Comment on Seeing the World in Radio Waves with the QuadRF by Mark Topham

In reply to Karl Sidney Jr.

It would be much more interesting if it could support frequencies below 4Ghz.

It would be practical to support down to about 2Ghz, maybe even 1Ghz; but practicality starts to limit it the lower frequency you go. Higher frequency waves require smaller antennas and small distances between them, so receiving multiple signal received and comparing them is much easier at higher frequencies.