FlightAware Discussions

RG-6? problem

Over the past year I’ve been successfully using my Flightaware dongle. My antenna is a homebrew spider-type and the feedline was about 3 ft. of 50-ohm coax. I’ve been able to detect most of the planes on final and takeoff from my local airport about 25 nm northeast of my location. The antenna was indoors, informally hanging from one of the spider legs to the top of a lampshade. Permanently/temporary-like.

I had intended to upgrade my system by placing my antenna outside about 10 feet above the peak of the roof, and had ordered 50ft of RG-6 from Amazon, but other things got in the way (like winter) and I was just today able to erect a suitable pole. I’ve raised the spider antenna to well above the roofline, It sits on top of a 6 ft. length of pvc, which is nylon-tied to the mast.

My results are profoundly disappointing. Whereas I could often track transatlantic flights at 35,000 ft out to 150 nm, now I can barely track aircraft directly overhead.

So the only factors that are different are:

  • longer feedline (from 3 to 50ft)
  • 75-ohm RG-6 (rather than 50-ohm RG-174)
  • antenna is much higher and outside

Any ideas why I would be getting what seems to me to be an extreme loss of signal power? Has anyone else ordered RG-6 from Amazon and had success, or not? Should I have not wasted my money on what could be cheap and counterfeit RG-6?

The center wire is probably broken. Or a short circuit of the central wire with a cable braid.

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Short circuit can easily be tested by connecting a continuity tester between core and braid of coax after removing it from dongle.

To check broken core is a bit difficult as you have to access spider where it is installed. Need to climb a ladder. Temporarily short the spider’s whip with radials, remove coax from dongle, and test continuity between core & braid at coax’s dongle end. After testing, again climb the ladder and remove the temporary short from spider.

NOTE:
50 feet of RG6 coax introduces 3 dB attenuation, i.e. reducing signal strength to half. The spider is a low gain (2 dBi) antenna and cannot cover this loss. You will need a dongle with built-in amplifier (like Flightaware ProStick) or a separate amplifier (LNA)

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Strictly it’s a ‘no gain’ antenna (depending on your reference), but the extra height/free space should compensate for the longer cable

To avoid climbing twice i would short the dongle side and test the antenna for continuity :slight_smile:

:+1:

:bulb: :bulb: :bulb: Smart guy, bright ideas…

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Any wet weather lately? Could water have infiltrated the coax? Was the antenna sealed well?

Can you check for a short at the Dongle before anything else?

That was what I thought, but apparently not!

No, the antenna and feedlines were all indoors until today (and no rain today).

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Thanks for your feedback abcd567. I did check the feedline for both open connections and shorts. And thanks weidehopf for the tip. I only went up on the roof once. This morning before I began erecting the antenna, the coax was rolled up in its original shipping configuration; I did was unroll it and string it from the antenna and then down through a hole in the side of the house. So I wasn’t surprised that the cable was in perfect condition.

However, I’ll now have to investigate the LNA option. Can you recommend any? I’d also be interested in trying to homebrew one, if schematics were available.

I may also try replacing the spider with my 9-element collinear. I tried it a year ago and found that it didn’t work as well as the spider, so I put it away.

3 dB attenuation shouldn’t result in performance that bad.

From the described performance the coax is that bad, that even an LNA might not give you the full potential an LNA normally does.

This is the best LNA for a good price: https://www.rtl-sdr.com/new-product-rtl-sdr-blog-1090-mhz-ads-b-lna/

50 ft coax seems like a lot. Even with a mast, going in via the roof should result in shorter coax.
Anyway good luck with the LNA. (don’t forget to get a bias-t)

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Thanks! One other thing: I took a look at my FlightAware dongle, and it’s a Pro Stick Plus, which already has an LNA built-in. So I’m right now at a loss on what to do next. Change out the RG-6 for something with less loss? The 50-ohm feedline is what I was using indoors for a year, and I tried a similar length of 75-ohm RG-6, and the 50-ohm was far superior. When I compared the short RG-6 with the 50 ft RG-6, the short RG-6 was better, but still vastly poorer than the 50-ohm cable, which indicates to me that maybe the LNA in the Pro Stick Plus doesn’t like connecting to 75-ohm feedline… ?

Re: the 50 ft coax, I absolutely need about 45 ft. The tower is at the side of the house about 15 ft laterally from the room where my gear is situated, so going through the roof would not result in a shorter feedline.

If it’s that noticeable at 3 feet … it’s not going to work at all at 50 ft.

Once the signal is below a certain level, you can’t recover it.
Placing the LNA at the antenna compensates the loss in the coax, but as i said with performance that bad i wouldn’t bother and get proper coax first.

(the 75 Ohm isn’t the problem, the coax you got is just bad quality. Quadshield RG6 can work reasonably well)

Well, the “gear” is only a RPi with dongle, so that can be situated rather easily in the attic directly under the roof.

Some people even put the RPi itself on the mast :wink:

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It is NOT the 75 or 50 Ohm which makes the difference. It is the quality of coax which makes the difference.

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Now you’re talkin’!
I think that mounting the RPi and dongle in a weatherproof box and feeding it with 5v via some telephone cable is probably the direction I’ll be taking.

That’s not gonna fly.
If you want to feed low voltage i’d suggest feeding 12 V, 24V or 48 V and then having a converter in the box that puts out 5 V.

Otherwise you end up with an undefined voltage feeding the Pi and that never works well.

Maybe check out this thread: Outdoor Enclosure

Can’t find the other threads about enclosure builds right now.

I run several RPIs in my attic powered by POE. The issue with putting them in weather proof containers is getting rid of the heat. They often bake in the sun which doesn’t help the CPU or device longevity.

It can be done. Just keep an eye on the temp. Putting just the amp on the mast is another option.

Feeding 5V on long PoE cable may cause excessive voltage drop and low voltage at RPi.

For long PoE cables, a 48V DC supply at router/switch, and a down convertor to 5V at RPi works satisfactorily.

Po_E_48_V.png

Below is one such complete kit . This item is given as an example for guidance only. If you search Amazon and eBay, you will find many other makes and prices.

https://www.amazon.com/itm/dp/B004UBUB7C

The kit contains:
Power Adapter AC to 48V DC
Power Cord
PoE Injector 48V DC
Ethernet Cable
PoE Splitter with integral down convertor to 12/9/5 V DC (dc output voltage selectable by a switch)

Above kit is NOT AF Compliant. Non-AF Compliant POE will fry your non-POE devices if you plug them in without the POE splitter.

Go for AF-compliant POE. It will only apply power after being “asked” for it, and will protect non-POE devices, if you plug them in.

AF-compliant PoE:

Injector TP-Link TL-PoE150S
https://www.amazon.com/gp/aw/d/B001PS9E5I

Splitter TP-Link TL-PoE10R
https://www.amazon.com/gp/aw/d/B003CFATQK

Injector User Guide / Specs:
Injector_Guide.pdf

Splitter User Guide / Specs:
Splitter_Guide.pdf

,

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What a coincidence. I just installed - a couple of hours ago - 50 ft of RG-6 to cover a distance of 20 ft inside my garage. The excess cable is coiled up. I thought performance was going to be dismal. Wrong!

So, unless your RG-6 is of even worse quality than mine - I did not use ‘brand name’ - I doubt the cable is the culprit, unless it’s damaged.

Mind you, if the signal coming from the antenna is already very weak, then the extra cable attenuation will make things worse.

For those in Canada, Walmart is clearing their stock of GE quad-shield RG-6, 50% off.

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I use RG6 from Dollar store: C$6.99 for 50 feet coil. Works good. :slight_smile:

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