I have several of the older dongles. How would I configure my pi if I were to add another 1090 dongle to the setup? I could put it in the front of the building using a USB extension. Would Amazon.com this work?
USB repeaters often create problems.
power up 250mA to devices
This might be not enough for the dongle.
Or the voltage might be low.
There is a thread on running two dump1090-fa and two piaware somewhere on the forum.
But i’m not sure where 
Antenna compare
Red Flightaware antenna + Uptroncis ceramic Filter amp + air spy 20Mhz gain 21
Blue Active Diapason “clone” + air spy 20Mhz gain 21
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Not sure how accurate this article is which i stumbled across the other day regarding noise vs. gain
" It’s not about the gain its about the signal to noise…"
I have been saying that from time immemorial, but it does not seem to register.
This is why some people love magnetic loop antennas, while others hate it. The all knobs fully clockwise syndrome is a factor here.
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Maybe te tinfoil head fraction has the best gain setting and signal strength 
It’s not about the gain its about the signal to noise… | Ava High Altitude Balloon Project says:
.
Point #1 above:
That is why way back in 2013, I connected $4 satellite amplifier to the antenna using zero length of coax 
how did you get the power there? Is the stick able to deliver the power for driving the LNA?
read the annotation
using a bias-t.
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DIY Bias-T
(The 2nd LNA on ground in this picture was removed subsequently as it overloaded the Dongle)
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This was in 2013, and such sticks were not yet invented. I used Generic DVB-T (Black)
Coax length between Desktop and antenna about 15 m / 50 feet
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replied in other thread Comparison of different dongles for 978 MHz UAT reception - #59 by turbodogfl
It’s interesting to see how the antenna position is having an impact to ADS-B CPU utilization.
Today i needed to move my indoor antenna temporarily to a more worse position.
I did not change the gain which is on a fixed level and not set to AGC.
In the graph you can exactly see the different position.
I did not expect that with a fixed gain setting.
And the corresponding ADS-B details:
That’s probably due to increased noise. The decoder looks for a certain bit pattern that is the pre-amble to a message. If there’s more noise, then these appear at random more often when there’s nothing there to actually decode.
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Yes, could be an answer. Interestingly while the message rate went down by 30%, but the number of messages > -3db did not change that much
Interesting results from changing gain on CPU usage
day gain
23 43->30
26 30->45
Did not expect the CPU to change that much at 30 dB
Used to have a feeder on a Pi 1B that used to stop feeding until power cycled every few weeks. Was the CPU usage too high for it? It seemed to work a lot better on a newer version of Pi.
I made some full day tests with different gain settings between 48.0 and down to 38.6 (current value) on my Raspberry 4
Could it be that the blue FA Pro Plus FA stick is somewhat resistant for gain changes?
I have the feeling that there’s not really a change in the values:
Only if i switch to -10 or a very low level <30 an impact can be seen.
Or is it simply that the values are changing but the variety of tracks/aircraft/messages per day is eating it up for a comparison?
The only real change is the number of messages > -3db which is currently 4% compared to 9% with gain set to 48
I am new to this; been feeding only since Dec 2, 2019.
My question is: Does anyone have any experience with long coax runs and using a preamp (Uputronics), and would my rig benefit from a preamp? (I am using the Flight Aware antenna with no external filters and the Blue Dongle.)
Some background:
I initially installed my antenna on a pole about 10 feet above ground (bolted to a fence), but on December 12 moved it so that antenna is installed on the top of my two story house, about 50 feet above the ground.
This resulted in much better numbers: from seeing about 2,000 aircraft a day to an average of about 2,700 a day and from about 300,000 messages a day to about 800,000 to 1,000,000 messages a day.
So I am pretty happy with my results so far being that I am new to this.
But my concern is that 150’ of LMR-400, which is almost 7 db of loss at 1,090 mHz may be reducing my results. I know I could install the Pi in a weather proof box outside, right under the antenna, and might do that. But first I want to try and optimize the setup keeping the Pi on the ground.
With the default setup, my Percentage of strong messages, was running about 30% even with the long run of coax attenuating the signals about 7 db.
FYI I am not very close to any major airports, being located about midway between FLL and PBI. But this area is pretty busy. During the day I usually see from 160 to 230 aircraft at any one time, and receive from 900 to 1,100 messages a second.
After reading this article about optimizing gain, I played with the RF gain setting and found that if I set it to 43 (43.4) I am now getting between 6 and 7% Strong Messages during busy times and I seem to have just as many, if not more, aircraft, and far out aircraft (over 200 miles) are still showing up. I will need to observe for a few days to see if I can see any definite trend.
Since I am having to reduce the gain to get the number of strong messages down from 30% to 5-7%, it does not seem to me that feeding the coax with a 15 db stronger signal using a preamp would make sense, if I just have to reduce the gain at the receiver another 15 db to keep the number of Strong Messages in the 5-7% area.
Unless, perhaps, this would overcome noise being picked up in the coax??? Could that be happening?
Does anyone have any experience with long runs of coax, preamps, etc., and any recommendations? I know it is working pretty well, but want to see if I can make it even better.
And one other thought after thinking about this: if I did install the Pi at the antenna in a weather proof box, I would probably have to reduce the gain another 7 db, from 43 to 36 to keep the signal from causing excessive Strong Messages. Is reducing the gain in the dongle different from reducing the gain via coax loss? Would that really be of any benefit? I guess the question is does running the signal through the coax cause it to become more noisy?
Any suggestions would be greatly appreciated!
Check your maximum range versus this:
What is the Maximum Range I can Get?
That you need to reduce gain is not an indication that an LNA at the antenna wouldn’t improve reception.
As you need a bias-t anyway to supply the LNA with power via the coax, i’d just buy the rtl-sdr LNA.
It’s proven to perform a little better than the uputronics (at least without an additional cavity filter on the input).
New Product: RTL-SDR Blog 1090 MHz ADS-B LNA
bias-t for putting power into the coax: Electronics, Cars, Fashion, Collectibles & More | eBay
With your current cable you’ll need some adapters from N to SMA and then back from SMA to N to interface with the antenna/cable.
You could always go for the really expensive and really reliable option: KU LNA 1090-2 A TM, Selective Low Noise Amplifier - Kuhne Electronic Amateur Radio Shop
Has N connectors, so that’s a plus
Anyhow i’d expect the rtl-sdr LNA to be just fine in a weatherproof box.
Giving the box a little shade won’t hurt if you can manage with an extra piece of plastic or something.
With an LNA you’ll have to reduce the gain significantly on the prostick+, but that’s not an issue really.
The signal will at no point in the signal chain be as weak as it was before, which is a should improve range if you aren’t already limited by terrain.
see this article re long cable runs. It’s not about the gain its about the signal to noise… | Ava High Altitude Balloon Project
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That gives me a warm tingly feeling inside 