By Dave Jensen, W7DGJ

Several months ago I asked my buddy Marty Buehring (KB4MG) to write an article for us on the topic of WSPR. Both Marty and I had been playing around with WSPR for quite some time, and we were impressed by the capabilities of an inexpensive gadget from ZachTek's Harry Zachrisson. What a terrific device for checking antennas or propagation just about any time you want. At the time, ZachTek had a receiver also but it had some limitations and we chose to review Harry's transmitter only. Now, the situation has changed and the improvements are many. Another little device that impresses us from this boutique supplier of cool ham goodies!

This short review and graph is, once again, thanks to Marty (President of the Cherokee Amateur Radio Society in Woodstock, Georgia). To reiterate why it is important to receive as well as transmit in this mode, I'd suggest you read the first article, at this link. There, you'll read about a community of WSPR users all over the world, where receiving WSPR and uploading that detail means that you've become a part of this community of hams. "The more the merrier" is the message for anything to do with WSPR.

The WSPR Receiver from ZachTek, by KB4MG

As a WSPR enthusiast, I love that there is a growing group of hams who have found the utility of WSPR mode for various uses in and outside their shack. For me, I like to have a dedicated WSPR receiver running whenever I am not actively using my antenna. I can refer to it and see what propagation looks like from my location. The main purpose however is to be a part of the WSPR community and to upload my received data to the WSPRnet server for others to use in their analysis. The more users in receive mode for WSPR, the better the tool becomes.

I have considered a number of solutions for receiving WSPR, including just using my ICOM7300 rig. I didn’t like the idea of having my rig powered on all the time, so I next tried the Airspy SDR. This is a marvelous receiver, but again I didn’t want to dedicate it to running WSPR all the time.

I was familiar with Zachtek products as I do own a Zachtek WSPR transmitter. They offered a WSPR receiver (SKU-1010) for some time, but I never thought it would do the job for my purposes. The original design was based on the SA612A as the front-end. Though this is a fine mixer and local oscillator, there was no amplifier that preceded it in this product. Further, it was decoding double sideband. The WSPR signals are always on upper sideband regardless of the band frequency. It could pick up WSPR stations, but not as well as regular ham radios.

In the newest product design (SKU-1055), these problems are remedied and the design enhanced with a preamp stage, which not only amplifies the incoming signal but helps attenuate the local oscillator so it does not interfere. This new design also uses an additional amplification stage after the mixer as well as a full SSB detector for upper sideband. The resulting audio output is filtered for 1500Hz bandwidth, which is the audio band in which all WSPR signals will be found. In the opinion of this EE, it is a very nice design.

In my testing I compared the Zachtek to my ICOM IC-7300 by using an antenna signal splitter to connect to both receivers. In WSPR you can use a “/ suffix” on your callsign so that WSPRnet will log your uploads from both receivers with different callsigns. When I looked at the data I found that the Zachtek receiver performed as well as the ICOM, which amazed me. The ICOM is a great receiver with direct sampling SDR technology. A good comparison is to look at the “spots” each receiver logged during a defined period of time. This graph was over a 3 hour period, but longer times have shown the same correlation. I am using the Zachtek receiver now as my full-time WSPR receiver -- Marty.

In Marty's graph, the red highlights the ICOM 7300 reception and the Green represents the ZachTek. His comparison is courtesy of software from Roland (HB9VQQ).  The ZachTek receiver is available at this link and is $87 USD plus shipping. I can testify to the fact that shopping on Harry's website is easy and that his shipping speeds are fast. Customer service, provided directly by the owner, is outstanding. I'm a Mac user, and Harry and I have had a lot of back-and-forth exchanges, but luckily both transmit and receive software is Mac compatible.

73 for now,

Dave Jensen, W7DGJ

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