Stellar WSPR receiver kit built and working

rk-1Last week I ordered a Stellar WSPR RK-1 Receiver Kit for the 30 meter band.

I received the kit today and built it after dinner in a little over an hour. There are about 40 through-hole parts to install on a board with plenty of real estate. Anyone who’s built a QRP kit will find this kit very easy to assemble.

The two necessary cables are included – a USB cable for DC power and an audio cable to feed received audio to the computer’s sound card. Alignment consists of transmitting a weak signal on the proper freq (with your main station rig or a sig gen) and then tweaking a small cap to put the received signal in the proper place on Spectrum Lab.

Once this was done, I started WSPR 2.0 and configured my laptop’s sound card to receive audio on the “Mic In” jack. Soon after, the first spots started showing up.

The antenna jack for this kit is simply a 2-pin terminal board and I’ll be replacing it with a BNC soon. With an alligator clip jumper I’m connecting the board’s antenna terminal to the center lead of the coax going up to my dipole so the connection for now is far from ideal.

Instructions that come with the kit reference the websites for downloading Spectrum Lab and the WSPR program.

It is a simple to build and align kit – almost perfect for its intended users. The manual could be more detailed – there’s a good amount of room for improvement in that department. While building the kit and going through the alignment, I noted several areas where non-hams could become confused.

The kit is not aimed at hams and certainly won’t compete with a dedicated ham rig at digging out WSPR signals – it is designed to be a part of school curriculum and I hope George WB9LVI is selling them by the score and increasing awareness of ham radio at schools. It provides students a way to participate in propagation studies and ham radio without needing a license to do so and that will be the eventual function of my receiver.

I think it would also make a great kit from a ham to an interested friend or family member – or as a father-son project.

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  3 comments for “Stellar WSPR receiver kit built and working

  1. January 25, 2014 at 6:38 am

    Hi John. This looks like a nice little kit. But there isn’t much information about the receiver around that I can find. From your picture I see a crystal but I cannot see any tuned circuits. I am guessing that it is some form of circuit built around a SA612 mixer, but perhaps you could comment on that?

    • January 25, 2014 at 7:49 am

      Good morning, Sverre,

      Yes, it is based on a SA612 and you’re right – no input filtering. This is definitely not a WSPR receiver for a ham but rather for a classroom of young students who might not be able to build something that would incorporate a better design with more complex circuitry/construction/alignment (mine will be going to a Cub Scout group, along with two unbuilt ones).

      As I tinkered with this one a bit more last night and listened to the received audio, I found that it was receiving a local AM station when connected to my antenna as described above. After replacing the terminal connector with a BNC (thereby allowing my dipole to act as a resonant antenna on 30m rather than the long wire it appeared as with the terminal strip configuration), no AM broadcasts were received and more WSPR stations were.

      It’s clear to me that the designer wanted to make the simplest receiver possible that would allow first-time kit builders and classrooms without a ham to still be able to build a working receiver that would pluck WSPR stations out of the air and therefore demonstrate the principles of this digital mode, propagation and other aspects of radio.

      But no – this is not a receiver that would impress any ham – but that is not its intent.

      73 from south Texas (where the temperature makes it feel like Norway this morning!)

  2. January 25, 2014 at 9:33 am

    Thanks for the info – a very basic design, but one which does the job.

    This weekend I am at an elevation of 800 m in the mountains of Norway with -7 C = 19 F. Minimum this week was -13 C (http://aprs.fi/weather/a/LA3ZA-3?range=week) I hope Texas is warmer than that!

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