Monday, December 23, 2013

Simple, light weight, stealthy QRP dipole

In a few weeks we will move from our current QTH, with room for antennas, to a flat on the 28th floor, with a small balcony and restrictions on what can be put out there. (We'll be back but not for 8 months).

I have a new interest in stealth QRP antennas and have been experimenting...

Targeting 20m, I've built this very successful dipole. The wire is 10.1m, cut in half, with the ends folded back on themselves for tuning.

The feed line is thin RG-174 co-ax that runs directly in to ten turns on an FT114-43 toroid. A twin screw terminal block is used to attach the dipole wires. The design comes from n5ese but has been further simplified.

Everything is held together with cable ties and it's light enough to be suspended by the dipole wires. At resonance the SWR is very low but for some reason the impedance is a little low too.

The FT114-43 should work on any band from 0.5 to 30MHz by the looks of it. My plan is to use this for 10W which should be fine.

I'm looking for better options for connecting the legs of the dipole but the screw terminal block will do for now. Waterproofing is plastic wrap for now.

This probably won't survive very long.

This arrangement is very light, removes the need to have a connector at the balun, which saves both an potentially crackly connection and the weight of plug and socket. Running RG174 coax is light and less visible than other alternatives.


I've had a series of test contacts with Mal, VK2BMS. This antenna is better than the short Ozi-pole dipole but not as good as a full dipole on the roof - pretty much what you'd expect.

Thursday, December 12, 2013

Getting started with Bluetooth LE iBeacons

Recent devices include Bluetooth 4 which is able to run in a low energy (LE) mode and ping out a beacon running on a small battery for up to a few years. I purchased a few samples from Estimote that look like this:

It's also possible to use a Raspberry Pi with a USB bluetooth 4 dongle (I bought a Targus one for $40) to make a beacon. I followed instructions and it worked out of the box.

With this software you can make a beacon that emulates either Apple's AirLocate samples or beacons from any other vendor including Estimote, Radius, RedBear Labs, TwoCanoes or any others.

To scan for beacons, (without writing a specific app), there are a few iOS apps including the Estimote app and "Locate iB". On MacOS there's an app that can find any beacons in range called iBeaconScanner:

By pretending to be an Estimote beacon you can use their app to scan too:

All good fun. I'm sure we'll see these things everywhere within the next few years.

Sunday, December 08, 2013

An earth stake for the shack

I seem to have problems with RF feedback in the shack when using any kind of end fed antennas. Dipoles do better for me. I'd commented on this a few times and today local amateur, Robert, VK2ZNZ very kindly arranged for a beautiful copper coated steel stake to be hammered in to the ground.

Robert has been mysteriously absent from the Sunday morning 80m callback in recent weeks but it turns out the reason was that he's had a hip replacement so he availed himself of my shack's comfy chair:

Thanks very much for your kindness Robert!

Monday, November 25, 2013

Home brew and mini Maker faire day

A very busy Sunday this weekend. Mal, VK2BMS, and I headed off first to Dural for the ARNSW Home Brew group where I hoped to learn how to use my pan brake folder to make metal boxes. That wasn't to be but a little YouTube searching has filled that void.

Peter Jensen showed some of his excellent portable valve radio gear including this terrific suitcase setup:

John, VK2ASU, is making good progress on a new transceiver for 40m, here's the interim receiver which works very well:

Next we headed off to Ultimo to visit the mini Maker Faire at the Powerhouse museum. As expected there were lots of 3D printers, which I'd love to have a reason to need one, and some slightly disturbing robots:

My local club, the Manly Warringah Radio Society had a very interesting display in the outside courtyard:

The Powerhouse is a great museum and I look forward to visiting again with more time to take it all in.

Tuesday, October 22, 2013

Blog comment spam examples

In recent months, comment submitted to this blog have increasingly been spam basically intended to slip in a link to another site.

Often the comments are rather complimentary in an attempt to schmooze a blogger into accepting the comment without thought. Here's a small collection for your amusement (without the links).

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Thanks for the advice!

There are many more. I always mark them as spam but Google Blogger doesn't seem to be doing any filtering based on this as far as I can tell.

At least these people haven't stolen my text and videos and re-published with their own ads - I've seen that too.

Friday, October 18, 2013

The Arts Party


For too many years the political landscape of Australia has lacked a clear voice for the
artists, the lovers of art & culture and the creative industries within Australia. We need to
reprioritise Australian creativity as a fundamental asset of this country.

