial, Scientific and Medical) band, including Blue
tooth, various WLAN (Wireless Local Area Network) and Home-RF systems. A simple test oscillator for the frequency band between 2.4 GHz and 2.5 GHz can prove useful in testing receivers. Such an oscillator is available from Maxim (www.maxim-ic.com) as a single IC. The MAX2750 covers the frequency range between 2,4 GHz and 2.5 GHz using in internal LC network that can be tuned using a varactor diode that is also built into the IC. An output buffer delivers a level of –3 dBm into 50 Ω.
This component is housed in an 8-pin µMAX package. The circuit is powered from a 9-V battery. The BC238C transistor stabilises the battery voltage at around 4 V. Although the MAX2750 can work with supply voltages
between +2.7 V and +5.5 V, the frequency stability of the free-running oscillator is better with a stabilised supply voltage. All connections to the IC are decoupled using 220pF capacitors, which must be located as close as possible to the IC pins. The tuning voltage at pin 2, TUNE, may lie between +0.4 V and +2.4 V, which provides a tuning range between 2.4 GHz and 2.5 GHz. If it is desired to switch off the oscillator, this can be done by connecting the Shutdown input (SHDN) to earth potential. When the IC is shut down, its current consumption drops to around 1 µA. Here the shutdown input is connected to the Vcc potential by a pull-up resistor, so that the oscillator runs. The –3 dB output level can be reduced using the indicated pi attenuator. A number of resistance values for this attenuator are shown in the table.

source: Elektor Circuit Collections 

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Step-up Switching Regulator with Integrated Current Limit

 


In the form of the LT1618, Linear Technology (www.lineartech.com) has made available a step-up switching regulator with a current limit mechanism. This makes it easy to protect an otherwise not short-circuit-proof switching regulator: the input voltage is always connected to the output via an inductor and a diode. We can limit the current at the input (Figure 1), which limits the current drawn by the entire circuit; alternatively, with the circuit of Figure 2, the output current can be limited. This enables the design of constant current sources at voltages higher than the input voltage. In the circuit shown the nominal output voltage of the step-up switching regulator will be around 22 V. The output voltage can be calculated using the formula

Vout = 1.263 V (1+R1/R2)

The output current can be set via R3 as follows:

Imax = Vsense / R3
where Vsense = 50 mV

The IADJ input can be set to a voltage between 0 V and +1.58 V resulting in a linear reduction of the limit current.
The sense voltage of 50 mV across R3 for maximum current is reduced as follows:

Vsense = 0.04 (1.263 V – 0.8 VIADJ )

Hence, for a fixed value of R3, the VIADJ input allows the current limit to be adjusted. Note that in the first circuit the sense resistor R3 is fitted between the input electrolytic capacitor and the inductor. If R3 is fitted before the capacitor, the inductor current can not be properly controlled.
The LT1618 operates on input voltages between +1.6 V and +18 V. Its output voltage must lie between Vin and +35 V. With a switching current of 1 A through pin SW to ground, an output current of around 100 mA can be expected. The switching frequency of the IC is about 1.4 MHz, and the device is available in a 10-pin compact MSOP package.
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Li-Ion Protection Circuit

 


When a lithium-ion battery is discharged below the minimum recommended cell voltage its life expectancy is dramatically reduced. The circuit described here can avoid this by disconnecting the load from the battery when the cell voltage reaches a set level.The voltage at junction A may be set to 3 V, for example, by selecting the correct ratio of R1 and R2. When the battery voltage drops below the minimum value, the voltage at junction A will be smaller than that at junction B. The latter voltage is equal to: 

VB = 1.25 V + I R4 = 1.37 V

where:

I = (Vmin. – 1.25 V) / (R3 + R4) = 800 nA
(Vmin. = minimum value)

At this point the output of opamp LT1495 will go high, causing SW1 (a P-channel logic level MOSFET) to block and break the connection between the battery and the load. Because the battery voltage will rise when the load is disconnected, a certain amount of hysteresis is created by the addition of R5. This prevents the circuit from oscillating around the switching point. The value of R5 shown here provides 92 mV of hysteresis. So the battery voltage has to
rise to 3.092 V before the load is reconnected to the battery. An increase or decrease of the hysteresis is possible by reducing or increasing the value of R5, respectively. The required hysteresis depends in the internal impedance of the battery and the magnitude of the load current. The switching point defined by the values of R1-R2 is
quite critical with a circuit such as this. If the switching point is too high, then the available capacity of the battery is not fully utilised. Conversely, if the switching point is too low, the battery will be discharged too far with all the harmful consequences that may entail. Using the values shown here and including the tolerances of the parts, the switching point is between 2.988 V and 3.012 V. In practice it may be easier to select slightly lower values for R1 or R2 and connect a multi-turn trimpot in series with it. This makes an accurate adjustment of the switching point possible and has the additional advantage that R1 and R2 may be ordinary 1%-tolerance types.

