Good morning gang. I've recently been intrigued by WSPR weak signal HF mode, and immediately started thinking of a simple transmitter that would allow me computerless beaconing.
What I need is a USB transmitter on a very narrow 30m frequency range (1 kHz) for a narrow bandwidth signal (<10 Hz). This requirement differs from all other approaches that seek as much wideband as possible. Since I own a 40.5504 MHz oscillator, I would consider building an SDR based transmitter, or an even simpler solution based on the popular NE602, then use a XTAL filter to reduce unwanted sideband. These are 3 approaches I've considered: http://i40.tinypic.com/1z318jt.png (picture) I'm writing here to ask a SDR TX question, because I realized I've completely forgotten the SDR basics I had read few years ago. As I remember, if I "mix" an I+Q signal baseband (say, 1 kHz) with a 4-phase carrier (say, 10'000 kHz) I obtain a single RF output at 10'001 kHz (or 9'999 kHz if I invert I+Q). Correct? If the above is correct, what if I feed the 4-phase switched-mixer with I+I signal? Do I obtain a DSB output at both 9'999 and 10'001 kHz ? Given the simplicity of my wanted transmitter, I would record the message in a simple playback machine that might not support both I+Q channels (but this morning I've found a software that does that!). So I could live with a DSB and filter out unwanted sideband. The SDR-based approach, especially #1 in the linked picture, would allow a simple bidirectional transceiver, that is the reason why I prefer to head towards such a solution. Any input will be greatly appreciated. Paolo IK1ZYW -- Build your FT-817 External Keypad at: http://www.paolocravero.tk GQRP #12058 + I QRP #476
