Where do you mount yours?

[trapdoor]

Be interested to know where in the aircraft you mount your box?

I own a Beagle Pup - there isn't a huge amount of real-estate especially on the coaming, and particularly for long antennae. To this end, I have ordered a few different sorts of stumpy 'correctly tuned' antennae, one for the 860Mhz band as the one supplied with the ARF is way too long, and one to replace the pathetic and incorrectly tuned DVB-T antenna which I am intending to either rewire the module to fit inside the case, or attach via an MCX to SMA adapter.

We could do with perhaps getting one of the Chinese manufacturers to make a pair of correctly tuned self-adhesive 'patch antennas', one for the 860Mhz band and the other for 1090Mhz which could be affixed to the sides of the front screen in an out-of-eyeline position. Perhaps less of an issue for a non-EASA aircraft as these could fit external aerials but doubt that would go down too well on something like a Pup, Cessna or PA28.

[Andy Fell]

I have been pondering this.

In a permit aircraft it should be fairly easy to install a decent antenna for 1090MHz and 868MHz (in a similar way to a transponder antenna already installed).  I can foresee some possible issues if not understanding the consequences of poor antenna installation.

It is important to maintain a good antenna performance otherwise detection range will be dramatically affected (which will reduce your early warning time).  I have been thinking of writing a short white paper on this, so folks can get the gist of what is good and what is bad - if that is useful at all?

As you say for non permit aircraft, you need something portable so as not to have to endue the regulation hassle.. How about wire 'dipoles' that stick on the window using suction caps?  It would be quite easy to make one yourself.  Be aware that in the cabin of a typical GA metal bodied type, you will get some considerable antenna shielding out of the back due to the fuselage.

rgds
Andy

[tj80]

A paper with antenna guidance would be very much appreciated.  For instance, would a pair of these work well enough for both the 1090mhz and 868mhz radios - I assume it would at least be an improvement on both the standard untuned items included as standard?

https://shop.pimoroni.com/products/right-angle-mini-gsm-cellular-quad-band-antenna-2dbi-sma-plug?utm_medium=cpc&utm_source=googlepla&variant=1086319769&gclid=CjwKEAjwgqWvBRC2kajZjqeOn0oSJADqBi-lzSLlh58oim4GYLeerd8AuBZAM4UaT9ziCFN2lWUJcBoC9sjw_wcB

Suction cup dipoles may be optimal, but for convenience if say renting EASA aircraft a "one box" solution with small attached antenna which just needs sticking on the coming would be ideal.

Cheers,
Tim

[trapdoor]

Not 'ideal' but I'm going to use one similar (ordered several different types actually) for the ADS-B Rx - but you'll need a straight MCX male to SMA female adapter to plug directly into the received dongle. The 868mhz antenna I have ordered the short one from WirelessThings to try as it's supposedly correctly tuned.

My only real concern is whether the dongle socket is man enough to take this sort of antenna directly, with the adapter on, and whether it will vibrate loose or rotate so it's no longer vertical.

Depending on how much space is inside the RPi case when I've finished, I may look to disassembling the DVB dongle and hard-wiring it to the RPi and then put an MCX to SMA pigtail on, fixed to the case in the same way the 868Mhz radio is. That would make it more robust.

It's a shame the RPi doesn't have one or two USB presented on the IDC header, or connected with a 4-pin jumper on the board. Would make it much easier than having to solder directly to the bottom of the USB socket.

[tj80]

I'm thinking of using a generic "instrument case" enclosure - something like a bigger version of this:

http://uk.rs-online.com/web/p/product/7733195/?grossPrice=Y&cm_mmc=UK%7CShopping-_-Google+PLA-_-Hammond%7CInstrument+Cases-_-7733195&kpid=&kpid=7733195&istCompanyId=f7e7b05b-2daf-4c0e-8825-3633baf8113b&istItemId=xitlrmxax&istBid=tztx&gclid=CjwKEAjwgqWvBRC2kajZjqeOn0oSJADqBi-lvvXMr23PpaV6dKis0-BZ0wTMEaIVxhurde7CwgedIxoCGfXw_wcB

Then use a pigtail to expose the ADS-B connector to the outside.  That way the Pi and the USB devices are all enclosed rather than just the Pi with the USB devices hanging outside.  It'll be a bit bigger but hopefully neater and more robust.  Alternatively, the USB ports on the Model B I'm looking at using are through hole so not too hard to just piggy back wire USB sockets on a fly lead to the bottom of the Pi...

