about SDR receiver

[fisherman_0415]

wideband receiver has the disadvantage of blocker and interference problem, is it possible to use a tunable duplexer or a tuable SAW filter to reject blocker?

[bill]

In most of the cases the blocker/interferer is inside or very close to your useful band. Thus even that it may be possible to use a tunable filter that would result into cutting also valuable frequencies from your own signal. In addition, I do not know how cheap are these kind of filters. A good choise is to use baseband techniques for antijamming and grequency avoidance.

[Stantheman]

fisherman, you certainly can put a preselector filter of some sort on the front end of your SDR radio. You will need to ensure you have a good match, most professional radio equipment is 50 ohms, as are commercialy available RF filters, so that should not be a problem.


You could use a mobile or base station type duplexer, if this is what you have available. Just make sure you terminate the unused port on the duplexer with 50 ohms, as you will only be using the antenna port and one of the other ports into your SDR receiver. Most mobile dupelxers are pass-notch response, as are a lot of base station duplexers. You may want or need a band-pass response.

A good preselector filter should help with key spurious responses, such as the image, 1/2 IF etc .. and it will reduce any blocking signals outside of the preselctor passband.


In general SAW filters are not field tunable, you have to order them tuned to frequency from the factory. Although this IEEE paper talks about the possibility of tunable SAW filters http://ieeexplore.ieee.org/iel5/5959913/5977269/05977297.pdf?arnumber=5977297 (I don't have the paper).

The correct solution to your problem really depends on what your problem is ... i.e. what is your operating frequency and what are you trying to protect your SDR front end from?