On Monday 21st October 2013 we are launching The Australian Arts Party to do exactly that.

Driving a broad social and economic platform, the Arts Party aims to transform the political
conversation within the state and federal parliaments of this country, by repositioning
creativity, cultural appreciation and arts in all its many and various forms, as central to the
future of Australian development and wealth creation. We believe the future of Australia
depends on the quality of our ideas even more than the size of our mines.

But to give Australians that voice, we urgently need members. Founding member registration
will occur at, commencing at 6am Monday 21st October 2013. We are
using crowdfunding to launch - an Australian and possibly world first for a political party.

For the next 4 weeks, any Australian can claim a three year founding membership of the Arts
Party for only $20 - a small personal investment to support a richer future for us all.

A quote from PJ Collins, the founding political officer of the Arts Party:
“For too long, I have felt a real lack of recognition and respect for the value Australian
creativity brings to our great country. The last federal election left me, and many of my
friends, more disaffected than ever before with Australian politics. Motoring enthusiasts and
miners now holding the balance of power in our senate - enough is enough! It’s time for
Australians, who believe art and creativity matters, to take a step forward and become
founding members of the Australian Arts Party.”

The Arts Party is a pro-industry, pro-education and pro-training platform. A platform that will
work for every Australian, to encourage and promote our amazing creativity. Art brings us
together. It should be a living part of all our lives.

For more information:
• Website:
• Join: (from 21/10/13)
• Contact: PJ Collins - 0404 116 310
• f: TheArtsParty t: @TheArtsParty #artsparty

I think this is a great idea. Please support it!

Monday, September 30, 2013

ARNSW Home Brew 40m antenna day

A beautiful day to be out doors in Sydney's Dural on Sunday. The theme was 40m antennas and there was lots of great talk, show and practical setting up of different antennas. A slinky antenna looks like a good idea but this one was too tangled to put up.

Stephen, VK2BLQ, had a big collection which began with the Ozi-pole short dipole for 40,20,10 and 6m.

Then a broadband end fed long wire the Ozi-Wire:

Peter Parker's end fed trap for 40 & 20m:

Outside antennas were put up using a variety of means, including a bow and arrow:

A telescopic flag pole (very patriotic):

There was a shortened vertical by Peter VK2EMU, here inspected by Mal, VK2BMS:

An impressive 40m quarter wave vertical seemed to perform well:

The stand-out for me was Owen's marvellous end fed half wave tuners, this one with a variometer, here being tuned by John VK2ASU:

An interesting comment was made about following detailed antenna instructions from Europe and the U.S. in that antennas perform differently here in Australia because our earth is much less conductive.

Ironically, antennas in Australia perform better when put up at night, when it's raining. There's a thought..

Sunday, September 29, 2013

Tune in to popular Downloadthisshow Sunday at 9pm

Downloadthisshow, a weekly panel and interview show by Marc Fennel, now has more than 300,000 subscribers on SoundCloud. Add that to subscribers on the iTunes podcast and of course radio listeners on ABC Radio National, some local stations and Radio Australia, and it's an amazing audience built by one talented and hard working producer, presenter and editor, Marc Fennell:

Maybe people are just following the oh, so subtle, command embedded in the program title?

This week, with co-panelist Karalee Evans, we chat about ads on Instagram, buying emerging art from Artsicle, and we play with the hand tracking Leap Motion.

While space wars might seem like a fun application for the Leap motion:

In the show you'll hear that I have a much more down to earth idea for the technology. RN, Sunday at 9pm.

Hornsby Ku-ring-gai fire control centre

Saturday was open day at the state of the art Hornsby Ku-ring-gai Fire Control Centre used by the Rural Fire Service to support local volunteer fire crews. It's an impressive communications and incident management setup.

The tour I had was hosted by Peter, VK2GPH and Leah, VK2FREE (great call sign!).

Originally the plan was to have a barbecue but ironically it was a "TFB" day and I had to bring cheese sandwiches instead.

Monday, September 23, 2013

Low cost vertical laptop stand from wood desk easel

Retina MacBook Pro screens are so sharp it's crazy not to use them as the primary screen when working at a desk.

Presumably Apple will introduce a range of retina desktop screens sometime soon (October anyone?), but until then I had a great idea for how to prop up my office laptop in a near vertical position while still being quite stable.

The trick is to use a little wooden desktop easel available for under $30 from art shops. At left is the one I bought and below is how my desk now look at the office. It's adjustable and has a nice pine wood smell and all. I've seen other stands at stationery stores and they are expensive and cheap plastic construction.

