Building your own wireless system - please read useful tips:

We will try to explain a basic and easy to understand  topics regarding the some wireless systems. If you have any question, you can email us.

• About small video transmitter CH 59 UHF 434 MHz:

 BLOCK DIAGRAM OF CH 59 VIDEO TRANSMITTER

The channel 59 video transmitter has a very stable saw crystal controlled circuit. The power output of this transmitter is app. 80 mW / 50 peak-to-peak - modulated. The oscillator was built in a stable Colpitz configuration. After the oscillator signal is going to an RF amplifier and mixer. Antenna ?wave is attached to the board. Modulator has two transistors in video amplifier configuration with a negative TV amplitude modulation over 75 %. The complete unit has 4 transistors. The currency consumption is 36 mA/ 9 V or 42 mA / 12V. This transmitter is inverse polarity protected. An RF output transistor is Motorola MMBR 941. The complete unit was built in surface mount technology. PC board is a high quality FR? material. Video amplifier was built in a stable configuration with an open video input. For Cmos cameras for the best results an resistor 220- 270 ohms must be added in serial connection to the video input. This video transmitter has excellent picture quality. The range is also great ?over 1000 ft LOS can be obtained with a high gain antenna on the receiving end. The signal 434 MHz very good penetrates trough walls so this unit can be successfully used for undercover operations. Similar unit is available for 900 MHz with a same power output and performances but it needs the receiver for 900 MHz.

Since the video input of this transmitter is not DC coupled some CMOS cameras will interfere the modulation with the DC voltage (app. 2 V out). The best way is to use a compensation resistor 100-270 ohms in serial combination with video input. The other method would be  the RC combination, 47 uF capacitor and a resistor 100 ohms before the input will work fine for any cameras. (see the picture).

• What is better 900 MHz or 2.4 GHz?

Most of 900 MHz systems are very good for transmitting the video signal trough walls. On the market you can get 900 MHz AM (amplitude modulation) or FM system. It is better to go with AM system. The reason is that 900 MHz AM system has 6 MHz bandwidth - compare to FM (frequency modulation) that has 18 MHz - 27 MHz bandwidth. This is why FM system is more sensitive for interferences. Sensitivity of receivers is important factor. For AM receivers the best results you can get with receiver that has app. -90 dBm /10 dB S/N or better. With 1 mW video transmitter (maximum allowed by FCC) and AM receiver you can obtain 100-300 ft range line-of-sight. Most of small video transmitters on the market have 5 mW -25 mW power and they can go maximum 500-750 ft or with a high gain antenna 6 dB  gain on the receiver side up to 1000 ft line-of-sight. If you transmitting trough walls it is much different. The range will be decreased drastically. The best results we've got with our World's smallest video transmitter SPX-916 model (clear 50 mW RF power) that will transmit up to fourth floor with amazing signal quality. The best unit was small HPX-916 with a full 250 mW RF power and an amazing range up to 3000 ft line-of-sight. This unit was built for Law enforcement and it was tested from the basement in the building that has concrete walls. The signal was excellent up to 8 floor! 

2.4 GHz systems are little bit different. The high frequency is not the best for transmitting trough walls even if you have a high power transmitter 1 W or more! Concrete wall will block the signal. Transmitters for 2.4 GHz will send a much higher video band then AM 900 MHz for example. They can transmit a broadcast quality picture. Tested results with SDX-1 video transmitter are excellent. This transmitter will send clear image up to 300 ft using the Wavecom or Lorex receiver. If you have a VRX-24L receiver the range would be two or even three times better with a high gain antenna on the receiving end. We have tested this system up to 1000 ft line-of-sight. With the World's smallest SDX-22 transmitter you can get over three miles line-of-sight from the airplane model that we have used in the open field. The receiver was again VRX-24L with high gain antenna 8 dBi. The range will be different and results may vary in the other areas and fields. The receiving section is critical. Some users think that they can increase the range of transmitters by adding different antennas - wires 2 m long etc; this is wrong. The cable from the high gain antenna 8 dB to the receiver must be only 1 ft- 1.5 ft long, otherwise the signal loss will be high. The cable has to be high quality with a proper SMA connectors on the ends. (see the picture).

• What kind of video camera is the best?

So many different cameras are on the market. Most of them are good quality, but sometimes they can break easily if you don't connect them properly. Most of small CMOS cameras on the market do not use a regulator 5 V (or 3V in some cases). By connecting the 9 V battery you can damage the board. Polarity is also important factor. Most of these cameras are not reverse polarity protected. The easy way is to use a universal diode as 1N4007 etc. They are only few cents but they will save your camera for a long time. Most of transmitters are polarity protected so you don't have to be worried. We have tested several camera models and some of the best are made by Sharp, Panasonic, Toshiba etc. Also some of Taiwanese and Korean companies make a very good camera boards. Make sure that camera has a good resolution. Over 320 lines will give you excellent picture quality for surveillance or experiments.