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

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