Gain of ProStick's LNA is NOT adjustable.
In ProStick as well as in generic (black/blue) DVB-T dongles, it is the gain of Tuner chip RTL2832U which is adjusted.
Gain of dongle is controlled and adjusted by dump1090. There are different ways to pass gain setting to dump1090, depending on which software you have installed.
First you have tell exactly what software you have installed on your RPi:
(1)Which image you wrote to your microSD card? Raspbian Jessie img, Piaware img or Flightradar24 img (Pi24 img)?
(2) Did you install dump1090 separately or using the built-in dump1090 of FR24 feeder, or built-in dump1090 of Piaware img?
(2) In which order you installed data feeders?
Last edited by abcd567; 2017-02-05 at 22:42.
To provide answers:
a).I am running the latest released and updated version of Raspian Jessie running on an RPi3 and having rpi-update run within the last week.
b).I am using the standard FlightRadar24 installation. This is the version you get by typing bash -c "$(wget, etc. from root login. //not enough post to give the full command line. It thinks it's a link. Duh.
2. No, I did not. It came with the install.
3. I just followed the standard install procedure. Everything is stock software and installation -- so far.
I run two systems T-KCLT3 which is my main system and T-KCLT19 which is for playing with. Both use indoor attic mounted antennas. I cannot use external Antennas, HOA rules. T-KCLT uses an 8 element collinear antenna made from RG6 that I had lying around. This has a downfeed of about 25 feet and is also RG6 (sorry). I see a daily max range of 138 nm which is okay-ish, I guess. This system has the ProStick.
T-KCLT19 is the exact same software but a system that I can take out of service immediately. It uses a 16 element collinear antenna made from RG6 and does not work so well as the 8 element one. I'll have another go at this antenna later on. It uses a USB stick from jetvision.de. This is not a very good device and, tomorrow (Thursday) it will get an upgrade to a ProStick - Yay!
That's what I got, now, how may I change the LNA gain please. I realize this may not be possible with the software I currently have.
On the way to this I have installed dump1090-mutability and removed it (re-format microSD card), FlaightAware (hated their web pages and reporting.) and any number of other LInux mods. Now, I'm back to stock but have learned a tiny bit more.
I have other questions mainly related to antenna construction but for now, let's stick to LNA gain. I need this because I have a Hungarian LNA and 1090 Mhz filter en route as well as a 10dB SMA pad. I am also about to replace my downfeed with a 25 foot RG58U feed with SMA connectors (thanks ebay).
So I guess my question should be, how do I adjust the gain of the RTL2832U tuner chip? Is this possible with my installation?
That's me and where I am. Thanks for your help.
Last edited by rederikus; 2017-02-09 at 02:13.
In order to reproduce your install, I formated my spare microSD card, installed Raspbian Jessie Lite (2017-01-11-raspbian-jessie-lite.img), then installed FR24 feeder by following command:
sudo bash -c "$(wget -O - http://repo.feed.flightradar24.com/install_fr24_rpi.sh)"
I then tried following commands, but did not succeed:
sudo ./dump1090 --gain 32.8
sudo fr24feed --gain 32.8
I then tried following method and it worked:
FR24Feeder-gain settings.png FR24Feeder-map.png
Code:In your browser, go to page: http://<IP of Pi on LAN>:8754/settings.html In settings field "Process arguments", enter --gain <db> as shown below. Process arguments: --net --net-http-port 8080 --gain 32.8 Click "Save" button, then click "Restart" button. Now SSH to your RPi and give following commands: #First restart fr24feed for new gain setting to take effect. pi@raspberrypi:~ $ sudo service fr24feed restart #Now check what is the Gain actually set. pi@raspberrypi:~ $ service fr24feed status -l ● fr24feed.service - LSB: Flightradar24 Decoder & Feeder Loaded: loaded (/etc/init.d/fr24feed) Active: active (running) since Sun 2017-02-12 00:20:00 UTC; 57s ago Process: 2045 ExecStop=/etc/init.d/fr24feed stop (code=exited, status=0/SUCCESS) Process: 2102 ExecStart=/etc/init.d/fr24feed start (code=exited, status=0/SUCCESS) CGroup: /system.slice/fr24feed.service ├─2115 /usr/bin/fr24feed -- --monitor-file=/dev/shm/fr24feed.txt --write-pid=/var/run/fr24feed.pid --quie... └─2135 /usr/lib/fr24/dump1090 --net --net-http-port 8080 --gain 32.8 --raw --mlat
Last edited by abcd567; 2017-02-12 at 12:32.
Wow! Thank you abcd567. This is much appreciated. I cannot yet post code quotes or links but I did what you said and, naturally, it worked. I had been Googling for dump1090 command line parameters aand I found the "gain" argument myself. I had used it a couple of times and have so far seen little or no difference in minor gain adjustments. What I did not have and, you provided was a metric for seeing if the command had actually worked. Using "service fr24feed status" gave me the confirmation that gain changes were happening.
Thank you again. That was a lot of work on my behalf. I have played with custom installations my spare setup and have used dump1090-mutability by following your own guide. However I felt that when asking noob questions it would be better to have a standard baseline install from which to start.
Okay, here is a question that is on topic for this thread. I am confused by the use of 75 Ohm RG6 cable and F-connectors when making collinear and other antennas and using RG6 as the downfeed to a 50 Ohm (SMA) input connector. I note that the balarad site uses a 75 to 50 Ohm transformer to convert from the antenna to the input. Most other designs I have seen do not do this. Can you explain, please.
I was practically weaned on 0.775 volts into 600 Ohms = 0dB. I have always taken great care to match the impedance of cables / connectors / inputs and outputs correctly. Power loss (via return loss) and extraneous noise have always been the penalty for not observing the rule.
your right about impedance matching, but we are not transmitting. So the effects of the impedance miss match are there but they are basically very small, you would probably lose as much if not more through the insertion losses of a convertor.
A good point. Thinking about this, it is pretty clear that dB losses due to a 75 to 50 Ohm mismatch are very small. Without doing the math, it will probably be less than 0.5dB. A not-so-good F-Connector termination will do more damage than that. I shall cease to worry about it.
You are right. I am more used to transmitter antennas than receivers.
I am working my was through all 264 pages of this thread. It is at turns inspiring, innovative, frustrating and fun. There's a lot of good information in here too.
I have been testing several antennas with exact same setup so here is a polar distribution comparison.
The only difference is that colinear was fixed on different pole which is about 40cm higher and therefore I believe the range looks a bit better.
My current setup is in my signature...
T-EBCI32 (Raspberry PI 3 + RTL2832U/R820T2 USB dongle + Axing SVS 2-01 inline amp + TA1090EC filter)
When 50 ohm is mixed with 75 ohm,
Reflection Coefficient Γ = (75-50)/(75+50) = 0.2
SWR = (1+Γ)/(1-Γ) = (1+0.2)/(1-0.2) = 1.2 / 0.8 = 1.5
Mismatch Loss in dB = -10 log (1 - Γ²) = -10 log (1 - 0.2²) = -10 log 0.96 = 0.177 dB