Category Archives: Technology

DMR and Talkgroups in EI

Quite often I get asked about DMR Radio and how to program Talkgroups (TGs) and Timeslots (Slots).

First, what it a timeslot? Your transmitted signal is broken into 30ms digital packets. Each slot is 27.5ms of data, 2.5ms of a gap, the result being your transmitter switches on and off very rapidly. Doing this allows your signals to share the same channel at the same time as someone else. One on Time Slot 1 and one on Time Slot 2.

Group A are using Slot 1 while Group B are using Slot 2 simultaneously. They don’t interfere with, nor can the be heard by one another.

A DMR talkgroup is a method of organising radio traffic such that the the DMR users can choose to hear the same thing and not be bothered by other radio traffic on a DMR network.

Talkgroups can exist for many purposes. On the Brandmeister network World Wide is TG91, Jamboree on the Air (JOTA) is TG907, a link to the Southern Ireland Repeater Group voice network is on TG27240. Just about any group of DMR users could have a talkgroup assigned to them that they can all monitor and take part in, without having to talk to each other one by one.

Given the demand for Talkgroups however, and how quickly their use can fade, no one is all that keen on allocating a Talkgroup number for everything. A good way to start out is to use one persons DMR ID as the Talkgroup ID and try it out. If the special interest group is still running after 6 months or so, then everyone can be fairly confident that it won’t be waste to allocate an ID to it.

Now what does this mean regarding programming them? Well, based on the current guidelines, I have updated my own DMR page with an example of three different repeaters, and how a memory bank (Zone) could be programmed in line with the guidelines. If it still isn’t making sense to you. Drop me an email ( details on HamQTH and QRZ). 73

Ham Radio… Now What?

I was looking for something to watch/listen to while tidying up my inbox today after being away for three weeks or so.  We took in the ARRL/TAPR Digital communications conference while in Florida. As I enjoyed this years DCC so much,  i went looking for last years DCC banquet speech.  Ward Silver, N0AX, gave an excellent talk on the direction the hobby should take for it’s second century.  I particularly liked his comment about contesting and being “able to heard the world turn”. Thanks to Gary Pearce, KN4AQ for attending the DCC and working so hard to make the videos available (feed the pig!).

Irish Summers getting brighter?

I’ve been recording the “Monthly Average” output from my PV system for a while (Since 2011). Looking at the figures for this summer.  The “Sunniest” month was June (91 Watts), followed by August (83 Watts) and then July (81 Watts).

Ok, so July sucked, I think we all knew that.  However what surprised me was when I looked at the results from previous years. It appears that the system has produced more power on average this year than any previous year.

To be continued…

Staying secure

Taken from Schneier on Security:

  1. Hide in the network. Implement hidden services. Use Tor to anonymize yourself. Yes, the NSA targets Tor users, but it’s work for them. The less obvious you are, the safer you are.
  2. Encrypt your communications. Use TLS. Use IPsec. Again, while it’s true that the NSA targets encrypted connections — and it may have explicit exploits against these protocols — you’re much better protected than if you communicate in the clear.
  3. Assume that while your computer can be compromised, it would take work and risk on the part of the NSA — so it probably isn’t. If you have something really important, use an air gap. Since I started working with the Snowden documents, I bought a new computer that has never been connected to the Internet. If I want to transfer a file, I encrypt the file on the secure computer and walk it over to my Internet computer, using a USB stick. To decrypt something, I reverse the process. This might not be bulletproof, but it’s pretty good.
  4. Be suspicious of commercial encryption software, especially from large vendors. My guess is that most encryption products from large US companies have NSA-friendly back doors, and many foreign ones probably do as well. It’s prudent to assume that foreign products also have foreign-installed backdoors. Closed-source software is easier for the NSA to backdoor than open-source software. Systems relying on master secrets are vulnerable to the NSA, through either legal or more clandestine means.
  5. Try to use public-domain encryption that has to be compatible with other implementations. For example, it’s harder for the NSA to backdoor TLS than BitLocker, because any vendor’s TLS has to be compatible with every other vendor’s TLS, while BitLocker only has to be compatible with itself, giving the NSA a lot more freedom to make changes. And because BitLocker is proprietary, it’s far less likely those changes will be discovered. Prefer symmetric cryptography over public-key cryptography. Prefer conventional discrete-log-based systems over elliptic-curve systems; the latter have constants that the NSA influences when they can.

If you haven’t already read the full post, you should.

Mirabox Kernel update

So the background is that I have a lovely little unit called a Mirabox but I need to update the kernel on it.   I spent a good bit of time looking at various forums and eventually managed to piece together enough information to get a 3.9 kernel to boot for me.

First, I installed a cross compiler, then I built a kernel, with default options, like so.

