RF Transceiver

Written by Lim Siong Boon, last dated 06-Jul-08.

email:    contact->email_siongboon 

website: http://www.siongboon.com



KRF-DTR401 FM Transceiver




My KRF-DTR401 is a low cost FM transceiver brought from Kingtronic RF Corp. It is brought together with the AM transceiver that I use for research in Teleradio Engineering. The AM transceiver seems working well with the signal generator, but I had never get to implement it to sent digital data. My test on KRF-DTR401 was a failure because I cannot get it to work. It was the discovery of the RF encoder and decoder IC, that motivated me to test my FM transceiver again. Subsequent transceiver test were successful and RF encoder/decoder were eventually used as a medium to send digital bits. In another term, RF encoder/decoder is like a modem. A modulation and demodulation for digital signal.

After working successfully on my first transceiver, I started souring for other transceiver for research purpose. It is at that time, I have noticed that some of the transceiver have similar specification. The circuit layout is compared and found very similar in various area. After further investigation, the IC chip they used in the PCB is the key to building this transceiver.


The circuit is simple and is mainly operated by the IC on the PCB board. It is actually originated from nRF401 IC from Nordic Semiconductor ASA.

The testing of the RF module couldn't have taken place without the development of my own dc-dc converter. Commercial module is available but cost is high. Voltage regulator is necessary for most electronics circuits project. Therefore learning to build a dc-dc circuit from discrete components is worth the effort.







Schematic for Data Encoder MC145026, Decoder MC145027.


2006-03-xx: There is a problem that was found during the attempt to use this design on my robot. The wire link from the transceiver and the decoder IC cannot be too far apart. Data error rate seems to be very high, and reception is very poor. It could be due to the weak signal strength, which should be resolve by using a digital buffer. The signal is digital from the output of the transceiver. If it is a transmission issue, then it will be quite difficult to troubleshoot without proper equipment.



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433Mhz AM Transceiver




433Mhz Transmitter

433Mhz Receiver

Dated: 2012-05-18

There are many RF transceiver module in the market. When the transmitting distance is a concern, my preference will be transceiver in the range of 80 ~ 500Mhz. Wireless module in the gigahertz range can achieve higher data transmission rate but transmission distance will be shorter, especially when deployed indoor.

433Mhz is a good choice for distance communication. These pair of wireless module form a one way communication. You can get these from PIC-STORE. Working in this frequency range, the antenna may be slightly long. The antenna can be just a simple wire. The interfacing can be easy as what is presented in this experiment, but in order to transmit useful information, data modulation will be recommended. Data modulation is a process which changes the physical signal to another format so that it is less prone to noise/error and is easier to decode.

The data rate for such a wireless setup is quite low, about 1~4Khz, but it is enough for most of the simple applications.

I have managed to setup a simple transmitter and receiver circuit. The schematic is attached below. The objective is to understand how the signal looks like. This will allows us to understand and make use of these raw transmitter/receiver for sending useful data. It is not so direct using these raw module. Pre-processing will be required in order to send information.

The picture shows two portion of the circuit. The left side is the 433Mhz transmitter, and a push switch (black). The right portion is the receiver which consist of the 433Mhz receiver and a LED indicator.

This is the schematic details of the simple setup. When the button is not pressed, the transmitter will send out logic 0. When the button is pressed, it will transmit logic 1.

The receiver will have a LED indicator which allows me to see the response when the button is pressed. When the receiver's data output is low, the LED will light up. When it is high, the LED will be off.

I have attached a video of how the response is when the button is pressed.

- Video of this setup. MVI_0275.AVI

In the video, you will be able to see that when the switch is not pressed (logic 0), the LED will blink continuously. When the button is pressed (logic 1) the LED will constantly light up (low output).

How the actual signal looks like? I managed to probe the data in of the transmitter, and data out of the receiver with my digital oscilloscope. They are presented in the following section.

Signal 1 (Transmitter, TTL input logic 0), Signal 2 (Receiver, TTL output pulsing signal)

The yellow line at the top is the signal input to the transmitter module (Signal 1). The blue line below is the signal output from the receiver module (Signal 2). The left scope display is the zoom out view, while the right is the zoom in view.

The transmitter is transmitting a logic 0. The output shows the periodic pulses indicating logic 0 or no transmission detected. This is the reason why the LED indicator keeps blinking. The receiver output is pulsing on and off.

The running pulse width is not consistent, ranging from 20ms to 30ms. The pulse period of 80ms is rather constant when I measure the falling edge.

Signal 1 (Transmitter, TTL input logic 1), Signal 2 (Receiver, TTL output signal pull down to 0.8V)

Now the transmitter is transmitting logic 1. The output signal is now constantly pull to 0.8V (I will consider it as logic 0). The logic 0 output will drive the LED constantly on, which is what we have observed earlier.

