Tag Archives: малошумящий усилитель

Low noise amplifier 1296 MHz

Low noise amplifier 1296 MHz

This article describes 23 cm LNA which was designed by UR7IJM and US4ICI together. A distinctive feature is the use of LNA MMIC in it in the input and second stages. The result is a high dynamic range and the big value of the maximum allowable input power. High dynamic range and big value of maximum allowable input power were achieved as result. Input SWR less than 1.1 what is unachievable usually when transistor is using at the input. Power can be supplied by use of transmission line or separate cable at the option. Polarity changing protection is provided. Interstage filter LPF and HPF, which features are extremely good linearity and possibility to withstand powerful input signal. It allows using this LNA on the contests, field days in conditions of radio amateur stations interferences which are working on the adjoining frequency ranges. Quite low noise ratio (less than 0.5 db) makes LNA attractive for EME QSO. Options with SMA and N input and output connectors are accessible for usability with different types of antennas. UHF design shell is made from aluminum by milling operation method and covered by composition for the tinning. Printed circuit board with via plating is soldered in the shell. It has allowed receiving perfect grounding between connectors and board. Amplifier has designed on base of chips MGA-633P and SPF5189. Input matching circuit was calculated by reflection coefficient for MGA-633P8. AVX company capacitors with low ESR and high Q was used in it. Input matching circuit has higher Q-factor against  SMD inductance because it is completed in form of microstrip. Thereby matching circuit has minimal losses it this versions and it benefit total amplifier noise ratio. Circuit diagram. Board size is 60х32 mm. It is made from FR4 1mm with via plating and mask. Printed circuit board. Comparative characteristic of LNA 23cm and well known LNA DB6NT, which has similar parameters and design, is provided below. Describable LNA 23cm has disadvantage by 0.1 db in noise ratio but it is better in IP3 and maximal output power. Difference in the price 3.5 times is undoubtedly attractive. Comparative characteristic of LNA 23cm and amplifier MKU LNA 132 AH from KUHNE electronic:

Parameters MKU LNA 132 AH LNA 23cm
Noise figure 0,4 dB±0,05 dB 0,50 dB±0,03 dB
Gain 33 dB 27 dB
Maximum RF input power 0 dBm 20 dBm
Output IP3 27 dBm ≈38 dBm
Supply voltage 9…15 V 9…15 V
DC current 80 mA 150 mA
Input connector/Impedance N-male/50 Ohm N-female/50 Ohm, SMA-female/50 Ohm
Output connector/Impedance N-female/50 Ohm N-female, SMA-female/50 Ohm
Input SWR ? 1,07

Noise ratio – frequency diagram

Noise ratio was measured by device Angilent N8975A. It is apparently from the picture that noise ratio is 0,47 dB. It is enough for performing routine QSO and participation in UHF contests.

LNA appearance in the milled shell

LNA in the milled VHF shell is represented on the photo. It is covering by tin-bismuth and has N-connectors.

LNA without cover.

LNA in the shell with SMA connectors.

Contacts us: Technical and others questions: us4ici@vhfdesign.com

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