PATH="/home/build/smile/armv7-marvell-linux-gnueabi/bin:$PATH" make ARCH=arm CROSS_COMPILE=arm-marvell-linux-gnueabi- mvebu_defconfig

PATH="/home/build/smile/armv7-marvell-linux-gnueabi/bin:$PATH" make ARCH=arm CROSS_COMPILE=arm-marvell-linux-gnueabi- zImage

PATH="/home/build/smile/armv7-marvell-linux-gnueabi/bin:$PATH" make ARCH=arm CROSS_COMPILE=arm-marvell-linux-gnueabi- armada-370-mirabox.dtb

cp arch/arm/boot/zImage zImage-with-dtb

cat arch/arm/boot/dts/armada-370-mirabox.dtb >> zImage-with-dtb

./scripts/ -A arm -O linux -T kernel -C none -a 0x00008000 -e 0x00008000 -n 'Linux-marvell' -d zImage-with-dtb uImage

This kernel booted, but could not find a root filesystem. After a spending a bit of time looking, I could not find a NAND driver, so I opted for a filesystem on MicroSD instead.

Next, I replaced the kernel configuration with the one in this post, and rebuilt it. While that was building, I followed the instructions in this post, to create the filesystem on a MicroSD card.

Finally, I dropped the uImage created above onto a tftp server, loaded it with

tftpboot 0x6400000
set bootargs 'console=ttyS0,115200 root=/dev/sdb2 rootwait'

and the result is a working system.

root@dreamplug-debian:~# cat /proc/version
Linux version 3.9.0 (root@ubuntu-smile-build) (gcc version 4.2.0 20070413 (prerelease) (CodeSourcery 2007q1-10. Marvell 2009q3-11 20090730)) #2 Fri May 3 15:27:05 IST 2013

A very satisfying way to finish up before a long weekend!

Micro PV

So, having moved the garden shed and the PV panels in August/September 2011 to a more sun friendly position, I was pretty sure that there would be more output from the system over the next 12 months. Now, that 12 month interval is just coming to an end.

When I checked this evening, the average power generated 24×7 for the last 12 months as per rrdtool is 40 Watts, with a peak of 357 Watts. Which equates to approximately 350kWh, or somewhere between 70 and 90 Euro worth of Electricity for the year.

So in short, yes there was an increase in output, an approximate 42% increase in average power and a 100% increase in peak power. At least now I can tell myself it was worth the effort!

Moving on.

About 9 Years ago I got involved in IrishWAN. It was great fun at the time getting links set up, upgrading to the newest and coolest kit, helping others get nodes running, getting new people connected, all who hadn’t a hope of getting Internet from any available commercial offering.

For some months, before Eircom enabled the local DSL exchange, one of the only ways to get Internet in my town was through a WiFi node on my roof, 5.8Ghz Backhaul, 2 x 2.4Ghz Access.

Recently the last person that was using my node for Internet access moved over to a 3G dongle, so today I pulled the plug on the node, and took down the last of the WiFi antennas.

One of the Westflex 103 cables has been re-used for a 70Mhz (the Amateur Radio 4 Meter band) antenna that I put up today, the other is now spare. Surprisingly enough both seem perfect after 9 or so years exposed to the elements, as was the 2.4Ghz Omni-directional antenna from Wi-Pipe. Now I just need to “upgrade” to a 70Mhz radio, and the fun begins again…

YFKtest on LHS#86

I finally got a chance to listen to Linux in the Ham Shack, Episode 86 in the last few days. I was delighted to hear Bob,W9YA on there being interviewed about YFKtest.

I have mentioned YFKtest explicitly before (here and here), its the only contest logger I use as my “roadkill” laptop is a bit too old to run windows. As Bob points out in the interview, YFKtest doesn’t need a GUI or a mouse to control it, so it’s pretty frugal with resources, and I share his hatred of being forced to use a mouse when it is completely unnecessary. I would like to think I have been doing my bit to assist Bob in improving it over the last while (a few minor fixes), along with trying to help him debug a few issues and quite a few of those fixes were tested recently when operating EI2WRC/p for the IRTS 80m Counties Contest, and it worked great. Now I just need to get on air a bit more!

Micro PV two years on.

Some changes since last year. Firstly the panels have a different orientation from last year.  I moved the shed last August/September and both panels are now facing South West (220deg), still at the tilt of about 5-10 degrees (which I really must measure), not ideal but better than before.

The same two Evergreen panels are in use, but I’ve a new Mastervolt Soladin Inverter from Nigel in Mysolarshop. Unfortunately I accidentally let the magic smoke out of the Steca, when moving things around and it had to be replaced. I might try and get the smoke back in some rainy afternoon when I’m bored. The measurement set-up is still the same using the Envi CC-128.

So for the last 12 months rrdtool is saying an ‘average’ of 28 watts is produced every day. So from the back-of-an-envelope, we get 0.028*24*365 or approximately 245 kWh produced, with a value of approximately €49.

However, I have reason to believe that output will be better this year. The first picture below is from the 3rd of June last year.

This one is from today:

Two things are immediately obvious. The peak instantaneous value, and the average are both higher. This should help increase the output from the system for 2012.

The experiment continues!