BITX Developments

Things have been moving on quite nicely with the little SSB rig over the past few days (when the pressures of work allow me to steal a few moments for leisure projects!).

First, I've switched away from the initial "development" configuration of a stack of Kanga/m0xpd DDS shields for the RF generation (BFO and VFO) to just the DDS modules themselves. They are mounted, at the moment, on a breadboard - along with an Arduino NANO and a little PSU.

The idea behind the NANO is that - eventually - I'll be moving to just an AVR microcontroller on a board with the DDS modules and the Nano puts us closer to that end-point in terms of physical size! All the parts will be available from Kanga UK if anybody wishes to follow in my footsteps (and the code will be published as freeware - see below).

Here's the RF generator in its original embodiment...

The digital RF generation scheme allows easy switch not only between bands but also between LSB and USB modes - requiring a change in the BFO frequency. To test this, I made up a pair of plug-in filter modules for 20m...

Both the low-pass and band-pass filters are built to standard G-QRP "recipes"; the LPF is described here, whilst the BPF is in SPRAT (v154, p25).

The 20m conversion was a piece of cake - just plug in the filters and modify the code to switch over all the frequencies required in the transition between lower- and upper-sideband operation.

The next development added a relay-based change-over from receive to transmit (I'd used a switch in the original build last week as a temporary measure). The switch remains as one controlling input to the relay system - but I also have a parallel input for a second (/third/fourth) switch (the Rx/Tx selection is a logical "OR" of any parallel switches) AND a TTL level input, such that (one day) a micro can control the whole system...

Also visible in the picture above is a new power supply for the 5V elements (the DDS modules, the Arduino and the display) - all implemented by a 7805 regulator on the main heatsink.

Given the additional Rx/Tx switching flexibility, I added a push-to-talk switch on my toy "fist" microphone...

Why - this is almost like a "real" radio HI HI.

Next, attention turned back to the RF generator system - I knocked up a mounting for the rotary encoder to make tuning a little easier...

The two push-buttons allowed me to cobble together a new version of the "Kanga Enhanced VFO System" suitable for this new Double DDS scheme with band-change via menu, automatic selection of LSB / USB as the 10MHz boundary is crossed, Rx/Tx detection (via an input to the Arduino from the power switching on the main board) which adds Receive Incremental Tuning, etc...

Here's a close-up of the display...

I'm gong to be working up the code into something suitable for publication - so please be patient!

Here's the entire rig smeared across the bench in my habitual style...

I've had fun building it but - I must confess - I've also enjoyed operating !!

Lots of FB QSOs in the UK and into Echo India, best dx so far into Germany, but the first prize in terms of operator satisfaction goes to my QSO with the RNARS London Group's gb2rn station on HMS Belfast...

"OK, I'll hand it back to you, from MIKE ZERO X-RAY PAPA DELTA"