Amateur Guide To Digital Radio
From the 'Lets Go Digital' series published by the Westlakes Amateur Radio club Magazine during 2017 
by Spero Davias VK2YHX

Let's Go Digital... By Spero Davias VK2YHX
So you want to join the digital revolution. This mode of our hobby is growing worldwide at a great rate of knots. I wont try and explain the operation and theory of DMR (Digital Mobile Radio) or any of the digital modes in this article, at this stage as there is enough information to get you going, floating around on google and its mate you tube.  I guess the best way to start understanding the systems is to jump in the deep end, register to receive your own unique ID, grab hold of a radio, then join in on the conversations where there are hundreds of Amateurs waiting to take you through the ropes.
The link to register your call sign and obtain your Id is here: https://dmr-marc.net/cgi-bin/trbo-database/userreg.cgi
DMR is just one of the many digital modes in use around the world today. Its a rival to Icoms long standing D-STAR and Yaesus System Fusion  and is actually a commercial system adopted by us Amateurs. DMR uses 12.5 Khz that is split in half, one for time slot one and one for time slot two. A good site to visit that explains a comparison of Amateur Radio Digital Voice systems is https://www.hamdigitaal.nl/?wpfb_dl=194
To clarify, just on DMR, there are a multitude of modes being used. There is the DMR Marc MotoTRBO network, DMR plus, dPMR and the BrandMeister Network, so, for all intents and purposes we will be refereeing to our local DMR as operating on the BrandMeister Network. To get a better idea of the system, check out the last heard or other associated pages on https://brandmeister.network/?page=lh
Even though there are a lot of modes to contend with, it seems that we are slowly moving to a single playground where we can all get along together.
To start the ball rolling, here in Newcastle, there are a number of MMDVM repeaters (Multi-Mode Digital Voice Modem) that have the capacity to run or repeat the four basic digital modes thats DMR, P25, Fusion and D-star. Unfortunately there is no single wide range repeater in the area at this stage (we are working on it). So as of today there are four low powered repeaters accessible to Amateurs.
One is located in the Hamilton area at my QTH, VK2YHX TXing on 438.750Mhz with a 7Mhz split and RXing on 431.750Mhz. Its Antenna of only around 10 meters ASL, is not in a good RF location but still manages a coverage to hand helds of about 4km plus radius.
Heading further south, Colin VK2GP is running a repeater from his QTH, which is at a fairly good site at Toronto which gets into most areas around Lake Macquarie and into the high areas of Charlestown. Cols MMDVM VK2RGP repeater TXs on 438.750Mhz with a 7Mhz split and RXs on 431.750
Just south of Col and around towards the Dora Creek area is Dans repeater, again mostly local coverage   TXing on 439.625Mhz and RXing on 434.625Mhz
The forth and most powerful repeater is running from Somersby on the central coast and is accessible from most higher parts of Newcastle and surrounds. Its callsign is VK2RAG and is TXing on 438.325Mhz and RXing on 431.325Mhz. but due to local intermods at the repeater site, Ian could be changing the repeater frequency soon.
Due to the amount of traffic on D-Star, Most of the above repeaters have this mode switched off but are still available for DMR Brandmeister, P25 and C4FM Fusion use. They are all fixed on the Australian 5051 Master network and transmitting on at least the 505-talk group. 505 is normally the AU talk group used by most Australians but its also available to anyone in the world.  So in other words anyone triggering the 505 talk group will fire up every repeater tuned to that TG
There are quite a few ways to get on air the simplest and easiest is using an existing repeater or for more versatility use your own local hot spot hooked up to your network router.
If you have a signal at your location from any of the local repeaters above, then all you need is a DMR Tier II, 2-slot TDMA 12.5 kHz wide radio such as the TYT-380 or 390. Eg.http://www.eham.net/reviews/detail/12544 the 380 seems to be the most popular radio on the network due to its cost and performance. You should be able to grab one on E-bay for around $120 plus programming cable, which is a great price for what you get.
Once you have the radio, its only a matter of programming the code plug which is a very confusing term that means to setup your radio with your ID, frequency for the repeater you are going to use, color code, repeater slot and talk group. This can become a bit messy until you get into it and learn some basics, so its easier to grab someone elses readymade code plug and just change the basics to suit your environment.
Hit the PTT and your away&
Keep in mind that all these modes are changing and upgrading continually and your technical contribution to the world of Digital could be very important during the progress of our Hobby&

