The system consists of a Raspberry Pi, Flightaware’s PiAware (SD Card) V1.20 running with dump1090-mutability.
The performance of my ADS-B monitoring system has been improved dramatically over the past several weeks using a homebrew coaxial collinear antennas of eight (8), and then eventually twelve (12) elements. The type of coax used to make the antenna was RG-6 quad shield coax. The antenna is mounted on the roof of the house with the base of teh antenna at about 20’ AGL and fed with 50’ of RG-6 quad shield coax. The ADS-B antenna shown in the photo below is the eight (8) element vertical coaxial antenna version just to the right of the weather station.
From memory the maximum reception distance of the telescoping antenna was in 50 - 100 NM radius with the majority being in the 0 - 50 NM radius. Unfortunately, I didn’t take any performance data of the telescoping whip antenna that came with the dongle to show the total system improvement that has been achieved over the past month because I had no intention of using it as a permanent installation. But that data would be an interesting comparison.
After doing some research on impedance transformation a twelveth wave coaxial transformer was made using RG-58A coax. This should help match the 75 ohm RG-6 coax to the 50 ohm impedance of the SDR dongle radio.
The following plots from the flightaware website data show the distribution of the aircraft received using the 8 element coaxial collinear antenna. My system has been activated 24/7 since the 10th of January 2015. I operated using the whip antenna that came with he dongle until I received the Raspberry Pi and the cables that I had ordered.
02-04-15 eight (8) element collinear distribution
The high traffic areas (Red and Dark yellow) are the locations of VORs. So the maximum range is 150 NM for the barebones 8 element antenna and reliable distance out to 100NM.
I then on 02-19-15 I decided to add four (4) additional elements to another coaxial collinear antenna that was built out of RG-6 direct burial polyethylene core coax this time. This was a little easier to work with than the quad shield RG-6 for making the antenna.
On 03-01-15 the twelve (12) element collinear was improved by adding a satellite diplexer which has a bandpass filter in the range of ADS-B frequencies. This immediately improved the message recption rate at the time from 100/second to over 160/second. I have seen the rate as high as 400/second now with this installed.
This screen capture taken on 03-04-15 shows the 12 element collinear with a satellite diplexer mounted inline with a mast mounted preamp and a homebrew power inserter using a 220pf DC isolation capacitor to block the DC preamp power from getting into the dongle. Note the distance improvement to the South.
Figure 7 above: Satellite diplexer from my junkbox. I have found that the performance is best is achieved with the power inserter installed towards the antenna and not between the dongle and diplexer.
Figure 9 above: 03-05-15 2138 MST the 12 element collinear antenna with a satellite diplexer installed just before the SDR dongle. The antenna has a mast mounted preamp installed at the antenna. the preamp has a homebrew power inserter with a DC blocking capacitor between the power inserter and the dongle receiver. the value of he capacitor is a 220pf and 20pf in series (18pf).
A Virtual Radar Server twenty-four hour plot of 03-05-15 using the 12 element Collinear with mast mounted preamp, satellite TV diplexer and 12th wave impedance transformer. The rings are 50 NM apart. The reception is out over 200NM to the South and nearly 200 NM to the East Northeast. This now seems to be a reasonably acceptable performing the ADS-B monitoring system. These directions are the best unobstructed views to the horizon at my location.
The daily plane count went from just over 500/day and a position report of about 30K/day within a 100NM radius using the 8 element coaxial collinear, to a high plane count of 950 aircraft/day and count of 52K position reporting packets/day. The reliable receive distance went from a maximum of 50 to 100NM to a distance of 200NM to the best unobstructed horizons by adding the improvements that have been described above. It’s been fun and a great learning experience to experiment and maximize the installation performance.