Designing a Low Noise UHF Front End with Sharp Filtering for SDR
Most wideband SDR’s do not come with any front-end filtering built in. This limits their ability to receive weak signals in the presence of strong signals. Recently Sivan, a reader of RTL-SDR.com wrote in to let us know about a paper he published through the ARRL detailing how to design a concrete front-end unit for SDR use. A front-end helps to filter out signals that are outside of the desired passband, thus reducing interference from nearby strong signals significantly. Although Sivan uses a USRP with WBX daughtercard in his paper, he writes that the same front-end design principals can be applied to the RTL-SDR as well.
In the paper he designs a 431 – 435 MHz front-end using low cost SAW filters, a low noise amplifier (LNA) and a limiter to protect the radio. He writes that the design could easily be adapted for other bands as well.
Glad to see this. I am currently working on a front end very similar to this, with the exception that the bandpass filter is tunable, with variable bandwidth and Q.
Did you finish your filter?