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Rs232/USB 1200 Baud Modem: Project & Kit

FoxDigi: 1200baud APRS Modem/TNC

MINI-TNC without MX614

Hamcom Interface : Project & Kits





 1200 Baud Radio Modem using MX614


Model: FD-RM1



Although Sound Card Interfaces are already there with good amount of free Sound Card software, there are always reasons to use a dedicated modem.

This modem is a true 1200-baud Bell 202 using a MX614 from Maxcom, making it ideal modem for VHF & Satellite digital work. Modem is self-powered as it takes power from either RS232 Com port of USB port.

MX614 is a low voltage low current modem chip. This modem is powered from RS232 or USB port. (Just like good old Hamcom!!)  Headers are required to be properly installed to select source of power: from a Com port or from an USB port.

For USB operation, a surface mounted FT232RL is used. This Chip includes crystal oscillator and requires minimum of external components: Get FT232RL Datasheet

Only required data Pins are used on PCB. BayCom Type Software Modem Requires : RTS, DTR & CTS. 

Please refer to FT232RL datasheet for details on use of C1 & C3, which may be installed to reduce EMI coming from USB port and so is C2, a 1000pf ceramic.

USB drivers for Win/Linux etc may be installed directly from FTDICHIP. When installed, these drivers create a virtual come port for your PC (com 3, 4, 5 etc)

Modem has front panel DIN5 connector to connect it to Rig Microphone and PTT line. A male connector is supplied with Kits to speed up Digital Mode setup. 

Basically this is RS232 Port Powered Radio Modem. USB is supported by using a RS232-USB Bridge Chip, which finally creates RS232 type of data lines.

Modem is presently available in RS232 Kits with Headers configured for RS232. USB chip version will be available soon. However, RS232 versions may be updated anytime by simply installing an FTDICHIP FT232RL chip.

Project is designed on 10cm X 5cm Double Sided PTH board and results were very encouraging. With this modem, perhaps, you will not require another modem in future

Schematic, Parts List Detailed Documents and USB Drivers are provided here for download.

Picture of the completed 1200 Baud Modem:



Click the image to enlarge



FD-RM1 1200 Baud RS232/USB Modem Document

1200 baud modem using MX614

Schematic & Parts List

1200 baud modem using MX614






Want to make your own PCB? Here are the Gerber files for double sided PTH boards

Baycom RS232 Connections

1200 baud modem using MX614

Component Datasheets

Datasheets for this project parts



With this modem, you can use many software available either as a freeware or shareware. Please go thru following links & find one suitable to your communication requirements.
USB Drivers for USB Kits

Digital Communication Software Collection


Digital Communication Software links


Understanding Digital Communication




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