Flightaware Antenna Anomaly


#1

Having recently bought a Flightaware 26 inch antenna I have noticed a marked difference in how my Prostick gain settings need adjustment due to the very varied reception levels.

Prior to buying the antenna I used to have combinations of receivers, Beast, Basestation, RTL-SDR, FlightRadar24 etc. and a combination of antennas, DPD, NZ made, FR24 and my last full configuration for my home flight tracking station was the Prostick and FR24 antenna.

For all these combinations I have always used either default or max gain settings on the receiver and this is true when I coupled the Prostick and FR24 and got very good reception ranges and message volumes. But with the Prostick and Flightaware antenna combination I get almost zero reception with the gain setting at -10. I seem to get very varied results at other levels to the point that I have no idea where in the range from 0 - 55 (or -10) I should set it for optimum performance.

With the previous configuration I never needed to adjust the gain from -10 and set the FR24 antenna as high as possible. With the Flightaware antenna not only has the gain gone skew wiff but also if I increase the height of the antenna by 1 metre I also get much reduced reception.

So now it seems I have to adjust gain and antenna height for the myriad of such permutations!

Has anyone else experienced this?


#2

Yes, when I replaced my home made Cantenna with FA 26 inch antenna, the performance drpped substantially.

Initially I thought it is because of bad connectors/adaotors, but trying different connectors/adaptors did not improve the performance.

Finally I added a FA Filter, and bingo! With filter, the performance shot up and became better than Cantenna. Gain tweaking further improved reception.


#3

I have thought about a filter but have never needed them in my part of the woods, maybe have to rethink that!

Thanks for your valued input…as usual!


#4

I am experiencing a similar issue.
At the moment my ADS-B setup consists in a FA Pro Stick Plus with a small telescopic antenna; currently I am forced to place the equipment indoor, next to a window. Recently I had the opportunity to try the 66 cm FA antenna, however, with a bit of disappointment, I registered a severe drop in performances both in terms of range and average number of aircraft seen. Only the message rate seems to be occasionally better. Note that I tested the FA antenna in the same conditions and with the same config (max gain) of my actual setup.
Even the use of a filter does not seem to improve the performances, it even get worse.

Is someone able to explain this unexpected behavior? Have you got any suggestion?


#5

You can’t simply use the same gain setting when the antenna is much better. It will overload the receiver.
Didn’t you try different gain settings with the FA antenna? Basically for each setup you need to figure out which gain you need.
If you use the same for all it might give strange results.

I wonder how @invergordon solved his problem.


#6

@wiedehopf I did not try systematically/extensively, however seems that lower gain levels reduced even more the performances. :face_with_raised_eyebrow:

EDIT: I know that the gain setting strongly depends on location/setup, however, people with FA Pro Stick Plus + FA Antenna, witch value are you using?


#7

The FA antenna has gain, 6 or 7 dB, I think. If you are already at -10, chances are that you have to reduce the gain a bit. Try new gain settings from 43.9 to 49.6 to see if it makes any difference.

Also make sure to use a good/correct antenna connector/pig tail.


#8

There were also threads about bad connectors being bought for this antenna. But if it looks like it fits i don’t know why it shouldn’t work.


#9

There are different center pins in the N plug. The 50 Ohms pin has a different dimension that the 75 Ohms pin.


#10

OK, I could try to those values and report back.
Yes, I think I am using the right connector and cable (50 Ohm, 1.5m x RG-58).


#11

Actually it turned out to be an issue with the FR24 supplied coax and my aluminium mast for some reason. I replaced the cable with some LMR400 and reception was fine at -10 or max gain. Since I had some LMR400 I tried that first before having to shell out on a filter.

Since that event I’ve applied for and received a Flightaware Flightfeeder system that seems to be all working nicely!


#12

I’m astonished how many people are using maximum gain with the pro stick and even better antennas than my spider.
I’ve set the gain at 38 and that’s with the antenna being in the attic and a flightaware filter in the line.
Granted it’s important to me to get the low and close flights in the box when they happen so i don’t turn up the gain very high.

But maximum gain or even -10 (AGC) seems ridiculous. Oh well :slight_smile:


#13

This -10 thing is so bad, it stopped being funny.:roll_eyes:

The first thing you read about amateur radio digital modes is: disable AGC.

One of the digital amateur radio packages even has an AGCc feature to mitigate AGC action on radios where AGC cannot be turned off completely.


#14

I just tried for a small amount of time (I will continue tomorrow) some of the values in between 40.2 and 49.6 and I performed a comparison with another dongle and my “reference” telescopic antenna; however with FA antenna+Pro Plus Stick I always see less aircraft (even nearby) than telescopic antenna + other dongle. :disappointed_relieved:

Is it possible to check if the coaxial is the culprit (unfortunately I don’t have another one on the fly)? Other ideas?


#15

Unfortunately it requires a fork/rebuild/repackaging of librtlsdr to fix it properly (and dump1090-fa would then require that version) and I haven’t found the time to do that…

(the “right fix” being to allow setting maximum gain on all tuner gain stages via the manual gain interface)


#16

Hi obj,

Sounds like you are receptive to the change. This is good enough.

As for finding the time, I understand, it’ll happen when it happens. There certainly are more important things.

In the mean time, I suggest people do not ‘automatically’ use -10. There are too many variables out there to reccommend a default setting this high. In the hamradio world we call this the “all knobs fully clockwise” syndrome. One won’t necessarily get better performance by max’ing out everything.


#17

In practice, all-knobs-clockwise is not a bad default for a rtlsdr dongle without an extra LNA on the front; that default predates the FA prostick, though…


#18

Yes, I fully agree, up to the time before FA released its own branded dongles with built in LNAs, and 3rd party LNAs were not widely available/known. Even the release of the FA antenna compounded the ‘problem’.:wink:

I agree in part nowadays, as I have a second receiver using a no name RTL-SDR, no pre-amp, no filter, and its best performance is with a gain setting of 49.6.

As I said, too many variables out there. If -10 turns out to be the best settings for a particular installation, not a problem.


#19

Checking the cable you can check the diameter of the inner pin and hole of the big connector towards the antenna. They should match exactly.

If they don’t you might be able to bridge the gap somehow by inserting some braid / litz wire making sure it does not short to the outer conductor.


#20

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This is how I made a temporary arrangement to connect FA antenna to dongle without proper connectors/cable/pigtail :slight_smile:
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