I recently obtained a NW Digital ThumbDV Digital Voice Dongle to use with DMR and DSTAR. It contains a built-in AMBE3000 vocoder chip. Paired with BlueDV software it turns a computer with a USB port into a device that can communicate on both DMR and DSTAR networks.
I am impressed with the quality of the hardware as well as the simplicity of use. It’s quite convenient to plug a dongle into the computer and be able to monitor and talk on DMR or DSTAR without a radio using just the computer’s speakers and microphone.
After a year of assembling, programming, troubleshooting and tweaking, we recently put up a MMDVM (Multi-mode Digital Voice Modem) repeater for the south end of Davis County, UT. Last year I entered the world of digital voice with a purchase of an MD-380 digital DMR handheld radio. Since our area lacked good repeater coverage, I decided to try to build a repeater to help fill in some of the coverage gaps.
One of the hardest parts of putting a repeater on the air was simply getting a frequency coordination for the 70 cm band. The key pieces of the repeater are the actual MMDVM board that sits on an Arduino Due board. The Due is connected to a Raspberry Pi which runs G4KLX’s MMDVMHost software that interfaces with the MMDVM software on the DUE and connects the repeater to the Brandmeister DMR network. The radios are two Motorola CDM-1550LS+ radios connected via duplexer to a Diamond X-50A antenna.
Last week I bought a used Uniden BC890XLT scanner and added a discriminator audio tap. Here’s how I did it: The first thing to do was open the case. The outer sleeves come apart on the top and the bottom. There are 2 screws on each side and one screw on the back that I removed. I took both the top and bottom sleeves off to explore the inside, and discovered I only needed to remove the top to tap the discriminator audio. Once inside I found the location of the discriminator audio which is pin #10 of IC #3, 3359DA. Pin #10 is on the top right corner of the chip:
Rather than solder to the chip, I preferred to solder to the lead to the resistor at TP3 which is connected directly to PIN #10 of the IC. I put a 10K ohm resistor in series with a 10Î¼F tantalum capacitor.
I wanted this modification to be removable so I didn’t drill a hole in the case. Rather, I ran a connected wire to the outside of the case through an opening in the side of the case.
I then ran the wire in the space between the case and the outer sleeve on the side. I then ran it around the corner to the back of the scanner. I connected the ground wire to the chassis via the screw that holds the accessory RCA jack. I put heat shrink tubing on the outside of the wires and connected them to a 1/8″ mono phone jack.
Radio Shack Part Numbers: 1/4-Watt 10K ohm resistors – #271-1335 10Î¼F Tantalum Capacitor – #272-1436 1/8″ Mono In-line Phone Jack – #274-0333 Assorted Heat Shrink Tubes – #278-1627
I put together a box for the 2 Arduinos controlling my Motorola Maxtracs for monitoring the local 800 MHz radio system. I used a stock project box.
I modified it with openings for the USB and ethernet connectors as well as openings to insert two LEDs to indicate when the Arduino is being tuned.
Here’s a couple of photos of the project:
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