With Digirig Mobile getting all the attention, let’s not forget about its larger sibling Digirig Shack. I finally got some long awaited components and the new prototype is built and looking sweet. To my pleasant surprise, all of the peripherals are recognized by the computer and I’ll be testing the rig side of things soon.
Let’s look a the changes, and there are many..
Isolation moved to computer side
In the previous revision I used a traditional transceiver isolation approach with transformers for audio and opto-couplers for PTT. Ignoring the bandwidth limitations of the audio transformers, this would work reasonably well. The problem is that digirig refuses to be a traditional interface and it really wants to offer a fully featured serial CAT interface. In the initial revision CAT was left unisolated which makes little sense because isolation is kind of all-or-nothing proposition.
Isolating a two-way serial communication is a bit more involving than throwing in a bunch of opto-couplers; it also requires the isolated power on both sides of the border to light them up. It is all doable, but since we are getting into all this trouble we may as well do it for the serial interface on computer side (USB) which will isolate whole interface and allow us to get rid of the transformers. This approach was well tested with Digirig Mobile using a stand-alone USB isolator dongle.
Digirig Shack Rev 1.2 uses B0505S-1WR2 module for power transfer and ADUM3160 IC for USB transfer offering isolation of up to 1.2KV.
New Connectors And Custom Pinout
On PC side a small USB Micro-B gave way to a more appropriate full size USB B socket. On radio side a single RJ-45 replaced three 3.5mm TRS sockets. The 8 pins on RJ-45 can be individually assigned their functions using jumpers in DIP socket – a method that has been around for so long that it must be working. The choices are:
- +5V (isolated from PC) up to 150mA capacity
- Serial CAT TXD (3.3V CMOS level)
- Serial Cat RXD (3.3V CMOS level)
- Double-isolated Serial CAT RST (can be used to drive hardware PTT, CW etc.)
- Double-isolated Serial CAT DTR (can be used to drive hardware PTT, CW etc.)
- Custom test point (can be jumped to additional signals in serial interface and audio codec, info on that later)
- Audio Out 1 (Left)
- Audio Out 2 (Right)
- Audio In 1 (Left)
- Audio In 2 (Right)
- Ground for RST & DTR lines
- Common Ground
LEDs on the jack are indicating RX/TX activity on the serial interface. The auxiliary downlink USB connector is gone.
Dual Channel Audio Codec IC
Popular CM108 is replaced by quite a bit more expensive CM118B which offers dual ADC channels. With dual audio inputs and outputs Digirig Shack can theoretically handle two radios at the same time, which is yet to be tested. More importantly two wide band inputs should allow I/Q encoding offered by many SDR transceivers. This in turn unlocks a range of really impressive digital signal processing and apps.
Extruded Aluminum Enclosure
As with Digirig Mobile, the shack version is designed to fit inside a rugged anodized aluminum enclosure. Here is the look at unfinished version of the case.
My plan is to make some cables and take this new interface for a spin. Stay tuned for the updates on that. Also I look forward to your suggestions and critique of the shack version as it takes its shape. Let me know what features would you like to see added or killed?