Low DBFS


#1

Ok, posting for a little help…I am seeing very low DBFS (highest is about -17 or so when planes flying directly overhead. I am seeing planes 40 miles out max.

Here’s my setup, Raspberry PI and RTL2832U, homebrew 1/4 wave groundplane mounted about 30’ above ground. 100’ RG8X coax run to hamshack. I do have lots of trees and live in a lower spot, however, still no idea why signal strength is so low.

I’ve tried adjusting gain…no better results
Shorter coax length…no better results

Any assistance would be much appreciated.

Thanks


#2

15db loss using RG8X.
That is a lot of loss, 97% using http://www.qsl.net/co8tw/Coax_Calculator.htm
Try moving the RPI closer to the antenna(power by POE or use WIFI) and using a shorter coax run.
Or you could use better coax. I use LMR400 but it isn’t cheap.

Or you could use an amp powered by bias-t (See uputronics and others).
This would allow you to use the current coax.

A filter could also help but the numbers are low so it will lower them even more(2-3db I think for the FA filter).

The FA pro-plus dongle has a built in filter(1090Mhz) and amp. Another choice.

Your range is horrible(I see receivers near your with a lot more aircraft). I got better than that with the RTL-SDR supplied antenna on my basement window bars. Could the dongle be faulty? Have you tried a different dongle.


#3

Thanks for the quick reply. I can move the setup and significantly shorten coax. I can also go to RG6 or 11.

Thanks for the suggestions…I’ll keep tweaking and report results. Thanks again…


#4

Wow…I should have known. Shortening the coax helped quite a bit…went down to 25 ft. Many more planes. Like I said, I’m in a really low spot with tall white oaks…

Going to continue with your suggestions…thanks!


#5

Trees are big attenuators at these frequencies. According to coverage prediction sites I should have great range in a 270 degree arc, but for the trees it might be correct.