(This project is on hold indefinitely)
This project is based around the recent HF1 QRP transceiver by Ashhar Farhan, VU2ESE. The transceiver is an interesting SSB design with wide tuning range from 0-30MHz and should cover several amateur bands. The schematic for the transceiver can be found on the Minima mail list in this post with a PDF attachment.
After a front end 0-30MHz filter, the transceiver uses a 45 MHz first IF and a 10 MHz second IF. The famous bi directional amplifiers are used in the bi directional SSB sections of the radio.
The first cut will be built as modules to test it out in sections. If successful, a much smaller version will be made for SOTA use.
The mixers will be swapped with Mini Circuits SBL-1s as I have a few in the junk box.
The main LO and second LO will use an Si5351a oscillator so the second 55MHz oscillator unit will not be required.
The Si5351a, controller and display will be taken from the earlier QRP 40m rig.
First part is to build up the bi-directional amplifiers as modules. The boards are SMD and designed on Eagle. They came out fairly well, although the laminator sort of jammed during the toner transfer and the board had to be coaxed through.
The boards were sprayed with lacquer before reflowing the components. This turned out to be a slight mistake as the flux spread out with the melted lacquer under heat. Anyway, they are fine electrically, just had to be brushed up a bit.
The controller / oscillator board is finished now. The Si5351 has three clock oscillator outputs. CLK1 is planned to be used as the main VFO from 45-73 MHz. CLK2 is planned to be used for the second mixer at 55 MHz, although there is some conjecture as to whether this will provide acceptable performance due to clock output crosstalk. CLK3 is planned to be used for the BFO at 10 MHz. The controller will switch it between upper and lower sideband. If the crosstalk becomes a problem, the 55 MHz output will be replaced by a separate crystal oscillator. The next job is to check the clock output crosstalk to see if it will be a problem.
The controller / clock board is single sided with a top ground plane and much the same as used for the 40m QRP rig. An 8 pin header is for connection to the LCD display.
The cross talk between the 1st oscillator and 2nd oscillator was tested by programming CLK0 with 52 MHz (45+7, simulating a 7MHz receive) and programming CLK2 with the 55 MHz second mixer frequency. CLK2 was terminated with 50 Ohms for the test. The results weren’t as bad as I thought they would be. As can be seen below, the 55MHz cross talk is down 59.5dB. Of more concern is a spurious at about 62.5 MHz which is just over 50dB down.
For the moment though, I will use the 55 MHz CLK2 output for the second mixer. Also need to look at the 10 MHz output from CLK1.
Out of interest, the 52 MHz output was moved to CLK1 with the 55MHz still on CLK2. The cross talk increased considerably to -45dB. So 1st oscillator will stay on CLK0.
The bidirectional amps work fine with a voltage gain of about 12 or 21.5dB @ 5MHz.
Progress has been a bit slow due to work and other things. Have been working on a main RF PCB that will accept the bidirectional amps and mixers. Things aren’t as modular as originally planned for experimentation, although the bidirectional amp boards are socketed, so it will be easy to tap into the input and outputs.
The power amplifier and digital boards are separate. So far the main RF board is 80 x 103 mm, and everything looks like it will fit in. This is the layout so far, not much will happen in the next few weeks due to some travel.