Single-Chip VHF RF Preamp


Here is a high performance RF amplifier for the entire VHF broadcast and PMR
band (100-175 MHz) which can be successfully built without any special
test equipment. The grounded-gate configuration is inherently stable
without any neutralization if appropriate PCB
layout techniques are employed. The performance of the amplifier is
quite good. The noise figure is below 2 dB and the gain is over 13 dB.
The low noise figure and good gain will help car radios or home stereo
receivers pick up the lower-power local or campus radio stations, or
distant amateur VHF stations in the 2-metres
band. Due to the so-called threshold effect, FM receivers loose signals
abruptly so if your favourite station fades in and out as you drive,
this amplifier can cause a dramatic improvement. The MAX2633 is a
low-voltage, low-noise amplifier for use from VHF to SHF frequencies.

Circuit diagram:

Single Chip VHF RF Preamp Circuit

Single-Chip VHF RF Preamp Circuit Diagram

Operating from a single +2.7 V to +5.5V supply, it has a virtually
flat gain response to 900 MHz. Its low noise figure and low supply
current makes it ideal for RF receive, buffer and transmit applications.
The MAX2633 is biased internally and has a user-selectable supply
current, which can be adjusted by adding a single external resistor
(here, R1). This circuit draws only 3 mA current. Besides a single bias
resistor, the only external components needed for the MAX2630 family of
RF amplifiers are input and output blocking capacitors, C1 and C3, and a
VCC bypass capacitor, C2. The coupling
capacitors must be large enough to contribute negligible reactance in a
50-? system at the lowest operating frequency. Use the following
equation to calculate their minimum value: Cc = 53000/ flow [pF].
Further information: http://www.maxim-ic.com.

Author: D. Prabakaran – Copyright: Elektor July-August 2004


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