FlightAware Discussions

Best location for indoor ADSB antenna?

Morning all,

I have an RPi2, successfully running PiAware for the last 48 hours.

Running a collinear wire antenna - based on this martybugs.net/wireless/collinear.cgi (tuned to 1090) - on c12ft of 75ohm coax.
Antenna is currently positioned in front of a 2nd floor, double glazed window.

Currently running 75ohm coax, in the belief that the better quality coax, less signal / SNR issues.
Although the antenna is mounted c10ft away from the RPi2, the RPi2 itself is running off a wired (RJ45) connection direct into my wifi router. The Rpi sits c5ft away and down from the router.

Yesterday (1st full day) the systems seen c1600 air craft with c67,000 track points.

Looking at the heat map / compass, these signals are strongest W/NNW, which I assume (ok, so I haven’t checked! :wink:) is the direction the window is facing (presumably becuase glass offers less “block” than the solid walls in that direction).

Ultimately, would like to mount the antenna on the “crest” (?) of the roof line, but before I get into the expense of someone getting up there - and grounding it etc, I see a lot of people here have had great results by mounting it in the attic.

So, my questions are this…

  1. Does the proximity of the router (2g /5g) make any difference? Im assuming not as wifi’s on a different frequency.

  2. I hear that an “Ohm mis-match” between the 75ohm coax and the 50ohm usb dongle can impact dB, <1dB. Should I use 50ohm, does the drop in quality to 50ohm coax outweigh the ohm mismatch?

  3. I understand ADSB needs line of site, can I assume that slate roof offers less “block” than solid wall? I assume that rather than having “good” reception in one line of site (i.e through the glass window), moving the antenna to the center of the attic would give wider reception (near 360 degree), but weaker - as slate is still more of a block than glass?

  4. To run the antenna to the attic, I’m going to need c40 ft plus of coax (50ohm), to get it from the RPi in my home office, up the wall and across to the center of the attic. Is this run of coax going to cause an issue? NB - I should be able to mount the RPi nearer the ceiling to reduce the cable run.

So - bottom line - should I move it to the attic?

I hear that an “Ohm mis-match” between the 75ohm coax and the 50ohm usb dongle can impact dB

Assuming a R820T tuner, it’s 75 ohm already, you’re fine.

You probably want to be looking at the cable specs more than anything if you have a long cable run - cable loss varies a lot from type to type.
For example WF100 (75 ohm cable commonly used for satellite installs here) quotes 20dB/100m attenuation at 1000MHz - a 40ft run of that will give around 2.4dB loss.

Putting the dongle as close to the antenna as you can is a good idea.

Thanks Obj,

Glad the Ohm mismatch isnt the case…

Will look at reducing the coax run, mount the RPi high, long USB etc.

Would like to put the Rpi on wifi or long rj45 - but dont have non-ring power in the attic (slightly nervous of splicing into the ring main, as I understand you’re not supposed to!).

I have not experimented with it myself, but given that you can get an ethernet cable there, I think it should be possible to power the pi via a PoE injector?

Is there a reason to keep the Pi in the home office and not put it in the attic too - if you can find power there (if you’ve not tapped it, you can usually fine L/N/E on the ceiling roses)

How well the antenna will work in the attic depends on your roofing materials

  • the tile / slate usually used in the UK will cut your range significantly
  • the ideal is to put it above roof level if you can.

Ooooops too late :open_mouth:

see this ceilingrosewiring.co.uk/ceil … e-colours/ for ceiling rose wiring.

Use it to fix a standard 13A twin socket in the attic.

put a sticker on the socket to say 3A maximum or something - if you pull too much current the breaker will trip and the lights will go out.

I’d use one socket to power the Pi, the other to connect a homeplug Ethernet extender amazon.co.uk/TP-LINK-TL-PA21 … B00D88HMZC (cries of “oh no” from radio hams, some of these devices have been found to be noisy on some frequencies)

Use the homeplugs to provide a network connection to the Pi from the router (less work than getting Pi Wifi to work)

I think it’s OK if you know what you’re doing, it’s minor work and it’s not kitchen, bathroom, distribution board or other area where there is likely yo be water.

