Thursday, 21 May 2015


I gave up on trying to find a telescopic pole and - instead - got some racquet balls and a ball of twine.

The ball is like a squash ball (only bigger) and I've tied the end of the twine to it, so I can pitch it over the limb of a tree and hoist up the "holiday dipole" that way.

Here's the entire travelling station, laid out on a bench...

You can see the twine and the ball at top left, a co-ax feeder (which I purchased at vendor evening at FDIM) and the antenna wrapped around the covers of a ring binder (a real convenient method of transporting it, which I will post about later) and the rest of the kit, including the new American Morse paddle (from the Hamvention) on the right hand side.

Here's your humble servant operating from the same bench, which is on the North bank of Lewis and Clark Lake, South Dakota...

I had a nice QSO with Art, k8cit, over in Michigan, who gave me 449 - it works!

...-.- de w0/m0xpd

Tuesday, 19 May 2015

Heading West

After a great time at Four Days in May, Shack Nasties is heading west...

We're heading out on Interstate 80 (as you see) inspired by both the Oregon Trail and by Jack Kerouac. I say "we" because the XYL seems to have joined the team in a very positive way at both FDIM and the Hamvention - she's much more than a passenger and companion now!

Talking of Jack Kerouac, I couldn't help buying this bag at the University Bookstore in Iowa City today...

Iowa City is a handsome place and the State University is built around the beautiful old State Capitol building.

I was lucky to get a nice Hendricks TriBander CW rig at FDIM (thanks Dennis) and I purchased a little paddle from Doug, w6ame, at American Morse, to partner it. But I can't find anybody to sell me a telescopic pole ( a "crappie pole") to lift the middle of the new holiday dipole and do some Stateside operating.

I 80 goes all the way to Laramie, but we'll be turning off North to take in some other sights in South Dakota before we reach our old hometown on Sunday.

Wagons roll!

... -.- de w0/m0xpd

Thursday, 14 May 2015

Parallel IF Code

The Parallel IF idea is getting an airing at QRP-ARCI's Four Days in May convention this week.

The Vero demonstrator has accompanied me across the pond and will be available for scrutiny at FDIM (and for demonstration, if we can cobble together an antenna and catch any signals)...

To celebrate and support the event, I've released a copy of the Parallel IF code, which is available at my Github repository. It is the same code as that running on the demo system above.

It is underpinned by the Si5351 device. Whilst my original Parallel IF rig used (and still uses) a pair of DDS modules, I'm not going to release any code for these AD9850 RF generators, believing the Si5351 to be the better choice for this application.

The core of the technique involves the establishment of a 2*2 MATRIX of local oscillator frequencies, where before there was just a two element vector...

One row of the matrix, indicated by a red box in the graphic above, is associated with each of the IF paths. In my case, there is a 10 MHz path, used for sideband applications and a 12 MHz path, used for CW applications. The particular frequencies in the matrix are associated with MY home-brewed IF filters. If you use the code, you'll need to change these frequency constants to suit YOUR filters!

The two columns of the matrix, indicated by the blue boxes in the graphic above, are associated with lower and upper sideband operation, respectively.

The code between the appropriate row, depending upon the user's choice of receiving bandwidth and the appropriate column, depending upon the band, to set the local oscillator (/BFO).

My presentation at FDIM presents the contrast in receiving response achieved by selection of one of the two parallel IF paths using a rather childish analogy with the width of an open door - the tight CW band presenting a narrow opening and the sideband channel giving a wider opportunity to pass the signal...

As ever, bug reports, comments etc., gratefully received!

...-.- de m0xpd

Friday, 8 May 2015

Another Rig for Occam...

The new Si5351 shield, shortly to be launched on an unsuspecting public at FDIM, and the new Rx shield, which made its debut only a few weeks ago at Blackpool, have tempted me to put together a new rig.

Following on with the idea of inflating Occam's famous razor (pun intended) up to the rather more dangerous proportions of a Dagger, I have taken the further liberty of fueling the arms race by suggesting that our pacific Franciscan should have a bigger weapon yet...

