Saturday, 5 June 2010

New Beacon on the Block

I'm pleased to be able to report progress on the QRSS Beacon project ...

I had managed to get some nice clean FSK Morse signals last week, but decided to make a more complex keyer/controller device. The idea was to augment the "open collector" output of my usual PIC keyer by adding a voltage output, which would directly control the VXO with high-resolution signals. The motivation for this increase in complexity will be seen later - read on...

I took the opportunity to port the code from the PIC16F84a (a choice which has its origins in Eamon "Ed" Skelton, ei9gq's PIC keyer in RadCom (Vol 84, No 12)) as I was "running out" of 16F84s! I have quite a handful of 16F676s in "stores", so that was the target platform. I also found a few MCP4922s - 12 bit D/A converters from Microchip and used one of these as the D/A converter to generate the control voltages. Yes - they are massively over-specified for this application, but they're easy to use (much more so than knocking something together from resistor ladders etc) so, in a strange sort of way, I am "keeping it simple".

Here's the lash-up of the new controller - made on a "breadboard", as it it more convenient than (e.g.) ugly methods for DIP packages and there are no high frequency issues to contend with - even the PIC is clocking very slowly...

You can also see my PicKit2 development programmer / debugger, which I use to program the PIC, the VXO and mixer (forming the "L" at bottom right) and the Si570 USB Synth (top right).

The PIC (the DIP package in the middle of the breadboard) "talks" to the D/A (further right) through an SPI interface, which I implemented in the PIC using some "brute-force" coding (the 16F676 doesn't have anything as sophisticated as serial output). I also took the opportunity to add a control line and some circuit modifications to the VXO which allows the PIC to mute the entire system.

With this enhanced control of the VXO, I could do more than just send FSK morse code - particularly, I could send S/MT Hellschreiber signals.

I set about designing a font for Hell characters (at least those in my callsign) and wrote some code to allow the new controller to send my call - here's the first try (monitored locally on Argo and before I'd implemented the "mute" between characters)...

Here's the result with the system generating FSK Morse and S/MT Hell sequentially, with the glitches between characters muted out...

This morning, I connected the system to a 10MHz Bandpass filter, the "Radio Times" amplifier and the 10MHz LowPass I'd used on the h/b WSPR beacon and fired it up...

The BandPass filter was built to lose the unwanted lower sideband (which, given my target frequency of 10.140 MHz and the 3.579 MHz xtal was going to be at ~6.5 MHz).

I measured an output of 150mW into my half-g5rv.

I was delighted to see myself appear first (as the faint signal towards the bottom right of the screen) on Guenael's grabber...

and then on the on5ex grabber in Belgium...

Here my signals are clearly seen, just below Bill n2cqr's "not-so square wave".

I was taking up too much of the spectrum, but (given the PIC programmable controller) adjustment was a simple matter of changing a few constants in the program. My FSK now only occupies 5 Hz or so.

This has been great fun and I look forward to seeing where else I can send my new Hellschreiber signals.

...-.- de m0xpd


Guenael Jouchet spotted my signals and put a report on his QRSS Reports page (see Guenael's comment below).

Francophones should visit Guenael's excellent "It's Raining Elephants" blog (well, everyone should - but if you can read French or arrange a translation you will get more pleasure from your visit!)

Johan, pa0tab, also spotted me on his "Tabber" grabber at locator JO33hf and kindly sent a report.


  1. Nice to read about your QRSS project.

    73, Tjeerd (Gose)

  2. Hey !!! A screenshot of my QRSS grabber is arrived on your web site :)


    I recently identified your callsign and after some google search and browsing, I discover with pleasure that my online grabber has been useful for one person at least :)

    I updated my report page, but I not yet received my callsign. So, it's a simple SWL report.

    Thank you for the link on your web page. Nice blog !

    Best regards, 73,

    PS: Email address or contact box not found, so I use the comments to submit my msg.