Digital Modes

 

Multi Mode Digital Voice Modem

The MMDVM has to be one of the coolest things in amateur radio to come along in recent history. Through the use of these internet-connected gateways, ham radio operators can talk around the world with near perfect audio clarity on less than one watt of RF, and in some cases, no RF at all. For the ever increasing number of Home Owner Association (HOA) restricted residential properties disallowing radio antennas and towers, this technology is being well received.

There are three primary device categories that take advantage of this technology, all of which are user-friendly, cost effective, and widely available in many configurations, each evolving as quickly as one can stretch their imagination.

Hotspots

This is probably the fastest moving category of the three. There seems to be a constant flow of new gadgets - and modifications for existing gadgets - streaming off the manufacturing lines. The ever-growing interest and technology advancements fuels the imagination to create the next best thing.

I started down this path with a simplex ZUMspot v0.4 and Raspberry Pi Zero W v1.1. I found it amazing that this little device had an on-board transceiver and codec chip capable of YSF, DMR, D-Star, and P25 modes. These are much like miniature repeaters on steroids. With an internet connection, talking around the world on an HT is now within everyone's reach. That is very cool!

New duplex hotspots, dual-band VHF/UHF hotspots, and other new devices keep coming out. There's also a variety of OLED displays, Nextion displays, and cases to accommodate almost any modification. And with the advances in 3D printing, cases and holders of any size or shape are now possible.

There's a number of reputable hotspot manufacturers to choose from, however, there's also a number of cheap Chinese knock-offs to be weary of, so do your homework.

AMBE Servers

This is one of the more interesting and yet least ham-radio-like options. The AMBE server is similar to a digital hotspot in that it allows one to talk around the world in near perfect clarity to anyone on an internet-connected repeater, hotspot, room, talk group, network, etc. The difference is that no radio transceiver is required; all communication is done via computer and audio headset. Maybe someone will combine a hotspot with an AMBE server(?). Pretty cool, but with no RF, it seems to be straying pretty far from amateur radio as we have known it. I'll be exploring AMBE servers more later. 

Repeaters

Using an existing MMDVM repeater is by far the easiest and cheapest option for those living within reach of one. The hardest part will be locating the repeater's frequencies, and even that's easy. Tune your radio to the repeater frequencies, learn how to use the system, and it's all good. Happy days!

On the other hand, if you don't live within reach of one, then you will have to make or buy your own. This is, on the other hand, is no doubt the largest undertaking and most expensive option. There are a number of components needed for this type of system, and some can be quite expensive. 

One option is to purchase a brand name, manufactured repeater ($$$$). A less expensive option may be to build one yourself ($$$). A transmitter, a receiver, a computer for the controller, wiring harnesses, coax, and at least one antenna, in which case a duplexer ($$$$) is needed. A collinear or two antenna system is another option, but as I am discovering, this can be more expensive than the duplexer option.

Super-Mode?

A fourth category is beginning to take shape with the rise of cross-mode, trans-code MMDVM devices that enable different modes to talk with each other in real time. The result will make it sound like everyone is using the same mode, but their not. This is already happening on a small level, and will soon grow to the mainstream, so stand by.

Code links

MMDVM host and mode client code - G4KLX Jonathan

MMDVM / ZUMspot firmware - CA6JAU Andy 

Hotspot frequency offset calibration - K9NPX Daniel

Nextion screen layouts - PD0DIB Rob

Nextion screen layouts - WA6HXG Ryan

FreeDV

Innovation

ambeboard.zumradio.com - KI6ZUM James - More innovation from the hotspot maker

mmdvm.blogspot.com - Several innovators making leaps in MMDVM technology

mmdvm hotspots - N5BOC David - Layered PCB serves as ground plane and RF shield

freedv.org - Open source Digital Voice mode computer software for HF radio

Rowetel.com SM1000 - FreeDV Digital Voice adapter connects directly to HF radio, no computer

Tips and Tricks

FT-70D

Stop the squeal/squelch after receive from hotspot. Long-press the AMS button to turn off AMS.

ZUMspot

Read about my ZUMspot.

Firmware updates can be done within the Pi-Star software by going to the dashboard and clicking on Configuration, then Expert, then SSH Access. Log in to Pi-Star. The default username is  pi-star  and password  raspberry . 

First, enter the following commands to update and upgrade the Pi-Star software.

 rpi-rw 

 sudo pistar-update 

 sudo pistar-upgrade 

 sudo reboot 

After rebooting, go back to the SSH Access window and log in. 

Second, enter the following commands to upgrade the firmware.

 rpi-rw 

 sudo service mmdvmhost stop 

 sudo pkill MMDVMHost 

 sudo pistar-zumspotflash rpi   *

Follow the prompts after the last command. When it's done, it will prompt for a reboot. I suggest doing a hard shutdown after the soft reboot. Enjoy your new firmware!

* This text "zumspotflash rpi" is the firmware file name. Be sure to use the correct firmware file for your particular MMDVM device. This is for a ZUMspot Raspberry Pi hat.