A versatile radio PC interface designed by IW6DFW Maurizio Malaspina
Inspired by the “Tone Keyed Sound Card Interface (Alternative design using opto-isolator output) [Rev 2]” published by Stephen H. Smith WA8LMF on 7 April 2003, I’ve designed the simple, cheap and home-brewable DIGIVOX interface documented in this paper.
The purpose of this project was to realize a simple to employ board able to connect, both handhelds and base station/vehicular rigs, to the audio board of a PC to easily start with digital communications at low-cost and reduced resources commitment.
All these preliminary requirements led to DIGIVOX (refer to schematic 1) with the following features:
· Power supply: 9÷13.8V DC (usually the same of the rig or a 9V battery).
· Galvanic insulation to and from PC audio board (2 x 600Ω 1:1 audio transformers)
· Selectable PTT handling mode between two settings:
o VOX: PTT is managed directly by the audio out signal of the audio board so no dedicated additional PC port is required. A long/short hang time up to about 100ms is settable via jumper to permit slow CW operation.
o UART: classical old style mode that requires a connection to a dedicated UART PC port. Note that, in this mode, the software must be able to handle this driving signal.
In every PTT operating mode, the coupling between the PC driving signal and the PTT input command of the radio is electrically isolated (either by opto-coupling or galvanically, as already mentioned).
Also a “transmission in progress” red led indicator permits the operator to check the communication status.
· Selectable PTT technology depending on rig: an RC network and a bypassable pure resistive attenuator network permit to connect to the PTT of an handheld radio (like my IC-E90) and fine tune the audio level of the signal entering the rig port, to prevent apparatus damaging. Alternatively it’s possible to connect a base station rig acting directly on its PTT pin. The configuration is selectable via dip switches.
To realize the interface I suggest to build the PCB (I’ve manufactured it using press-and-peel technique), using the 1:1 scaled master of Figure 3. Then all the THT components listed in BOM (Table 1)has to be soldered to get something similar to the the preview shown in Figure 1. Subsequently it’s necessary to realize seven wired links, like the ones shown in Figure 2.
All the necessary connections are reduced to a custom DB25 terminated cable that will connect DIGIVOX CON1 and on the other end to the rig and the PC using customized connection (jacks), and two power supply cable directly screwed on CON2.
Once the PC will be connected to the rig by DIGIVOX interface, setup it following the instructions of Table 1 to configure the DIGIVOX wished operating mode, then power up the system and run your favourite radio digital communication software to perform some tests.
If all is ok, welcome to the digital ham radio world and see you on air! Otherwise don’t esitate to contact me by e-mail.
Maurizio M., IW6DFW