Here's how my desk looks now. (I do have an external screen on the right for running the iOS simulator and viewing documentation).

Saturday, September 21, 2013

iOS 7 adoption soon to exceed iOS 6

After only a few days, my apps are starting to show the amazing uptake of iOS 7. Here's my proportions in WSPR Watch from yesterday.

39.2% iOS 7.0 compared to 40.5% iOS 6.1.3 plus 7.6% for iOS 6.1.4.

iOS 7 seems a bit rough at this point so I can only assume they rushed it out to be able to launch with the new iPhones last week. I'm sure there will be some updates in the weeks ahead. Having said that - it's fine for daily use and a refreshing change.

Update a day later. iOS 7 is still growing fast.

Note that Google Analytics swapped the colours around. iOS 7 is now at 50.8% which exceeds the total for iOS 6 for my app.

Friday, September 20, 2013

Queuing for an iPhone 5s in Sydney - human nature on display

Even though I generally have no trouble picking up a new Apple product soon after launch, I decided to get up early and queue outside the Sydney George Street store this morning. It was an interesting experience.

Oddly, the crowd was overwhelmingly of Asian origin.

I arrived at 6:15am and there were hundreds already lined up around the block and down York Street. The woman in front of me was from Thailand, and behind me were a group of ten from Vietnam.

Without exception, everyone I spoke to wanted a gold iPhone 5s (clearly Apple has missed a key desire in the Asian market until this year). Many were in the queue to buy stock to resell at a profit in countries where the launch will not be for some time.

The group of ten from Vietnam were a "team" that planned to buy the maximum and then go back and re-join the queue. That means two 5s and ten 5c phones that would leave on a flight later in the day.

Given the long time involved (I joined at 6:15 and got to the store at about 10:00) a major annoyance was people surreptitiously jumping the queue. I saw a couple join in a driveway gap, they played dumb and said they thought that was the end of the queue, hmm. Without too much prodding they backed off and left.

Another pair kind of stood beside the queue for a while in front of the woman in front of me and then started walking with the queue until they gradually merged in. The woman was annoyed but didn't say anything - I was not so easy going.

I told them they could not just join a queue hundreds of people in - the main chap looked me in the eye and said he'd been there all morning "since 4:30am". I said that was nonsense. Next he claimed to be with a guy in front - I tapped him on the shoulder and asked to confirm the connection, there was none.

What I found amazing is that this guy was calm and while behaving in a rather vague way was able to look me in the eye and lie repeatedly. I called the security guards and they agreed that these interlopers had pushed in. The guards assured them that even if they stayed in the queue they would not get a phone. Even so, the queue jumpers remained in place for some time. They asserted that the guards would soon forget and all would be well.

I asked how they could lie so blazingly, they explained that everyone is like that. In the end they did give up and we reached the door of the shop.

Overall the mood was good, with lots of chat and good organisation from the Apple store staff on hand. I do feel manipulated though, Apple took a lot of time to process orders - offering a full service including SIM swaps, carrier plan activation and data migration. Many customers, like me, just wanted to purchase outright and could be in and out in a minute, but we had to wait.

The queue attracted the normal media attention with TV stations, plus a helicopter and I was briefly interviewed by @ClaireRPorter of News Ltd (until she figured out that we've met as fellow commentators).

The iPhone 5s is great by the way, the Touch ID fingerprint unlock is a truly differentiating feature that will lead me to use the phone much more than in the past. The other great unexpected feature, at least in Australia is the amazing tiny charger:

Oh and the 64bit processor and M7 motion chip which will hopefully replace the need to carry a FitBit dongle.

Gold 16GB and later 32GB phones sold out first, the same story was reported at Broadway which I visited at lunch time. They said they had "plenty" of the lower priced 5c phones.

I can see why Apple is not too concerned about going "cheap", even when they do the high end phone seems to sell more - at least near launch. Time will tell but I think the colour phones will be the big seller in the months ahead.

Next time, I'll skip the queue, but it was an entertaining experience.

