During my unsuccessful test flight with my PAW (ADSB only currently) due to connection issues with my Nexus 7, I realised that the DVB antenna was too long to comfortably mount on the coaming of our 172 under the rake of the windscreen. It ended up laying on its side at the base of the screen.
The DVB Antenna which comes with these USB TV tuners is a fairly basic device, It has a quarter wave tuned length to pick up broadcast stations in the 450MHz to 700 MHz band roughly. The screw off monopole top is around 12cm long. The ideal quarter wave resonant length at 1090Mhz is calculated at 68.9mm
I have a small telescopic antenna that can screw onto the DVB-T antenna base. It varies from 60mm up to around 200mm. I was using this on the PAW to find I was getting the best results with it at it's shortest length. While I was experimenting with the PAW in the garden and the antenna up on a fence post, I realised that even without the aerial present, just the base, I was still picking up aircraft around 50NM away!
This alone is actually good enough for PAW use!Antenna base with monopole removed
The exposed coaxial centre is, in itself, an antenna of around 19mm in length.
So, to complete the construction of a properly tuned ADSB antenna, I
cut down the top whip to 50mm in length, gently twisting off the end protector and gluing it back on the new (very sharp) end.
Results of ADSB reception is improved over the original antenna length, seeing targets out to 175Km in my fairly overlooked garden.
Tuned antenna
I know this sort of sensitivity is way over the top in terms of PAW usage but having an antenna tuned to the correct specific frequency is a good start in eliminating other unwanted frequencies, specifically in the natural case of this DVB antenna in its unmodified state, strong TV broadcasts and phone masts!
I now have a much shorter 1090MHz specific antenna which can sit easily on top of the pilotaware unit itself under the windscreen . I also took the opportunity to shorten the cable from the MCX plug as its easy from the antenna end of the cable. The braiding isn't clamped under the metal disk anymore, but soldered to it aiding with strain releif.
So, my tip is to unscrew the top whip of the DVB antenna and cut it to a total of 50mm in length. Hope someone finds this useful!