Digital “Crystal” Breathes New Life into Old Radio

[Bill Meara] of the Soldersmoke Podcast has a nice old Drake 2B radio, and wanted to use it for the 12 meter amateur band. These old radios normally make switching tuning bands easy — you just swap out one frequency crystal for another and you’re set.

Only [Bill] didn’t have the 21 MHz crystal that he needed. No problem, because he had a junk crystal, a hacksaw, and a modern direct-digital synthesis (DDS) chip sitting around. So he takes the donor crystal, cuts it open, and solders the two wires directly from the DDS to the crystal’s pins. Now he’s got a plug-in replacement digital oscillator that doesn’t require modifying the nice old Drake receiver at all. A sweet little trick.

The video’s a little bit long, but the money shot comes in around 5:00.

Now, one might worry about simply plugging a powered circuit (the DDS) in place of a passive element (the crystal), but it seems to work and the proof of the pudding is in the tasting. We wonder how far this digitally-controlled-analog-receiver idea could be extended.

WSPRing across the Atlantic

wspr

Host of the Soldersmoke podcast, [Bill Meara], contributed this guest post.

WSPR is a new communications protocol written by radio amateur and Nobel Prize winner [Joe Taylor]. Like the very slow QRSS system described in a previous post, WSPR (Weak Signal Propagation Reporter) trades speed for bandwidth and allows for the reception of signals that are far below the level of radio noise. WSPR takes “low and slow” communications several important steps ahead, featuring strong error correction, high reliability, and (and this is really fun part) the automatic uploading (via the net) of reception reports — [Taylor]’s WSPR web page constantly gathers reports and produces near real-time Google maps of showing who is hearing who. The WSPR mode is very hack-able: [Bill Meara] is running a 20 milliwatt homebrew transmitter from Rome, Italy that features an audio amplifier from a defunct computer speaker pictured below. This contraption recently crossed the Atlantic and was picked up by the Princeton, New Jersey receiving station of WSPR’s esteemed creator, [Joe Taylor]. Continue reading “WSPRing across the Atlantic”

QRSS: Radio amateurs’ slow-speed narrowband

qrss

Host of the Soldersmoke podcast, [Bill Meara], contributed this guest post.

While the rest of the world is moving toward high speed broadband, some hams—including one Nobel Prize winner—are going in exactly the opposite direction. Our ‘QRSS’ mode makes use of an unusual mixture of modern digital signal processing (DSP), ancient Morse code, and simple homebrewed transmitters. Very narrow bandwidth is desirable because this reduces the noise in the radio communication channel, greatly improving the S/N ratio.  But Shannon’s communication theory tells us that narrow bandwidth comes with a cost: slow data rates. In QRSS, beacon transmitters using only milliwatts churn out slow speed Morse ID signals on 10.140 MHz that are routinely picked up by DSP-based receivers on the other side of the globe. Many of the receivers, ‘grabbers’, have visual outputs that are available online in real time. QRSS has been getting a lot of attention on the Soldersmoke podcast and on the Soldersmoke Blog. For more information check out this overview and the hardware involved. Here’s a gallery of received signals.