More next time& 73s Spero VK2YHX



Lets Go Digital Part 2.....  By Spero Davias VK2YHX

Now that you have your DMR radio setup with the appropriate code plug you should be on the air & whats next& Lets put the hot spot aside for the time being, we should get around to talking about that soon. For now, lets concentrate on the basic operation of the MMDVM repeater.
Just to put you in the right frame of mind, on how old all this mmdvm technology is?, then check out this extract from less than 12 months ago on the MMDVM Facebook page&
The article says Adrian VK4TUX has reported the first DMR QSO via the MMDVM&. Adrian says, there is still some way to go, but we're getting there, Wow... weve come a long way in the last few months.The mmdvm repeater modem, as we know it today, is undergoing massive change so it could all be totally different by tomorrow.  Well funny you should say that, Im about to replace the Arduino DUE board with the new STN32 Nucleo in my MMDVM repeater
.
typical Amateur mmdvm repeater (top shelf) 2019

My MMDVM repeater, which is similar to others, comprises an Arduino DUE board or the newer STN32 Nucleo, an MMDVM board hooked up to a Raspberry pi, preferably a RPi3, or an Odroid C1+ device running the mmdvm image file on its micro SD card or the eMMC card on the Odroid. www.hardkernel.com/main/products/prdt_info.php?g_code=G143703355573
All this feeds a couple of standard Analogue Radios that have flat audio take-off point, then out into the network via a router. I found that the RPi2b will work ok but the newer RPi3 is more stable and reliable.
Today there a myriad of image files available on line, they all have very similar functions. I downloaded my image file and other helpful utilities from Adrian VK4TUX. Thanks for your support Adrian.
The Raspberry Pi holds the smarts that allows the 4 modes to live on the one repeater at the same time& the repeater scans the Receiver white noise listening for one of the 4 modes.
On DMR, it listens for a tiny bust of 30ms data, it recognises the sync pulse then the repeater allows your hand held or mobile radio to  go ahead on TX then it continues to hold up the repeater on transmit for the length of the over following the sync pulses.  
The repeater software is designed to keep the repeater transmitting continually for about 10 seconds of time after the over has ceased, this is called a modehang.  Once the time is up and no one else comes back to the DMR call the repeater receiver is free and waiting for another DMR call or any other mode such as P25, D-Star or C4FM fusion.
One of the benefits of DMR is that the repeater is transformed into TWO separate repeaters thus allowing two totally separate QSOs at the very same time on two different talk groups.
This results in spectrum efficiency of 6.25 kHz per channel. Comparing the spectrum efficiency of DMR to a wideband analogue FM, DMR only uses 25% of the bandwidth per talk channel or talk group.
This is done by Time Division Multiple Access. TDMA provides two logical channels. These are also known as slot 1 and slot 2.
Currently most amateur DMR repeaters utilize both channels for voice and some limited text messaging.
The BrandMeister mmdvm repeaters are all linked, normally via the internet back to a master controller in the country of use then out to a world master server.
An advantage of a DMR hand held is the extended battery life. By cutting the effective TX time in half, two slot TDMA can enable up to 40% improvement in talk time in comparison to analogue radios.

