LNAs assembled

I have assembled the LNAs a couple of weeks ago and I have already made an update to the project on hackaday.io.

Assembled LNA

I have not had much time to test most of their functionality yet because I am really busy with studying for the finals right now but I have managed to improve my ADS-B reception significantly.

One problem I am currently facing is that the RF shielding is not optimal. I might have to look into other ways of providing a good shield around the LNA to keep noise out. The FM broadcast stations also prevent me to turn up the gain of the internal LNA of the SDR dongle too far because together with the external LNA they overdrive the mixer input and create intermodulation products. I may have to install an FM trap, unfortunately my first attempts at using a quarter wave length stub filter did not work out as planned.

I have also been asked if it was possible to modify the board design to incorporate a SAW filter. I think it would certainly be possible to add a SAW filter to the design, the problem is once you decide on a particular footprint you are locked in to one specific component by a single vendor (of course this is true for the LNA too…). At the same time SAW filters are only available for certain frequency ranges so you might not even be able to get a SAW filter for what you are interested in.

I know that Adam 9A4QV has made some SAW filter boards that could be used externally to the LNA.

I may be able to do some more experiments and testing after the finals. Elia

*****
Written by Elia on 25 July 2015