UHF Preamplifier by MPSH10 transistor

This circuit is designed to work at UHF frequencies in the range 450-800MHz. It has a gain of around 10dB and is suitable for boosting weak TV signals. The circuit is shown below

The MPSH10 transistor used is available from Maplin Electronics order code CR01B. Alternatives that may be used instead are BF180 and BCY90. The tuned circuit comprising the 15nH inductor and 2.2pF capacitor resonate in the centre of the UHF band. The 2.2pF capacitor may be exchanged for a 4.7pF or a trimmer capacitor of 2-6pF to improve results. The approximate frequency response is shown below. N.B. This is a simulated response using the TINA program produced by using a swept 20uV input swept over the frequency range 400-800MHz. Output was measured into a 1k source and the frequency generator has a 75ohm impedance.

Construction
The coil is half a turn of 18-20 SWG copper wire bent around a half inch drill bit. This ensures a low Q and therefore broad tuning. High frequency work requires special construction techniques to avoid instability (unwanted oscillations) caused by feedback from output to input. Veroboard is not suitable for this project as the capacitance between tracks is around 0.2pF. A better approach is to use tag-strip or a PCB. The circuitry should be enclosed in a metal case and a screen made between input and output. As the transistor is used in common base mode,its low input impedance is a good match for 50-75 ohm coax cable, whilst at the same time providing full voltage gain to the upper frequency limit of the device. The 15nH inductor load, having almost a short circuit impedance at DC, has an impedance of 56ohms at 600MHz. This inductance and 2.2pF capacitor form a tank circuit at the transistors collector, providing maximum gain at resonance. Note however that the voltage gain will be reduced under load, when the circuit is connected to the input of a TV set or a very long piece of coaxial cable for example. Hence the simulated Tina plot.

Source : http://www.zen22142.zen.co.uk/Circuits/rf/uhfpreamp.htm

TV Signal Amplifier by BFR90, BFR91, BFW92
This is a small, broad band, TV signal amplifier which covers the frequencies from 40 to 900 MHz. These frequencies include TV in VHF and UHF and also the radio broadcasting frequencies in the 88 - 108 MHz FM band. It is connected between the antenna and the input of your receiver and boost ...
UHF TV linear amplifier 4W by BF136
That Circuit is a UHF TV linear amplifier for small TV transmitters with output aroun 100-200mW. The transistor BGQ136 comes with SOT-122 case has gain of 13dB at 800MHz. So with input 100mW you get 2W output and for 200mW you get 4W. Read Source: http://www.next.gr/inside-circuits/4Watt- ...
UHF TV Linear amplifier 5 W by BLW98
This small circuit is a Linear amplifier for driving small UHF TV transmitters. Its gain is 7dB and can amplify a signal between 450-800 MHz. You can drive the circuit with 1 to 1,5 Watts signal. Better use double layer PCB with the second layer connected to earth. Use a stabilized power sup ...
FM Wireless Microphone
Here is a very simple, inexpensive and interesting project which provides lot of fun to a home experimenter or hobbyist. This simple transmitter can transmit speech over a short range. It can be used as a simple cordless microphone. The circuit uses two integrated circuits from Maxim. IC1 a MAX4 ...
VHF Audio Video Transmitter by BF494
The circuit presented here is a simple audio/video transmitter with a range of 3 to 5 metres. The A/V signal source for the circuit may be a VCR, a satellite receiver or a video game etc. A mixer which also operates as an oscillator at VHF (H) channel 5 TV frequency is amplitude modulated by vid ...