The only real disadvantage of DMR is its ability to communicate long distances. I dont think you will break any distance records using DMR due to the TDMA timing issue versus distance. Its theoretical working distance works out at 150km round trip from the repeater, thats a distance of about 75km from your hand-held radio, back to a repeater. The mobile equipment must synchronize accurately to the base station timing to avoid overlap of the TDMA slots.
But in saying this there have been reports from DMR users saying they have accessed repeaters over 200km away when atmospheric conditions allow.
One of our locals, Damian VK2XDL had a QSO recently with Adrian VK4TUX in Qld whilst Damian was at the Strzelecki lookout going in via the Sydney repeater on Governor Phillips tower, over 117km away.
During your digital experience, you might hear words like Color code. DMR repeaters use Color Codes (CC) much like analogue repeaters use CTCSS (PL) or DCS. To access a repeater, you must program your radio to use the same CC as the repeater. There are 16 different CCs (CC0-CC15). The use of Color Codes is not optional on DMR systems. If your Color Code is not set correctly, you will not be able to access the repeater.
Another one is talk group which is a virtual radio channel assigned to a country or group. Here in AU we mainly use talk group 505. As TG 505 becomes busy we have other local TGs assigned and available like TG5052 (for NSW)G5053 (for Victoria) TG5054 (for Qld) etc.
That might do us for now. Coming up in lets go digital part 3, we should get a start on the various Hotspots available& thats the DVMEGA, the Shark RF and a few others..
LOCAL FREQUENCY CHANGES:  Since our last post, the ACMA has issued a couple of new digital repeater licences in the Newcastle area. I now have been allocated VK2RHX which remains on the existing frequency of 438.750 Mz TX with a -7Mz split and 431.750 Mz RX.
Colin VK2GP has also been allocated a new digital repeater licence VK2RGP on the new frequency of 438.7375 Mz TX with a -7Mz split and 431.7375 M RX.
In the meantime, there is a massive amount of information available to look at on google and YouTube, check it out& see you next month.
If you have any burning questions, you can drop me a line at vk2yhx@gmail.com
73 Spero VK2YHX 



Let's Go Digital Part3... By Spero Davias VK2YHX

This month, lets check out what is around in the world of hot spots&.
Back in the old days of D-Star there were a Plethora of hotspots on the market. They came in various forms, including the DVAP and all the way through to the home brew hot spot. I chose the old DVRPTR V1 by Bruce Given VE2GZI, driving an RPi2 which fed the Kenwood duel band 50w radio running on 9600bd& that worked and is still working fine today, giving me a hot spot range all over the Newcastle area mobile.
Typical D-star HotSpot setup
With all the various D-Star hotspots on the market, one little fella snuck through the hoops with flying colours and managed to cross to the other side&. the DMR side. That was the DVMEGA&
A UHF DVMEGA sitting on the GPIO pins of the Raspberry Pi
The DV-MEGA is the brain child of Guus van Dooren PE1PLM. www.dvmega.auria.nl/
Guus could see the writing on the wall. He knew that to be in the race he had to develop software/firmware to bring the DVMega into the DMR field as well as Dstar. It was just a few months later, Guus managed to release firmware that enabled the DVMEGA to be used for DMR as well as D-Star, which opened up a whole new can of worms.
I had two of the DVEMEGAs lying around from the old D+Star days so I upgraded one of them with the latest firmware to get me into this DMR that I was hearing about on the D-Star reflectors.  The DMR we were talking about at the time was DMR plus, not to be confused with DMR MARC which was more a motorola toy or the DMR Brandmeister which hadnt been thought of at that stage.
Armed with our updated DVMEGAs, I and a handful of other VKs would log into the UK system and use the UK reflectors which would key up 15 or so UK repeaters spread across the country. Lucky it was 3 o'clock in the morning in the UK putting most of them in bed by then so we had a clean run using their repeater systems and chatting all night& I do recall that there were a couple of UK hams that got a we bit stroppy that we were using all their repeaters so one night we offered to pay for their power bill&
About September 2015, there was talk of the Hungarians introducing a brand new little gadget called a DV4Mini which was a USB stick about 3 inches long.
                                                The DV4Mini USB Stick
Well it didnt take long before it set the world on fire. This little fellow was a tiny but powerful USB stick that can change any PC into a HOTSPOT for the all amateur digital modes, 
C4FM, D-Star and DMR.  It's also able to do DPMR and P25. It contains a powerful 32-bit micro controller as well as a complete 70cm transceiver and modulator/demodulator for GMSK and 4FSK (including raised cosine) as well as a USB interface. It does not require its own power supply as it is powered through the USB interface.
I ended up with two of these fellows and with the latest firmware, they still work well today.
Most used the DV4Mini attached to the USB connector of the Raspberry Pi wich ran the software on its SD card to operate the various modes.
DV4MINI Dashboard
 Unfortunately, the little DV4Mini had a few shortcomings when it came to DMR, due to its uncontrolled Bit Error Rate BER, it produced a series of squawks and squeaks along with the audio which saw it been banned by most DMR users& Lucky enough it ran quite fine with the other modes. C4FM, DMR+, D-Star and P25.
The DV4Mini attached to the Raspberry Pi by USB
As it was, just a few months ago, new firmware was made available for download that allowed the DV4Mini to sound like a professional repeater on DMR & so not all is lost, the latest firmware for the DV4Mini has made it also capable of NXDN. This has brought the old DV4Mini back into play.      