Cheers,
Tim

[Alan Walker]

I like the sound of that Tim. I was concerned about a plethora of cables curled across the instrument panel area.

Al

[Andy Fell]

It is very important to take care with flying leads and adding length to USB ports.

What happens is that the digital noise from the RPi may get radiated into the radios.. this can cause de-sensitisation of your receiver and effect detection performance.  Additionally, it could affect the transmitter quality.

If  you have to do this, try to screen the cabling to reduce emissions issues.

An antenna combiner may be possible to integrate the 1090MHz and 868MHz functions (with some considerable care).  I have been thinking about this, but don't have much time to do it at the moment.

Rgds
Andy

[SouthLat]

A paper with antenna guidance would be very much appreciated.

I definitely second that.

There are some cheap antennae on eBay which claim to be tuned to 1090. They look similar to the provided DVB-T antenna but with a pigtail coil in the middle. Are they likely to really be optimized for 1090?

I've read several tutorials on building your own 1090 antenna, but they look a bit on the ugly side for placing in an aircraft.

[Andy Fell]

A paper with antenna guidance would be very much appreciated.

I definitely second that.

There are some cheap antennae on eBay which claim to be tuned to 1090. They look similar to the provided DVB-T antenna but with a pigtail coil in the middle. Are they likely to really be optimized for 1090?

I've read several tutorials on building your own 1090 antenna, but they look a bit on the ugly side for placing in an aircraft.

Ok... I'll have a look... I hope you're not in a rush though, it might take me a while to get around to it :-)  Are you guys totally against building your own (if it's an easy wire assembly thing with maybe a touch of soldering)?  I'm not sure what there is 'off the shelf' which would be like a suction cup mounted wire dipole.

[SouthLat]

For instance, would a pair of these work well enough for both the 1090mhz and 868mhz radios - I assume it would at least be an improvement on both the standard untuned items included as standard?

TJ80 is referring to a GSM quad band antenna. I know nothing of these things - is it a reasonable premise that an antenna designed for, say, 900 and 1800, will be pretty good for 1090 because it falls between these design frequencies, or are these effectively 2 antennae specifically for 900 and 1800 rather than the intervening spectrum?

[Andy Fell]

A single antenna is possible, but there are complications.  the signal needs to be split between the TV tuner and the ARF module and duplexed so that the 868MHz transmitter doesn't feed into the TV dongle and cause some de-sensitisation.

That would be the correct technical thing to do anyway... there are other bodge ways of doing it.

[trapdoor]

The supplied DVB-T antenna can be cut down to 68.8mm or as close as you can. That gives a better tuned 1090mhz 1/4 wave antenna. If you put the tip in boiling water for 30 seconds, it can be pulled off.

Ideally, the cable leading to the Rx dongle should be a multiple of the 1/4 wave length to ensure the VSWR is as low as possible. That is an easy mod and in fact if you are going to use the DVB antenna in the cockpit you need to remove the magnet out of the base ideally. The bottom peels off, there is a metal plate with a small magnet stuck on. The magnet pops out. The plate can be prised out and that traps the screen (a ground plane supposedly) and you'll see the core soldered. Measure out and trim in multiples of the 68.8mm measured from the end of the plug.

I am initially going to stick the antenna on top of the case so will trim mine down to the minimum to cut down on cable clutter. When my other DVB produce arrives, it will be chopped down to mount inside the RPi case....

[Andy Fell]

The supplied DVB-T antenna can be cut down to 68.8mm or as close as you can. That gives a better tuned 1090mhz 1/4 wave antenna. If you put the tip in boiling water for 30 seconds, it can be pulled off.

