Jun 152014
 

This is a simple vertical groundplane antenna intended for mounting atop a 10m Squid Pole. These can be made to nearly any frequency you desire, and can be self-supporting if needed. The main limitation is the stiffness of the wire used.

The antenna gets its name as the original was one I quickly knocked up just prior to a horse endurence ride event that took place at Donnybrook in 2011. I was assisting Brisbane Area WICEN with the emergency communications at this event, and this antenna, worked very well. 10W was more than sufficient to get back to base on 2m FM.

The design is very simple. You’ll need some stiff copper wire, and a panel-mount BNC connector. I used some strands from a thick mains cable: this was being tossed out at a ham radio meeting some years back. The cable had a black plastic coating and inside were 7 strands of solid copper, each about 2mm thick. Perfect for small antennas.

Similar wire can be found in non-stranded house mains cable.

First step is to work out what length to cut the elements. They should all be roughly the same length. This can be calculated by the simple formula:

v=f\lambda

which if you take v as being the velocity of light in a vacuum (~3\times10^8 m/s; radio will travel a little slower through air, but who’s counting?) and f as being 147.050\times10^6 and solve for \lambda you get 2.04m as the wavelength.  We want ¼ of this, so I’ve aimed for 51cm long elements.

Don’t worry about them being perfectly straight when measuring, extra length is good at this point, you’ll want a good 2cm extra.  You can make a wire shorter, you can’t make it longer.

Measuring the elements

Measuring the elements

Measure and cut the 4 elements. 3 will become your groundplane, and the 4th the radiating element. Also cut off about 10cm or so, give or take, which will be the ground wire used to hook the groundplane elements to the BNC connector. Also add to your parts list, some small velcro strips: you’ll find these handy to strap the coax to the squid pole.

Procured parts

Procured parts

Start with the short piece of wire. You’ll want to bend it into a rough triangle shape, with loops of wire at the corners. The groundplane radials will loop through these holes. The excess wire should be coiled up to one side: this is the loop the squid pole will pass through. The BNC connector will be fitted in between the 3 small loops.

Ground wire

donnybrook-03-ground-wire Ground wire

Be sure you can still put the nut back on.

Take 3 of the four elements, and make a hook at one end. Pass this hook through each of the small loops in the triangle. Try to make them sit roughly straight out from the centre of the triangle, then solder each hook into the loop.

Hooking the radials

Soldering the radialsAttaching the radials

Having done this, put the BNC connector in and do the nut up tight. You can do away with the eyelet with the solder tag. To finish off, take your remaining element, make a hook just big enough to go around the centre pin of the BNC connector, then solder into place.

Preparing radiating element

Hooking radiating elementSoldering the radiating element Attaching the radiating element

To finish off, bend this until it is vertical. The antenna is now ready for tuning.

Completed untuned antenna

Completed untuned antenna

Double check the length is about right. It should be around the 51~52cm mark.

Checking length

Checking length (close) Checking length

To check the tuning, use a SWR meter or antenna analyser if you have one. Here, I used the built-in SWR meter on my Yaesu FT-857D. When using a SWR meter, ensure you’re running minimum power. The following are some results from my set.  It is at this point, you do any trimming of your antenna.  The following are without trimming the antenna, you’ll note that in most examples, the SWR is very low, just a point or so showing up on the left side of the screen.

On 2m:

donnybrook-13-test-144500 donnybrook-13-test-145500 donnybrook-13-test-146500 donnybrook-13-test-147500

On 70cm:

donnybrook-13-test-432100 donnybrook-13-test-433100 donnybrook-13-test-434100 donnybrook-13-test-438100 donnybrook-13-test-439100 donnybrook-13-test-440100

To mount the antenna on your squid pole, feed the tip of the squid pole through the remaining loop.  Bend the tip of the antenna around the tip of the squid pole.  Hook your coaxial cable to the BNC connector and use velcro straps at regular points to hold the coax to the side of the squid pole.

Mounted antenna

Mounted antenna

Recommended coax for this purpose is RG-195.  RG-58 will work, but is lossy, RG-213 and LMR400 are too heavy to use on a squid pole and will cause it to bend or collapse.

