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HF & VHF propagations

D is for Digital

D is for Digital

BY WAYNE YOSHIDA,* KH6WZ

A “Ham Notebook” Look at D-STAR and the “Mini-Industry” of Products It has Inspired Hams have always been an innovative group, so it comes as no surprise that when Icom introduced its implementation of D-STAR in 2004, early adopters saw something useful in this new digital communications protocol. (Notice I said protocol, and not mode. D-STAR is not a mode, it is a digital protocol.) I am not going to discuss DSTAR pros and cons; instead, let’s take a look at what Icom has brought to the amateur radio community by planting the D-STAR seed.

First, we should begin at the beginning. D-STAR stands for Digital Smart Technologies for Amateur Radio. It is an open standard digital communication protocol for digital voice (DV, 4800 bps) and digital data (DD, 128 kbps) established by the Japan Amateur Radio League (JARL). The JARL is an organization similar to the American Radio Relay League, ARRL, in the USA.

Up until just one year ago or so, Icom was the only radio manufacturer that produced ham radio equipment using this technology, so it may seem like the system is a proprietary offering in Icom radios and repeaters. I think Icom took a brave and risky step in committing the resources and finances to develop and sell off-the-shelf ham radio equipment for D-STAR. I am sure other radio companies are watching the Icom line of D-STAR capable radios from a business perspective, but we can watch those other companies from a consumers’ perspective to see if anyone else will step to the plate and introduce equipment for D-STAR. Some healthy competition will be good for this communication protocol, since it can help drive further innovation and continue to expand the number of users.

Since D-STAR is a digital thing, and digital means computers, it may be something mysterious and scary to analog-and RF-oriented folks. Think of this protocol as a wireless version of a computer network in your office, where various terminals are interconnected and each has access to the internet. In addition, there are levels of network connections, and stations can be configured to include or exclude certain individuals or groups (other D-STAR stations).

Since D-STAR operates on the VHF and higher bands, the radios look like traditional FM mobile and hand-held portable units, and so many may think D-STAR is “FM,” but it is not. In fact, the DSTAR modulation scheme is not compatible with FM. However, repeater and simplex operation does occur with D-STAR. But, because D-STAR is incompatible with standard FM, operations must be coordinated and comply with local band plans (a topic for another day; for a general discussion of repeater coordination and coordinators, see the “Riley’s Ramblings” column in last month’s CQ).

*28181 Rubicon Court, Laguna Niguel, CA 92677

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Technically Speaking

Bob Witte, KØNR, “FM” columnist for CQ’s sister publication CQ VHF, published an introductory article on D-STAR in the Winter 2009 issue of CQ VHF magazine. In addition, on his blog site, Bob explains that D-STAR uses Gaussian Minimum Shift Keying (GMSK), the same modulation format that Global System for Mobile communications (more commonly known as GSM or “2G”) cell phones use. Therefore, for those of you who, like me, find it hard not to call D-STAR a mode, its mode is GMSK.

As you look at the products briefly examined in this article, keep in mind what D-STAR is: It is a protocol, or in other words, a specification or definition of how a signal must be configured in order to be understood by the receiving party as it goes from one point to another. In addition, understand that D-STAR consists of two layers—a “transportation” layer (the RF channel) and the “encoding” or “digital” layer. Just like the computer term compatible, we should define what or how much compatibility there may be. If one defines compatible as “it just works,” we must understand how much compatibility there may (or may not) be: Does it work for both voice and data and text, or does it work only for voice? For example, many devices may be called a gateway to a D-STAR system, but only handle the DV portion, and may ignore the DD portion of the D-STAR protocol. Yes, the device may “work,” but there may be some limitations. For example, an e-mail or text message may or may not be received because a routing feature in the digital layer is missing. This is an oversimplified explanation, and the more technical articles mentioned in the References section provide more detail on the D-STAR specifications.

For units that use traditional “analog” FM radios, bear in mind that D-STAR uses a very narrow bandwidth of 6.25 kHz, while a typical FM signal occupies about 16 kHz.

Who’s Using This Stuff and Where are They?

Now that we basically know what D-STAR is, the next question is: Where are all these D-STAR stations located? A quick Google search finds sever-al pockets of D-STAR activity, and there is an interesting DSTAR repeater location map to see where these folks are. See the screen capture, fig. 1.

I asked my good friend and digital radio expert George Zafiropolous, KJ6VU, what he knew about D-STAR. He pointed me to his local radio club and its library of presentations. The Bay-Net radio club has been pretty busy with D-STAR projects. Take a look at its presentations, saved on its website, for some introductory information and interesting club project ideas.

Hot Spots

Meanwhile, those inquisitive and creative hams have been busy developing accessories and other items to supplement D-STAR activity. One example of the more popular gadgets is the D-STAR hot spot. Hot spots are a great way to get started with D-STAR, since they create a “gateway” into a D-STAR network without having to buy a complete radio.

Generally speaking, if you can gather and properly interface an analog FM rig with a 9600-baud data port (or access to the FM discriminator and modulator; . . . → Read More: D is for Digital