Sunday, June 23, 2013

Knobless Wonder build

Over the past few weekends I've been building VK3YE's "Knobless wonder" a fixed frequency SSB transceiver for 40m. It's at the point of starting to work, although transmit sound is very poor right now.

A scan of the circuit is here. I've enjoyed the build, it's simple enough for me and I was careful to build and test stage by stage, stopping if something didn't work and figuring it out before going on. The main thing that goes wrong for me, aside from failure to follow the circuit accurately, is that sometimes I have mis-filed components that I grab without checking.

The technique I've used is "Manhattan" ugly construction using snap off squares I purchased on-line and super-glued to the base boards. This turns out pretty neatly and makes the board look like the circuit diagram so it's easy to debug.

So far the receiver seems pretty deaf, although it hears my shack oscillator sweeping quite well. The transmitter has been heard by VK2BMS a few Km away although the audio is not good at this stage. I think the oscillator isn't tuned correctly yet - I need to figure out the best way to adjust this.

My thanks to Peter for a nice design that is easy to reproduce. I think this is a great group project for people who live pretty close together.

Friday, June 21, 2013

Updated ABC rage app in the Australian app store

It's been a great pleasure working with the ABC TV rage team, a wonderful graphic designer and producers to do an update of the popular rage app.

The design is pretty wild but from a software developer's perspective I've focussed on minimising internet traffic by doing HEAD requests and only pulling down playlist data, artist images and bios as required.

Playlists are cached in a local core data store so that opening the app is fast and memory use is minimised.

It's amazing that this TV show has been on air since 1987.

Please check out the app and if you like it, give us a rating and review. (If you don't like it, I hope you'll contact us).

Saturday, June 15, 2013

Raspberry Pi as an OpenVPN server

Many of us work inside fire walled networks where virtually all ports are blocked and web traffic goes through an annoying proxy server. A VPN connection makes your computer appear to be on another network and these issues go away.

Another big reason to operate through a VPN is if you are on someone else's network, perhaps a cafe Wifi service, and are (rightly) concerned about your traffic being snooped.

There are commercial VPN services available but I've recently set up a raspberry pi as a server and it works really well sitting on my home internet connection.

OpenVPN requires a single port, either TCP or UDP, between client and server.

Installation is well documented in several places, but I referred to the excellent instructions on Remi Bergsma's Blog.

I made two changes:

  • Used tcp rather than udp as for some reason I couldn't connect via udp - update the setting in /etc/openvpn/server.conf
  • Enabled nat on the pi as I was unable to set a static route on my home router - an Apple Airport extreme.
The command to enable nat on the pi is:

iptables -t nat -A POSTROUTING -s -o eth0 -j MASQUERADE

I added that to /etc/rc.local so it will be re-applied on each boot.

Finally I forwarded the TCP port I want to use to connect from my home router to the Raspberry Pi. My home internet connection occasionally changes public IP address so if that becomes a problem I might use a dynamic DNS service to keep track of it.


I use MacOS mostly and I'm using the Viscosity client which has a 30 trial period (which I'm still in) and then costs just US$9 which is very reasonable. At first I tried the free Tunnelblick client but it doesn't quite work at the moment with Mountain Lion (I can't get it to correctly set the DNS to the remote end of the tunnel).

Wednesday, June 05, 2013

Digital data transmission tests on Radio Australia

Please be advised of the second Radio Australia HF test using the digital text modes MFSK and FLARQ.  Freeware fldigi will handle these automatically - see   and

The text will contain text and images from Radio Australia's web site as well as contact details for sending responses. Note 2150 UT Sunday is Monday morning 0750 EST in Melbourne etc.

All dates/times are in UT, all frequencies in kHz
Saturday/Sunday 8/9 June 2013

0850-0857 UT on

 7410 (PNG & south-west Pacific)

11945 (south Pacific, NZ, central America, Europe)

1230-1237 UT on

 6080 (PNG, west Pacific, Philippines, Japan),  new freq for MFSK

 9580 (central Pacific, NAM)

12065 (central Pacific, NAM)

2150-2157 UT on

11695 (south-east Asia, Europe)  new freq for MFSK

21740  (central Pacific, NAm)   new freq for MFSK

with 40s of RA tuning signal (Waltzing Matilda) at the start of each session.

Extremely poor reception here this morning of 11695. I could barely detect that there was a station there and only a few words were decoded.


The tests have been a success and reports are coming in from around the globe. The Voice of America's Dr Kim Elliot, reports on his reception in Northern Virginia where despite poor audio reception, the digital text message was perfect.

Monday, June 03, 2013

Knobless Wonder 40m SSB QRP circuit from VK3YE

Peter, VK3YE, recently showed me a new home brew fixed frequency single sideband rig he dubbed the "knobless wonder". I think this is a great group project where the fact that it's fixed frequency is an advantage in encouraging contacts between builders.

He's given permission for the circuit to be published here (click to enlarge).

I highly recommend Peter's walkthrough video complete with a series of contacts on the actual rig.

Thanks Peter!

Sunday, June 02, 2013

Tune in to "Download this show" tonight

If you are near a radio this evening, tune in to ABC Radio National where I join host Marc Fennel and co-guest Claire Porter (from to chat about human technology matches and mis-matches.

Can't tune in? guess what, you can download this show or subscribe to the podcast by searching for it in your podcast app or iTunes.

Always a pleasure to join Marc and other guests on my beloved Radio National.

Tablet friendly M65 Jacket - as seen on TV

You don't get much fashion advice on this blog, until now. If the M65 field jacket seems familiar, it's because Robert De Niro wore one in Taxi Driver, Al Pacino wore one in Serpico, Sylvester Stallone wore one in multiple movies and Arnold Schwarzenegger wore a decorated one in Terminator. And that's just the start, check Wikipedia for about 40 references.

Introduced into the US military in 1965 to replace the M51 which replaced the M43 (you can figure the years).

The exterior is poly cotton mix, there is a 100% cotton lining and a further, buttoned on detachable inner warm layer. The instructions warn not to dry it on a stove, so I guess that was a problem.

What's amazing is that in 1965 they correctly predicted the dimensions of the now popular seven inch tablets and a Nexus 7 fits nicely in the side pockets. Great forethought there. Available at army disposals stores globally.

Saturday, June 01, 2013

First test with cheap $5 AD9850 DDS board and Arduino

News of the availability of very low cost AD9850 DDS boards from China via eBay has swept the home brew radio community in recent weeks. These chips alone were quite expensive and the surface mount soldering was a challenge.

Now the chip, mounted on a nice carrier board, with 125MHz crystal, is available for a very reasonable price. Here's mine sweeping a few frequencies near 10MHz:

The Arduino code I used is from NR80 which in turn is based on code from Andrew Smallbone.

I simply powered mine from the 5V on the Arduino and it seems to work just fine.

Our plan is to make a little crystal replacement board for QRP purposes with a multi-position switch to select the frequency.

Purchased a blank Arduino shield board and have now mounted the DDS board nicely for future software development.