This is the latest status from the BARS Constructors group.
Our aim is to interface our ICOM 718 to a PC so that we can transmit the digital FSK (audio) on USB SSB from the ICOM, and receive audio for decoding digital FSK on the PC. Using for example the new WSJT-X software which supports many new digital modes.
FT-8
One digital mode that was introduced only in July 2017 is called FT-8. This has taken the amateur fraternity by storm, and hundreds of QSO are pouring across the ether using this mode. Attached is a short presentation I gave last week about FT-8. Have listen on 7074kHz to hear the signals.
BASIC DIGITAL COMMS
We are making progress in the development and design of a digital interface for our ICOM 718. I have read the manual twice, and tried to understand the connections, modes and numerous front panels buttons. One thing we did discover is that our ICOM needed a RESET before it was in the mode to output/input audio and provide more than 10W output!
Digital Mode Interfaces do three things:
Audio IN/OUT
PTT ON/OFF
CAT Data IN/OUT
1. Pass audio in and out between the ICOM and the Soundcard of the PC (if it has one, if not an external Soundcard is used) via isolating transformers and volume controls to avoid ground loops and set the levels for TX & RX.
We have tested this by connecting an audio output tone from my MacBook via a Soundcard - the STARTECH one we all purchased when we built the SRD receiver two years ago, to the ICOM. It needed 200mV p-p to output 10W RF on 40m (into a dummy load of course). We also tested the audio output which provided up to 500mV peak, by connecting to an external small Amp+LS. We also tested the use of the ICOM SEND connection (PTT) and this switched us to TX with no problems.
2. We need a cable on a 23 pin DIN plug to connect to the ICOM ACC port on the back of the Transceiver. This ACC plug provides some signals we need:
+8V
GND
AFO - audio output, 200-500mV
MOD - audio input, 100-200mV
SEND - PTT, low = TX
John tackled this, bought a 13 pin DIN and built a cable. I have to apologise to him as I told him we need only four wires, I forgot the +8V supply wire, sorry John… we need to add this.
In order to connect these signals to our interface we will need a multi-pin plug on the other end I have ordered a 5pin DIN plug and socket for this. Connections to be defined...
3. We need to connect to a USB port on the PC and derive from this virtual COM Port the RS232 signals (as you would get from a DB9 connector in the PC if it had one, but most PCs today do not support a DB9 RS232 connection). So a USB<->RS232 convertor has to be used, this is best implemented using a FT232 chip (a driver must be installed on Windows, the MacOS has one already). A cable can be purchased for a few pounds as a USB plug incorporating the chip and providing the six signals we need:
+5V
GND
TXD - used for CAT data
RXD - used for CAT data
RTS - used for PTT/SEND
CST
I have a cable in purchase. Note: the signals are not RS232 (+/-13V positive logic) but TTL 0/3V3 or 0/5V negative logic, active LOW.
4. Develop an isolated interface between the RS232/TTL RTS signal (active LOW) and the PTT/SEND connection (also active LOW) on the back of the ICOM. The RTS/TTL signal from the RS232 convertor is inverted by a BS170 MOSFET and drives the input to an optical encoder, the output pulls don the SEND line (PTT) of the ICOM718.
BOXING IT UP
After we have done this initial development, which is quite simple, it will be time to wire up a PCB and put the stuff in a box. This will give us basic digital comms.
CAT or CI-V
Then we can tackle the CAT system. CAT is called CI-V by ICOM (Computer Interface V-five). It is a single wire serial bus used for two way communication between the PC and the ICOM. The bus line is normally pulled HIGH by a resistor in the ICOM, and is pulled low by either our interface or the ICOM itself. When the interface pulls it LOW it is transmitting data to the ICOM, and when ICOM pulls it LOW it is sending data to the PC.
The USB to RS232 convertor (above) has two signals /TXD & /RXD to send data in/out of the PC from/to any digital software we are using for controlling the ICOM. Over the link a lot of the operating modes of the ICOM can be controlled, the most common of which is to switch bands and change frequency. Data is sent at a baud rate which can be programmed in the ICOM (I think/hope) as I read it the default is 19200baud which has to be set up in the PC software.
This hardware interface has yet to be designed.
SOFTWARE - volunteers please
We need a group of us to investigate, download and learn about the many software packages that are on the web so we know how they interface for Audio, PTT and CAT. And so we know what they can do (RTTY, PSK31, digital modes like WSPR, FT-8, JT-65, SSTV…).
So that’s where we are right now, progress. See you in a couple of weeks for more for the nest step - checking out our audio isolation transformers, both the ones I found on eBay or the one’s that Franks has kindly given us, to see which is best. We need to check also the audio signal levels coming out of the PC sound card (both Mac and PC I suggest).
