By James Reinholm
Although most people probably haven’t given it much thought, the invention of the coaxial cable was probably one of the most important discoveries ever made. Telecommunications and radio broadcasting would not exist as they are today without the invention of the coaxial cable.
Coaxial cables first started to appear in various applications back in the 30’s as a need developed for more efficient cabling systems with less interference. As more coaxial cables were used, standardised versions became available. Probably the most important parameter used in coaxial cabling is the characteristic impedance.
This is the main electrical characteristic that determines the level of power transfer and attenuation along the cable length, and also controls the amount of reflected and standing waves. Any type of coaxial cable is typically chosen based on the characteristic impedance. The main consideration is that impedance levels should match both at the transmitting and receiving end.
Although there are many standard impedances levels, the most common ones by far are the 50Ω and 75Ω impedances. These two standards are used for most coaxial cable applications, but other standards are also available in lesser quantities. For ordinary signal and data transmission applications, the cable that almost always chosen is the 50Ω type, while the 75Ω type is almost exclusively used for video signal and high-frequency RF applications, such as VHF (Very High Frequency) and UHF (Ultra High Frequency).
I’ve finally gotten around to assembling a breakout board for the Skyworks SKY65116 UHF amplifier. It’s really amazing how the state of the art in RF ICs has advanced. They can still be on the expensive side ($6 at digikey), but still relatively cheap when you consider the cost of all the support parts that it takes to build an amplifier from a RF transistor. This particular amplifier has a 50 ohm input and output, and 35dB of gain. It works from 390Mhz to 500Mhz, which means its perfect for the 70cm ham band. The breakout board is stupid simple, copied directly from the evaluation board schematic in the datasheet, but I’ll include schematic and design files anyway.
SKY65116 Amplifier - [Link]
A long time ago I built a radio using a Philips UV616/6456 TV tuner that is capable of receiving radio signals over a large range of frequencies. It ranges from 47MHz up to 860Mhz which gives me the possibility of decoding either Over-the-Air or Cable TV signals.
The problem is that the radio doesn’t have a frequency display, so tuning a particular frequency is always a challenge.
This project is about building a frequency counter, using a 2×16 LCD and a small PIC 18F1320 micro-controller.
VHF/UHF Basic Frequency Counter - [Link]
Atmel’s ATA874x single-chip UHF ASK/FSK RF transmitter family targets a broad range of proprietary wireless industrial and consumer applications such as metering, alarm systems and home control applications. This new AVR® product family offers RF performance operating in the license-free ISM frequency bands (868 to 928 MHz, 433 MHz, and 315 MHz).
AVR mcu with integrated RF transmitter functionality - [Link]
Dimitris at users.otenet.gr/~meteo writes:
I make simple RF field strength meter to test the remote control from doors ,alarm e.t.c at frequency VHF-UHF, i used one μΑ meter ,2 diodes ,2 ceramic capacitors,a potentiometer,a box ,and one telescopic antenna. When I press the button at remote control, there is small RF current and with this meter it can be detected. In that way you can understand if the remote works.
Simple RF field strength meter - [Link]