Hi I am looking at making my own ADS-B outdoor station and wondered if i bought 60cm 1090MHz Antenna for ADS-B and 5m SMA Male to N-Type Male Antenna Cable that would go straight from antenna to my RTL-SDR dongle that’s plugged in to my pi how much signal loss would i expect to get with that type of setup and is there any way to minimize that Thank you also not sure if it makes any difference i am a ham operator and have a 2m/70cm setup Also what height is best for the ADSB antenna Thank you in advance
Use good quality coax. LMR400 gets mentioned a lot, very low loss but stiff to work with. A search of this forum will find various other types people use. I used to use CLF200 cable which is much easier and that gave great results. Get your antenna as high as you can; the more of the sky it can see down to the horizon, the more aircraft and range you will get.
ADS-B is mostly line-of-sight. You want your antenna as high off the ground as you can get it to clear any obstructions such as your roof, neighbor’s houses, even trees or any other objects. My roof is 12 feet (almost 4 meters) and my chimney extends about 2 feet (half a meter) above that. So I want my antenna to be to be at least 14 feet (4.5 meters) off the ground. My nearest neighbor’s roof is probably 16 feet (5 meters) tall. My plan is to get my antenna about 23 feet (about 7 meters) high this Spring.
If you can’t get high off the ground to clear obstructions, don’t worry too much. You can still pick up a lot. I had my original whip antenna in a basement window for a while. It had a clear Western view that faced an approach to KMCI so I picked up all of those, but I still had about 80 miles (130km) range, even that low to the ground, and I still picked up some aircraft within about 40 miles (65km) to the north, south, and east.
As for the type of cable, you’ll want to use good quality coax. If your antenna is within 10 meters (about 33 feet) of your RTL-SDR dongle, then LMR-240 is just fine. LMR-400 would give you a little better performance, but it’s barely noticeable. If the cable run is longer than that, you’ll want to upgrade to LMR-400 (or you can substitute KMR-400 or similar for a very slight drop in performance but a lot of cost savings). My cable length is 50 feet and I bought KMR-400 and the difference in performance compared to LMR-240 was substantial.
Try to keep the number of cable connections to a minimum. Every additional connector attenuates your signal a bit, reducing what your RTL-SDR can decode. So if you can have one just cable between the antenna and the RTL-SDR, it gives you better options for adding a LNA and in-line filter.
Also, try to keep your ham antenna at least 60cm away from your ADS-B antenna (farther, if you can). Nearby antennas and other metal objects can interfere with your reception.