Hi Dave,
The tuned low profile antenna and extension are both intended to allow better antenna placement
for the P3i 869MHz side - for example to allow the PAW unit to be mounted inside your pod, with the antennas mounted remotely. I have my unit fitted in this manner, and get excellent cover with the dipole fixed vertically just inside the knee hole of my pod.
The 1090MHz ADSB/Mode C/S side receives its signal from the supplied short thin antenna with the smaller mcx plug. As signals on 1090MHz are MUCH stronger than the P3i side, we have never found a need to substitute this antenna (other than that a few people have either cut the vertical wire part of the antenna in half - which actually makes it nearer the correct length for 1090 MHz - or replaced the supplied antenna with a short helical GSM 900MHz phone band antenna to make their unit 'smaller' e.g to fit more easily on top of an aircraft coaming - if going down this route, I recommend not cutting the wire any shorter than half length). Otherwise changing this antenna hasn't proved necessary. For this reason PilotAware Hardware do not stock alternative 1090MHz antennas.
FWIW, for convenience I currently use a second P3i dipole fitted inside the other side of my pod and attached to the SDR receiver using an SMA female to mcx male adaptor - available from ebay...
http://www.ebay.co.uk/itm/SMA-female-jack-to-MCX-male-plug-RF-coaxial-adapter-connector-F957663K-/262496365620?hash=item3d1e00ac34:g:RqUAAOSwkNZUpHq- Cheaper versions of this adaptor are available but usually from china with a longer wait.
Although tuned to 869 MHz, the centre fed dipole antenna works perfectly well on 1090MHz as the 1090 Mhz signals are 'receive only' and are as I said above MUCH stronger, so antenna 'tuning' is much less critical.
Hope this helps
Regards
Peter
