FlightAware Discussions

Antenna Efficiency


#1

Folks,

I am just running an ADS-B tuner with supplied antenna, the aerial is not even the optimum size but I still get a decent aircraft count quite acceptable for my needs.

Experimenting with the antenna it is mounted on a tin can as a ground plane but surprisingly if I unscrew the aerial just leaving the antenna base on the tin can I still end up with a similar aircraft count.

Is the ground plane actually giving me the signal rather than the aerial?

Geffers


#2

Or just the shield on the co-ax.
I suspect that’s how many antennas described here are really working.

(unscrewing the ‘antenna’, is actually a really good reality check to get a baseline performance)


#3

So you know the aerial is the wrong length.

Why not compare somewhat correct length aerial to no aerial.
That might give a somewhat more useful comparison.

If you are not interested in planes far away and the antenna has a clear view then you can get away with a very bad antenna indeed.


#4

Sometimes the cable is NOT properly soldered to whip. In one of my whips, the cable slipped out with just a little pull on the cable.This incident 5 years ago plunged me into DIY Antenna making which gave birth to Cantenna & Quick Spider :slight_smile:


#5

I am just a week into PiAware.
I had a small antenna sitting on top of a wooden bookshelf in a windowless room with a skylight.
The listing says 1m, but the cable is 3m.


It fell over at some point, so it was flat instead of upright.
I put a metal bracket in the skylight well, and set the antenna on it.
I put a 75mm aluminum disc under it
I put a 170mm aluminum disk under it.

You have to know what the traffic patterns are in your area.
Because I am about 80 miles north of SFO, it is quite possible that there would be more flights outside of 50 miles than inside.
I look at three things to judge efficiency.

I look at SkyView, and judge where the visible flights are, with tracks on so I can see where they appeared, and watch the distance as they disappear.
I look at the statistics page for the polar view, to see the distance and direction of views.
I look at the statistics page “Positions Reported by Distance from Receiver”
I look at the ratio of <50, 50-100, and >100.
Adjust for different days, including today, as different from the default last 24 hours.
Today, with a 170mm aluminum disc as a ground plane, I am at 13,000; 1,000; 4. That’s 7% over 50.
With just the metal arm, I was over 10%.

Days of the week might have different traffic, but the SkyView shows flights consistently disappearing at ~50 miles.

On hand:
Raspberry Pi 3, PiAware image, 64GB MicroSD
Delivered Nov 2, 2018:
FlightAware Pro Stick Plus ADS-B USB Receiver Built-in Filter
1090Mhz Antenna MCX Plug Connector 2.5dbi gains ADS-B Aerial with Magnet Base RG174 1M+MCX Female to SMA male Adapter Connector
Miuzei Raspberry Pi 3 B+ Case Fan, Heat Sinks, 2.5A Power Supply ON Off Switch, Open-Air Cooling Case


#6

Try unscrewing the top part of the antenna and replace it with around 6cm of wire.

If i remember correctly i had a similar antenna and it gave me a good improvement.
That is quite strange but that’s how it is :slight_smile:
Might not work as well when you are not using a metal base.


#7

.
Unscrew the whip from base, and use steel tie wire OR a thin wire from old/scrap network or telephone cable as whip :slight_smile: The vertical length 67 mm, plus some quantity to wind few turns on the screw on base.

58
2018-09-26 09.39.58.jpg2114x2079 2.05 MB

.

Steel%20tie%20wire

.
Network%20cable


#8

Some other bright folks have said this is a specific 1090Mhz antenna, and shouldn’t need trimming.
The shorter ones, with no “loading coil” (?) in the middle, seem to be too long, and can stand a trim to 67mm.

I’ve seen other commentary that the coax is acting as the antenna for a lot of people, and removing the “antenna” has very little effect.

In my case, maybe my ground plane is not helping, and only blocking the signal from reaching the coax.


#9

Optimizing Supplied Mag-mount Whip, and Introduction to diy Antennas

Cantenna

Quick Spider


#10

Trial Run Results for Three Types of Whip Antennas

Trial Run Results for Four Sizes of Ground Planes


#11

Maybe try mounting the antenna outside or at the very least in an open window on a side of the building facing a major traffic route (often into or out of major airports).

If the walls and/or roof of your windowless room have any metalized material in them you are essentially in a Faraday Cage.

This is a really good collection but compared to some other receivers nearby (as seen on the Stats Page) there are others receiving 5 times as many planes and 9 times as many position reports.

