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YAM Multi-speed Modem


View of the AAPRA YAM modem 		AAPRA has introduced a new multi-speed modem to augment the existing very popular BlakPak 1200 baud FSK modem. The YAM "Yet Another Modem" was designed by Nico Palermo, IV3NWV originally for use at 9600 baud. It wasn't long before it was realised that the design was just as useful for 1200 baud FSK, not to mention 2400 baud FSK. Perhaps 4800 baud is next...

How is this possible?
The modem uses hardware that is reconfigurable to allow the different speeds to be chosen. What's more, this is all done under software control - there are no switches to flick or components to change. The secret is the programmable gate array - that big square chip on the picture below. The chip contains a huge number of gates that are hooked together when the chip is programmed. The program defines what the chip does - whether it's a modem or a LED flasher and what speed it operates at.

Nico, YAM's designer has put together an excellent web site which includes information on how the chip is programmed with an amazing amount of detail. It also has the circuit diagram and files for downloading including all the drivers and configuration files. Check it out at: http://www.microlet.com/yam

The YAM modem is housed in a small black "remote control" case measuring 138mm by 70mm by 28mm. At one end is the DB25 socket for connection to the computer COM port. On one side of the case there is a 5 pin DIN socket for connection to the radio. There are also three LEDs to indicate the state of the modem. There is no power supply input as the YAM is completely powered from the COM port of the computer just like the BlakPak modem.

YAM logo The AAPRA version of the YAM modem contains a number of modifications that improve the original design. The main one is the inclusion of a watchdog timer on the PTT signal allowing the modem to meet regulatory requirements for use unattended in Australia. The PTT circuit has also been changed to boost it's current sinking ability. Some changes have also been made to reduce the current consumption. These improvements are exclusive to AAPRA.

The YAM modem is assembled and fully tested "on air" by AAPRA and is supplied, together with WinPack software and drivers, an excellent manual which includes a full circuit description and cable connections for several popular radios for just $120. The modem is not available in kit form from AAPRA. We want to make it as easy to get going with the YAM as possible.


View of the AAPRA YAM circuit board

Specifications for the AAPRA YAM modem

Interface Serial asynchronous - DB25 socket
Operating modes: 1200 bps FSK
  2400 bps FSK
  9600 bps DFM
Radio interface 5 pin DIN (TNC2 compatible)
Power source Serial interface (DTR and RTS signals)
Current consumption Positive rail: < 8 mA, Negative rail: < 2 mA
Status indicators Power LED, Transmit data LED, Receive data LED
Transmit level Adjustable from 0 to 3.6 Volts p-p
Receive level 200 mVolts p-p minimum
Receive input impedance > 27 kohm
PTT current sink 300 mA maximum
PTT timer 10 second timeout in hardware
Physical dimensions 138 mm x 70 mm x 28 mm
Application software supplied WinPack 6.4
Driver software supplied SV2AGW PacketEngine v.2000
FPGA configuration time < 2 seconds at 115.2 kbps

Note: Specifications are indicative only and are subject to change without notice.
There have been: YAM count accesses since 22/2/00
Last update to this page: 29/2/00