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Image-free 2G

Posted: Fri Jan 07, 2011 4:27 pm
by Sam
With the recent discussion of using a down-converting front end to bring high frequency signals into the 0-1GHz range, it occurred to me that you could view most of the 2G signals by using LO2 (1024 MHz) as the LO for the front-end mixer. In SA mode you don't need to mix LO2 and LO3 for a TG signal, so you could use that extra LO2 output for the external mixer. With filtering limitations, this would probably let you view 1074-2024 MHz by shifting it down to 50-1000 MHz. The advantage over normal 2G would be the absence of ghost images.

An alternative way to do this would be to build an extra PLO1 (or PLO3) module to use as the external front-end LO. This would give you a lot of flexibility to view signals in the 1-3 GHz range, once you had a way to control the new LO frequency. Since its frequency would be changed only occasionally, a slow communication method such as a USB-Parallel converter could be used. Or see this page for the use of a thumbwheel and a USnooBie board to control an LMX2326:

That extra LO could also be used as a signal generator independent of the MSA, although it would only produce frequencies at fairly large increments unless you combined it with a DDS.

To carry this a step further, the above-cited page shows how to control a YIG tuned oscillator by means of a Stellex control board (which in turn uses the LMX2326). Both the control board and the YIGs have become widely available on eBay. The control board supposedly can handle the range 2-12 GHz (subject, of course, to the limitations of the YIG range.) This would let you reach very high frequencies.

Sam W.