The DUC/DDC HF/VHF SunSDR2 transceiver
Description of the transceiver SunSDR2
This transceiver has been worked out subject to the long-standing work of the company on the issue of SDR-technical equipment. It combines advantages of direct conversion and direct synthesis of radio signals, namely: high image rejection for reception and transmission, high blocking dynamic range. Interface for connecting to the PC – local network (Ethernet LAN) allows the remote work with the transceiver, using local network. For instance, transceiver can be located in the radio shack along with noisy kilowatt amplifiers, and operator can carry out connections at the PC, sitting in a quiet flat tens meters far.
Main outstanding features
For normal work of the transceiver PC must have the following system characteristics. Transceiver can work with more up-to-date platforms, which surpass these system requirements.
PC system requirements:
Transceiver is being processed at the moment. Preliminary technical characteristics are in the Table 1.
Description of the SunSDR2 transceiver construction
SunSDR2 is performed on the 4- layers-PCB, 160х160 мм sized. The majority of the components is put on one layer. This board is set into the light anodized aluminum frame 165х165х35 mm sized. On the upper lid of the frame there is a radiator for heat removal. Passive cooling system is used in the transceiver on account of natural air convection.
Receiver (radio-frequency part) is divided into 2 separate parts for HF and VHF bands. Full block diagram is given below in the application with photos.
HF band receiver is composed of the following functional nodes:
VHF band receiver is composed of the following functional nodes:
The heart of the receiver is a specialized RF-unit LTM9001CV-BA, which consists of high-speed ADC with 160 MHz sample rate and operational amplifier with 20 dB gain. This unit produces instant analog-to-digital conversion all the radio signals incoming. After the conversion the signal turns into the digital code. All the further conversions are performed in a digital form and are the set of mathematical functions. A signal, conversed by RF-unit comes to the programmable logical scheme (FPGA), which has 2 (it will be possible to use 4) independent quadrature DDC – receivers. The main task of the DDC – receiver is the transfer of the incoming signals from the high-frequency region into the low-frequency region and receiving IF signals in quadrature (with the 90° shift). Then the signal enters PC via local net (Ethernet or WiFi) for further processing. It should be mentioned that first DDC – receiver is used for demodulating of the incoming signal, DSP processing and giving it to headsets, second DDC – receiver is used only for calculation and spectrum mapping on the panadapter of the ExpertSDR software.
Here there is a block-diagram of FPGA firmware.
Figure 1. Two independent quadrature receivers inside FPGA
NXP Cortex-M3 LPC1778 MCU performs functions of relay control, by ExtCtrl connector signal conversion from the current sensor of PA and power-meter/ SWR-meter and data transfer between the PC and receivers/transmitters of the transceiver. All the basic processing, namely: filtering, demodulating, digital processing of the signals (NB, NR, NF, ANF) occur inside of the PC with the help of SDR-software.
Transmitter is based on the direct synthesis of radio signals and is separated physically from the receiver. This way of the transceiver construction allows to use receiver and transmitter simultaneously, working in full duplex mode or using transmitter as signal generator, and receiver as spectrum analyzer.
The heart of the transmitter is a specialized Digital Up Converter chip(DUC). IQ-signals generated in FPGA are transmitted by bus in a digital form to the DUC chip. DUC produces mathematical operations on IQ-signals and generates a signal of the required modulation type. Generated signal is transformed from the digital form into analog one by built-in digital-to-analog converter (DAC). DAC works with 640 MHz sample rate and has 14 bits of resolution. Present DUC chip is able to fulfill direct signal synthesis of any form from 0 to 300 Mhz frequency range. There is LPF in the DUC output with 220MHz stripe cut for high-frequency components filtration inherent to digital/analog converters. After this LPF there is signal switching to HF and VHF transmitter. As it is known, different boosting elements are used in HF and VHF frequency bands, including powerful output stages, that’s why its effective to separate HF and VHF.
Transmitter is separated into two parts: HF and VHF.
VHF transmitter is also based on two-staged circuit. In the first stage of VHF transmitter there is a SGA-6286 chip of the wideband power amplifier. Through the capacitive connection boosted signal is given to the next amplifier stage. Output stage is based on the Mitsubishi RF power module RA08H1317M. This power module gives out up to 10 W of output power to load in the 135 MHz-170 MHz frequency range. Boosted signal is filtered by LPF with the 170 MHz pass band frequency. On the LPF output there is a measuring of output power. Filtered signal is given to load through antennas switch.
SunSDR2 has been designed in such a way that ExpertSDR software can update FPGA and microcontroller firmware automatically, meanwhile transceiver will be endued with new functions, which will be working out during all the product’s life.
For the HF transceiver has a 2 built-in antenna switch, giving the possibility to work for 2 antennas both with duplex and half-duplex. For VHF 2M band there is only one antenna connector. In figure 2 there is a PCB with the mounted antenna connectors.
Figure 2 – transceiver antenna connectors (1 and 2 – for the HF and 3 – for VHF).
Both chips, ADC and FPGA heat the board strongly enough, therefore there is a thick aluminum base, fixed on the other side of the board (Figure 3).
Figure 3 – Aluminum heat-removing base
LAN interface allows to use Wi-Fi access points, providing wireless work of the PC and transceiver, making it more convenient. PC user can be anywhere in a flat, while the transceiver can be in one place, for example, on the table, connected to the powerful amplifier. Moreover, optionally, access point can be integrated inside SunSDR2 transceiver to reduce the quantity of additional devices. This access point is a small up-to-date unit of the 802.11n standard.
Figure 4 – WiFi unit can be optionally integrated inside SunSDR2 transceiver.
Ethernet-cable and software CD disc are supplied with your transceiver.
You can purchase in addition transceiver power supply EE-PS-02 15В 5А