Multiple RF modules under one D-STAR gateway

As part of my effort to help a friend to configure and setup a system comprising of two D-STAR RF modules under one gateway (all running G4KLX software), I created this schematic layout of the system, assuming two different scenarios.

In the first scenario all the elements of the system are located within an internal private network operating within a NAT environment. In the second case, the gateway and one RF module are inside the private network and then there is a second RF module remotely located. All IP addresses are just examples, you will need to adapt the settings to your circumstances but the principle is correct and will allow you to get your system working.

Here is the file, I hop it helps. Please remember to quote the source if you intend to redistribute.

XRF D-STAR Reflectors explained

Having recently developed an interest in how reflectors work, I soon realised that the best way of coming to understand how these vital pieces of D-STAR pieces of infrastructure work and interact with the rest of the network was to build my own. The software I used is called dxrfd and is available on the web. The below article is more an overview than a detailed installation guide. One reason of this choice is that I will not be able to maintain this page updated with all the changes that developers around the world will be making over time. All the installation instructions are included in a README file that is normally included in the package and those who wish to try this experience will be able to install it by following those installation guidelines.

It makes sense to revisit a few points regarding D-STAR.

Let’s start by restating that D-STAR is a digital radio communication mode that needs no infrastructure to work, a D-STAR radio works out of the box both in FM and DV modes, with no need of repeaters, hotspots, reflectors, or anything else. I recently heard someone saying that D-STAR is like Skype with a radio – this is simply incorrect and if you know what your radio can do you can make good use of it and it has nothing to do with Skype et similia. So, similarly to FM, if you have someone else tuned on your same frequency and press the PTT button, you can talk to this person and hear their reply. The added infrastructure is used to enhance the possibilities of communication within VHF and UHF (or any other) bands by overcoming the range limitations typically encountered at these frequencies.

The first step to increase this range is to add a repeater in the area, so stations that are normally unable to communicate with one another can use the advantage of the favourable positions where normally repeaters are located within a given area – same as with FM analogue radio.

The second step to this is to add a gateway to an access point, which could be a repeater as discussed above. As nowadays repeaters are likely to be managed by a computer (with small board units such as the Raspberry Pi being very popular) with a repeater controlling programme running on it, the gateway can be, and in most cases is, another little programme which runs on the same machine. If you are new to this and you think all this sounds like rocket science, let me reassure you: it isn’t and once you understand your way around you will be able to setup your hardware relatively easily – sure some skills are required but this is true for almost everything.

People tend to believe that a gateway needs to be connected to a network to make contact with other entities in the D-STAR wider infrastructure; this is simply incorrect. Over the years there has been a lot of development in the D-STAR world, with open source repeater/hotspot and gateway software being created with open and flexible communication in mind. The most popular open source software allows a system to be setup with a collection of internet addresses of many of the thousands of repeaters and hotspots located all over the world. Since a gateway is able to connect directly another gateway or reflector by just having its address, nothing other than an internet connection and the correct address is needed to make contact with other users linked to one of them.

Enter the XRF reflector. It consists of a small server programme that requires little space and resources to run on a Linux platform. It accepts linking connections on port 30001 (DExtra protocol) and also allows DV dongle and other software clients connections through port 20001 (DPlus protocol). As explained above, XRF reflectors can run outside a network and don’t need to propagate their IP addresses through a network; all it’s needed is the reflector’s address in the DExtra – NOT DPlus – list of reflectors added to a gateway.

Building an XRF reflector consists of having an available Linux machine connected to the internet via a good broadband connection and into installing dxrfd on this machine. The system cannot be the same where you also run a gateway, I don’t know why this is the case but it is clearly stated in the instructions. It also needs a separate IP address otherwise there will be a reflector port conflict with the DExtra protocol activities running on the gateway – this could in fact be the reason why the reflector cannot run on the same machine where the gateway is running at the same time.

Once installed and configured, the reflector accepts connections from all the entities linked to it, one at a time, and redistributes to all of them at the same time. This process can run five times simultaneously as the XRF reflector offers five independent modules. In simple words it acts as a cyber repeater, if there is such definition. The difference is that input and output are data streams rather than RF carriers, with the RF conversion happening remotely.

An XRF reflector can also be enhanced by adding a dashboard page that can then be made available on the web. The dashboard will list all the ongoing reflector’s links and QSO activities.

This is how XRF400 was created. The system is now live, it can be enabled by adding the reflector’s address to the DExtra list of your gateway and then linked by using XRF400xL in your radio’s UR field (where ‘x’ is any letter between A and E).

Cyprus – operating as 5B/M0ZZM

I’m currently in Cyprus, able to operate after 2100 GMT as 5B/M0ZZM. I tried yesterday to launch a few calls with my small antenna (see my previous post on the subject), the propagation wasn’t great nevertheless I made some good contacts with Europe’s mainland.

I’m not sure about how often I’ll be able to do this but I’ll definitely try again during the next few days on the 20 metres band.
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Super Antenna SuperStick MP1

Holiday time again: this time I’d like to take my IC-7100 with me and use it from time to time. Trouble is that apart from the usual luggage everyone normally carries I also have a rather large and full bag containing my camera kit and my computer. You can see how adding a rig, a 30A power supply, cables, wires, poles, etc., when travelling on a plane, does not go down very well with the rest of the family. Besides, I am not sure I will be able to extend up to 10 metres fishing pole and couterpoise in the place I go.

