Frustrated with my site

FlightAware ADS-B Flight Tracking
1

Hello everybody,

I’ve been working on my setup over the past couple weeks and I’m frustrated to the point where I’m close to tossing it all into a bin. I’m pretty much stuck.

From the beginning…

One of my experiments after I received my first rtl-sdr-dongles was to setup one of my old Raspberry Pis (in fact the oldest one I own… an MKI model from the very first batch with just 256MB memory) out on the balcony to track aircraft. I did not really care too much about it back then, I stuck two pieces of wire on a wine cork to form my first dipole, and it was tracking away. I was actually running on a battery pack for the first days, but then upgraded to POE. I put a bucket over it at first to protect it from the weather.

Some time later I started optimizing. I read about the PRO stick and ordered one. Tinkered a little with the gain, but then filters became available a week later or so, and I got one of those, too.

I ordered a nice weatherproof housing and mounted everything inside (and switched to a different Raspberry in the process, since the original one did not offer any mounting holes).

Then I wanted to go full scale. I decided to put up a nice antenna. I made a 16-segment coaxial collinear antenna out of RG58 cable. I posted about that in another thread and ExCalbr informed me that this might actually not yield the best results. So i started experimenting with different lengths and found that he was right and 8 segments gives me the best results. Or, that’s what I thought.

Up until yesterday, I didn’t bother to slip the antenna into its designated PVC pipe. To speed up the testing, I just used e-tape and stuck it kind of loosely to the outside of the pipe. With bad weather coming up, I decided to change that yesterday, and… well, the result is devastating…


The easiest conclusion here might be that the pipe is made from the wrong material… Well yeah, I’m not really sure it’s actually PVC. I got it at the local hardware store and wasn’t really paying attention. It is some kind of plastic… But here’s what makes me think that it’s not the pipe: When I took the original 16-segment out and stuck it to the outside, I did not see any kind of impact whatsoever.

The thing I’m more suspicious about is actually noise:


As you can see, the noise usually dropped down to around -30dB at night before the operation. Last night, the best figure seems to be somewhere around -23dB.

I do have two suspicions about what might be causing this… Number one is the network cable, that was very close to the pipe (and not very close to the loosely hanging feed cable during my various experiments… The antenna itself starts above the point where the network cable passes the pipe). I have removed the cable now and put it at some distance to the antenna and feed line, but could not really see an improvement.

Number two is the metal frame that the pipe is attached to. Since the CoCo is a symmetric antenna, the shielding of the feed line might be doing some strange interactions (capacitive coupling or similar) within the 40cm it is now running strictly parallel to the metal part of my balcony. And I don’t really have many other things to attach it too. I have thought about drilling a hole sideways into the pipe and put the feed line through there just to get it away from any metal parts, but I don’t know if that would work…

So far for receiver number one. In the meatime, I also started experimenting with a second receiver, that has very much potential, but will be entailed by different problems.

That second receiver’s position is up in the attic, which is one floor higher than my primary one. It’s positioned inside, but since the roof’s insulation seems to be free of any metals, it has very nice potential reception. To confirm that, I ordered a second PRO stick + filter, and did some experiments. I have managed to establish a (very weak) wifi link (that gives me 10-15% loss of mlat messages) and am currently running off a battery pack. I equipped the receiver with the remainder of my balcony antenna, so it’s running a 8-segment CoCo as well.

This screenshot shows VRS range plots after less than 24h of total receiving time (not consecutive, the battery just gives about 14h). Rings are 50NM:

800×634 179 KB

Hell yeah. 3 indents from the west up to the north due to 3 houses standing in the way. some range loss in the southwest due to the building wall. And one major indent to the northeast that is caused due to a huge metal tank (I suppose it’s the expansion tank of the heating system, so it’s very likely filled with water, too) and the elevator service room. That latter indent partially blocks the view of the local airport, so the receiver currently has a very nice range distribution. Some of these might be overcome by a better placement of the antenna.

But here’s the problem: I don’t have any power up there to run the receiver 24/7. And I really can’t get used to the idea of having to switch the battery twice a day.

So here I am, having set up two receiveres, and happy with none of them. If you happened to have read all of what I have written I already owe you a big thanks, and if you have any ideas to help me out, I’d be very, very happy.

Cheers!

2

That doesn’t look so bad. After the map fills in, you’ll apparently be averaging about 200NM except for that one direction. I have the same problem to the North. Big hill there in the way. In the opposite direction I get up to 400+NM so it balances out :wink:

The noise is perplexing. Is the antenna connection shield perchance touching or connected to a different ground potential than the receiver? Is the metal railing bolted to structural steel? That your noise level even with the filter in place jumped up points to a feedline system problem, IMO.

