Monday, August 10, 2015

New Radios on the Bench at N6QW ~ A 20M SSB Transceiver

More Surface Mount as Applied to a New 20M SSB XCVR

 
Peter Parker VK3YE is probably one of the most prolific ham radio homebrewer's and you only need to look at his YouTube channel and you will be well convinced. One of his creations is called the Knobless Wonder. Basically Peter has built a simple SSB transceiver using crystals in the 40M ham band and by doing so has eliminated the need for a local oscillator. The 7 MHz BFO serves as the main frequency determining element and thus becomes essentially a single channel SSB transceiver. Brilliant idea, Peter! This keeps the circuitry simple and power consumption low. So why not?
 
 
I had thought about duplicating that project and I think Peter's crystals were in the 7.150 MHz range. That would be ideal. Alas I was unable to find those crystals from US distributors but did purchase some cylindrical crystals at 7.2 MHz from Digi-Key. Somehow I don't think those are going to work too well and 7.2 Mhz here on the left coast (California) is a major net frequency. My milli-watts would quickly be swallowed up by the big guns. But I did really like his architecture.
 
 
That led me to a slight twizzle where I would use a 9.0 MHz filter and I have in the junk box crystals at 5.185 MHz and 5.238 MHz and there may even be others in the 5.15 to 5.35 MHz range lurking in the dark corners. So those two crystals would give me a SSB signal on 14.185 and 14.238 MHz. Now we are cooking. (Just checked and I have a 5.068 MHz for the CW portion of the band).
 
So why not use most of Peter's architecture only put the radio on 20M. BTW a Google Search will turn up schematics for the Knobless Wonder. This led me to a board layout that was 6 Inches long by 2 Inches wide. See below. What is not on the board is the 5.0 MHz LO (2 crystals) and the final RF amplifier, TR switching and the LPF. A similar board is now in the works just for those items.
 
The build will be mostly Surface Mount and the 6x2 size was done with a thought of making it like a Walkie Talkie. If this works out with the two channels there is a possibility of adding some VXO capabilities and perhaps even an Arduino driving an AD9850.
 
Stay Tuned --the real fun begins at N6QW!
Real Estate Allocation of the Main Board
Part Layout for the 2N3904/2N3906 Bilateral Amplifier Stage ~ Size 805 Parts. Copper Width = 0.12 Inch

Board with the SBL-1 and Band Pass Filter