Update: This antenna performed quite well.  Saturday, we used it for 2m packet, providing a digipeater for the stations in our area in case they couldn’t reach the main node (at “the pineapple farm” just outside Imbil).  We had stable packet communications all day.  Since the stations around us found they could work the main node directly, we swapped antennas around and used it instead for a VHF/UHF cross-band voice repeater.  Signal reports were good through the Imbil state forest.

Jul 152013
 

Well, this year’s International Rally of Queensland didn’t go the way everyone expected. We were there with Brisbane Area WICEN, providing the backup communications for the event. Our primary role was to relay the scores given to us by the post chief in the timekeeper’s tent. They looked after scheduling the cars, getting times, and sending the cars through. We just passed on scores (start/finish times) and other traffic.

Saturday went well. My father and I were set up at Kandanga North running the WICEN checkpoint for stages 6 and 12 of the rally. After some early hiccups getting the packet radio network going, we had the scores being sent out on time and everything running smoothly. Apart from some cows holding up traffic, there were no delays.

Sunday however… just about everyone would have heard about the fatality. My father and I ran the WICEN checkpoint at the start of the fateful Michell Creek Special Stage 14.

Having now seen the ABC website footage, looking at the competitor lists and my own logs, I can say with 90% certainty which car (and therefore 45% certainty who the deceased is) the unfortunate car was and when they left the stage.

My condolences go out to both driver and co driver at this difficult time.

Update: The names have been released.

Mar 312013
 

Recently I purchased a second hand Kantronics KPC-3 packet TNC. Brisbane Area WICEN make heavy use of packet at one particular event, the International Rally of Queensland, where they use the 1200-baud network to report the scores of rally cars as they progress through each stage.

Now, I’m a newcomer to radio compared to most on the band. I got my license in 2008, and I’ve only had contact with packet for the last two years, and even then, mostly only at a distance.  I had a hand-held that did APRS, and I’ve also done some APRS using soundmodem and Xastir.  Full-blooded AX.25 has taken me some time, and I’m slowly coming to grips with some of it.

One thing I wanted to try and figure out, is how to re-lay traffic from a host connected to the RF world, to a host on a local network.  I knew there was some protocol that did it, but didn’t know what, or how it worked.  Turns out the protocol I was thinking of was AXIP, which basically overlays AX.25 frames directly atop IP.  There’s also a version that encapsulates them in UDP datagrams; AXUDP.

The following are my notes on how I managed to get some routing to happen.

So, my set-up.  I have my FT-897D set up on 145.175MHz FM, the APRS frequency in Australia.  (I did go hunting for BBSes the other night but came up blank, but since APRS uses AX.25 messaging, it’ll be a start.)

To its data port, I have the KPC-3, which connects to my trusty old P4 laptop via good ol’e RS-232 (the real stuff, not pretend USB-RS232, yes the laptop is that old).  This laptop is on my local LAN, with an IP address of 192.168.64.141.

In front of me, is my main workhorse, a MacBook at the address of 192.168.64.140.  Both laptops are booted into Linux, and my target is Xastir.

First thing I had to do was compile the AX.25 kernel modules, and the ax25-tools, ax25-apps.  The userspace tools needed for this are: ax25ipd and kissnetd.

On the RF-facing system

This is the P4 in my case, the one with the TNC. First step is to get the TNC into KISS mode. In the case of Kantronics TNCs, the way to do this is to fire up your terminal emulator and run int kiss followed by reset.

Important note: to get it back, shut down everything using the serial port then run echo -e '\0300\0377\0300' > /dev/ttyS0. This sends the three-byte exit-kiss-mode sequence (0xc0 0xff 0xc0).

Configure /etc/ax25/ax25ipd.conf. Three things you’ll need to set up:

  • mode: should be tnc
  • device: should be whatever your serial device is (more on this later)
  • your default route: this is the host that will receive ALL traffic

In my case, my ax25ipd.conf on the P4 laptop looks like this:

socket ip
mode tnc
device /dev/ttyS0
speed 9600
loglevel 2
broadcast QST-0 NODES-0
# This points to my MacBook; d means default route
route 0 192.168.64.140 d

Once done, we start the ax25ipd service as root, it should fork into the background, and checking with netstat should show it as listening on a raw socket.

On the client machine

Here, we also run a AXIP server, but this time to catch the packets that get flung our way by the other system. We want Xastir to pick up the traffic as it comes in. Two ways of doing this.

