A new block of flats with terrible reception. Up on the roof we found this box. This is what the electricians installed to connect three flats to the aerial. Impedance matching aside, the box is made from plastic so provides no screening at all. However, before we could sort this mess out we had to investigate why the signal directly from the aerial was so poor. Then we discovered the aerial, mounted in a position which caused a deep notch (-30dB) in the middle of the Group A band. Relocating the aerial and sorting out the mess above resulted in perfect reception to all flats. Ahh much better!