25WATT - RF DUMMY LOAD

Greetings Everyone,

A rugged  RF load - Dummy Load was tested in our RnD lab. Normally we use 20 No.s of  1K Resistors in parallel to make the RF load, it gets extremely hot while testing. In this circuit we are using a attenuator type of arrangement to equally dissipate the power. Resistors used is 2 watts rating but suspiciously seems to be 1 watt only. Circuit is given below:

                     
TEST RESULTS:
Tested the RF dummy load with 33 Volt D.C. at 600 mA Current for 1 hour. The resistor value changes from 49.7 to 48.9 which is really good in performance.

The picture below is the one before etching:

Ardunio - Silly Ohm Meter

Good Afternoon Everyone,

Well, our recent fever in Arduino is cracking up with silly projects. Although I have used it for many years now, the introduction to a new budding Engineer is always intriguing. The Arduino main site many simple and silly projects and tutorials to play and study. After going through some site, we found that something as simple and silly such as Ohm Meter, Voltmeter and Ammeter were not really covered. It may sound quite silly but for new aspirants its something new to learn.

So, getting back to the silly ohm meter, the setup is quite simple. Arduino has a very interesting way to display circuits in a picture manner. Hence, we would like to follow the same. Here is the wiring of the silly ohm meter.

Just a simple project that calculates the resistance of a resistor.  The circuit is based on a simple voltage divider.  First, a wire is connected from the 5V pin on the Arduino to the breadboard +5V bus. Then, another wire connects the Gnd pin on the Arduino to the GND bus on the breadboard.  

Now that you have power, put two resistors in series.  One should be your “known” resistance, we have used a 10K ohm resistor.  The other is the “unknown” resistor that we are trying to find the resistance.  In between these two resistors, another wire should be connected to one of the analogue pins on the Arduino, here we have used the Analog 0 pin.

Here is the Arduino code which calculates the unknown resistance, and outputs it to Serial Monitor on the Sketch program:

 
 //Silly Ohm Meter - RnD LAB's

 int aPinIn = 0;             // Analogue Input on Arduino  
 int val = 0;               // The raw analogue value  
 float Vout = 0.0;          // Voltage at point between resistors (relative to ground)                  
 float Vin = 5.0;           // Vcc (5 Volts)     
 float Rknown = 10000.0;    // The known resistor (10 kohms)   
 float Runknown = 0.0;  
    
 void setup(){  
    
  Serial.begin(9600);  
  digitalWrite(13, HIGH);  
    
 }  
    
 void loop(){  
    
  val = analogRead(aPinIn);           // Read in val (0-1023)  
  Vout = (Vin/1024.0) * float(val);   // Convert to voltage  
  Runknown = Rknown*((Vin/Vout) - 1); // Calculate Runknown  
    
  Serial.print("Vout: ");  
  Serial.println(Vout);               // Output everything  
  Serial.print("R: ");  
  Serial.println(Runknown);  
    
  delay(1000);                        // Delay for readability  
    
 }  

Arduino Fever

Greeting Everyone,

We recently conducted an introductory presentation on Arduino in SRJC College, Bangalore.

We have generally seen many people hesitating to use Microcontroller's as the complexity is large. Rather a sterotype myth has been created that one should know C-Language to program a Microcontroller and also study the architecture of the microcontroller in order to use it for basic purpose.

Hence many hobbyist, enthusiasts and thinkers have been withdrawn from implementing great ideas. Well lets bust that myth with the introduction of Arduino. The boards are developed such that the common board serves as a development board as well as a programmer. The board is quite cost effective and a very good method to adopt microcontrollers in hobbies, projects and everyday scenarios.

Homepage: www.arduino.cc

A short video of the presentation and the PPT is given below:-

Presentation: Click Here (PPT)

Loop Skywire Antenna

Good Morning and Season Greetings.

We setup an antenna in Jyothi Nivas College for the students who had recently participated in the workshop.

A Loop Skywire antenna was setup in the premises. The college had a good open area on the terrace with some building surrounding. We first constructed a base made of car tyre rims, which were welded with 2 feet of 3 inch diameter  poles. Later a 10 feet of 2.5 inch diameter poles were erected on four sides. Couple of concrete blocks were placed on the tyre bases for providing some stability.

Below is the sketch of the Loop Skywire.

Few calculations:

Length of the Antenna wire in feet is given by L(Total) = 1005/Freq.

Where, Freq. is measured in MHz and here we have taken 7MHz, so as per the calculation L(Total) = 144 Feet (approximated to the nearest value). So, each side of the the antenna is given by L(Total)/4 = 36 Feet.

Once the antenna was setup, we tested the antenna performance with a commercial HF rig. Sudhindra, VU3PWT was able to make receive stations from Spain, Tokyo and Northern India(New Delhi).

 

RF Amplifier using IRF510

Greetings Everyone,

Our old man Marcus,VU2VTM, has a golden principle of making any prototype more than once. And as a strong believer of the golden rule, we at RnD Labs have been playing around with RF Amplifiers a lot lately.

We had earlier made a RF Amplifier using IRF510. Again today we made yet another amplifier using the IRF510. Both the amplifiers are giving the same results and performance.

More details and description will be posted later once the complete analysis as been made.

Version 2

The earlier version is shown below:

Version 1

WIDE BAND RF POWER AMPILIFIER USING RD16HHF1

This RD16HHF1 pushpull amplifier specially designed for two band transceiver project.The circuit diagram is mentioned below.This amplifier uses pushpull configuration technique.

Advantages of pushpull amplifier

1.Low distortion.

2.High efficiency.

3.High power output.

FUNCTION:

Operating voltage of this wide band amplifier is 13.8volt dc

Each transistor is biased to draw 400ma without feeding input signal

In this pushpull amplifier two output devices operate in antiphase(ie180deg apart.)The two anti phase outputs are connectedto a load in a way that causes the signal outputs to be added.

This circuit consists of an (input 0-180deg) power splitter driving two identical devices in antiphaseand a (0-180deg) output power combiner adding the output of the two devices in the amplifier load. Splitting is done through the input coupling transformer T1. When Q1 is driven positive using the first half of its input signal the drain current of Q1 increases. At the same time Q2 is driven negative using the first half of its input signal and drain current of Q2 decreases.  Each transistor produces one half of an ac.

The transformer combines the two outputs to form full ac cycle. As a result an amplified version of input signal obtained in the transformer secondary.

Biasing in this circuit is given using the 5volt regulator through the resistor networks to the gate of the transistor.

REQUIRED POWER IS 5WATTS (AVERAGE), 10 WATTS PEP

TEST RESULTS:

4MHz - 16 watts average

7MHz - 14 watts  average

14MHz-12 watts average

    

TRANSFORMER DETAILS:

T1-4TURNS BIFILAR 26SWG ON 10MM TORROID

T2-3TURNS BIFILAR 26SWG ON 10MM TORROID

T3-3TURNS TRIFILAR ON 10MM TORROID

PRI- 20SWG

SEC-22SWG