But what's bigger than a dagger?

How about a Dirk...

I want to reserve the obvious "Occam's Sword" name for a rather bigger rig (yet to be built) - but this is something of an upgrade from the earlier "Occam's Dagger" rig, so I had to find a half-way house and "Occam's Dirk" just about covers it.

The new rig uses the new production Si5351 board (an application I have already explored) and the new Rx board. But I wanted to include - for the first time - switchable multi-band operation in an Occam's rig (having only had plug-in band-pass filters in Occam's Dagger and a hard-wired low-pass, which made it really a single band rig). So, I set about making some simple switchable filters...

These were not to be the complicated, four-band, I2C-controlled devices of the "Parallel IF" rig. Rather, they are the smallest step-up from a single filter - namely, a double filter!

I designed the band-pass board around some double-pole change-over switches I gt in a job-lot from Jabdog at some rally many moons ago. Here's a finished board, populated for 40m (switch out) and 20m (switch in)...

Having hit on a useful format for the band-pass filter, I decided to make a matching low-pass - seen below...

The idea is that the filter boards stack, in such a way that the switches are next to each other - press them both (and operate the menu change in the software) to change bands.

Here are the filter boards stacked...

The new filter stack, coupled with the stack of...
make up the hardware of Occam's new Dirk...

As you see, it is still a plate of noodles spilling onto the bench (in truth, it is spilling onto the top of a nearby Leslie 825, the bench already being full). Perhaps one day it will get a case.

The potentiometer between the LCD and the tuning knob is a volume control, as described in the Rx Shield notes.

You can download the code for "Occam's Dirk" from here and try it for yourself.

This new spin on the original Occam's Microcontroller rig is great fun - it validates the use of the Si5351 in this application and it has been putting out a nice signal - both from the main station g5rv and from the new "mobile" dipole - all over Europe, on both its bands.

...-.- de m0xpd

Sunday, 3 May 2015

Excess Aerial Baggage

Having turned over another page on the calendar and frightened myself by seeing the word "May", there's no avoiding the fact that I soon need to pack my bags and wend my weary way to Dayton.

I see with a mixture of surprise and amusement that I've been billed as "The Man from Laramie" (on QRP-L)...

I'll give James Stewart a run for his money!

Particularly fitting as my trip to Dayton is the first leg of a longer trip to my old hometown of - you guessed it -  Laramie, WY.

Those bags I need to pack are going to be pretty stuffed - not least because the XYL is coming along on the trip too and she has her ornithological paraphernalia - as well as the proverbial kitchen sink.

I've decided I need to take an HF antenna - partly to demonstrate the Parallel IF receiver which I'll be talking about and partly because I might be doing some operating (I'm getting a new rig - more about that when I get back). But what antenna to take?

I'm not exactly big on mobile operating - so my mobile antenna choices are limited. There's the Walkabout that I've used on marine mobile exploits and damaged on the beach. Then there's my "holiday dipole", which actually is the very first HF antenna I ever had here at the home station - so it is a rather clumsy QRO affair, hardly suitable for sticking in a suitcase...

I decided to make a new antenna, more in keeping with the "mobile" label. It would be - in the first instance, 40m only. Perhaps in the fullness of time and given a rush of blood to the head I might add traps for 20m but - for now - 40m only.

I looked in the junk boxes and found some BN-34-301 bino cores that looked as if they offer the right balance between sufficiently small size for porterage and sufficiently large size to handle a few Watts to make a viable 1:1 balun for a QRP antenna, which I set about making according to the following scheme...

The schematic above is well-configured for seeing how the balun should be wired up, but not especially helpful for developing any sense of how it actually works - specifically how it achieves the necessary 1:1 impedance ratio (as compared to the familiar and simpler 1:4 balun which can be made with only two windings).

So, here's a re-arranged version of the schematic in a form which (I think) carries a little more teaching...

Note carefully the phasing of the coils (indicated by the dots) without which it will not work!

Here's the balun, realised in a little potting box...