3

Yep that attic would be a nice location for a receiver. If only I could make it permanent. I will need to find somebody to talk to about the power situation before anything… and while I’m at it, might as well ask for some network cable to be run. Wonder what it will cost me. No, I would not invest it for a simple adsb receiver, but since I’m also currently acquiring a ham license, it might also be clever to put an SDR transceiver and some hamnet equipment up there. I’m pretty new to this whole stuff, but I’m pretty sure that power + ethernet will be a good base to build things on.

As for the balcony one… There’s no electrical connection between the antenna and the balcony rail, neither accidental nor intentional. The insulation is fully intact, and I checked with the multimeter. Anything that could be is purely inductive or capacitive, and I don’t have the tools to measure that.

The balcony rail is going into the wall on both ends, so it might be connected to other metal parts of the house. not sure what it could be picking up. I’ll try to add some pictures when daylight is available again, just to clarify this a little.

About the filter: I noticed that the filter performs best when it is directly connected to the pro stick. Unfortunately, the assembly filter → pro stick → usb socket is too long to fit into my outside casing, and so I have to use a small 15cm pigtail between the filter and the stick. This has given me issues before, but since I rearranged the insides of the box with matching length cables, there’s some clearance around it. I have thought about opening the pro stick, desoldering the usb plug and putting a short length of usb cable on it to make it fit… might be worth a shot… but since i have not touched the insides of the receiver itself during my antenna tests, i doubt that that’s the root cause…

4

It can definitely be frustrating at times but very rewarding when you eventually figure it out.

I am also very new to all this but as i read your post it sounded like you had a working 8 segment COCO.
Then when you added the plastic pipe as a cover you got a huge drop in signal.
So the pipe material is likely not transparent to RF signals.

But then it sounds like you attached the COCO to the outside of the pipe to fix it.
I was just thinking if the pipe is not RF transparent then it may be affecting the COCO just by being attached to it.
Sort of like the pipe was a metal pipe and it is throwing off some of the COCO’s parameters resulting in the segments being no longer the correct length.
The COCO is very dimensionally sensitive and it wouldn’t take much to change things.

Maybe try just hanging the COCO from a piece of string or something very RF transparent.
Just temporarily to see if you get back you previous performance.

I had a similar experience where a COCO i built was performing really poorly. Loads of checking and double checking. New segments, I am ashamed to say exactly how long i messed about trying to find the issue. Eventually i found it, i had been testing the antenna by putting it near an upstairs window. What i didn’t realise was that the curtains have a very fine metallic thread woven in to them and the fold in the curtain was almost totally surrounding the antenna. Doh.

5

As promised, here’s a few pictures. They’re certainly not the best, but they should help with clarification.

Overview:

444×600 25.5 KB

Antenna:
444×600 25.3 KB

Receiver box:

The (supposedly) problematic mount (Feed line exits the pipe at the bottom):
444×600 34.8 KB

6

Well, as I said, I’m not sure about the pipe. I can only suspect that the pipe is not the issue since when I did the 16-segment one before inside the pipe, and afterwards attached the same antenna to the outside of the pipe, I did not see any change so far. The problem is, I don’t have a source at hand that will reliably provide me with something that works. I believe that shipping something like a 2m pipe will most likely do damage, so I’m limited to local hardware stores, and they’re not really interested in the RF transparency of pipes that are meant to be used in electric installations or plumbing ^^

When i attached the antenna to the outside, i did it in a way so that the antenna was facing away from the house, so I probably wouldn’t have noticed the drop in signal quality in that direction.

I’m pretty sure I could get it back to perform if I remove and attach it to the outside of the pipe again. It’s just that since I was certain to have found the optimum antenna configuration, I already sealed the ends. It would probably be quite a mess to get it back out again…

I’ve had another idea, though… I’ll try to fire up rtl_tcp and gqrx and have a look at the signal. If there’s a significant noise source around, maybe I can at least see what it is that way.

7

OK so… I can’t deny that it bothers me…

I’m by now pretty sure that it’s a noise / coupling problem of the feed line.


The big dip is me taking down the antenna, removing the sealing and cleaning it up… And putting it back up, with an experimental balun element. The latter does not really work well, plus it doesn’t fit inside the tube… oh well. Thought i’d give it a try.

But watch the noise in the time after the dip: That’s me moving the feed line to three different positions, without touching the actual antenna. The message rate of course moves into the opposite direction… less noise, more messages.

