Where do you mount yours?

[tj80]

How critical is the antenna going to be in the real world?  Obviously the ideal is for a properly tuned antenna for both radios, but in reality you're only concerned with traffic in the area which might be a threat - clearly the more warning the better, but in the air I guess even a sub-optimal antenna is going to work in a 10+ mile range?  I was a bit surprised how large the ARF antenna was when it arrived this morning - certainly bigger than I'd like to have vertical sat on the coaming.  I was wondering if a pair of 900mhz GSM antennae would be close enough in frequency matching for both radios (1090mhz and 868mhz) while being nice and small.

Cheers,
Tim

[Andy Fell]

Indeed.

The 1090MHz antenna doesn't need to be critically tuned to an inch of its life.  Afterall, aircraft transponders are quite high power and can be picked up for miles using the supplied antenna with no problem (even if not optimised) - we don't need that kind of range.  You would likely do fine with a GSM900 antenna (perhaps with some tweaking if desired, but might not be entirely necessary).

It's worth putting some effort into the 868MHz antenna though, as this is a key factor in determining pilotaware detection range and hence the amount of early warning you could get.

The guys have been getting around 25km with the prototype system though, which is plenty - and nice that it's not too critical, since as previously mentioned it's not possible for everyone to install an antenna on the airframe.

[Andy Fell]

Note that the 868MHz antenna must not be more that 0dBi gain.  So, simple dipole or quarterwave monopoles only - no collinear antennas (unless you are receiving only)!

Radio module outputs 500mW.  ETSI limit is 500mW - no antenna gain allowed on the transmitter.

[trapdoor]

Note that the 868MHz antenna must not be more that 0dBi gain.  So, simple dipole or quarterwave monopoles only - no collinear antennas (unless you are receiving only)!

Radio module outputs 500mW.  ETSI limit is 500mW - no antenna gain allowed on the transmitter.

Better not use the one supplied with the ARF then. It's quoted at 3dBi gain 

[Andy Fell]

Note that the 868MHz antenna must not be more that 0dBi gain.  So, simple dipole or quarterwave monopoles only - no collinear antennas (unless you are receiving only)!

Radio module outputs 500mW.  ETSI limit is 500mW - no antenna gain allowed on the transmitter.

Better not use the one supplied with the ARF then. It's quoted at 3dBi gain 

That's a Far Eastern ebay supplier 3dBi gain :-) .. aka -5dBi. (8dB worse than spec!)