Antenna height - cable length

FlightAware General
1

hi all .
so i had my entenna on my cb tower for about 10ish months , was occasionally getting the 200nm planes but not as much as i thought i would with it being 33 ft above the ground . I spoke with cody in the help section (about other issues i was having ) and he was saying i can have the antenna ( i believe it was 80ft) so i bought a 50 ft extension run and hooked it to the already 20 ft that came with the antenna (70 ft in total ) and ran the antenna up to 46 ft on the tower .

since then i just get out of the 100nm ring , and not very far out of it .
i figured that being higher would be a good thing and its line of sight would be better since up that high it is almost higher then all the trees .

should i move it back down . do trees cause issues for 1090 ?

i dont know a whole lot and i am trying to read up on stuff but im getting to a loss . i played with the gain , and for the life of me cant remember what the factory gain was .

i appreciate any info .
ive got no problem climbing the tower and moving it back down or even relocating the antenna on my man cave shed .

thank you in advance

2

The default gain with the flightaware pro stick is 49.6 dB as a maximum.
If you have a RTL-SDR v3 this is a value of 58.6 dB.

70 ft is quite a distance for the signal. Depending on the quality of the cable it might induce some additional loss of signal. Are you using any filters or amplifiers ?

In order to get a good view on the performance of your setup it might be usefull to install graphs1090, this wil show you a lot of information on your system, range, gain settings etc.

Underneath the description there is the command to install it, once installed it wil take 10 minutes to gather some data and show that graphicly.

I see you are using the Piaware 7.2 SD card image, did you enable automatic gain ? This will try to find the optimal gain for your setup in your environment.
See this post by abcd567 for the needed steps;
SOURCE: https://github.com/flightaware/dump1090/blob/master/README.adaptive-gain.md#default-settings

Where to configure adaptive gain options

How to configure adaptive gain varies depending on how you have installed dump1090.

If you are using a PiAware sdcard image, adaptive gain can be configured by editing /boot/piaware-config.txt or by using the piaware-config command.

If you are using the Debian package, adaptive gain can be configured by editing /etc/default/dump1090-fa .

If running dump1090 directly, adaptive gain options are set directly by command-line options.

Default settings

For new PiAware or Debian package installations, adaptive dynamic range mode is enabled by default and adaptive burst mode is disabled by default.

For upgrades of PiAware or the Debian package from versions older than 6.0, both adaptive gain modes are disabled by default.

These defaults can be overridden as described below.

Adaptive gain in dynamic range mode

The dynamic range adaptive gain mode attempts to set the receiver gain to maintain a given dynamic range - that is, it tries to set the gain so that general noise is at or below a given level. This takes into account different or changing RF environments and different receiver hardware (antenna, preamplifiers, etc) that affects the overall gain of the system, and usually will pick a reasonable gain setting without intervention.

To enable this mode:

  • Set adaptive-dynamic-range yes in piaware-config; or
  • Set ADAPTIVE_DYNAMIC_RANGE=yes in /etc/default/dump1090-fa ; or
  • Pass the --adaptive-range option on the command line.

The default settings for dynamic range will use a dynamic range target chosen based on SDR type (e.g. 30dB for rtlsdr receivers). This is usually a good default. To override this target:

  • Set adaptive-dynamic-range-target in piaware-config; or
  • Set ADAPTIVE_DYNAMIC_RANGE_TARGET in /etc/default/dump1090-fa ; or
  • Pass the --adaptive-range-target option on the command line.

Adaptive gain in “burst” / loud signal mode

The “burst” adaptive gain mode listens for loud bursts of signal that were not successfully decoded as ADS-B messages, but which have approximately the right timing to be possible messages that were lost due to receiver overloading. When enough overly-loud signals are heard in a short period of time, dump1090 will reduce the receiver gain to try to allow them to be received.

This is a more situational setting. It may allow reception of loud nearby aircraft (e.g. if you are close to an airport). The tradeoff is that when there are nearby aircraft, overall receiver range may be reduced. Whether this is a good tradeoff depends on the aircraft you’re interested in. By default, adaptive gain burst mode is disabled.

To enable burst mode:

  • Set adaptive-burst yes in piaware-config; or
  • Set ADAPTIVE_BURST=yes in /etc/default/dump1090-fa ; or
  • Pass the --adaptive-burst option on the command line.

This mode is more experimental than the dynamic range mode and tweaking of the advanced burst options may be needed depending on your local installation. In particular, --adaptive-burst-loud-rate and adaptive-burst-quiet-rate may need adjusting. Feedback on what works for you and what doesn’t would be appreciated!

Burst mode and dynamic range mode can be enabled at the same time.

