ADS-B with R820T and inverse J-Pole?

[mzac]

So I was trying to find a good place to put my stock antenna that came with my R820T SDR dongle, and the only place I found at my kitchen table was on my ceiling light above the table. I have a feeling that the way I have set it up it is quite close to being a reverse j-pole as my lamp is all metal and is grounded to my electrical panel.

This said, with this configuration I am getting ADS-B signals up to 200km away and I am about 30 meters above sea level.

Can anyone else confirm if this could be the cause or am I just lucky?

[KD6W]

Nice picture. The stock antenna is actually pretty good for ADS-B operation and best when stuck on something metallic like your light fixture or the top of your refrigerator. J pole antennas are easy to make, omnidirection folded dipoles designed to easily match the impedance at a specific frequency to a transmitter. That said, a half wave length hunk of wire sticking straight up in the air will have the same receive gain compared to a j pole. For really good gain, you need a really good gain antenna like a YAGI but those are directional and why most folks simply use co-linear antennas including high power broadcasters. The simple vertical antenna gain can be greatly improved by simply putting a back plate ground plane behind it but then the pattern would become cardioid in shape. 200km readings are fairly common when the aircraft are at cruising altitude.