The Ultimate3S QRSS/WSPR Transmitter Kit transmits various QRSS, Hell, Opera, PI4 and WSPR slow-signal modes on any LF, MF, HF or VHF band (all amateur bands from 2200m to 2m or 222MHz). This kit includes:

  • Main U3 PCB with LCD module and all components
  • Si5351A or OCXO/Si5351A (see note below) synthesiser module kit (Si5351A chip is pre-soldered at the factory)
  • Low pass filter module kit for one band (choice of any band from 2200m to 222MHz)

The kits are easy to build, with through-hole components only (no surface mount soldering). Additional plug-in low pass filter modules are available for any of 16 amateur bands from 2200m to 222MHz. The kit can transmit on any frequency up to over 200MHz (222MHz band works fine), though at VHF the power output is lower. Changing bands is a matter of plugging in the appropriate low pass filter kit to attenuate unwanted harmonic output.

A relay-switched LPF kit is also available, that allows the U3 kit to automatically switch between up to 6 bands in an operator-defined sequence.

Printed instructions are not supplied with the kit! Please see the Ultimate3/3S web pages at the main QRP Labs website to the kit instructions, and for further information.

NOTE regarding enclosure: if you order the optional enclosure, please note that it is shipped separately via tracked airmail from China where the enclosure is custom-manufactured for QRP Labs. Please also refer to Shipping FAQ

NOTE regarding receiver kit option: The receiver kit includes a Band Pass Filter kit for your choice of band from 160 to 10m. By default, the BPF band will be the same band as the LPF that you select on this order page. If you would like a different band instead, please mention this in the customer notes field when you checkout. 

NOTE regarding OCXO option: The Ultimate3S kit INCLUDES the standard Si5351A module kit. Optionally you can also purchase the OCXO/Si5351A module kit, which is plug-in compatible with the Ultimate3S. The OCXO/Si5351A kit has high frequency stability. However, the OCXO/Si5351A kit is more difficult to build and adjust than the other kits. If you want to build the OCXO kit, we recommend that you build the standard Si5351A kit first, and get everything working, THEN build the OCXO/Si5351A kit. In general the standard Si5351A module kit is good enough, particularly if you are using a GPS for frequency calibration and drift correction. You would only need the OCXO/Si5351A module kit if you want to operate in an environment with wildly changing temperatures, or you do not want to use GPS for drift correction, or if you have some particular requirement for extreme freuqency stability, or if you are a perfectionist or just want the challenge and interesting OCXO kit!

NOTE regarding TCXO: The 25MHz TCXO option is another option to provide excellent frequency stability. The supplied Si5351A Rev 3 Synth board exactly fits the 25MHz TCXO option, as described in the assembly manual for the Si5351A Synth kit. 

NOTE regarding the GPS option: Connecting a GPS like the QRP Labs QLG2-SE kit is a very nice and inexpensive addition to your U3S kit. The GPS provides the initial frequency calibration as well as regular drift correction. Furthermore it sets the location and time, and keeps the realtime clock accurate (important for some modes such as WSPR). 

Please read manuals and understand your kits before purchase. 

The kit supports the following modes:

- QRSS mode (plain on/off keyed slow CW)

- FSK/CW mode (frequency shift keyed slow CW)

- DFCW mode (dual frequency CW)

- WSPR mode (Weak Signal Propagation Reporter)

- Opera and PI4 beacon modes

- WSPR-15 experimental WSPR mode with 15-minute frames

- JT9 modes (5 speeds)

- Slow-Hellschreiber (frequency shifted slow-Hell)

- Full-speed Hellshreiber

- Half-speed ("DX") Hellshreiber

- CW (plain CW)

- FSK (0-999Hz shift, fast-speed FSK CW)

- Customisable FSK patterns

Other features:

- Si5351A synthesiser module (no SMD soldering required)

- Plug-in low pass filter boards (available for bands 2200 to 222MHz)

- 2-row by 16-character blue back-lit LCD + two-button user interface

- User-programmable (callsign, message, speed, FSK, mode, etc.), settings stored in EEPROM

- GPS interface, for locking the frequency, timing and location information

- On-chip generation of WSPR encoded message (no PC required)

- WSPR maidenhead locator can be generated from GPS-derived latitude/longitude

- Selectable “frame” size, for stacked QRSS reception

- Plain CW callsign identifier at selectable interval

- Produces 250mW RF output on 30m (lower output on higher frequency bands)

- Higher output power by additional PA transistor and/or higher PA supply voltage


NOTE: 18-Dec-2021: The ATmega328 chip is now unobtainable at any distributors, due to the global semiconductor shortage. We have managed to obtain stock to be able to continue offering this item, however, the price was very high and this has necessitated a temporary price increase of $2.79 which is currently included in the price of this item. 

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Ultimate3S QRSS/WSPR kit

  • Product Code: U3S
  • Availability: 69
  • $35.99

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