Construction of a Mini Kits GALI-74  Broadband Driver-amp kit - June 2023

In the pursuit of enhancing the output from the NanoVNA to facilitate VHF and UHF antenna gain range testing with the NanoVNA, the GALI-74 driver amplifier kit from MiniKits SA was chosen as a suitable broadband UHF amplifier.
 
The GALI-74 driver amplifier is a straightforward design with a wideband gain of +21dB, specifically designed to operate within the frequency range of 500kHz to 2GHz. Its primary application lies in serving as a transmitter driver, delivering an output power exceeding +18dBm at 1dB compression across the entire HF to 2GHz range. Notably, a mere input of approximately -6dBm (equivalent to 0.25mW) is required to drive the amplifier to its full power potential.
 
The basic kit includes a PC board and all the necessary on-board components. Furthermore, it provides additional components for optimizing the design to accommodate two distinct frequency ranges spanning from 500kHz to 2GHz. For detailed specifications and information about the GALI-74 amplifier, one can refer to the GALI-74+ Data Sheet. To ensure proper operation within the voltage range of +9 to 15VDC, a 78M08 regulator is mounted beneath the board.

Construction

The construction of the Mini-Kits GALI-74 driver amplifier was successfully carried out, with the assistance of a USB microscope, due to the small size of the SMD (Surface Mount Devices) components involved. However, individuals with good eyesight may not find the microscope necessary.
  
Throughout the construction process, a specific soldering technique was employed. It involved applying solder flux to the designated pads on the PCB board where the components were to be installed. The components were then positioned using tweezers, and while exerting gentle pressure on the part with either a toothpick or the tweezers, a small amount of solder was picked up with the soldering iron and applied to the contact side of the component and the corresponding PCB pad.

  
Once the PCB assembly was completed, it was housed within a compact aluminium enclosure. The enclosure featured SMA connectors at each end, allowing for convenient connectivity. 

Photo 1 Construction of the PCB under a USB microscope.

Photo 2 Completed assembly of the PCB

Photo 3 Completed PCB installed in aluminium encoser.

Photo 4 Completed amplifier.

Photo 5 Amplifier gain measurements with a NanoVNA.

The amplifier testing aimed to determine whether the desired gain was achieved using a NanoVNA. The basic set-up involved connecting Port 1 of the NanoVNA to the input of the amplifier. Subsequently, the output of the amplifier was connected to a 30dB attenuator, and then to Port 2 of the NanoVNA.
The inclusion of the attenuator served two purposes: first, it acted as a safeguard against potential damage to the NanoVNA; and second, it ensured that the signals remained within an appropriate range for accurate measurements.
As is customary with the NanoVNA, calibration was necessary following the through calibration procedure for the general set-up, excluding the Device Under Test (DUT) which, in this case, is the amplifier.

With the amplifier reinstated in the set-up and the NanoVNA configured with a bandwidth ranging from 100MHz to 800MHz, it displayed a gain of 22dB at the frequency of interest, 436MHz. This gain result across the spectrum from 100MHz to 800MHz generally aligns with the specifications outlined for the project.
 
Additionally, it was observed that the GALI-74 chip, which was utilized in the amplifier, exhibited only a slight increase in temperature. This indicates that the chip was operating within an acceptable temperature range, suggesting efficient performance.

Video of the construction and testing of the Mini Kits GALI-74  Broadband Driver-amp kit 

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Page last revised 07 September, 2024