Tag: 2020

Raspberry Pi4 Remote Mount ADSB Receiver.

I know I am late to the party as ever, but I wanted to try and increase my knowledge of the Raspberry Pi and Linux so decided to try my had at 1090 MHz ADBS reception.

I wrote up some initial thoughts in a previous blog, this was my attempt to improve the reception and remote mount the Pi close to the antenna.

The problem with traditional deployment is the antenna and SDR receiver (FlightAware) are mounted some distance apart. High quality coax is needed, and even then the losses at 1090 MHz are high. I calculated 10 m of RG213 would equate to at least 3 dB loss, my antenna would need 25 m or coax to mount it in a convenient location. Factor in connectors and I was looking at a 9 dB loss, close on 90% or my received signal lost in attenuation.

The Pi has WiFi, and previous tests had shown me the range and reception was very good, so the idea of mounting the Pi in a waterproof box close to the antenna was conceived. Its not new, im not the first but this is my process and lessons I learned.

The rule of thumb in a box, is think of a size then double it, its not the pi that causes the issues, that is small.

85 mm x 56 mm in new money.

Its the routing of power, USB, SDR and the coax socket that need some consideration. Cooling may also be an issue, a sealed box could get very warm in the summer without some fan and ventilation.

Box options, I selected something marked waterproof and 150 x 110 x 70 mm and it cost £6.25 delivered.

Next was some waterproof sealant, I was going to be drilling holes in the box, and some waterproofing would be required. A tube of Silicon bathroom sealant seemed suitable. I would use this to seal around the power and coax cable entry points. I was going to be drilling all my holes on the bottom of the box, but everything needs to be sealed

The next issue was around the USB ports, I wanted the flexibility to mount the Flight Aware USB receive in a location of my choice and not be limited to the position of the USB ports.

Right angled USB extension cable

The short extension cable offered the ability to mount the USB receiver flush to the case, with a hole drilled for the SMA to poke out.

USB C Power cable with break out for wires.

Only suitable for short runs of power cable.

Powering the Pi needed some thought, was I going to connect 5v directly onto the board (this would have been easier) of could I look for some way to wire directly into the USB C connector. In the end this connector cause me a few concerns, it worked exactly as described, but in a tight box it takes up and incredible amount of space. If I could have got a right angled version, this would have made for a much neater installation. They are also quite expensive, but needs must.

For longer power cable runs voltage drop will become significant, and so I used a DC to DC converter from PIMORONI. They have one detailed on their website as Wide Input voltage SHIM, and you can power it with 3 to 16v

Wide input DC to DC converter

The last piece of the puzzle for me was a coax cable, I wanted N type on one end to connect to the antenna, and SMA on the other for the Flight Aware receiver.

If you wondered why I selected the blue Flight Aware receiver, in the tests I completed the band pass filtering and amplification out performed a standard RTL dongle by 10 to 20% range.

You will need a good 1090 MHz antenna, having something with some gain mounted as high as possible will make all the difference. I opted for a commercial made option, but if you have the equipment you could consider making a co-linear.

Have a look at the antenna options on amazon or ebay.

So having gathered all the items together, it was now just a case of positioning them in the box, the flight aware receiver has a long SMA shaft, so the hole can simply be drilled through the box and SMA pushed out. Once the SMA plug with coax is connected you can use a liberal application of silicon sealer to prevent water ingress.

I added a fan into the box, and made sure the Pi had a large heat sink fitted to the processor. The fan isn’t running right now, but this in itself provides a challenge. Not much point adding a fan if it doesn’t extract or force air into the box. I decided to drill 4 x 6 mm holes, and then as it turned out badly align these with the fan. I fitted some foam to the inside of the box, and then bolted the fan down, sandwiching the foam to the inside of the box.

Temperature readings of boxed Pi4

This again was mounted on the bottom of the box, as with every hole, to hopefully prevent water ingress. The other issue is likely to be insect infestation, they like nothing more than a warm dry home high up on a pole!

You may want to consider the application of some grease on the pole, its amazing how earwigs can find these warm homes.

Power was the final thing to do, I did try and power it direct from home, but the voltage drop was just too much. I decided to use a DC to DC converter, this allowed me to feed with anything from 3 to 16v.

PoE was considered, but i couldn’t really see the advantage over WiFi and separate power cable.

Under voltage messages would indicate I still have some issues to resolve, but its working.

The box on a pole, cable ties used as a temporary fix

Pi 4 with DC to DC converter fitted

You can view my live map here

Typical text display

50 MHz Trophy Cup

The 50 MHz trophy cup is a great opportunity to work some stations, with lots of activity from both the UK and EU. Due to the current situation with Covid 19 this years event wasnt going to be on the same scale as previous events.

It was decided the event needed to me small scale, and to comply with the RSGB rules it needed to be a fixed station as no portable operating was allowed. Unfortunately that meant we could only put in a check log this year, as our operating site is away from home.

George M1GEO

We operated from our contest site at Kelvedon Hatch, using a 6e 50 MHz beam. The beam was located on the 12m scam mast, and the radio was the Icom 7610. 400w RF power was delivered by the Expert 1.3KFA.

Dave M0TAZ

The contest was somewhat different to usual, no portable and hence many contest stations stayed away. Conditions on Saturday was flat, with just a few SPe openings towards the end of the day. Sunday was much more interesting, with the band packed full of stations all over the EU.

QSO map for 50 MHz Trophy Cup 2020

We worked 161 stations in 21 DXCC, best DX was UY1HY @ 2288 KM