Finally, before using the protection circuit it is advisable to first connect it to a power supply instead of a battery and carefully verify the operation of all its features!
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Measuring Inductors


Often you find yourself in the position of needing to wind your own coil for a project, or maybe you come across an unmarked coil in the junkbox. How can you best find out its inductance? An oscilloscope is all you need. Construct a resonant circuit using the coil and a capacitor and connect it to a square wave generator (often part of the oscilloscope itself) Adjust the generator until you find the resonant frequency f. When C is known (1000 pF) the inductance L may be calculated from:

L = 1 / (4π2⋅f2⋅C)

If you are also interested how good the coil is i.e. what is its quality factor or Q, you can use the oscilloscope again. If the level of the damped oscillation drops to 0.37 (= 1/e) of the maximum after about 30 periods, then the Q factor of the coil is about 30

The Q factor should be measured at the intended operating frequency of the coil and with its intended capacitor. The coupling capacitor should by comparison be a much smaller value.

source : Elektor Circuit Collections 
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Two Position Dimmer


This super-simple dimmer consists of only two components, and it can easily be built into a mains switch. If you do this, don’t forget to first switch off the associated branch circuit in the fuse box, since the mains voltage is always dangerous! The circuit does not need much explanation. When S1 is closed, the lamp works at full strength, and the position of S2 does not matter. When S1 is open and S2 is closed, the capacitor causes a voltage drop, so the lamp is dimmed. The power dissipation of the capacitor is practically zero, so the circuit does not generate any heat. The resistor prevents sparking when S2 is closed while S1 is already closed. The value of the capacitor can be matched to the power of the lamp to be dimmed; it should be between 2 and 6 µF. Be sure to use a class X2 capacitor. Also, don’t forget that thiscircuit works only with resistive (non-inductive) loads. Unpredictable things can happen with an inductive load!

source : Elektor Circuit Collections 2000-2014


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Wideband PC Radio

 

PC radios are certainly nothing unusual. However, unless you are prepared to spend a lot of cash you can't buy a wideband PC radio that receives short-wave signals — if you want one that will not break the bank, you will have to build it yourself. There's no need for a battery or power supply, since power can be drawn directly from the PC serial interface. The audio signal is fed into the PC sound card. The circuit diagram in Figure 1 shows this simple audion receiver. The transistor in the common-emitter circuit demodulates AM signals, thanks to its exponential characteristic curve. Since the base-emitter junction is already biased, RF potentials of a few millivolts are sufficient to achieve demodulation. For this reason, the audion circuit is significantly more sensitive than a simple diode detector.


So where is the tuning capacitor? It's not needed, since the receiver has an extremely wide bandwidth and (simultaneously!) receives all strong signals ranging from the 49-m band to the 19-m band. The coil is wound in two layers with 15 turns on a pencil. This yields an inductance of around 2 uH. The resonant circuit capacitance of around 100 pF is composed of the base capacitance of the transistor and the aerial capacitance. This places the resonant frequency at around 11 M Hz. The low input impedance of the transistor damps the resonant circuitto the pointthat its Q factor is 1, so the bandwidth is also around 11 M Hz. The receiver thus picks up everything between 6 MHz and 17 MHz. This complete elimination of the usual selection leads to surprising results.


Less is more. For communications technicians, this means: less selectivity = more bandwidth = more information. Indeed, here you dive into a sea of waves and tones. The special propagation conditions for short-wave signals cause first one signal and then another signal to predominate. You hear messages in several languages atthe same time, music ranging from classical to pop and folk songs from distant countries. Without the bother of the usual dial spinning, you can roam at your leisure through the entire short-wave region.


