Updated: Oct 16, 2020
My direct conversion receivers for WSPR was one of the first products I made and sold two years ago when I started ZachTek.
It was a commercial success and many Hams liked the idea of a small low power receiver with no settings that could be on 24/7 to monitor the WSPR segment on one band.
However it was designed with a front end that required me to wind three coils and transformers by hand. This was a taxing task for me and limited the number of receivers I could manufacture and sell. My girl friend helped me out for a while and wound several hundreds of toroidal coils and transformers before it became to much of a burden to continue to produce them. They therefore have been out of stock for more than a year now while I instead used my time to produce my line of WSPR transmitters.
I made an effort to redesign the the receiver once but I could not find the time to complete the task.
The thing that changed all of this came this summer when I purchased a small Pick-And-Place machine that greatly helps to cut the production time for my products.
It enabled me to get ahead in my production and get enough of a stock that I had some free time for my design work again.
So for the last couple of weeks I have finished the prototype run for version 3 of the WSPR receiver. For each band I had to find the optimal values of a bunch of fixed capacitors in the front end band pass filter to get the optimum coupling and thus the correct input impedance that I had to validate with an VNA for each band . I also measured the sensitivity of the complete receiver on a few bands. All of this trying out and measurement validation took its fair bit of time as there are currently eight bands. But now I have eight working prototypes with all the values measured and documented.
The front end came out fine and are not to hard to adjust which is a good thing as every receiver will be individually adjusted
The design has been improved in some other areas besides replacing the handmade coils.
One improvement is that the receiver now uses a TCXO instead of a crystal for the frequency reference. This improves the frequency accuracy of the receiver from about 20ppm to 2.5ppm.
Another improvement is the addition of a pre-amp before the mixer stage. This lowers the Noise Figure of the receiver compared to the earlier versions.
The improved sensitivity resulting from this will probably only be noticeable on the higher bands were the noise level is lower. Users in RFI quiet rural locations will be the one that mostly benefit from this.
The new coils, the pre-amp MMIC , the TCXO and included Audio and USB cables will increase the price of this version with about 19$ so the new price will be 87$ for this version of the WSPR Receiver.
I will start building some boards in the upcoming week.
The first twenty or so will be half manual and half machine mounted and then I will slowly increase the build speed as I get the PnP machine to mount more of the components for me.
If you want to be notified when a specific band is available just email me and I will put you on the notify list.
I will produce the following versions in my fist run 80m, 40m, 30m, 20m, 17m, 15m,12m and 10m.
2190, 630m, 160m and 6m band version will take some more work before they are ready as I will need another set of variable inductors for these bands.
73 and catch you on the bands.