I’m seeing 65/45 (81 msgs/sec) versus 122/105 (645 msgs/sec) on an identical ads-b setup on my roof. The only difference is a collinear antenna 4 feet down the mast on the 122/105 system. Let me describe the setup and what made me choose that tentative root cause.
I have 2 ads-b systems setup on my roof separated by about 30 feet, both are around 45 feet above ground level with each other). Each uses a 20ft run on RG8x down to a RPI powered by POE.
The antennas are 2 spider antenna’s that I built (8 radial groundplanes) and tuned with my VNA.
The dongle’s used on both are: Flightaware Pro Stick Plus (gain setting -10 on both).
This morning I noted both were sitting around the 80-100 positions per second value, which was odd since before I went on vacation the higher performing one was typically over 700 messages per second. I double-checked the dump1090-fa settings between both and then went out to inspect the antenna’s.
Here’s where it gets weird: I noticed the RG-174 lead on the collinear antenna that I had built and installed 4 feet down the mast of the higher performing system had come unscrewed and was dangling down the mast.
I hooked it back up and immediately noticed the messages per second jumped back up to over 700 per/sec on the OTHER antenna + dongle.
This collinear lead is connected to a different dongle on the same higher performing RPI setup but is not being used. That dongle is a RTL blog + RTL blog LNA.
To me this is very strange that all I have to do is unscrew a lead to an essentially unused collinear antenna and get much lower positions per second. How could a 1090mhz collinear 4’ft down the mast from the active spider antenna + dongle effect the active one?
EDIT: changed positions/sec to messages/sec