The Cantenna performed better than FA antenna, till I added a Filter. Adding filter reversed the performance, and the FA antenna +Filter performed better than Cantenna. Reason is FA antenna is high gain, and, although I am not sure, but guess that possibly it is tuned at multiple frequencies, and picks much more RF noise than low gain DIY Cantenna.
Is your FA receiver a:
(a) Pro Stick Plus, blue (a dvb-t with integral amp and filter)
OR
(b) FlightFeeder (an FA supplied box containing RPi, Filter, ProStick which has integral amp).
In case of (a), an external Filter between FA antenna and ProStick Plus often improves performance. If you have an external filter, just give it a try.
I don’t have a spare filter so it’s not a quick job just to slap one in. Is the FA manufactured inline filter any different to the one built into the Pro Stick Plus?
Look at the clipped/strong signals. I had to lower my gain because the planes near-by where too “loud” for the total gain and where discarded. Internal_IP/dump1090-fa/data/stats.json
Yes, these are different types. The integral filter is a SAW Filter chip, while the external filter is an LC ladder filter.
However, the reason for improvement is not the type of filter, rather it is due to location of filter. The integral filter is located between amp and tuner, and does not block interfering rf signals to reach amplifier, causing overload and cross a modulation. The external filter is placed between antenna and amplifier, and prevents interfering rf signals reaching the amplifier.
Graphs below show the results of the tests I conducted last year.
The stats page from the FlightAware is just text, sorry.
The design is not strange, the preamp should be more “immune” to the overloading than the first stage inside the RF chip. Theoretically, to save as much as possible signal/noise ratio, the preamp should not have a filter in front.
But in my experience, even from planes far away, I have +6…10dB margin, so adding a filter in front (-3dB) doesn’t make enough “damage”. Personally I am limited by the horizon, not by the gain/signal level.
In your case you can pick up planes from 220 miles… so you have plenty gain.
NOTE: The script will offer to upgrade piaware data feeder and dump1090-fa. It will also offer you to install or upgrade FR24 feeder, Planefinder feeder, and Adsbexchange feeder. Say NO to everything (except system update) , till you reach the stage where you are asked about web portal installation. Say OK to web portal installation, but NO to “advanced options”.
Thanks - My original installation was using the ads-b receiver project image so I’ve missed out on how to add a few tweaks to a standard installation.
I’ve updated my second link in the original post so although it still goes to the map, it’s possible to get the performance graphs as well - I’ll monitor this for a couple of days and see how it compares to the other receiver.
Although the number of aircraft, messages and reports have gone up since adding the filter, this setup is still a long way behind the homebrew two element j-pole aerial.
Again for reference.
Two element j-pole performance graphs ** link removed **
Flight aware vertical performance graphs ** link removed **
These two receivers are quite literally next to each other in the loft.
I added the filter around 10:50 today and then you can see the gap where I ran the gain script.
My plan is to put the new receiver with the Flight Aware vertical outside, about 10m up in the air but I’m just concerned by the apparent lack of performance compared to what I’ve already got.
The 2 element, 1/2 lambda, j-pole might get better results. It’s difficult to build correctly, so most of users will not attempt.
As for the cost… If you would build your antenna for sale, you wouldn’t sell it just for material cost, add the labor cost (let’s say $90/hour if you are a firm that pays taxes, insurance, etc) and see where you end up with the cost.
PS: leave some distance between antennas, they can influence each other.
Hi Keith, looking at the 2 RPIs you have, as you say, quite a difference between the two. I can’t think why they are different - sorry.
Can you post the dimensions of your j pole and I’ll have a go at building it and compare with the FA antenna I have.
I tried the longer version and apart from the stability, I just couldn’t get it to tune.
I wonder how much of the difference may be down to the (effective) radiation pattern of the FA aerial compared to the colinear. Without knowing what’s actually in the FA stick, there’s no way to know what it’s doing.
It was all built and boxed properly ready to go outside but I’ve had to bodge it a bit to get the bandpass filter in. I might still see if I can get it outside tomorrow anyway, even though it is bodged at the moment. I know that in the loft I’m quite heavily blocked in one direction.
