Ever since I started with the AirNav product, my never ending quest is to get maximum range out of my unit. I have tried various cables/antenna's etc. Your #1 friend is height. Get that antenna up as high as possible! When I was living in my apartment I had my antenna on the roof thanks to the landlord. I was up around 130 Feet and was getting a solid 200 to 300 Nm range. That was with a 80 to 90 foot run of LMR400 Coax, I cannot stress enough about proper connections. Use N Connectors as they are best suited to higher frequencies. Also, make them waterproof!!!!!!!!!!!
If you do not have many buildings around you, I would have expected slightly better range then your polar diagram was showing. I am in a residential area now with nothing but houses around me, and you can see how good my range is from my polar diagram. You also have to remember ADS-B is not manditory until 2020 in North America, so there is not as much to see as in Europe. We are getting there...years ago it was mostly the transatlantic heavies that had ADS-B, now I am seeing more regional aircraft being equipped with it. I also live a few miles away from Canada's busiest airport CYYZ. I am close enough to get ground returns as well, from Snow Plows, service vehicles etc.
Height, Height, Height...good cable, good connections... Done
regards,
Jason