QRP2000 LVDS transformer and EIA232 interface

As part of my experimental SDR setup with my AVALA-01 transceiver, I needed a accurate and stable squarwave clock generator. I wanted to use the Si570s that I had obtained as samples. I wanted to control the frequency via a computer, and I figured that a clock generator with a USB interface would be a good choice. I didn't want to designone myself, as I had did not have previous experience in developing a USB-interface. After investigating the various kit products that were available, I selected the QRP2000, developed by SDR-Kits.net. In the United States, the QRP2000 is available thorough the KM5H Store. Given that I already had an Si570, I purchased a kit with no Si570 included.

Assembly of the QRP2000 was very straightforward. There is a mixture of surface-mount and through-hole components, though, so assembly can be tricky, if you are not comfortable with soldering surface-mount components. The first assembly step is soldering the surface-mount capacitors to the bottom of the PCB. This is the most tricky part, as the the capacitors are small and surface tension caused by the molten solder tends to cause the capacitors to either stick to the soldering iron or flip up onto one of the circuit pads.

The second assembly step is soldering all of the through-hole components to the PCB. This is quite easy to do. Prior to performing the last assembly step, the QRP2000 is connected to a computer via the USB interface and tested for proper operation.

The final assembly step is soldering the Si570 to the bottom of the PCB. This was actually quite easy compared to the surface-mount capacitors. The Si570 is a comparatively large component with well-separated pads. Tests performed were successful, indicating successful completion of assembly.

The Si570 sample that I used is a LVDS (low-voltage differential signal) component (Si570BBB), capable of oscillator frequencies of 810 MHz, although actually up to 945 MHz in practice. The LVDS outputs specified to have an impedance of 100 ohms. In the QRP2000 manual, they mention transformer T1, which is a optional part that is used to convert the 100 ohm LVDS signal into a single-ended, 50 ohm signal. While SDR-Kits.net sells the transformer(Coilcraft WBC4-1WLB), they do not sell a breakout board to connect the tiny surface-mount transformer to the through-hole pads of the QRP2000.

The illustrations below shows the relevant circuit on the QRP2000 PCB and the breakout board I designed for the Coilcraft transformer. The left-top and left-bottom illustrations show, respectively, the circuit layout without and with the breakout board in place. The right illustration show the mirror image of the breakout board, which can be scaled and printed form a circuit mask for the breakout board. The through-hole pins have spacings for a standard DIL-6 package.

The picture below shows how small the Coilcraft transformer is. Fortunately, it was not too difficult to solder to the breakout board.

Here is the finished QRP2000 with the transformer breakout board soldered in place and a short length of RG-174 coax connecting the transformer output to an SMA connector. I mounted the QRP2000 inside an LMB Heeger TiteFit chassis (TF770, Grey).

After my initial build of the QRP2000, I determined that I needed to make use of the transmit and key control lines to control my AVALA-01. I used EagleCAD to design a simple EIA232 interface board. I wired it to the QRP2000 and mounted both boards into a new Tite Fit enclosure.

The attachment points for wiring the EIA232 interface board to the QRP2000 is illustrated in the file QRP2000_TX_Control.pdf. The EagleCAD schematic and single-sided PCB layout for the interface board EIA232 are found in the files QRP2000_EIA_Adapter_Schematic.pdf and

QRP2000_EIA_Adapter_Layout.pdf, respectively.