I’ve had my antenna mounted outside on the chimney for the past week or so now and have enough data to make a comparison with the same system mounted in the loft.
The setup is as follows:-
The LNA is mounted on the mast below the antenna. It’s not waterproof itself, so I found a small waterproof junction box on eBay that it fits quite neatly inside:
The PG9 size cable glands are large enough for an SMA connector to pass through but nothing larger, so I removed one of them and used some self-amalgamating tape to protect the connection on the output. It also means that should any water somehow get inside it will drain out the bottom rather than accumulate. The picture doesn’t show the silicone rubber gasket that seals the lid.
The antenna and mast were mounted on the chimney using a standard TV antenna mast and mount:
The total height above the ground is about 12m.
So here’s some data - settings and hardware between the two are identical and only the position is different. Gain is set to 18 on the airspy.
The median max. range has increased by 12.3% from 201.2nm to 226 nm.
The median message rate has increased by 11.8% from 1945/s to 2175/s.
The number median number of aircraft received has increased by 28.7% from 226 to 291.
It’s clear from the graph that the number of messages received per aircraft has increased across the board, and the peak number of aircraft seen has increased from 323 to 417, or 29.1%.
A pretty worthwhile improvement for the cost of the mounting hardware and some lunch for my brother who helped me put it up.
It’s useful to see where the increase has come from:
Range has increased in every direction, but especially to the North and South, which was expected because that’s the direction the gable ends of the roof are, with brick walls that were obstructing the signal in those directions. There is also a good increase to the West.
The distributions show that proportionally more aircraft are seen at longer ranges, and the signal histogram shows that there are far fewer weaker signals.
The high-altitude heatmap shows the difference in coverage best:
The areas of reduced shading are quite obvious. There are still some shaded areas that are due to a few tall buildings nearby. The elevation plot clearly shows the improvement as well:
And just for completeness, here is a comparison of the rtl-sdr v3 dongle with antenna in the loft, compared with the airspy with antenna outside:
There’s no contest really.