Friday 27 September 2013

Occam's Microcontroller

I just arrived home from work to find that our beloved SPRAT has landed on my doormat, in its 156th issue. Perhaps your copy has arrived too.

I am delighted that it contains what the editor, George, g3rjv, generously describes as my "Major Article", which I've given the intentionally oxymoronic (some might just say moronic) title:
"Occam's Microcontroller"...

The article explores the use of microcontrollers within simple QRP projects. One such simple project is the little rig, pictured above (and gracing the front cover of SPRAT 156), which was built to demonstrate the article's ideas.

Neither the article nor the initiatives connected with it deny or detract from the work which experimenters with special digital interests and expertise are conducting in the area of  
"QRP Computing" - 
"If I have seen (any distance at all) it is by standing on the shoulders of giants." 
The present Occam's Microcontroller article deals in simple, accessible ideas of interest to all QRP experimenters, especially those contemplating taking their first steps with digital methods.

The link with our dear Franciscan, William (of Occam /Ockham), is through his famous parsimonious principle, which G-QRP members may have seen paraphrased on various club artefacts such as carrier bags (and indeed on George's email 'signature').

I've taken liberties with the club logo and an image of William from painted glass to produce the icon above, which also serves as a new fixed link at the top right of these ramblings to a dedicated support page of resources for the article, containing full details of the rig - code, hardware and more.

If you're not a G-QRP member, the support page provides links for you to join (and you can download a copy of the article too).

George mentions in his editorial that I have been given the honour of speaking at this year's Rishworth QRP Convention, where you have chance to come and meet the rig pictured above!

...-.- de m0xpd

Thursday 26 September 2013

Suddenly, best-ever beacon dx

Last weekend I saw my new Arduino Sudden Tx Shield and the DDS Shield sitting on the bench and an idea struck me - I'd work up a beacon which combined some of the flexibility of my multi-mode beacon with the simplicity of the Arduino beacon.

I took the code I'd developed for the Kanga enhanced VFO system and hacked it to make a beacon capable of sending QRSS FSK-CW, QRQ CW and WSPR.

 Here's the set-up on the bench...

I had arranged for the software to use VFO A of the Kanga Enhanced VFO for the CW transmissions and VFO B for WSPR.

Here's the screen in close-up during the "Rx" phase between transmissions...

Notice the band display at lower right - not only could I adjust the frequency of the transmissions (to fit between other signals showing on the grabbers) but also I could change bands at will (as you'll see later in this post). Here's the display in transmit mode - in this case I'm sending the usual QRSS FSK-CW as you see at the top of the screen...

I started on 40m in the evening of 23 September and immediately got some decent reports on WSPR and QRSS - here's the overnight performance from 23 - 24 September...

Gratifying and consistent with the sort of results I'd obtained before with other beacon systems (Blogs passim) here at m0xpd (although I'd never before been spotted in Bermuda - thanks John, vp9ni !)

 I decided to exercise the flexibility of my new system and switched to 30m for the night from 24 to 25 September and was rewarded by my best-ever beacon performance...

I was so excited by the journey to Oz that it took me a while to notice that Dick, vk7dik, is actually further away in Tasmania. Brilliant.

Also the little beacon had bagged some nice new reports from Greenland and the Canaries (where I've never "been" before). Note further how Chris, 4x1rf (who has received my beacon signals before) spotted this new system's output in Haifa on both 30 and 40m - thanks Chris!

After that exhilarating performance, the next day (today) was a wash-out.

Changes in propagation conditions are seen by the sudden-ness (pun intended) of the "cut-on" as reception wakes up - as seen in this example at pa1gsj...

I also noticed a slight droop in the frequency during the course of reception at the same grabber - a rough "guesstimate" of the gradient suggests the VFO is drooping by about 0.8 Hz/minute (during the transmit phase) in this application...

This is interesting, as its the first shred of non-ideal behaviour I've seen in the DDS module - perhaps it doesn't like sitting close to the 2N3866 sweating away on the nearby Tx shield.

All-in-all a really pleasing result.

Now for the good news - I'm going to be making the beacon software freely available for you to download and use as part of the supporting materials for the joint Kanga / m0xpd projects.

It will be a great application for the DDS Shield and (once we get round to completing it) the Sudden Tx Shield.

Watch this space.

...-.- de m0xpd

Thursday 12 September 2013

Arduino DDS Shield Available Now!

Delighted to see that the Kanga / m0xpd Arduino DDS Shield is available for purchase NOW...

Even more delighted to see that Kanga is offering it at (what seems to me to be) a very attractive price!

I've posted some details of construction, testing and applications on the Kanga Resources page.

There are more exciting developments in the pipeline - watch this space!

...-.- de m0xpd

Sunday 1 September 2013

Sudden Transmitter Shield

After the fun and games with my original Arduino Transmitter Shield and experiments with an ugly version of George, g3rjv's "Sudden" transmitter, I've now closed the loop and built the first prototype of a "Sudden Transmitter Shield"...

The shield includes a buffer/amplifier stage on the input, allowing it either to derive RF from the "RF Bus" which is a common feature of all my Arduino devices (driven by the Kanga/m0xpd DDS Shield) or from any other source (such as a mixer for sideband signals). The shield also hosts a power supply to derive 5V for the Arduino from the conventional "radio" 12V power supply. The DDS Shield is pretty power-hungry and when its 5V is derived from the 12V line by a linear regulator, there's quite a lot of power dissipated - so I think it best to have all the "hot" objects (like this regulator and the PA final) on one shield, where they can sit basking at the top of the "stack".

The keying arrangements follow those used in my own "Ugly Weekender-derived" Tx shield, whilst the remainder of the circuit follows George's words and music closely.

Here's the system with the individual functional blocks annotated...

You can see that I've not fully populated the Rx Mute section - 'cos I've no 2N7000's in stock!

Anybody who doesn't know the Sudden can learn all about it (and learn a lot of useful practical tips besides) by downloading the excellent construction manual from the G-QRP site.

On test, my Sudden Transmitter Shield delivered a nice clean signal through a test 40m Low Pass Filter, when driven by a 7 MHz signal from the Kanga/m0xpd DDS Shield running in the Kanga "Enhanced VFO".

It produced "a shade less than 2 Watts", just as George said it should...

We're looking at ways of making this transmitter shield available for purchase as a kit - once that's sorted, I'll post the complete schematic, in true open-source spirit!

 ...-.- de m0xpd