I needed the magic antenna (I hear you laughing): small, efficient, with good bandwidth, and of course covering all bands, whatever that means. After a search and a good read I picked the SuperStick MP1. The reason why I picked the MP1 is that the alternatives seemed to be worse. Also, I have no time to make an antenna that may work before I leave, so a commercial ready made unit was the only realistic option. It arrived and I tried it, here’s how it went.

First, I was expecting a bigger and heavier box – this box is truly small at 38x13x9 cm! And light. I haven’t weighed it, but I think it’s less than 1Kg. It includes the antenna, a little tripod, the 80m coil, and a counterpoise made of three wires of different lengths attached to a connector. It took me anything between 5 and 10 minutes to open the box, assemble the antenna and lay it in the grass with all its wiring attached. Without using the manual, and with the help of an antenna analyser it took me less than 5 minutes to be on the air on the 20m band. Another 10 minutes later I spoke with a guy in Latvia, one in Italy and another one in Greece. The latter was a “59” even if he couldn’t hear me (I needed to repeat a few times and the last time he was wishing me 73 while I was still talking). But the other two were good copies as we exchanged a few overs and they answered sensibly.

Too early to say how good it is, however it works. Not as good as a magnetic loop, from my first impression, but it works. Tuning it is a breeze, you can do this very quickly even in the dark by counting the coil turns. After you do this a few times you learn by memory how many turns it takes to go from 10m to 15m, then to 20m. For the 40m it’s a bit of a long run on the coil but not impossible. Bandwidth is great – if you used a magnetic loop this is like a wideband antenna 🙂 – and the SWR goes pretty quickly down to very close to 1:1. I’m not sure if this is a good thing as it may be the cable being tuned, however it works without causing obvious EMC problems even without a ground rod and this is what matters in the circumstances I will be using it.

The only HF band I couldn’t manage to tune is the 80 metres. It does tune it but the SWR remains high, beyond usability. I didn’t dwell into the problem as I have no time at the moment, but will try and test in the next few days before I leave.

All in all, this antenna ticks the boxes: it’s small, easy to install and uninstall, you get heard (your signal is quite low but this was to be expected), it’s quite inconspicuous, and the bandwidth is good enough even on 40 metres. I will write another post as soon as I test it from my holiday location but after this initial test I am really looking forward to testing it during my holiday in Cyprus!

Magnetic Loop and PSK31

After having had some fun in SSB and DV with my IC-7100, it was time to try a few more digital modes. Having had to remove my antenna this week to allow some works to be carried out in my garden, I decided it would be a good idea to pull my MFJ-1786X magnetic loop out of the shed and use it to test my IC-7100 in data mode. What a great combination. Have a look at this image, fresh out of pskreporter.de:

One of the highlights of this image is the green flag showing my position, of course. The other highlights are the flag of KB8U, located in Missouri (USA) and the flag of VK7KT, located in Tasmania (Australia). These two receiving stations are 6881 Km and 17189 Km, respectively, from my location. I know there are people doing this every day, however this was achieved with approximately 30W power on 20 metres, in PSK31, radiating from a magnetic loop at the top of a garden table ‘secured’ with four pieces of cord.

Whilst testing a RTTY software, with the same antenna and still on 20 metres, I received a station located in Sakhalin (I hope the name is correct) which is a Russian island located just north of Japan, approximately 8500 Km from London. They were calling CQ, their signal was very weak, I tried to contact them but had no luck.

For those who are interested in magnetic loops, this type of antenna is a real little monster. I am not one of those who tried all sort of compact antennae, but I think the magnetic loop is very hard to beat. I am so fascinated by its performance that I am now considering mounting it on a 6 or 7 metres high mast and horizontal, to see what it will be capable of if I install it in a more favourable position.

Watch this space!

IC-7100 DSTAR Test QSO in HF (10 metres)

Today, Roberto IZ5ILH and I ran a DSTAR test QSO in HF, each of us running an Icom IC-7100. After exploring a few bands we managed to have a clear copy on 10 metres.

I recorded a video of this QSO with my mobile phone. The QSO is in Italian and the image a bit shaky, though if you never had a chance of testing your radio in DSTAR mode in HF and wish to see how the DSTAR works in HF under QSB conditions I believe this will give you an idea.

I have to say that as a first experiment I am impressed by the DSTAR performance under low signal and bad S/N conditions. However it’s too early to draw conclusions on how efficient DSTAR is in HF given its 6 KHz bandwidth. More testing should be done and maybe compare decoding and voice legibility between SSB, FM and DSTAR on the same frequency and during the same session to see where the signal becomes too hard for the IC-7100 to decode.

I’d be happy to run similar direct contact testing sessions with anyone who has a radio that can get on 10 metres and above (I don’t have an antenna for the 4 metres band but I can build one quickly if anyone is interested), so if you are within reach – meaning Europe on 10 metres or London and vicinity on 6 and 4 metres – please let me know.