Monday, September 09, 2013

Chinese HF transceiver X1M initial impressions

Just arrived in the shack is a very compact 4.5W all band SSB HF transceiver of Chinese origin. With a price of US$350 + shipping and an all surface mount (except the final) construction it was hard to resist. Here it is next to my trusty Yaesu FT-817:

While construction is a little "home brew" by comparison to the Yaesu, the X1M has a very informative display that is easier to read than the '817. The buttons are pretty flimsy but ok and the volume and tuning knob are basic but will do the job. Here's the top view:

This is a very solid feeling, compact rig that runs on 9.6 - 14.5 Volts DC and will be terrific for portable QRP operation drawing 500mA on receive. The receiver is quoted as being better than 0.45uV and the pre-amp seems to make a huge difference.

Received audio is strong (the Elecraft KX3 could learn from this rig!) but bandwidth is fixed.

Receive: 0.1 - 30MHz continuous.


Band 1 3.5 – 4.0 MHz (80 Meters)
Band 2 7.0 – 7.3 MHz (40 Meters)
Band 3 14.0 – 14.35 MHz (20 Meters)
Band 4 21.0 – 21.45 MHz (15 Meters)
Band 5 28.0 – 29.7 MHz (10 Meters)

There is a DB9 serial connector on the back and the rig can be controlled as if it was an FT-817 (ah the irony). I'd love to see something like this with a USB cable for both control and audio - that would make a terrific digital modes transceiver.

F1 and F5 increase or decrease the tuning rate while F2-F4 operate soft buttons which show on screen.

I'll report back next weekend when I've had some contacts, but my feeling so far is that this is a pretty good little short wave radio that covers 0.1 - 30MHz continuous and as a bonus transmits too.

The user manual pdf is here.

Here's a contact with Mal, VK2BMS.

Thanks Mal.

Saturday, September 07, 2013

Raspberry Pi interfacing with piface

The Raspberry Pi has turned in to a very flexible platform for dedicated computing tasks. I run one as an OpenVPN server, in the office we have one displaying server stats on a big TV. This week I purchased a PiFace board that provides a bunch of I/O controlled via an SPI interface.

I found the documentation covering getting started is a bit confusing so here's my summary based mostly on the Element14 document.

sudo apt-get update
sudo nano /etc/modprobe.d/raspi-blacklist.conf 
# comment out blacklist api-bcm2708
sudo modprobe spi-bcm2708
bash install.txt

sudo reboot

And here's a simple python script to cycle one of the relays on and off along with the indicator LED.

# flash an led with piface

import piface.pfio as pfio
from time import sleep

    pfio.digital_write(0,1) # turn on
    pfio.digital_write(0,0) # turn off

So that's "hello, world", the rest is easy. (Control-C to get out of the loop by the way).

The board has 8 output bits. Bit 0 and 1 have relays connected to them, all have little on-board LEDs. They can be turned on or off like this:

import piface.pfio as pfio

There are 8 input bits, the first 4 have push buttons on the board. Here's how to read the first (0th) bit:

>>> import piface.pfio as pfio
>>> pfio.init()
>>> print pfio.Switch(0).value
>>> print pfio.Switch(0).value


For that last Switch() probe I'm holding down the push button nearest to the edge of the board.

Saturday, August 24, 2013

Airplay video to a Raspberry pi - yes and no

Messing around with a Raspberry Pi recently used as a Wifi hotspot, led me to an idea for a box installed on the projector in a meeting room that creates a wifi network that you can join to send your screen to the projector without the need for annoying cables and adapters. It turns out that recent versions of XBMC support AirPlay. I first tried Raspbmc but had more luck with OpenELEC.

It works pretty well, and is able to use the tiny Edimax Wifi USB dongles to join my home network and do all the amazing XMBC stuff pretty well - I've spent the afternoon watching fantastic Apollo videos and TED talks.

If you turn on Airplay it works on my iPhone when I'm using apps like YouTube but not apps like ABC iView - why?

It turns out that Airplay is not just one thing, it's a combination of technologies and while YouTube works because the controlling client passes the HLS m3u8 url over to the XBMC server which then streams it from the server, clients with either secure video or doing video sharing are not able to stream to XBMC over the network.

I think the solution to my problem is to combine a Wifi hotspot, probably an Airport Express, with an Apple TV box, but where's the hacker fun in that? (I wish Apple would make an Apple TV box with some sort of "AirDrop" for video for use in meeting rooms).

Sunday, August 18, 2013

Reverse engineering network traffic with a Raspberry Pi

Sometimes it's useful to monitor traffic between a client and the server for debugging or to figure out how something works. In the past I've used a Linksys WRT54gl router which can be flashed to run OpenWRT. These devices don't have much free space so recently I've started using a Raspberry Pi for the same purpose. It's much more compact and more capable.