Here are a couple of interesting you tube videos i've found, using the dv4mini with c4fm Helitron DV4mini C4FM testshttps://www.youtube.com/watch?v=4oYpyrjcXBc

 

Ive watched most of this guys video presentations and found them  very informative.
About 12 months or so ago David PA7LIM, introduced to the world the BLUEDV.  It was a very interesting project&
BlueDV in the blue box on top
The BlueDV originally was introduced as the Blue Spot but unfortunately David found that the name had already been registered so a few months later there was a change of name to the  present BlueDV.
This is a unique little fellow in the fact that all the work is done on your Android phone via Bluetooth. Which make life so much easier if you are using the device whilst mobile.
It sits in its little box as seen in the pic above and it has a DVMEGA plugged into the top of it with its UHF sma antenna pointing out. She is capable of D-Star (DExtra, DPlus, Dcs) Fusion (YSF and FCS) and DMR (BrandMeister and DMR Plus)
There is also software available to use the BlueDV on the Windows pc system.  As you can see in the pic above all you need is the Blue DV box and a small battery power pack of the USB 5v variety available on eBay for a dime a dozen, a spare mobile phone and a DMR radio, the radio shown in the pic above is the MD-380.
As I already had a spare DVMega, I bought just the BlueDV module and fitted it to the DVMEGA ran the software on an old Android phone that was floating around and Bobs your Uncle& . Its still ticking over in the shack today.
About a year ago the guys from Estonia developed a tiny device under the name of Shark RF they called it the One Spot. It was released to the public about the same time as the Friedrichshafen international amateur radio exhibition in Germany.
The Shark RF One Spot
As it happened, a friend of mine, Andy VK3AS, was over at the Friedrichshafen show around the time of release. He was going to pick one up and grab one for me at the same time but a day or so later there was a massive worldwide scare campaign launched on social media and other forums regarding how bad the Open Spot was.
There were enough bad vibes to start us all talking about it. A lot of Hams that were hanging out to grab one changed their mind.
I had read the story on the SharkRf, I had also studied the specifications and watched the YouTube videos on how it all worked until I was satisfied it was worthwhile to go ahead, the scare campaign was a load of rubbish. So, I suggested to Andy to go ahead and pick one up.
It looks like the latest stats are showing the SharkRf has taken the world lead in digital hotspots as the most popular dongle in the world&..
I just bought one and Im wrapped. As Rick says its the best thing since sliced bread&
   
BrandMeister records showing the use of different devices
One big advantage with the open spot is that you dont have to use a DMR radio if you dont own one. If you have a Yaesu C4FM capable radio, the SharkRf device allows intramode TX RX onto the BrandMeister DMR network using the C4FM radio. Pretty cool&
If you have any burning digital questions, you can drop me a line.... Spero Davias VK2YHX
73 Spero VK2YHX
2017