Limiting the gain range

If you know in advance approximately what the gain setting should be, so you want to allow adaptive gain to change the gain only within a certain range, you can set minimum and maximum gain settings in dB. Adaptive gain will only adjust the gain within this range. To set this:

  • Set adaptive-min-gain and adaptive-max-gain in piaware-config; or
  • Set ADAPTIVE_MIN_GAIN and ADAPTIVE_MAX_GAIN in /etc/default/dump1090-fa ; or
  • Pass the --adaptive-min-gain and --adaptive-max-gain options on the command line.

If you know approximately where the gain should be, then a good starting point would be to set the max and min adaptive gain to +/- 10dB around your gain setting.

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Depending on the size and the distance: yes

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I would confirm the cables are joined with a high quality adapter. Also, ensure you have waterproofed all connections. Water is not your friend in this case.

I would be suspicious about the loss characteristics of this cable.

What type of coax is it?
What is the quality of the coax?

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Signal level of the far-away aircrafts should tell the story…

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You might want to look at moving the pi closer to the antenna and powering it via PoE. It solves a lot of the signal lost from cable issues and the hardest part doing it is a nema box for the PI and buying a PoE switch (example TP-Link TL-SG1005P) or injector and a PoE splitter to USB-C. PoE can power things up to 100 meters but we are not taking about max distance with these types of setups. I have fought with both long cable runs for USB (to have the radio close to the antenna and near the ground) and the antenna and was just a pain to work with.

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7

Length of coax makes a big difference to signal strength. My antenna is a meter above the outdoor box containing my Pi and dongle which is at 5meter height. Feedline is 3m of LMR200 from N-Type on my homebrew collinear to SMA. I’m seeing planes over 220 nautical miles away at 30 to 40 thousand feet, best being 247nm. If I move my antenna to my HF mast the antenna will be six meters higher, I will then run LMR400, but the antenna and kit will not be as easily accessible as it is now. Being the highest it will also then be first in line for a lightning strike.

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thank you for the post . i will have to slip the card out and see exactly what i have settings set to . i believe it is set to what ever the download comes set as . at the moment i am at work so i will definitely get knees deep into this when i get home and let you know what i see .

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im not sure off hand about the coax . when i get home ill take a look . i do remember that it was a low loss , it is thicker then the line that came on the 1090 antenna .

as for water , i used the same thing i used to waterproof my cb lines (had a friend in the cell tower sector who gave me some tubes of what they use on the connections) .

im thinking that it may just be the coax i bought !

when i get home tonight im going to try and move the pi to a different location (depending on the forcast for the next week , and see what i get with the antenna still in same spot but the run of coax pulled .

10

Might be the best to put a LNA right at the antenna before the long coax. It will compensate for the loss of the cable, and most importantly, improve the noise figure.

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ok. so update . i put the pi on the mast at the base of the antenna cable and removed the extension . wired everything up, powered it on …

went from 43 planes one the map to 152 on the map . went from inside 100nm to now over 150 nm

now i have to make a box to hold the pi and keep it out of the elements . as well as get a poe so i dont have to have an extension cord out on the tower .

now my next step is to figure out this ssh to be able to get into the pi since it will remain in its location .

i greatly appreciate all the advice . i am still going to play more with it and go through more of the settings i had seen earlier in the replies .

and im throwing the “low loss coax” in the garbage lol . low loss my butt .

12

No 2 is the same. What is marketed low loss on rg6/8 and say 174. Is likely low loss at uhf/vhf.

Not high frequency/microwave 1000mhz

Check out the ‘attenuation’ rating table for each type.

Every connection in the path can also lose up to 3dB.

Rg6 for instance. 6-8dB /100ft. Lmr400 down to 3-4

Almost a dB every 20ft. + Connectors for 6.

Get a 4dB antenna on the end and you zerod your gain.

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Almost all coax says “low loss” so that means nothing. Check the Numbers. There are some handy “coax attenuation calculators” online. They dont all do all the different feedlines so you have to check them. My experience with imitation brands has not been good, if possible get original. If your antenna has a 1.5:1 SWR you’ve lost a few dB’s already, without the loss on the coax and on the connectors. You must also limit the number of adaptors and never use UHF connectors for 1090, use N-Type and SMA, you can also use BNC’s. I like BNC’s for testing as they are quick disconnect, but on final build it’s N-Type on the antenna base and sma at the dongle.

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dB’s gain or loss are logarithmic with dBm’s being in milliwatts your input is approximately halved for the first -3dB’s and then that figure is halved again for the next 3. So 1mW input with a 6dB loss gives you 0.5mW in for the first 3dB’s loss and 0.25mW in for the second -3dB’s loss.

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15

Without knowing exactly what coax you’ve got, it’s impossible to say for sure but it sounds like the loss in the extra length is responsible for negating any benefit you get from raising the aerial.

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