To create a Wifi hotspot with a Raspberry Pi, I followed the instructions at Adafruit. The system needs a dhcp server to give out addresses to wifi clients, hostapd to authenticate clients and some iptables commands to nat the addresses of TCP requests going through the device.

The Wifi USB dongle I purchased is an Edimax Nano USB WiFi adapter (EW-7811Un) which cost $35 over the counter. These seem to work well with the Pi's limited power budget and are capable of being a hotspot.

My network is called "honeypot".

The simplest way to snoop on what an app is doing is with tcpdump. I monitor traffic on the wireless interface and display the first part of each packet in ascii. The command is "sudo tcpdump -i wlan0 -A". Here's what I see on opening a TV guide app:

You can see they are talking to flurry and crashlytics, but the display is not very convenient for seeing what's going on.

A more friendly way to watch HTTP traffic is to use a proxy such as mitmproxy. Then set the proxy on the device to point to it. Now in our terminal we see a nice summery of each request.

Pressing return lets us drill in to the request and see the headers nicely formatted:

Pressing tab switches over to the response:

Lots of interesting things to learn in there! I typically then use the MacOS JSON Edit program for exploring json data (there's lots of tools around for this).

iOS apps seem to honour the proxy setting but I find that often Android apps do not, or only do some. It's possible to use iptables to set up a transparent proxy. I've got this mostly working although most https requests mostly seem to fail, here's my magic incantation:

# start a transparent proxy
sudo sysctl -w net.ipv4.ip_forward=1
# clean old firewall
sudo iptables -F
sudo iptables -X
sudo iptables -t nat -F
sudo iptables -t nat -X
sudo iptables -t mangle -F
sudo iptables -t mangle -X

# nat on the local lan
sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
sudo iptables -A FORWARD -i eth0 -o wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT

# forward all requests to the proxy
sudo iptables -t nat -A PREROUTING -i wlan0 -p tcp --dport 80 -j REDIRECT --to-port 8080
sudo iptables -t nat -A PREROUTING -i wlan0 -p tcp --dport 433 -j REDIRECT --to-port 8080

mitmproxy -T --host

So, a $38 raspberry pi plus a $35 Edimax wifi dongle, makes a pretty nice Wifi hotspot with advanced network inspection capabilities.

Saturday, August 03, 2013

Knobless Wonder 7.16MHz SSB transceiver is on the air

I'm excited to report that my build of Peter, VK3YE's, simple fixed frequency "Knobless Wonder" transceiver is complete and I've just had my first contact with Stephen, VK2BLQ.

Aside from a few errors along the line of me pulling out incorrect component values a few times, the circuit was very simple to build. The major problem I had was that the RF transmit side was unstable due to some long runs of unshielded wire but that was fixed with some thin coax.

My thanks to Peter Parker for this excellent design and to Mal, VK2BMS and Stephen VK2BLQ for giving me signal reports.

Sunday, July 28, 2013

Amateur Radio Home Brew group - "making frequency"

The theme of today's ARNSW Home Brew group meeting was "making frequency" and we had a diverse range of approaches on show. It's fascinating how technology has moved from crystal oscillators, to phase locked loops to computer controlled DDS in a few short years.

John, VK2ASU, demonstrated how to raise the frequency of a quartz crystal by carefully grinding it to make it thinner.

This is done first with 600 grade sand paper and later directly on a glass sheet using a fine compound such as toothpaste.

The evolution of a flexible Atmel processor controlled DDS based oscillator was shown, starting with the prototype and ending with a very nicely boxed up unit with plenty of space to house perhaps an entire transceiver at a later date.

Here's the prototype:

Here's how the completed project turned out:

Stephen, VK2BLQ showed a "Huff and Puff" stabilised oscillator he had constructed.

It's amazing to me how even non-computer nerds are getting in to embedded processors for ham radio applications these days. Mostly the Arduino and Raspberry Pis are popular but here's a nice board Bob made:

Peter, VK2EMU, explained phase locked loops and DDS and the crowd had a great time.

In other news, my build of Peter, VK3YE's "Knobless Wonder" is now transmitting well - I had a good report on my audio and signal from Mal, VK2BMS.

I've been having some trouble with transmit RF oscillation - due mostly to my use of long, unshielded wires, but I'm gradually improving things. Both transmitter and receiver work but I have yet to add a relay to allow easy switching.

My transmit audio is reported to be clear but "thin", Mal does say it's very readable and "communications quality". Great progress!