Two Antennas: Strange Performance


#1

I have two coaxial antennas side by side 600 cm apart. HiAnt is of 8-116 mm elements and LoAnt is 5 -113 mm elements some 2.5 m lower. Both feed RPis which feed to FA and FR24 i.e. two radars at FA and 2 at FR24.

Here is the data collected over 10 days from FA and FR24 stats pages as well as VRS software. Can anyone explain the last two results? Percentage shown is HiAnt relative to LoAnt.

+11.4% more messages received by VRS
+6.8% more positions reported per FR24 stats
+5.6% more hits reported per FR24 stats
-1.8% fewer positions reported per FA stats
-27.0% fewer messages received per VRS for an airway ranging from 80 to 120 nm distant.


#2

I don’t have an answer, but I like the question!

Just for interest, your element lengths are slightly different - are they made from the same coax?


#3

Your observation about different element lengths may be the key to explaining the conundrum.

My guess is that HiAnt is not tuned correctly because elements are too long. Thus HiAnt is doing a poor job at distance even though it is higher.

Both antennas are made from cheap coax cable with foam insulation. My best estimate of the tuned length is 113 mm… In a few weeks I will take down HiAnt and trim down its elements to 113 mm then examine the performance. Will then post results in this thread.


#4

My first thought was maybe it has something to with mlat included or not in the various counts or other differences in counting messages?


#5

Maybe just switch the antenna positions so you know which position is better?