Still not to sure what to make out of this…

8

It sounds like a connector or cable problem. Solid core cables can break then re-connect based on position.
I have seen a post or two regarding professionally made connectors that were not so professionally made. They had to be fixed.

You may be able to use a tablet to view your stats and see what happens when you move parts of the antenna system.
Maybe connect a conductivity sensor(Multi-meter) to one end(Short the other end) and see if it changes when you move the coax.

Could you have turned on any lights during the changes? Some LEDs produce a lot of electrical noise(they can cause havoc with HAM radios).
AC can have the same affect.

9

We run a POE (power over ethernet) setup on the FlightAware office to the roof. Instead of running a power line you use the ethernet cable as the power line. Max distance is 100m (or about 300 feet) from the injector to the splitter.

You need two parts to turn normal ethernet into POE ethernet. You need an injector to put power on the ethernet line and then a splitter to take the power off the ethernet line.
Stores usually sell kits that include both the injector and splitter together.
amazon.com/TP-LINK-TL-POE10R … B003CFATQK

Some network hubs and switches also have POE included but these are used for multiple POE ethernet lines. You would still need to have the splitter near the Raspberry Pi.
amazon.com/TP-LINK-8-Port-Et … B003CFATT2

Once you have that setup you select 5V on the splitter and connect a barrel to micro-USB cable to the Raspberry Pi. This cable is not usually included in some kits.

This setup has been running on the roof for years.

10

I should also mention the other way people are running Prosticks is with very long USB lines.

USB normal spec is about 15 feet max length. With a powered USB extender people are getting 50+ feet from the raspberry pi to the prostick. Then run a short coax cable from the prostick to antenna. This might work for some people that don’t want to run POE.

The quality of USB extenders is iffy. We have some reports of MLAT not working on some USB extenders but then work with another USB extender brand. Normal ADSB message don’t have the same timing problem.

11

One thing I should mention is that we use a very small amount of foam inside the FA antenna to prevent it from touching the tube.
Using a small amount of tape and a small amount of foam wrapped around the antenna every few feet or so.
This might not be a problem depending on how the segments are soldered together but it does help everything stay in place.

There also might be some strange coupling and/or grounding on the tube and the coax. We got some professionally made antenna that have this problem.
IE. depending on how it was mounted it would change drastically on how it performed.

12

To find out if you have the correct type of PVC just put a small off cut in the microwave, if its warm to the touch after 20 or 30 seconds then its the wrong stuff.

If not really well sealed COCO’s eventually absorb moisture and other contaminants. The copper and aluminium conductors tarnish and the non soldered joins don’t always form a good electrical connection again after being disturbed. Maybe making up a new one EXACTLY the same dimensions and seal it up straight away will be more successful.

My station location is not far from the ocean so with the salt spray and moisture even what I thought was a well sealed cocos started to degrade after a few weeks, when pulled apart the tarnish and corrosion was quite noticeable. No doubt your location isn’t as bad but the corrosion can still happen over time.

13

It is easy to make a DIY “High Gain” antenna (5dBi to 9 dBi), but very hard to get it right. This is particularly true in case of the CoCo. Also, if the construction of coco is “push pin” instead of soldered pieces, it further aggrevates the problem as antenna parameters may change with movement. If you want a high gain antenna, purchase one made by professionals like Flightaware.

If you are keen on DIY, then make a low gain 1/4 wavelength groundplane antenna, such as Spider or Cantenna. These are easy to make and very easy to get right. Their disadvantage is their low gain, typically 1.5 dBi to 2 dBi. With a short length of feeder coax, these give reasonable performance, but in outdoor roof/mast mounted situations, which require longer lengths of feeder coax, the attenuation of coax eats up 1/4 groundplane’s tiny gain and reception is very poor. Fortunately this can be overcome by adding an rf amplifier between antenna & receiver. A satellite amplifier is an economical solution, but some prefer to use better quality custom made rf amplifier like LNA4ALL, but this a costly solution. The Pro Stick has a built-in rf amplifier, ans is a good receiver for low gain antennas. It however requires a filter in most cases.

If I was in your situation, after all this frustration, I will prefer to spend $45 and purchase Flightaware 1090 antenna. In fact I did purchase FA antenna, although my Cantenna gives me very good & trouble free service, and is my primary antenna. My reason to purchase FA antenna was that I wanted to use it as bench mark antenna in my antenna designing & testing experiments.

14

[quote=“david.baker”]We run a POE (power over ethernet) setup on the FlightAware office to the roof. Instead of running a power line you use the ethernet cable as the power line. Max distance is 100m (or about 300 feet) from the injector to the splitter.

