mobo43

Description: The Motherboard, or Mobo v4.3.4 BETA, is an add-on board designed to connect to the Softrock v6.3 RxTx, transforming it into an all-band (160-10m) HF transceiver that is electronically controlled via USB. Developed by a team of radio amateurs, including core members Alex Lee (9V1AL), Mike Collins (KF4BQ), Loftur Jonasson (TF3LJ), Marc Olanie (F6IT), and Art Allen (KY1K), with contributions from many others, this motherboard eliminates the need for PAF modules. J2 provides power to the Mobo, while SW1 is a DIP switch that should not be installed; instead, a 4-pin female receptacle should be placed on the second row to facilitate the signal path for controlling the Si570 on the SR v6.3. A fully operational RXTX v6.3 is crucial for successful integration with Mobo v4.3. During the installation and removal of the Mobo, care must be taken to ensure that connections remain secure, as issues may arise from loose components. The Mobo supports up to eight onboard filters that can be multiplexed for both receive and transmit functions, with each filter housed on a plugin minifilter board, allowing for flexibility in filter topology and characteristics. Two sets of minifilters are available in the BETA: SET B, which includes 10 minifilters providing narrow bandwidth coverage from 160-10m. Each filter is configured as a bandpass filter (BPF) using three inductors and series and shunt SMT capacitors. For lower frequency bands (160-40m), builders can choose between SMT inductors or toroids, while higher frequency bands utilize toroidal inductors. Builders have the option to order SET A, SET B, both, or none (custom filters). The Mobo features eight plugin slots, enabling experimentation with different filter combinations. Isolation between the PC/USB and Softrock is achieved through separate digital and analog ground planes that are not galvanically connected. Control signals from the PC via USB to I2C are isolated from the analog side using the ADuM1251 chip, significantly reducing RF noise and spurious signals during reception. The Class A power amplifier, based on the Mitsubishi RF MOSFET RD16HHF1, achieves linear output for SSB and digital modes when biased appropriately through software control. However, linearity decreases when driven beyond Class A limits. Measured intermodulation distortion (IMD) ratios indicate the linearity of the entire transmit chain in the ALPHA build. For construction, builders can refer to common techniques for inductors to understand winding specifications, core specifications, and the assembly of toroidal and binocular inductors. It is recommended to consult Tom N0SS’s tutorial on basic soldering techniques, especially for those with limited experience. For advanced users, a reflow process utilizing solder paste and an electric oven can be employed to install SMT chips on the PCB, as demonstrated in a tutorial by Guenael Jouchet. Additionally, it is important to dissipate static electricity before handling components by touching a grounded metal object.The Motherboard, or Mobo v4. 3. 4 BETA, is an addon board to plug onto the Softrock v6. 3 RxTx, to transform it into an all band (160-10m) HF transceiver electronically controlled via USB. Mobo v4. 3. 4 BETA is developed by a team of radio amateurs. The "core" members are Alex Lee (9V1AL), Mike Collins (KF4BQ), Loftur Jonasson (TF3LJ), Marc Olanie (F6I TU), and Art Allen (KY1K), with valuable contributions from many others. (footer P19) J1 and (footer P15) J2 - thus replacing the PAF modules. With the Mobo, there is no need to use any of the PAF modules. J2 will also provide the power supply to the Mobo. (footer P30) SW1 - the 2nd row of headers underneath the DIP switch. Do not install the DIP switch SW1 and install a 4-pin female receptacle on the 2nd row. This will provide the signal path for the Mobo to control the Si570 on the SR v6. 3. A correctly functioning RXTX V6. 3 is essential to success with the Mobo 4. 3. You will be plugging the Mobo into and out of the RXTX several times during the project. When trouble-shooting, one wants to be able to rely (at least initially) on a proven assumption that the problem does NOT lie with the RXTX! From Robert NQ0T: "Make sure your RXTXv6. 3 is working properly. The MOBO didn`t work for me when I first threw the switch. In the midst of inserting and removing the MOBO over and over again, things came loose on the 6. 3 that I had thought were fine. On several occasions, I had to pull off the MOBO, put on the PAF, and BPF`s and verify that the 6. 3 was doing what it was supposed to. Having a functional 6. 3, I found, helped immensely in getting the MOBO to run. " Use of up to 8 onboard filters multiplexed for both Rx and Tx and electronically switched. Each filter is on a plugin minifilter board, with flexibility of filter topology and characteristics.

Two different sets of minifilters are offered in the BETA: SET B - 10 minifilters provide narrow bandwidth coverage from 160-10m. Each filter is configured as a BPF with 3 inductors and series and shunt SMT capacitors. For the lower freq bands, 160-40m, the builder can choose to use SMT inductors or toroids. Higher freq bands use toroidal inductors. The builder can order either SET A, or SET B, or both, or neither (roll you own). As there are 8 plug in slots on the Mobo, the builder can mix and match SET A/SET B/own minifilters for experimentation.

Isolation of PC/USB from Softrock. There are separate digital and analog ground planes that are not galvanically connected. All control signals from the PC->USB->i2c on the digital side are isolated galvanically from the analog and SR side with the ADuM1251 chip. This reduces the RF noise from the PC/USB/uController from reaching the sensitive Rx circuitry, resulting in almost complete elimination of PC/USB caused spurious signals during Rx.

Class A PA based on Mitsubishi RF MOSFET RD16HHF1 When biased to Class A (the biasing is done via software control and user customisable), a very linear output for SSB and digital modes is possible. When driven hard (beyond CLASS A limits), the linearity will decline. Measured IMD Ratios (a measure of the whole Tx chain`s linearity) on the ALPHA build are: You can review the common construction techniques for inductors for details on deciphering the winding specifications, core specifications, and construction of toroidal and binocular inductors.

If you are not experienced at soldering (and even if you are somewhat experienced at soldering), refer to Tom N0SS`s excellent tutorial on basic soldering techniques. For the more adventurous, there is a process using solder paste and an electric oven called the reflow process, which can be used to install all the SMT chips to one side of the PC Board.

This is documented by Guenael Jouchet in the following Youtube segment: Dissipate static electricity before handling any system components (PC cards, memory modules) by touching a grounded metal object