The Zachtek WSPR Transmitter

The building blocks of the Desktop transmitter.

Note: picture shows an older revision with hand wound coils.
Source: WSPR Desktop Transmitter Documentation page:


Lightning Protection


Note: that we used a test point for the antenna connection and the side of the SMA as the ground for the GDT

Full credit to Ash, VK4ASH for the foresight in recognising this requirement and providing the technical solution.

Gas discharge arresters are ideal for quenching high voltage, fast rise- time interference transients. They are very high impedance (virtually open circuit) in the normal state with a typical capacitance of 1pF between electrodes. When a voltage spike appears, they arc over and present a relatively low impedance in this condition effectively quenching the spike. They are suitable for protection of telecom lines and antenna circuits. They are not recommended to be fitted across mains circuits as the low source impedance of the mains could destroy these device after the fault spike has cleared. - They are a well- proven and reliable device.- Four models are offered.- PCB Mount- 2 ELECTRODE TYPED.C. Spark-over Voltage (100V/s)90V +/- 20%



Github Repository:

Serial Interface API
1012 WSPR-TX_Desktop Serial API as used from sofware version 1.10:

1012 WSPR TX_Desktop Serial API 1.10 [pdf] (local)


Configuration and Setup Application


The Windows only PC software is here:

A python based App is in early community development.
WSPR-TX-Config - Configuration tool for the Zachtek WSPR TX products:


Testing a Desktop Transmitter

I set up the unit with the GPS antenna inside a window looking out from under a steel roof to the east. A tough test for a GPS. However, it locked with several satellites afer a minute.

I loaded the PC setup applicaton and after a few hours I had the spots appearing on the map that proved the unit was operational.

Spots-2021-12-04 15-19-57.png


Serial USB Interface

Desktop Serial API 1.10:


International WSPR Project Version


Developmental Config Tool

This program written in python roughly follows an MVC method. More comments on this are in the code.

The program purpose is to allow users of the Zachtek WSPR Transmitters to graphically configure their devices on:

Source is available here:


The importance of clean power

These are photos from my IC705 during two 20m Zachtek Desktop TX sessions. The traqnsmittin antenna is a vertical 15 meters above on a metal roof with a 1.5 VSWR on frequency. The IC705 has a small whip inside the shack.The first is powered straight out of a Dell 3040 desktop's USB ports. The USB cable has ferrites both end, but nothing else. The second is powered by a power bank. The artifacts at about 17.5KHz both sides are no longer present. Such is the quality of Dell's USB ports. A clean PSU or extra power filtering is important.



Glenn Lyons VK4PK
Ver:gnl20211204 - pre published v0.9