I've arranged for some thick monofilament nylon to take the strain at the dipole centre (rather than the conductor itself) and the feeder is connected by a BNC, as you can see. This would be useless in a permanent installation due to moisture ingress - but this isn't a permanent installation!

I set the length of the dipole elements by matching them to the original "holiday dipole" and gave the new antenna a quick check with the FT 817 - it showed a nice low SWR across the 40m band.

Some hot-melt to stop the bino core wagging around and the box top to tidy things up had the new dream catcher finished...

It is, as you see by comparing the centimetre grid on which it is standing, rather more appropriately sized for portability than the old QRO antenna it replaces.

That's one more thing I can cross off the list of things to do before setting off for the New World,

...-.- de m0xpd, aka the Man from Laramie !

Update (4 May)

The weather being a little more cooperative again, I took the new antenna out into the back garden and hoisted it into an inverted vee - flying the centre from a telescopic fishing pole. Had chance to check not only that it returned "a nice low SWR" - but also that I could radiate a decent signal from it, courtesy of spots on the Reverse Beacon Network from all over the place and a QSO with Steve, g0evj.

I was using my FT 817 and a new version of the Occam's Dagger rig, which I'll tell you about when I get chance for a longer post...

Saturday, 25 April 2015

Si5351 Shield Production PCBs

After a long gestation, the production version of the Kanga / m0xpd Si5351 Shield PCBs is now back from the delivery room...

I just finished populating the first full board and - like all proud fathers - I'm pretty pleased with it...

The board now uses the full Arduino 1.0 pin-out, so logic voltage level selection is automatic, being set by the host board through the "IOREF" pin.

Whilst this board is offered in the format of an Arduino shield, it calls upon very few of the resources of the Arduino and can run perfectly well within another computing framework. It has, for example, already been demonstrated with a Raspberry Pi and can be controlled by any system capable of generating the necessary I2C commands.

As has been explained in previous posts describing "engineering" versions of the shield, the "m0xpd RF Bus", first seen on the Kanga / m0xpd DDS Shield,  has been enhanced to support the three RF outputs of the Si5351, whilst retaining backwards compatibility with the original RF Bus. This allows the Kanga / m0xpd Tx shield and the new Rx shield to be used with this new RF generator.

In addition to quadrature square wave outputs derived from CLK2 (Q and I outputs were also provided on the DDS Shield) the new shield also presents the complements of these quadrature square waves on the RF bus to make it easier to drive certain implementations of "Tayloe" detectors.

The new shield  also includes two of Pete Juliano, n6qw's "Afterburner" amplifiers, which are seen on the annotated picture below...

The Si5351 alone only produces about 0.7 V into 50 Ohms. The addition of Pete's reheat livens things up nicely (to leave a diode in no doubt as to which way is up!)...

This - remember - is provided on two independent channels, derived from the Si5351's CLK0 and CLK1, and these amplified outputs are transformer isolated (see the binocular cores near the SMA sockets).

Kanga UK are planning to launch this new shield at the Four Days in May event in Dayton, Ohio where it will be supported by plenty of software application examples - including for my Parallel IF scheme.

Even if you don't get one of these shields, do yourself a favour and check out the Si5351 - you'll be glad you did,

...-.- de m0xpd

Friday, 10 April 2015

New Receiver Shield

The new Kanga / m0xpd Rx Shield is here...

I stuffed the first production PCB yesterday evening and had it running on 40 in a matter of moments!

There are no great surprises from the original "Sudden Rx Shield" from way back in 2013 - but I've done some tailoring of the audio frequency response and we've been forced to change to an SMD package on the SA602 due to supply issues.

The shield retains the external audio processing loop, which allows the introduction of everything from volume controls to filters and audio processors and includes software-controlled Rx muting.

You can see the new shield on the Kanga stand at the NARSA show, where it is being launched this Sunday

in the luxurious surroundings of the Norbreck Castle Hotel in Blackpool.

I was going to say "Sunny Blackpool", but they tell me our recent spell of settled weather is going to change this evening, so all bets are off.

See you on Sunday!

...-.- de m0xpd