Thursday, June 21, 2018

Watch! Two Time Slots & SDRangel In Action

DMR is confusing for some people. SDR is even more confusing for others.  What happens when you combine the two?  Mass hysteria?  Global epidemics? Accelerated excitement?

Due to a delay in circuit board re-design for the the Modern Field Strength Meter project, we bring you something different for this week (and possibly next)

This article builds on past written content and accompanying videos to show some of whats possible today when combining the two.

Some Brief Background First

DMR has seen a lot of growth because it is cheap to get started and talk around the world.  SDR adoption for many started with inexpensive USB dongle type of receivers before moving to something more capable. Many SDR dongle purchasers hoped to hear signals from around the world using these cheap receivers.

For a sum total to a new ham who may invest less than $300 in the amateur radio hobby, they can purchase a dual band DMR/FM hand held radio, multi-mode digital hotspot, USB SDR dongle and a few accessories such as antennas, power packs, etc. All this gear permits both local, global and emerging aspects of the hobby to collide and find people with like interests to talk with others about.

For comparison, when I got started in the hobby in the mid 1990's, the starting point for many was a VHF only Radioshack HTX-202 handheld radio for about the same $300! This permitted only local communication and while it still works today, there is a world beyond 2m.

“You realize that our mistrust of the future makes it hard to give up the past.”
Radio Shack is out of business by the way...

With DMR being the most popular digital voice mode that permits  local and global communication and an SDR being able to receive voice and non-voice communications locally and globally, there is a lot of capability at hand today for a new ham. Compared to local VHF activity, DMR provides the ability to talk with not the same local people all the time, but with the voice quality of local repeaters.

Many new hams experience getting on the air for the first time on the VHF 2m band and some quickly tire by talking to the same few people generally about the same thing. If there are not enough common interests with those locally, that new ham often decides the hobby is not for them.

Even so, many new hams who tire of 2m and move on to HF for long range discussion, get frustrated by higher expense, more planning for antennas and potential lack of people with common interests to talk to depending on when HF bands are stable or not.

The Best DMR Feature

DMR uses similar technology to second (2G) and third generation (3G) cellular communications known as TDMA.  The unique thing about TDMA based DMR is its ability to have two discussions on the same frequency at the same time with zero interference.  More about that here on HVDN.

Many have heard this, but not seen it in action.  Here is a brief video:

The laptop in the foreground is running SDRangel software that is receiving signal from a dual time-slot hotspot on a SDR nano3 USB dongle. The frequency for this test on my dual time slot hotspot is 432.565 MHz.

The SDR Nano v3 retails for less than $30 and is very small.
A standard SD card is shown at left for size comparison

On the laptop in the video background is showing the call-sign, time slot and talk group (virtual frequency) as its received by the hot spot.

The audio is being output by the foreground laptop and you will see how it coincides with the information on the background laptop.

This test was conducted at a time when a lot of activity is present on popular DMR talk groups known as TAC310 and Worldwide 91.

The same SDR dongle can be used to receive signals from local amateur radio repeaters that are DMR, analog FM or even some less popular modes such as Yaesu Fusion, Icom D-Star and commercial focused NXDN and P25.

As evidence by the video,  both local US and international amateur radio operators are able to talk to one another without having to invest in large antennas or high powered radios such as those used on HF for voice communication.

What is fascinating about DMR is how many of the older ham radio operators have taken to DMR for casual discussion instead of just using HF.

You never know who you will hear on amateur radio and where they are from. Investing in modern technology will allow a new or experienced ham to try new things for little expense before deciding where else to invest in.  This "modern ham" starter package may cause reason for purchase for things such as:

  • An HF radio
  • Outside HF, VHF or UHF antennas
  • A better computer 
  • A higher end SDR
  • Getting better educated about SDR and DMR
  • More education on computer/ham convergence
If there is interest in anything mentioned in this article, look for many of the HVDN members on DMR TG 31368 which is geographically focused for those residing in the mid Hudson Valley of New York. 

You can also look for discussion of combined topics on the new STEM talk group 313630.  More detail about that and its focus here

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