One is to configure kissattach to give us a PTY device which we then pass onto ax25ipd, then run Xastir as root and tell it to use the AX.25 stack directly. Gentoo’s Xastir ebuild ships with this feature disabled, so not an option here (unless I hack the ebuild like I did last time).

The AX.25 tools also come with kissnetd: this basically generates several PTYs and links them all together so they all see eachother’s KISS traffic. So ax25ipd will receive packets, pass them to its PTY, which will then get forwarded by kissnetd to the other PTY attached to Xastir.

There is one catch. Unlike in kernels of yore, kernel 2.6 and above (3.x is no exception) do not have statically configured PTY devices. So all the AX.25 docs that say to use /dev/ptyq0 for one end and /dev/ttyqf for the other? Make that /dev/ptmx for one end, and the tool will tell you, what the other end is called. And yes, it’ll change.

Run kissnetd -p 2; the parameter tells it to create two PTYs. The tool will run in the foreground so make a note of what they’re called, then hit CTRL-Z followed by bg to bring it into the background.

vk4msl-mb stuartl # kissnetd -p 2
kissnetd V 1.5 by Frederic RIBLE F1OAT - ATEPRA FPAC/Linux Project

Awaiting client connects on:
/dev/pts/1 /dev/pts/4
^Z
[1]+  Stopped                 kissnetd -p 2
vk4msl-mb stuartl # bg 1

Now, in this example, PTYs 1 and 4 are allocated. I can allocate either one of them to Xastir or ax25ipd, here I’ll use /dev/pts/4 for ax25ipd and the other for Xastir. It is possibly best if you make symlinks to these, and just refer to the symlinks in your software.

# ln -s /dev/pts/4 /dev/kiss-ax25ipd
# ln -s /dev/pts/1 /dev/kiss-xastir

Whilst you’re at it, change the ownership of the one you give to Xastir to your user/group so Xastir doesn’t need to run as root.

Set up /etc/ax25/ax25ipd.conf on the client. Here, I’ve given it a route for all WIDE* traffic to the other host. It might be possible to just use 0 as I did before, I wasn’t sure if that’d create a loop or not.

socket ip
mode tnc
device /dev/kiss-ax25ipd
speed 9600
loglevel 2
broadcast QST-0 NODES-0
# This points to my P4, attached to the TNC; d means default route
route WIDE* 192.168.64.141 d

Now start up ax25ipd and Xastir, you should be able to bring up the interface and see APRS traffic, more over, you should be able to hit Transmit and see the TNC broadcast your packets.

Some stations visible direct via RF

Some stations visible direct via RF (click to enlarge)

Jun 142011
 
  1. The BP servo on the way to Donnybrook is bad when it comes to caravans… the one heading back to Brisbane is even worse.
  2. Horses have an aversion to orange and red coloured clothing (pity the organisers handed out red caps and orange shirts… also good thing we’re not the SES).
  3. Do not shine a torch in the eyes of a horse, especially not a 3W LED torch!
  4. Be prepared for organisers to give you information at the last possible minute, and not consider the needs of the radio communications people.
  5. Sometimes a short-cut, isn’t.
May 202011
 

During the International Rally of Queensland, it was interesting to observe how people made use of the radios provided for the event. In fact, watching peoples’ behaviour to me, made it clear that none of them had any training in how to use one of these devices. And they all struggled, mostly as a result of each others’ bad habits.

This isn’t an isolated case… my mother who works at the Brisbane International airport, often complains about the radio etiquette of her fellow colleagues. A lot of people have a radio thrust into their hands, and haven’t a clue how to use them. In trying to figure it out, they often fall trap to the same bad habits.

I myself have found a lot of this by mistake, and by observing others. A lot of this is also applicable to using regular telephones … I found the tip of standing still when talking helpful when I needed to make a call to emergency services on my mobile phone — the particular spot where I was at the time, the phone would drop out if I moved more than 6 inches in any direction. Learning not to talk too close, or too loudly into a microphone, also helps.

The following is a little chart I came up with. No, the stick figures are not XKCD grade, they’re not meant to be. Click on the image below for a copy as a PDF, or get the SVG source here.  File is provided in the public domain, but attribution would be appreciated.  If you use radios in your workplace, and observe this kind of behaviour in your colleagues, you might like to print this out and stick it on a wall somewhere.