FlightAware Discussions

Antenna Ground Plane

Folks,

Want to make a wooden base for a portable PiAware system. For temporary mounting of the antenna is a can lid sufficient as a ground plane, and of course for stability? Just wondering if it is the actual can body that is the main advantage.

Geoff

Just use a spider, they tend to work better anyway: QUICK SPIDER - No Soldering, No Connector

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Thank you, shall give that a try at some point.

Just thought of the can lid for neatness of transportation really.

Geoff

Ground plane is provided by the lid.
The can’s cylindrical body provides decoupling sleeve.

For temporary purposes, lid only should do.

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As the name implies, a coaxial dipole is a dipole and the sleeve is part of the dipole. It is not a decoupling sleeve.

Properly constructed and tuned it has more gain in the horizontal plane which is ideal for airplanes at the horizon.

A ground plane antenna will have a radiation pattern elevated above the horizon and will not hear aircraft as well on the horizon.

S

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My ground plane on cookie-can receives not less than my pcb dipole :slight_smile:

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Only one of your sites has any significant numbers beyond 130NM

(don’t leave the sticky tape on the blinds for too long. the adhesive will be affected by UV and leave stains)

That one is Flghtaware antenna in another window in another room. (Station #76000). Can’t compare 1/4wl ground-plane & 1/2wl dipole with it as both the antenna gain & location is different. :slight_smile:.

Compare stns 5252 & 6396

Station 76000’s Flightaware Antenna

One is significantly better than the other.

I’m sitting in the lounge at HEL using my phone so i can’t cut and paste pictures but the coverage graph for 6396 shoes significantly more positions reported and significantly better range. The airplane count is also higher.

How are you comparing them?

Just for interest are the amplifier, filter, receiver chains the same as well for the comparison?

S.

No, the hardware chains are somewhat different, though both use same RPi.

Stn 5252: PCB antenna >> 1m RG174 >> FA light blue filter >> FA orange ProStick >> Pi-1 >> instance-1 of dump1090-mutability >> instance-1 of piaware

Stn 6936: 52 mm mag-mount on cookie-can >> 1m RG174 coax >> Radarbox green FlightStick >> 1m USB extender cable >> Pi-1 >> instance-2 of dump1090-mutability >> instance-2 of piaware

When I compared the two antennas, I used FA orange Stick hardware chain, first with magmount for some period, then with pcb antenna for some period.

SCROLL RIGHT TO SEE RIGHT SIDE IMAGES IN FULL
SCROLLBAR IS BELOW IMAGES

Station 5252 :
PCB 1/2 λ Dipole
1m RG174 coax
FA Filter + FA Prostick Orange
Station 6396
Mag-mount 1/4 λ GP (cookie can)
1m RG174 coax
RadarBox24 FlightStick Green
station 5252 station 6396

Don’t think that’s accurate.

Couldn’t really find a good source showing the exact radiation patterns for a ground plane and dipole antenna.
But i think the ground plane antenna has the maximum gain towards the horizon just like the dipole, it’s just cut off below the horizon.
https://ham.stackexchange.com/questions/3675/what-is-the-effect-of-using-different-number-of-radials-with-ground-plane-antenn

Maybe the whip on a metal surface is not an ideal ground plane though.
Could be that the gain towards the horizon is better for a monopole with sloped radials.

Thanks for putting up those images.

One is clearly better than the other but it is a bit hard to work it out on a phone.

It’s this borne out by the graphs you provided?

Noting that the cookie can antenna is less than a quarter wave length from the edge of the ground plane, it is within half a wavelength of a resonant element, it is magnetic based pierce of crap widely known as the poorest ADSB antenna around and with completely unknown impedance yet it is no t worse than a pcb dipole.

I suggest there is really something amiss with the dipole or the test process itself is questionable.

Here is some interesting Research into ground plane antenna .

As yet i haven’t found any convincing research that a PCB dipole antenna behaves the same as a true coaxial dipole.

The coaxial dipole was the vhf and uhf antenna of choice for vertical mount from late 1960s through to the 1990s when computer designed multi element arrays in a raydome proved cheap enough to manufacture…

S.

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.
Yes, the graphs I have posted above, AND comparing instanteneous message rates /plane counts shown on dump1090-mutability maps for the two
.

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It is NOT less than 1/4WL. It IS 1/4WL (52mm + 15mm = 67mm = 1/4WL)


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I’m curious what the FA stats will do when you switch each antenna to the other setup.

If the antennas are the main difference, the 50-100 nmi position numbers should move with them to the other setup.

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That’s exaxtly what I had in mind, but was lazy to do it, as I never bothered about stats or rank.

OK, I will swap the antennas tonight or tommorow, and leave the system running for few days for stats to buildup.

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Have to agree here.
abcd, you really are demonstrating that a dubious antenna performs as well (but not significantly better) than a really crap antenna.
Can I suggest that neither will occupy significant space in your rubbish bin and that’s probably the best place for them.

image

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Personally i found the ebay PCB antenna to be similar in reception to a DIY monopole with radials.
If someone doesn’t want to go to the DIY route, it’s an antenna that is cheap and with some tape wrapped around the bottom you can even make a little splash safe space for the cable connection.

Without switching the rest of the signal chain and checking the result, this isn’t really an antenna comparison.
It’s pictures and numbers without much meaning in regards to comparing the antennas.

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Ah - but ‘which’ ebay pcb antenna do you have?

There is the short antenna - either naked or in a PVC case
image

This one with an elevated feed
image

this one with elevated feed and tuned lower elements
image

I use three of ‘elevated feed, not trimmed’ types. Not because they are great antennas, but because they are repeatable.
I can then run a legitimate comparison between two receivers, filter vs no fiter etc.
The point is I can (as far as possible) reduce my comparison down to one variable.
Comparing different antennas feeding different filters into different receivers and expecting it to tell you anything meaningful about an individual component is just silly.

Mines in a tube, the short one (translucent).
Haven’t opened it so i can’t say for certain.

Comparing it to a DIY monopole with radials is also an arbitrary comparison, i’m well aware.
Was just saying it’s not necesarily crap, especially if you compare it the REAL crappy antennas (non-shortened mag base without ground plane … NooElec rubber ducky antennas … ).
But some of the PCB antennas are crap indeed, missing solder joints and you never know what you get obviously.