The first beacon transmitter, my Ultimate 3, is such a success that I have ordered another. The new kit, is the latest version, the Ultimate 3S QRSS/WSPR QRP transmitter. This updated model has a little more power, 250 milliwatts, and uses the Si5351A synthesiser module kit at its hart replacing the AD9850 DDS module. Using the Si5351A should provide better frequency stability at the higher frequencies, so the Ultimate 3S can be used on all frequencies from 360 kHz up to 145 MHz with the appropriate RF filters. The firmware is being actively developed adding more modes with each update. Firmware updates can be downloaded from the developers website or update PIC’s can be purchased. Modes included at the time of writing are: QRSS, WSPR,WSPR-15, FSK/CW, DFCW, Opera modes (8 speeds), PI4 beacon, Hellschreiber (Slow, Field, DX), CW (CW-ID and Plain CW), FSK (0-999Hz shift, fast-speed FSK CW). The plan is to use my current Ultimate 3 for operation on 60M, 40M, 30M, 20M, 17M, and 15M bands, and this new beacon for operation 12M, 10M, 6M, 4M and 2M bands. However at the time of writing, filter kits for the 4M and 2M bands are not yet available.
The kit turned up, the only difference between the U3 and the U3S kit is the need to construct the Si5351A frequency generator module. The module is designed to replace the AD9850 DDS module used in the U3, and uses small high density through the hole components.
The output power of the transmitter is adjustable from zero to about 250mW by careful adjustment of the variable resistor on the main PCB, I have adjusted mine for 200mW output maximum. The RF output varies from band to band and tends to reduce on higher frequencies.
I have fitted filters for 20M, 12M, 10M, and 6M bands. When testing I found the transmitter stable on 20M, 12M, and 10M band with drift when using WSPR between -1 and +1 Hz but on 6M band the frequency drifted by as much as 10 Hz. I fitted the synthesizer (27 MHz) crystal with a heat sink and this helped but I still had unacceptable drift between -5 and +5 Hz depending on the temperature in my shack.
I visited the QRP Lab website and purchased the OCXO/Si5351A Synthesizer. This synthesizer kit is a temperature controlled crystal oven. The kit is high density and not for the faint hearted but once built and setup proved to be the answer to the drift problem. A word of caution though, when setting the temperature of the oven start with the variable resistor fully anti-clockwise and turn the resistor a minuet amount at a time while monitoring the frequency output using Argo. Allow the frequency to stabilize before making the next adjustment. keep adjusting and waiting for the frequency to stabilize until the frequency rises and stabilizes (it is a very fine adjustment) this is the correct setting for the oven.
I fitted a SMK61 GPS module for timing and frequency stability, together with automatic location setup. The SMK61 needs 4.7k pull up resistors fitted between the PPC and +Vcc, and TX and +Vcc to work properly. I also recommended that 47nF decoupling capacitor are fitted between +Vcc and GRD. I fitted all of the components to the Veroboard at the GPS module.
To make the Ultimate 3 compatible with my radio shack power supply, and still keep it portable, I once again fitted a variable voltage regulator module based on the LM317 from Ebay. This module allows me to connect the Ultimate 3 to a any AC or DC power supply between 8 and 35 Volts.
The output is very stable, it has an Input range of 6 to 37 Volt AC or DC, Output range of 1.7 to 37 Volt DC, DC output current of 1A, Ripple rejection ratio of 80dB, Typical load regulation of 0.1%, and Typical linear regulation of 0.01% . These modules are built around the LM317 linear regulator, and are very good value for money.
Argo – Argo is a program to visually show QRSS, DFCW and other slow digital signals,
into an easily configurable waterfall, taking its input from the PC sound card. I used this software to monitor the TX drift during setting of the HP CAL.
AC/DC to DC Adjustable voltage regulators based around the LM317 are available on the internet auction sites such as Ebay.co.uk for a couple of pounds.
Samlex RPS-1202HQ, 2 Amp, Regulated Power supply, available from Damsu Limited. (Any regulated, DC, power supply rated at 1 Amp or more can be used).
Visit the WSPR website for more information about the WSPR low power project.