You need two parts to turn normal ethernet into POE ethernet. You need an injector to put power on the ethernet line and then a splitter to take the power off the ethernet line.
Stores usually sell kits that include both the injector and splitter together.
amazon.com/TP-LINK-TL-POE10R … B003CFATQK

Some network hubs and switches also have POE included but these are used for multiple POE ethernet lines. You would still need to have the splitter near the Raspberry Pi.
amazon.com/TP-LINK-8-Port-Et … B003CFATT2

Once you have that setup you select 5V on the splitter and connect a barrel to micro-USB cable to the Raspberry Pi. This cable is not usually included in some kits.

This setup has been running on the roof for years.
[/quote]

Yes, I’m aware of these, in fact I’m already running two pairs of POE kits, one for my primary receiver. Unfortunately, it would require a network link into the attic, which does not exist, and since I’m only living for rent, I can’t simply drill holes through other people’s appartments…

[quote=“david.baker”]One thing I should mention is that we use a very small amount of foam inside the FA antenna to prevent it from touching the tube.
Using a small amount of tape and a small amount of foam wrapped around the antenna every few feet or so.
This might not be a problem depending on how the segments are soldered together but it does help everything stay in place.

There also might be some strange coupling and/or grounding on the tube and the coax. We got some professionally made antenna that have this problem.
IE. depending on how it was mounted it would change drastically on how it performed.
[/quote]

This might be the problem I’m having here. I will see if I can find some suitable foam or other insulation to prevent that from happening. Thank you :slight_smile:

That’s actually a good idea. Will need to find a microwave somewhere. Thank you :slight_smile:

Well, my antenna is in fact soldered, so the joints should be fine. It’s also not happening over time (but as soon as I put it into the pipe), so I don’t think that’s the problem… I will try to confirm by removing the balun later on, In theory it should jump back to full performance then.

Well, I know how good the dipole has worked for me, and I know that my CoCo, even though kind of challenged, still easily outperforms that. Also, I know that the antenna itself works beautifully, as long as the surroundings are correct. It’s just a matter of putting things together the right way. I’m pretty sure that any kind of antenna would suffer from the noise problem, even commercial ones.

In the meantime, the noise has been fine last night… Of course, the antenna’s not inside its pipe. But the balun allows the feed line to be grounded now, which has dropped the noise some more. Unfortunately it also impedes performance. But I must also admit that I didn’t really put too much effort into it. So maybe I can still make it work…

15

From your graph I’d say your level is set way too high, back it off some, the noise will come down as well as the percentage of messages above the -3 as compared to the total usable.

Here’s one of my sites.

http://tjowen.ddns.net/collectd/graph-images/dump1090-rpi-signal-1h.png

16

@jketterl
Yes, I understand your feelings. I have experienced this myself. The pleasure and satisfaction I get from DIY stuff is far greater than what I get from purchased stuff, even if the purchased stuff performs better.

17

My very first antenna was a dipole (1/4+1/4), but my coax being long (50 ft) it did not work well till I added a satellite amplifier. This was in 2013. Later I found that 1/4 groundplane (Spider & Cantenna) worked better than the dipole.

I did try Coco, made about one dozen of these over a period of 2 years, but all ended in trash bin. Only the last one servived because it improved to an acceptable performance after I improved its swr/impedance match by inserting a 2pF capacitor in series with core wire of feed coax at 0.85 x half-wavelength (i. e. 0.85 x 138 mm x V.F. of coax) from the feed point (Transmission Line+Capacitor impedance matching technique).

My First 1090 Antenna, Sept 2013

18

Just make sure you put a mug of water in there too.
If the PVC is RF transparent and it is in the microwave by itself then that is the same as running an empty microwave.
Most microwaves do not like running empty.

And if you put a mug of water in, then afterwards you can have a nice cup of tea or coffee while you ponder the next step. :slight_smile:

19

Another thought.
Does your feed line go up the tube to a height higher than that metal hand rail?
Just wanted to make sure you didn’t have any of your COCO segments blocked/reflected by the handrail.

20

[quote=“david.baker”]I should also mention the other way people are running Prosticks is with very long USB lines.

USB normal spec is about 15 feet max length. With a powered USB extender people are getting 50+ feet from the raspberry pi to the prostick. Then run a short coax cable from the prostick to antenna. This might work for some people that don’t want to run POE.

The quality of USB extenders is iffy. We have some reports of MLAT not working on some USB extenders but then work with another USB extender brand. Normal ADSB message don’t have the same timing problem.
[/quote]

Thanks for the tip. I tried tons of options, but none really worked. After reading the above, I ordered a 10m active USB extender and was able to move my aerial to the loft. Much, much better now, thanks :smiley: