Using the free AppCAD RF design assistant software, Anthony explains how the noise figure of a system increases with longer coax cable runs, and how it can be reduced by placing an LNA right next to the antenna. He also explains why the sensitivity of the radio won’t increase if the LNA is placed close to the radio instead.
In addition to this, he also explains why adding more LNA’s to a system decreases the linearity (IP3) of the system and that if the receiver has a built in LNA that the system linearity can be severely degraded by adding extra LNA’s, causing easy overloading and intermodulation. In conclusion Anthony writes the following:
In summary, a setup with a good antenna system connected to a receiver with a built in LNA:
May not benefit from having a preamp at the antenna.
The presence of a built in LNA is detrimental to the linearity and may degrade the signals.
So in conclusion:
Put the preamp as close to the antenna as possible.
Receivers with a built in LNA may not get the most out of an antenna system or preamp.
Proper gain distribution guarantees better performance than one-size-fits-all solutions, both in terms of sensitivity and strong signals handling.
To do the exercises in the course you will need a HackRF or other similar SDR radio. Most exercises involving reception only should be compatible with the RTL-SDR with some small modifications relating to things like the changing sample rate.
Hands-on guide to hear to world using the 10-dollar RTL stick. Easy-to understand text covers software installation, antennas, noise reduction, guides from shortwave to airplane information reception – and many more. Diagrams and photos help the beginner, common tools and materials used: no soldering or expensive gear used. Useless tales, anecdotes, complicated theoretical explanations left out: only relevant information included. If you ever had problems setting up the RTL stick, wish to significantly improve your reception or simply want to hear airplanes talk to tower, receive AIS information on a yacht or track airplanes, this book is for you.
If you’re new to the world of low cost software defined radio, and have just been through our Quickstart guide, this YouTube tutorial video by Clayton Smith on using the SDR# program may be useful to you.
In the video Clayton explains how to use SDR# and some of its many features, how to calibrate the RTL-SDR offset in the software, and he also shows how to receive a few interesting signals in his area.