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From: | Carles Fernandez |
Subject: | Re: [Discuss-gnuradio] How to use USRP to detect and collect weak satellite signals |
Date: | Sat, 7 Sep 2013 18:12:49 +0200 |
LNA into filter is the line-up we use in radio astronomy, which might be described as the "limiting case" of weak-signal work.On 09/06/2013 03:33 PM, Ian Buckley wrote:
Filters will all to some degree attenuate your signal of interest, but by how much varies dramatically depending on the type and design of the filter, it could be 0.5dB or 20dB, but the point is that it attenuates potential interferers and noise by a great amount. An LNA cascaded into a bandpass filter as close as possible to the antenna is generally an ideal setup for this type of weak signal work.
A circular-waveguide feedhorn designed for the band of interest will act as a high-pass filter with a "knee" at the design frequency of the feedhorn. This,
combined with directionality of a dish is often enough to eliminate the worst of the interferers *before* the LNA, and then apply a filter after the LNA.
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