Signal 1 (Transmitter, transition from logic 0 to 1), Signal 2 (Receiver, output signal response)

This is how the transition looks like when the transmitter transmits from logic 0 to logic 1.

The response is pretty simple and within my expectation.

Signal 1 (Transmitter, transition from logic 1 to 0), Signal 2 (Receiver, output signal response)

This is how the transition looks like when the transmitter transmits from logic 1 to logic 0.

The response is a bit tricky. The receiver took some time to pulse it's output periodically. There is a consistent delay between the first pulse and the subsequent pulse. First pulse width is able 50ms, followed by a 150ms delay, before the periodic pulses return.

The pulsing period of 80ms (12.5Hz) is going to cause some issue when decoding the transmitting data. It will be very slow differentiating logic 0 and 1 from the transmitter.



The setup is further tested. The transmitter and receiver module is now 2m apart using separate power supply.

The experiment fails. The receiver did not response. Even when both circuit is place very near each other (10cm apart), the receiver fails to response. The pulsing signal is more random than the experiment above.

The antenna was then pulled very near the receiver module, the receiver starts to function properly as before.

I have came to read a relating article online. The symptom is very similar to what I have describe. The issue is due to improper tuning of the receiver. The module should works after proper tuning. I may have to verify this for my next experiment.






Experience on working with RF and magnetic field technology

During my work in Teleradio Engineering, I am task to research in the area of magnetic field. Eventually some ideas were came up with to test out on radiated electromagnetic field. Electromagnetic field is simply the energy form by magnetic and electric field. The theory details on electromagnetic field is very mathematically intensive as what I had go through during my diploma and degree courses. However the concept is actually quite simple. Mathematics is simply one of our human language which can accurately be used to describe the physical property of electromagnetic. The deriving of the mathematics has gone through a lot of work. Eventually electromagnetic can be accurately predicted by the famous Maxwell Equations.

Wow, you may think, four simple equation and they have describe almost over 90% of electrical and magnetic phenomenon. These four equation are headache to study.

Electromagnetic theory is a form of geometry mathematics. If you can understand the concept of volume, area and vector in school, you have the potential to master this subject. It is not as difficult as it seem to be. You will have to apply some imagination and interpret the electromagnetic concept because these thing is physically not visible.

A book that have great influence in my understanding in electromagnetic is "Electromagnetism for Engineers (An Introductory Course) 3rd Edition by by P.Hammond (University of Southampton, Southampton UK)". This book is fully recommended for beginners like me, as it has minimum mathematics which is very easy to read and understand. Most importantly, the book is thin and have sufficient pictures illustration.

Electromagnetic theory is a very useful in practice. The learning experience is applicable to a lot of engineering problem. I had manage to apply the knowledge to resolve lightings issue during my research work in Teleradio Engineering. It all started when I was confronted with my first commercial system (UV3, Under Vehicle Surveillance System) that I build for the company. A new chassis design were already in place before I join the company. After a test run, it is found to have lighting problem. The lighting positioning is wrong, resulting in dark images captured. We have to resolve this immediately because the delivery date to our oversea buyer is near. I am confronted by a problem which I was not trained to resolve in school. Number of simple reflector were made for testing but it does not seems to work well. I decided calm down and rethink the problem all over again. All our office's fluorescence lighting were switch off. The bulb is being switched on, as I observed the bulb glow, the radiation pattern of the bulb. Within the next few moment, electromagnetic concept surface in front of my mind. I had come up with a simple custom reflector design base solely on the radiation pattern and managed to resolve the lighting issue for delivery. Although the concept of reflector is quite simple, it took me over a year to be able to understand and explain the lighting's intensity distribution from all the various reflectors I have designed. I have spent much of my time in Teleradio doing reflector design and lightings research for camera vision.

The illustration of the light radiation from a bulb is very much similar in a way to electromagnetic theory.




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Singapore Customized, custom made Electronics Circuits & Kits



email:    contact->email_siongboon  

website: http://www.siongboon.com






RF reference:


RF IC chip manufacturer



Encoder/decoder controller

MC145026 (encoder), or SC41343

MC145027 (decoder), or SC41344

MC145028 (decoder)

HT-12E (encoder)

HT-12D (decoder)

HT-12A, HT-640, HT-648L, DPC-64, DPC-2400




Hobby Website









RF transceiver (Transmitter & Receiver)

RXLC-434, TXLC-434, TR-900-SC-PA, TR-xxx-SC-P,

TWS-434A $6.60 each, RWS-434, TX-99 $9.00 each, RX-99







Keyword: FM transceiver, nRF401 IC, KRF-DTR401, Transmission RF radio frequency, communication, encoder, decoder, MC145026 MC145027, Electromagnetic, wireless remote control