(I'm sending this again through the Yahoo Groups web interface, 24h after the first attempt with an email client.)
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 mixer 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
