W5OLF’s WSPR kit

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Jay Wilson W5OLF has developed a small QRP kit designed to transmit WSPR signals without the usual phone rig/computer/sound card interface/audio cable entanglement.

I ordered his kit just a few days ago and – with nothing more than my 12V supply, dipole antenna and the very tiny circuit board that constitutes the kit – have been “spotted” on 4 continents in fewer than a dozen transmissions. Power output is 2 watts on 30 meters.

Kit assembly is simple and consists of two dozen components and the same high quality circuit board you’d get from any of the top QRP vendors. Alignment is a two-minute, two-part procedure: adjust a cap for power out; adjust a pot for freq.

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Prior to sending the kit to you, Jay programs the new owner’s callsign, grid square and power output (ie, the contents of the WSPR transmission) into a PIC. Power output is determined by what your power supply for the transmitter will be – in my case 13.8 volts.

Transmissions are initiated manually with a press of an onboard button at the :00 second mark on an even minute. My WM-2 QRP wattmeter indicated 2 watts for the entire 1-min 50-sec transmission time with no decay of output power over that time. The VCXO-AXE WSPR kit’s final is a 2N7000 operating Class E. It is heatsinked to the board via clipped leads from previously installed components acting as tie-down straps to hold the transistor fast to the board.

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In both his eBay ad and the included documentation, Jay mentions the spectral output of the kit noting that the 2nd harmonic is only 30dB down from the fundamental. This may suffice, depending on the antenna in use. If not, details are given on how to make a simple LC filter. Additional values can be ascertained here, if necessary.

Prior to transmitting, Jay recommends allowing the ocsillator chip to stabilize for a couple minutes after applying power to the kit. During this time, the oscillator can be monitored with a nearby receiver tuned to ~10.140.200 MHz. In fact, the kit can be tuned to freq without even transmitting simply by monitoring the oscillator’s tone on your big rig. Or you can simply adjust the tuning cap until Pin 1 of the oscillator chip reads 1.65 volts. That’s what I did and was immediately rewarded with more spots than a litter of leopards.

In addition to full-color photos of assembly and operating instructions, the documentation included with the kit includes two notable nuggets of info: (1) programming language for reprogramming the PIC to reflect a new grid location, power out or callsign and (2) an idea on how to automate the keying of transmissions for those who may want to go refill the coffee cup instead of monitoring the clock to see when to push the button.

And speaking of timing…I guess we all have atomic clocks or internet-sync’ed time on our computers. Those are perfectly adequate – any human delay in pushing the button at some precise, exact instant is a non-issue. I’ve received spots when transmitting 2 seconds prior and 1 second later than the ideal time, so timing tolerances are not tight and allow plenty of play for the human element.

How will I use this kit?

I doubt I’ll ever implement an automated transmission method. My real interest in WSPR is not so much to see myself spotted or even to investigate propagation but rather in the mode’s utility of being able to compare antennas. I currently have two antennas – a standard, horizontal dipole for 80 meters (used 10-80) and a vertical dipole for 40 meters (for 10-40).

When you’re received on WSPR, you’re not just spotted – your received level is posted and available for all to view at this website. An A/B test of two antennas, and the corresponding dB level at which they’re received on the far end, can be very illuminating in terms of which antenna is best over a given path at that time.

Dipole, 2 watts

To me, WSPR is not so much a mode, but a tool for the DXer or antenna experimenter, incorporating elements of a propagation program with a hypothetical “results-based antenna analyzer”.

This kit greatly simplifies the process of that implementation. I’d love to have one for 40/80 meters.

Others wanting to inquire/order one of these transmitters may reach Jay via email: w5olf@comcast.net