Single-Chip VHF RF Preamp

Description: This document presents a high-performance RF amplifier designed for the entire VHF broadcast and PMR band (100-175 MHz), which can be constructed without the need for specialized test equipment. The grounded-gate configuration offers inherent stability without requiring neutralization, provided that suitable PCB layout techniques are utilized. The amplifier exhibits commendable performance, with a noise figure below 2 dB and a gain exceeding 13 dB. This low noise figure and high gain facilitate better reception of lower-power local or campus radio stations, as well as distant amateur VHF stations operating in the 2-meter band. Due to the threshold effect, FM receivers may experience abrupt signal loss; thus, this amplifier can significantly enhance reception quality when signals fade while in motion. The MAX2633 serves as a low-voltage, low-noise amplifier suitable for frequencies ranging from VHF to SHF. It operates on a single supply voltage of +2.7 V to +5.5 V and maintains a virtually flat gain response up to 900 MHz. Its low noise figure and minimal supply current make it an excellent choice for RF receiving, buffering, and transmitting applications. The MAX2633 features internal biasing and allows for user-selectable supply current adjustment through the addition of an external resistor (denoted as R1). The circuit consumes only 3 mA of current. Besides the single bias resistor, the MAX2630 family of RF amplifiers requires only a few external components: input and output blocking capacitors (C1 and C3) and a VCC bypass capacitor (C2). The coupling capacitors must be sufficiently large to ensure negligible reactance in a 50-ohm system at the lowest operating frequency. The minimum value for these coupling capacitors can be determined using the formula: Cc = 53000 / flow [pF].

The RF amplifier circuit described is particularly effective in enhancing signal quality for VHF applications, making it suitable for various consumer electronics, including car radios and home stereo receivers. The design's simplicity allows for easy assembly and integration into existing systems. The grounded-gate configuration not only contributes to stability but also minimizes the need for additional components that could complicate the design or increase costs.

To further optimize performance, careful consideration should be given to the PCB layout. Proper grounding techniques and component placement can significantly reduce parasitic inductance and capacitance, thereby enhancing overall amplifier performance. The choice of capacitors for C1, C2, and C3 is critical; they should be selected based on their voltage rating and frequency response characteristics to ensure they perform adequately at the operating frequencies.

In applications where the amplifier is used for signal reception, it is recommended to implement additional filtering stages if necessary, to eliminate unwanted signals and improve selectivity. The amplifier's ability to operate efficiently across a wide frequency range makes it versatile for various RF applications, including communication systems and broadcasting.

In conclusion, the MAX2633 RF amplifier represents a robust solution for enhancing VHF signal reception, with a well-balanced design that prioritizes performance, simplicity, and adaptability for various electronic applications. The specified design parameters and careful component selection will ensure reliable operation and signal integrity across a range of conditions.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 no ise 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. 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:.