By Ivan De Cesaris IZ0JNY/HB9ETO
News: 2021-12-30
Introduction
Some users have had negative experiences with driving LDMOS amplifiers via their rigs; few transceivers are suspected of generating voltage spikes, which, even for a short time, greatly exceed the set output power, damaging the LDMOS of the linear power amplifiers. This scope of this test report is to analyze the behavior of the output voltage of SunSDR2 DX transceiver to understand if this problem is present.
Another additional test was done, to measure the maximum output power in different bands.
The ExpertSDR2software package is used to control the SDR transceiver. In receiving mode the software provides two independent receiving channels with up to 312 kHz bandwidth. Each receiver has its own sub receiver. ExpertSDR2 runs under Windows XP/7/8/10 x32 or x64, Linux Ubuntu x64 and MacOS (MacOS currently beta). Minimum hardware requirement Intel Core i3 1.6GHz or higher, video card supporting OpenGL 1.5 and RAM 256 MB or more.
An alpha version 0.10.0 of ExpertSDR3 software is already available for download on the official website of Expert Electronics: https://eesdr.com/en/software-en/expertsdr3en . Video card supporting OpenGL or Vulcan.
Instruments setup for output voltage spikes measurements.
The tests were carried out using a SunSDR2DX transceiver connected via a cable of about 20cm of the RG58 type, via UHF-259 connectors to a dummy load MFJ-264, capable of dissipating 1.5kW for 10 minutes.
To measure the output voltage we used a Tektronix MSO2012B oscilloscope, with a
10:1 probe connected directly inside of the MFJ-264 dummy load, as shown in Fig. 5.
This test was made using a PC equipped with an external sound card, brand Focusrite model 2i2 2nd generation, and a Marantz microphone connected on it.