Low-noise RF Preamplifier

Overview

A low-noise 50-ohm broadband amplifier for early gain stages that functions at at a range or radio frequencies. Functions using the PHA-13LN+ (see parts list at bottom).

Project contribution by Lincoln Craven-Brightman, Research Engineer in the MR-PIGs group.

Design

The LNA is housed inside a 0.75" X 0.5625" X 0.58" RF enclosure from Lotus Communications Systems (see parts list at bottom). The enclosure takes SMA input and output, and requires 6+ V DC with ~75 mA of operating current. The enclosure is connected to the board and SMA GND. The current model does not have impedance matching incorporated.

This layout is adapted from the PHA-13 datasheet from Mini Circuits.

Specs

Gain

The LNA demonstrates a gain of above 20 dB over 1-100 MHz. Gain slowly falls off to 17 dB at 1 GHz, and drops sharply below 1 MHz.

Safety limits

The enclosure is fitted with a crossed diode on the input to protect the pre-amplifier. Preliminary testing showed the circuit survived 200 Watts of transmit RF power (~5% duty cycle). With >1 KW of power, the PHA-13 was damaged and had to be replaced. The other components inside the enclosure survived.

Testing

The LNA was tested on the Halbach table-top scanner (~3 MHz center frequency) as a gain stage, along with the Minicircuits ZFL-500LN+ [1]. It demonstrated similar SNR to the lab's current AU-1583 amplifiers when total gain was comparable, using different gain stages. The domain chosen as "noise" is delimited by vertical dashed lines. All testing data is included below.

Files

KiCAD file:
Media:lna_kicad.zip
Parts list:
Media:lna_parts.txt
Testing data:
Media:lna_test_data.zip