Oh no! :slight_smile:

Actually using a couple of those and have found them to be far more reliable than WiFi

Thanks for all the feedback here gents!

As it turns out, my next “upgrade” will involve pole-mounting the antenna on the end of the house above the ridge of the roof (including grounding etc), running as short as poss coax to get from the antenna to the RPi through the wall (c3ft), then PoE for both power and ethernet (funny that, from PoE! :wink: to the RPi.

Only thing with the PoE’s that i’ve seen, power comes in / out on a 2.1mm “round” jack - of course the RPi is micro usb… have made enquiries re 2.1mm -> Micro usb pigtail.

Re those “extend your network over the ring main doodahs”, I had one of those a couple of years back - worked but I’ve found full cat 5 or wifi better for my needs.

Amusingly - or horrifyingly for you hams out there - in the early days of these things, they put out so much interference / leaked signal, that they actually connected more through a form of “wifi” than the actual ring main!

ONe last on that - ‘cos its interesting - I’m aware of how much “discussion” there is in the wider market regarding PoE interfering with radio signals - but if they could sort that - just imagine EVERY product connected to the mains being a internet connected, networked, mutually-aware device… think lamp posts and road traffic conditions etc.
Just sayin’ :wink: .

Just to clear things up:
PoE (power over ethernet) is where low voltage is supplied over the Ethernet cable. You then only have to run your ethernet cable to the Pi and power supply goes with it. You will need to have a so called power injector on the other end.
Powerline communications (PLC or Ethernet over power) modulates a HF data signal on top of the mains. Nowadays the Ham Radio frequency bands are spared by filtering but it indeed creates an ugly broadband noise.
Your idea about getting internet provided through your mains is not entirely new. Back in 2001 a Dutch power provider experimented with it, providing internet to 180 households. The experiment was cancelled two years later. The technology is clearly overtaken by broadband fibre to the home initiatives which became attractive in our dense populated country.

Tried that - found that I had too much volt drop on the Ethernet cable - so stuffed 15v up the wire and used one of these ebay.co.uk/itm/151346691650 to run the Pi (they are good from about 8v to 20v in and run cold)

also needed a pair of these ebay.co.uk/itm/200841109556

The extra volts might come in useful in the summer if you need a blower on the Pi when the attic warms up

@paulmerkx Sorry mate, - you are of course correct, I was referring to the “EoP” boxes.

@PeterHR - interesting idea. I’ll look into that.


Wow - some really interesting stuff there mate, been looking for those bare->barrel plugs for ages! :slight_smile:

C£9 all in - will make a long cat 5 (which i’ll need for the PoE anyway) then run off an extension cable for a few days to see what impact attic mounting has on reception.

Thanks for the heads up!

Don’t OEM/non-homemade POE solutions use much higher voltages? Somewhere in the 45 volt range. It reduces your amp draw and your voltage drop becomes tolerable. Only downside is needing the adapter at the RPi to regulate the output at 5V.

Standard for PoE (802.3af, 802.3at, hereinafter 802.3) is 48 volts. Compliant systems can deliver up to 15 watts (af) or 25 watts (at) to the load. Nonstandard embodiments promise to deliver up to 50 watts.

In addition to signaling, PoE converters use a small switching power supply to deliver power at the needed voltage.

NOTE that a lot of POE kit floating around these days, including a lot of Ethernet connected cameras, and the PoE kit I like (TP-Link TL-POE200, around $20 for DC wall wart, injector, splitter, and cables) IS NOT COMPATIBLE with 802.3 PoE systems. The TL-POE200 even mentions this (on page 4 of their manual). While they don’t define the level of “not compatible,” they do mention that “Pairing the devices with any other PoE adapter is dangerous,” which I’d put on the magic-smoke-leaking-out level of “not compatible.” Whether the magic smoke leaks out of their splitter, the attacked device, or both, is not stated and is an experiment I’ve not performed. From having worked with 802.3 PoE systems in the past, you should be able to put a dead short on a real 802.3 PoE port without causing damage to the port; that’s what the signaling phase is all about.

The good news on the TP-POE200 is the output voltage is switch selectable for 5, 9, or 12 VDC.