<?color><?param0100,0100,0100>Dear LF Group,<br><br>Transmitted the usual beacon signal on 135.923kHz last night from about 1845 to 0240. The weather was still and clear, so I did not have to keep re-tuning the antenna for once. Thanks for the reception reports - monitoring at odd times during the evening, I saw up to 3 other signals at once within a couple of Hz bandwidth, although I did not pause to identify them. I received a phone call from EI0CF, and I was able to hear my signals as received at Malin Head.<br><br>As regards simultaneous 2-tone transmission, It has been pointed out that a bi-phase PSK signal with properly shaped envelope is the same as a 2 tone signal generated by a linear (SSB) transmitter. The PSK carrier would be the mean frequency of the two tones, and the phase modulation would be at the difference frequency between the two tones. So if the mean and difference frequencies were available from sound card or DSP, it would be possible to u se a class D or other non-linear TX to generate the 2 tone signal - although it would still be a little harder to do than sequential tones. <br><br>As a general point for computer-generated signals, if the soundcard or DSP could be persuaded to generate the output at a few kHz instead of 800Hz or whatever, it would be a simple matter to mix the signal directly up to 136kHz, with a fairly simple bandpass filter to give good unwanted sideband rejection. This would eliminate the need for an HF tranceiver as an IF stage, and the resultant problems with frequency calibration and obtaining LF output with reasonable levels of distortion products.<br><br>I think VK2ZTO has already carried the multi-tone idea to one of it's logical conclusions, with seperate tones for each different alphabetical characters - see 'FDK' on his web pages <u><?color><?param0000,8000,0000>http://www.qsl.net/vk2zto</u><?color><?param0100,0100,0100>.<br><br>Cheers, Jim Moritz<br>73 de M0BMU<br> <br>
|