The supply voltage for the radio must be first switched on by using a program (HyperTerminal is adequate) to switch the DTR lead of the serial interface from -10 V to +10 V. If you want to avoid this trouble, you can use a PNP transistor. The alternative circuit diagram shown in Figure 2 shows some additional improvements. The coupling capacitor prevents the dc component from reaching the input of the sound card, and residual HF components are shorted out by the parallel capacitor. With these modifications, the radio is also quite suitable for direct connection to a stereo system, final amplifier or active speaker. In such cases, you can do without the PC and use a battery (1.5 to 12 V) instead. A downpipe from the eavestrough can be used as an aerial if it is insulated at its lower end (where it connects to the sewer system) by a rubber ring or concrete. If you are not so fortunate as to have access to such an arrangement, you will have to rig a wire aerial (at least 5 m long).

source : Elektor Circuit Collections 



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Single-Opamp 10-MHz Bandpass Filter

 


A bandpass filter is usually used to pass frequencies within a certain frequency range. If a high-performance opamp is used, such a filter can also be used at relatively high frequencies. As shown in the schematic diagram, here we have chosen an OPA603, which is a fast current-feedback opamp with a 100 MHz bandwidth for gain values between 1 and 10 (0 to 20 dB). If the circuit only has to handle a narrow range of frequencies, as in this case, the gain can be increased.


 With a current-feedback opamp, just as with an ordinary opamp, the negative feedback between the output and the inverting input determines the gain. In addition, the impedance of the feedback network determines the open-loop gain and the frequency response. With the component values shown in the schematic diagram, signals outside the passband are attenuated by 22 dB. The centre frequency of the filter is 10 MHz. As indicated by the printed formula, the centre frequency can easily be altered. However, keep in mind that 10 MHz is roughly the maximum frequency at which this circuit can be used. The circuit can be powered by a supply voltage of ± 15 V.

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0-44 dB RF Attenuator

Anyone who has to reduce the amplitudes of RF signals in a controlled manner needs an attenuator. Linearly adjustable attenuation networks using special PIN diodes are available for this, but they require quite intricate control circuitry.

A simpler solution is to use an integrated attenuator that can be switched in steps. The RF 2420 is an IC built using gallium- arsenide (GaAs) technology, which works in the frequency range between 1 MHz and 950 MHz. It can thus be used as an attenuator for cable television signals, for example. The attenuation can be set between 0 and 44 dB in 2-dB steps. An insertion loss of 4 dB must also be taken into account. This base attenuation can be measured in the 0-dB setting, and it forms the reference point for switchable attenuation networks that provide 2, 4, 8, 10 and 20 dB of attenuation. These are all controlled by a set of 5 TTL inputs. The control signals must have Low levels below 0.3 V and High levels of at least +2.5 V The RF 2420 works with a supply voltage between + 3 V and + 6 V, with a typical current consumption of 4 mA. A power-down mode, in which the current consumption drops to 0.8 mA, can be activated by removing power from the bussed V DD - pins.

The sample circuit diagram for the RF 2420 shows that the only external components that are needed are decoupling capacitors. The coupling capacitors at the input and output determine the lower operating frequency






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10 to 1000 Oscillator


Nowadays, it is no longer necessary to use discrete components to build oscillators. Instead, many manufacturers provide ready-made voltage-controlled oscillator (VCO) ICs that need only a few frequency-determining external components. One example is the RF Micro Devices RF2506. This IC operates with a supply voltage between 2.7 and 3.6 V (3.3 V nominal) and provides a low-noise oscillator transistor with integrated DC bias setting. In addition, it has an isolating buffer amplifier that strongly reduces the effects of load variations (load pulling) on the oscillator. If a voltage less than 0.7 V is applied to the power-down input (pin 8), the oscillator is shut down and the current consumption drops from 9 mA to less than 1 uA/A. The VCO is enabled when the voltage on pin 8 is at least +3.0 V

Connecting the feedback capacitors CI and C2 to pins 3 (FDBK) and 4 (VTUNE) transforms the internal transistor into a Colpitts oscillator. A resonator is also needed; here this consists of C4 and LI, and it is coupled via C3. Keep the Q factor of the coil as high as possible (by using an air-core coil, for example), to ensure a low level of phase noise. Since most applications require a tuneable oscillator, the varicap diode Dl (BBY40, BBY51, BB804 etc) can be used to adjust the resonant frequency. The tuning voltage is applied via a high resistance. The value of the tuning voltage naturally depends on the desired frequency range and the variable-capacitance diode (Dl) that is used. The table RF2506 shows a number of suggestions V o for selecting the frequency-determining components.


