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Hi Tom,
I think the loop antennas are pretty quiet compared to wire antennas and you might need some gain. But, since the antenna is high Q and tuned, it might have enough voltage output to drive the soundcard more or less directly. I don't know for sure. But, if the switch is anywhere near linear, you would not want your gain stage before the switch, would you?? I can't see using an rf amp at the antenna that just creates non linearity when you could use a nice quiet audio amp op amp on the far side of the analog switch. An all software based receiver shoulnds like a neat idea until you realize you run out of dynamic range by trying to sample such a wide bandwidth directly. I think the analog switch (hardware) is here to stay, at least for ashile. GL. T On 12 Sep 2005 17:13:12 -0700, "K7ITM" wrote: I'd hardly call it heresy, John. In my search for really good op amps to use up to 50 and 100MHz (very low distortion and low noise), I've come across some that would be really outstanding up to a couple hundred kHz. In fact, since you can get 24bit ADCs that cover up to that range (e.g., AD7760, AD7762) with very good linearity and low noise, you could make the whole LF receiver with just the tuned antenna, the preamp out at the antenna, _maybe_ a bit of gain, and the ADC feeding into a PC. Then the "quadrature mixing" would all be done digitally, with much better accuracy than you'll get with an analog mixer. Yeah, yeah, you have to write some software to get it to work...but a modern PC should have no trouble keeping up with doing all the signal processing. There may even be sound cards out there with response out to 100kHz--that's an area I don't keep up with. Cheers, Tom |
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