FlightAware Discussions

Optimizing Gain

Hi all:

I have been playing with some scripts that were posted here in the forums, I would like to see for some more help in figuring out how many of you are running your feeders. I understand, no two feeders are alike, but there has to be some rule of thumb and pitfalls to watch out for.

based on the scripts results, I settled on running the Prostick Plus on gain of 28 or 29.7 and I am getting the following

dump1090-localhost-signal-24h

dump1090-localhost-range-24h

Given that the noise floor seems to be lower , I would have thought my range would be pushing to the limits of the horizon, but seems to drop off well before that.

Edited info below:

280’ AGL, ANT220K discone, 7/8 Heliax
Discone is what I have access to - The feedline is terminated into a Minicircuits splitter
ZESC-2-11+, one port feeds into a Minicircuits VBFZ-1065+ filter prior to going into ProStick Plus.
without the filter, there is front end overload. The other port is a second RTL, I have been experimenting with UAT

Usual set of questions:
How high is your antenna?
How obscured is your horizon?

Knowing nothing of your location, I plotted your coordinates and got a predicted range of about 200 miles.

image

Thoughts on optimizing gain

Gain seems a bit low.
Also the noise floor you see is after the gain of the SDR, so it’s not an absolute thing.
As only the SNR matters … well a low noise floor after reducing the gain a bunch doesn’t really give you anything.

If you have the antenna in clear view of the horizon and would expect more due to your terrain, think about how lossy your coax is and maybe also consider a filter.

Terrain limited reception: https://github.com/wiedehopf/tar1090#heywhatsthatcom-range-outline

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280’ AGL, ANT220K discone, 7/8 Heliax

heywahtsthat range rings about 250nm

Great height, fantastic coax, but the antenna … not so good.
If you must run a discone, you’ll need a filter - it is after all designed to pick up everything.

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sorry , yes I thought I include this in my OP.

Discone is what I have access to - The feedline is terminated into a Minicircuits splitter
ZESC-2-11+, one port feeds into a Minicircuits VBFZ-1065+ filter prior to going into ProStick Plus.
without the filter, there is front end overload. The other port is a second RTL, I have been experimenting with UAT

1 Like

That seems like an awful lot of insertion loss between the receiver and the antenna to me, especially given that the antenna is a discone.

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I think you need a better filter. That one is much too wideband and is only giving about 4dB of rejection at GSM frequencies.

ok, I would have thought, the internal filter would be narrow enough to suppress the gsm channels. I guess it doesnt

The problem is, with large levels of gsm signals, you can overload the amplifier that is in front of that filter.

 

RF Scan of Various Combinations of Dongles, Filter, and LNA

 

been testing out various gain settings, and options, including combination of filters, amps and splitters.

so, far I can claim - that I am getting closer. have almost tripled the # of crafts tracked and expanded the range by an additional 130nm

image