Notice in your neighbours Positions Reported by Distance from Receiver graphs they are seeing more planes further away and you are seeing only the planes that are very close.

I suspect your antenna efficiency would improve very significantly with a known working antenna mounted in free space with the best possible view to the horizon at least in the direction of your interest and a single run of suitable good quality coax.

If you are not interested in building antennae/antennas then the Flightaware antenna is very very good.

S.


#12

“Should not require trimming”
I had a very similar and changing it improved the performance quite a bit.

I’m not suggesting you cut anything but just temporarily try :slight_smile:

With crappy antennas experimenting is king.
Also especially indoors moving the antenna literally one inch can change performance a lot so keep this in mind when you compare the two configurations.


#13
  1. An aerial located outdoor performs far better than the same aerial located indoors.

  2. An aerial gives maximum range in those directions in which it can see the horizon. Hence a location from where the aerial can see horizon in all or most directions is the ideal location. Normally this is achieved by mounting the aerial slightly above the height of surrounding buildings and tall trees.

  3. The shorte the coax cable between antenna and DVB-T/ProStick dongle the better it performs.

  4. The lower the attenuation/meter of coax, the better it is, as it gives better performance.


#14

For those two points, a low-noise amplifier located at the antenna, can make them irrelevant.
So what truly remains an issue is the height above obstacles. And of course that includes the walls when located indoors.

I basically doubled my message and planes count just by raising the antenna somewhat higher (and I am yet to clear all the obstacles in the way of horizon line-of-sight)


#15

Looking at my “nearby”, I see one with outstanding performance, and several with very similar performance. The polar view is even the same, indicating that traffic patterns have some impact on coverage numbers.

I would be inclined to build a spider. I have built a few over the years, for different radios.
There aren’t any parts stores here, like there were down in the Silicon Valley ;-(

My best with the little antenna is no ground plane, sitting on a metal arm touching the skylight.
The 170mm pan seemed to hurt.

Today, I think I’ll try a spider, using the existing base, and some 67 mm pieces of 12AWG copper house wire.

FlightAware conveniently sent me a welcome letter with a shopping list
5 meter cable
FlightAware Antenna

I might just put the FlightAware antenna on my Christmas list, and mount it on the outside of the skylight housing, if Santa brings it to me.


#16

You could order 2 or 5 meters of CFD200 or LMR400 which is already terminated with SMA. (on amazon for example)
That should be 10 to 20 $.

Then you chop of one end and build the spider into the cable by shoving some copper rods into the insulation.


#17

I thought maybe my little antenna had bad wiring in the base, which I’ve seen mentioned in discussions. I only saw one aircraft on SkyView.
I wondered how many I should see, so I went to a FlightAware Live view.
Hey! Only one plane within 50 miles of me.
That makes it hard to measure performance.

My range seems to be about 60 miles at high altitude. 50 miles at 20,000 feet.

SFO airport is 55 nautical air miles, but the altitude of most flights would be low.
My range in that direction is about the Golden Gate Bridge, 40 NM at 10,000 feet.


#18

I can get 60 miles with the default RTL-SDR antenna sitting on my basement window bars(3ft above ground).
In my attic, at about 60 ft AMSL I can get over 100 miles.
Chimney antenna at 70ft AMSL I can get out to 200NM.


#19

Try this one. It needs only a 1m piece of satellite coax like RG6 or WF100, and a F-connector.

Quick Spider

Edit:
You will also need RG316 F-female to MCX-male Pigtail. It has added advantage over a solid connector that it will not transfer mechanical stress of heavy RG6/RG58 cable to dvb-t’s delicate mcx socket.

F%20female%20to%20mcx%20male%20pigtail


#20

I unscrewed the antenna, leaving the base on a 67mm aluminum disc.
I saw a flight at 20,000 feet, 42 NM out.
With a 67mm piece of steel wire threaded onto the base, 30,000 feet, 56 NM.
A five legged spider (six, but one is along the mounting arm), with the legs 45° down at the edge of the 67mm disc, so 67+67+67 per leg, underneath the disc, with the mag base on top.
That doesn’t seem as good, for range. Should the legs be at the edge of a 67 mm disc, or closer in? The one built on the “Easy” SO-239 looks like the angle of the legs meets the base of the antenna at 45°, but the Coke can with the splayed sides looks like a 67mm disc with legs at the edge.