If the frequency range is narrow, FDE a parallel-resonant circuit should vtui be connected between the output pin and +V CC , to form the collector load for the output transistor. This can be built using the same components as the oscillator resonator. With a broadband VCO, use a HF choke instead, with a value of a few microhenries to a few nanohenries, depending on the frequency band. In this case C6 is not needed. The output level of this circuit is -3 dBm with an LC load and -7 dBm with a choke load.

The table that accompanies the schematic diagram provides

rough indications of component values for various frequencies. It is intended to provide a starting point for experimentation. The coupling between the variable-capacitance diode and C5 determines the tuning range of the VCO. The manufacturer maintains an Internet site at www.rfmd.com, where you can find more information about this interesting oscillator IC


source : Elektor Circuit Collections 2000-2014

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Simple RF Detector for 2 m

This simple circuit helps you sniff out RF radiation leaking from your transmitter, improper joints, a broken cable or equipment with poor RF shielding. The tester is designed for the 2-m amateur radio band (144-146 MHz in Europe).

The instrument has a 4-step LED readout and an audible alarm for high radiation voltages. The RF signal is picked up by an antenna and made to resonate by CI -LI. After rectifying by diode Dl, the signal is fed to a two-transistor highgain Darlington amplifier, T2T3. Assuming that a 10-inch telescopic antenna is used, the RF level scale set up for the LEDs is as follows:


When all LEDs light, the (optional) UM66 sound/melody generator chip (IC1) is also actuated and supplies an audible alarm. By changing the values of zener diodes D2, D4, D6 and D8, the step size

and span of the instrument may be changed as required. For operation in other ham or PMR bands, simply change the resonant network CI -LI.

As an example, a 5-watt handheld transceiver fitted with a half-wave telescopic antenna (G = 3.5 dBd), will produce an ERP (effective radiated power) of almost 10 watts and an e.m.f. of more than 8 volts close to your head.


Inductor LI consists of 2.5 turns of 20 SWG (approx. 1 mm dia) enamelled copper wire. The inside diameter is about 7 mm and no core is used. The associated trimmer capacitor CI is tuned for the highest number of LEDs to light at a relatively low fleldstrength put up by a 2-m transceiver transmitting at 145 MHz.

The tester is powered by a 9-V battery and draws about 15 mA when all LEDs are on. It should be enclosed in a metal case.

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Noise Injector



This Circuit is primarily intended to be used by persons who want to experiment with audio. For example, you can determine whether your own audible threshold for noise is different with and without music, or whether a particular CD sounds better with a little bit of noise. However, since this circuit produces white noise, it can also be used for test measurements, such as comparing the sounds of different loudspeakers, measuring filter characteristics and so on. The measured characteristics, as shown in Figure 2, show a nearly flat amplitude distribution (averaged over 64 measurements). The effective value of the noise signal at the output is around 100 mV maximum (with both potentiometers set to maximum), measured over the frequency range of 22 Hz to 22 kHz.

The noise is generated by reverse-biasing the base-emitter junction of a PNP transistor (BC557B) so that it zeners. In our prototype, the voltage across Tl was approximately 10 V. PI is used to set the level of the generated noise so that it is just audible, following which the output level can be adjusted using the logarithmic potentiometer P2. For making measurements, PI can also be simply set to its maximum position. The noise is amplified by two opamp stages. Depending on the transistor manufacturer, or the type of transistor if you use a different type, the level of the generated noise can vary significantly. Using two amplification stages in series provides more options and considerably more bandwidth, and you can implement various filter characteristics around ICla and IClb according to your own taste. The gain of the two stages has been kept equal to ensure the maximum possible bandwidth. The amplified signal is then passed to a simple summing amplifier (IC2). We have used a stereo arrangement, in which both channels receive the same noise signal. If you want to expand on the design, you can provide each channel with its own noise generator. In this case, you will have to use a dual potentiometer for P2.

The well-known NE5532 is used for the amplifiers, but any other good dual opamp would also be satisfactory. The opamps are fed from a standard, symmetrical ±15-V supply. In order to suppress possible positive feedback via the power supply, and to reduce the effects of power supply noise (since the opamps are non-inverting), the supply for the noise diode circuit (Rl and Tl) is separately stabilised by IC3 (7812) and extra filtering for the ± 15-V supply is provided by C8 and C9. IC3 must be located as close as possible to Rl, Tl and IC1. The coupling capacitors CI and C2 are necessary to prevent the DC component of the noise signal from appearing at the outputs.

The table lists some measured characteristics of the circuit, for a bandwidth B of 22 Hz to 22 kHz and a reference level of 2V eff .









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