[TenTec] Bandswitching the 253 with OMNI VII or Orion

[CSM(r) Gary Huber]

I recently purchased a new OMNI VII and had to figure out how to band switch my model 253 Automatic Antenna Coupler (my Omni VI+ had the capability).  DXLab Suite Commander can take the Omni VII frequency information and with a device table unary code output a 4.4 VDC on one pin, 2-8 of the computer's parallel port (DB-25). The seven pins can drive pins 2-8 of a ULN2803 which outputs a higher current / voltage on pins 12-18 providing the 10-14 +VDC at 300 mA needed by the 253 tuner.

A ULN2803 is an Integrated Circuit (IC) chip with a High Voltage/High Current Darlington Transistor Array. It allows you to interface TTL signals with higher voltage/current loads. In English, the chip takes low level signals (TLL, CMOS, PMOS, NMOS - which operate at low voltages and low currents) and acts as a relay of sorts itself, switching on or off a higher level signal on the opposite side.

A TTL signal operates from 0-5V, with everything between 0.0 and 0.8V considered "low" or off, and 2.2 to 5.0V being considered "high" or on. The maximum power available on a TTL signal depends on the type, but generally does not exceed 25mW (~5mA @ 5V), so it is not useful for providing power to something like a relay coil. Computers and other electronic devices frequently generate TTL signals. On the output side the ULN2803 is generally rated at 50V/500mA, so it can operate small loads directly. Alternatively, it is frequently used to power the coil of one or more relays, which in turn allow even higher voltages/currents to be controlled by the low level signal. In electrical terms, the ULN2803 uses the low level (TTL) signal to switch on/turn off the higher voltage/current signal on the output side.

The ULN2803 comes in an 18-pin IC configuration and includes eight (8) transistors. Pins 1-8 receive the low level signals, pin 9 is grounded (for the low level signal reference). Pin 10 is the common on the high side and would generally be connected to the positive of the voltage you are applying to the relay coil. Pins 11-18 are the outputs (Pin 1 drives Pin 18, Pin 2 drives 17, etc.).

see http://www.dxlabsuite.com/commander/Help/Devices.htm and http://www.dxlabsuite.com/commander/Help/Configuration.htm#Device tabs 

Best regards,

CSM(r) Gary Huber - AB9M
9679 Heron Bay Rd
Bloomington, IL 61705
(309-662-0604)
www.csm-gh.com
glhuber at msn.com
gary.huber at us.army.mil