Ideally, the cable leading to the Rx dongle should be a multiple of the 1/4 wave length to ensure the VSWR is as low as possible. That is an easy mod and in fact if you are going to use the DVB antenna in the cockpit you need to remove the magnet out of the base ideally. The bottom peels off, there is a metal plate with a small magnet stuck on. The magnet pops out. The plate can be prised out and that traps the screen (a ground plane supposedly) and you'll see the core soldered. Measure out and trim in multiples of the 68.8mm measured from the end of the plug.

I am initially going to stick the antenna on top of the case so will trim mine down to the minimum to cut down on cable clutter. When my other DVB produce arrives, it will be chopped down to mount inside the RPi case....

What you are experiencing there is a fluke .  The reason changing the length of the feeder is helping (or it might not) is because the antenna is poorly matched in the first place and must have a decent ground plane.  It could just as easily make things worse as it makes things better because unless you know exactly what the impedance is at the antenna you don't know what matching network is required to the receiver input.  It could also be possible that the TV tuner input isn't what it 'should be'  (i.e. 50 Ohms) either.

If the antenna is 50 ohms and the RX input requires a 50ohm feed, then the length of the (50ohm) cable doesn't effect impedance, it only affects signal loss as longer cable means more losses.  It's always best to keep as short as possible to reduce losses.  if improved performance is found by changing the length it means you don't have a good match.  Dipole really need a balun to stop signal radiating on the screen of the coax, this can be achieved in a number of ways.

[Andy Fell]

The supplied DVB-T antenna can be cut down to 68.8mm or as close as you can. That gives a better tuned 1090mhz 1/4 wave antenna. If you put the tip in boiling water for 30 seconds, it can be pulled off.

Ideally, the cable leading to the Rx dongle should be a multiple of the 1/4 wave length to ensure the VSWR is as low as possible. That is an easy mod and in fact if you are going to use the DVB antenna in the cockpit you need to remove the magnet out of the base ideally. The bottom peels off, there is a metal plate with a small magnet stuck on. The magnet pops out. The plate can be prised out and that traps the screen (a ground plane supposedly) and you'll see the core soldered. Measure out and trim in multiples of the 68.8mm measured from the end of the plug.

What you are experiencing there is a fluke .  The reason changing the length of the feeder is helping (or it might not) is because the antenna is poorly matched without a decent ground plane.  It could just as easily make things worse as it makes things better because unless you know exactly what the impedance is at the antenna you don't know what matching network is required to the receiver input.  It could also be possible that the TV tuner input isn't what it 'should be'  (i.e. 50 Ohms) either.

If the antenna is 50 ohms and the RX input requires a 50ohm feed, then the length of the (50ohm) cable doesn't effect impedance, it only affects signal loss as longer cable means more losses.  It's always best to keep as short as possible to reduce losses.  if improved performance is found by changing the length it means you don't have a good match.  Dipole really need a balun to stop signal radiating on the screen of the coax, this can be achieved in a number of ways.

[SouthLat]

The supplied DVB-T antenna can be cut down to 68.8mm or as close as you can. That gives a better tuned 1090mhz 1/4 wave antenna. If you put the tip in boiling water for 30 seconds, it can be pulled off.

Ideally, the cable leading to the Rx dongle should be a multiple of the 1/4 wave length to ensure the VSWR is as low as possible. That is an easy mod and in fact if you are going to use the DVB antenna in the cockpit you need to remove the magnet out of the base ideally. The bottom peels off, there is a metal plate with a small magnet stuck on. The magnet pops out. The plate can be prised out and that traps the screen (a ground plane supposedly) and you'll see the core soldered. Measure out and trim in multiples of the 68.8mm measured from the end of the plug.

I am initially going to stick the antenna on top of the case so will trim mine down to the minimum to cut down on cable clutter. When my other DVB produce arrives, it will be chopped down to mount inside the RPi case....

Trapdoor, the simple formula found in several places on the Internet for calculating the length of a VHF antenna gives 65.4mm for 1090 1/4 wave. Can I ask why you're suggesting 68.8mm?