best antenna

[buenti]

My approach to building an antenna with a sma connector and copper wire:

sma.pngthreaded.jpg
bottem.jpg
solder.jpgfranklin_spider.jpg

[abcd567]

Mag Mount Antenna’s Whip Replaced By V-Stub Wire Collinear

Comparison of "V-Stub Wire Collinear Whip" with "52mm Optimized Whip"


V_stub_wire_collinear_vs_52mm_whip-c.jpg


Thin (0.5 mm dia) Steel Tie Wire used to make collinear whip with V-stub.
Thin wire can easily be wrapped over threaded stud of magnetic base.

Steel Tie Wire.jpg


MEASURED PARAMETERS: V-Stub Collinear Whip


SWR.jpg


R_X_Z_SWR.jpg


AIRCRAFTS SEEN & MESSAES RECEIVED (per sec)

aircraft-messages.png


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[abcd567]

Do you suggest to keep the plastic bottom of these antennas or to remove it before putting it on a metal surface?

No need to remove plastic adhesive covering of the base. I have once removed the black plastic adhesive circle from base, but it did not give any improvement. Even with plastic in place, there is enough capacitive coupling between base metal and the food can.

[Mephisto]

2. If you keep the magnetic base, and place it on a large metallic can, you get a good ground plane, and dont need to add radials. This is exactly what I have done. The Butter Cookies lid is providing a good ground plane, no need of radials.

Do you suggest to keep the plastic bottom of these antennas or to remove it before putting it on a metal surface?

[abcd567]

So this modified eBay antenna (minus it's magnetic base) is installed waiting for tomorrows signals. I've added a short piece of wire at the bottom to compensate for length that was inside the base that I have removed. As soon as I connected it, even from the bedroom window a couple of aircraft were visible at 200nm. It certainty looks good but with only 8 aircraft over the UK at the moment I'll have to wait until tomorrow to see just how good.

Scroggie

1. Vertical length Inside magnetic base is about 10 to 15 mm depending on make of antenna.

Optimized whip inside.jpg


2. If you keep the magnetic base, and place it on a large metallic can, you get a good ground plane, and dont need to add radials. This is exactly what I have done. The Butter Cookies lid is providing a good ground plane, no need of radials.


Coiled Collinear and Quarter Wave.jpg

[Scroggie]

Any one interested to run simulation himself/herself, can download modelling software 4nec2 (free of cost) fromhere:

Download 4NEC2 Software (free of cost)


Also, I have uploaded my following simulation model files to DropBox. Anyone can download these from Dropbox and run in software 4NEC2.

Monopole with Coil and Ground Plane.nec

Super J-Pole with Coil.nec

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That great - will have a look at that.
Incidentally I've been experimenting today and cannot replicate the success I had at first with the close wound coil of 10 turns. Throughout today your design has been noticeably better albeit with 1 mm wire.(same dimensions 60,53,137)
In the last hour I've modified an eBay purchased magnetic -mount identical to the one you show in an earlier post. I too found it to be very poor but it occurred to me that if the top section was 137mm it might be usable. So I exposed the metal at the top and soldered on some 1.5 mm copper to increase that section above the coil to 137 mm. Yesterday I had made six quarter-wave radials at 45 degrees mounted on an F - SMA adapter so it's now a simple matter to experiment with different elements by just plugging them in. So this modified eBay antenna (minus it's magnetic base) is installed waiting for tomorrows signals. I've added a short piece of wire at the bottom to compensate for length that was inside the base that I have removed. As soon as I connected it, even from the bedroom window a couple of aircraft were visible at 200nm. It certainty looks good but with only 8 aircraft over the UK at the moment I'll have to wait until tomorrow to see just how good.

Scroggie

[abcd567]

Any one interested to run simulation himself/herself, can download modelling software 4nec2 (free of cost) fromhere:

Download 4NEC2 Software (free of cost)


Also, I have uploaded my following simulation model files to DropBox. Anyone can download these from Dropbox and run in software 4NEC2.

Monopole with Coil and Ground Plane.nec

Super J-Pole with Coil.nec

.

[abcd567]

Could I please ask you to run your computer simulation using your measurements 60,53,137 mm but with 1.5 mm copper wire coil (1.54 mm with insulation) of 6.9 mm diameter (Wire centre to wire centre), 8.44 mm overall. It should be much worse than what you achieved but I'm curious as to how different it is to the 10 turn close wound.

Scroggie

Will run simulation this weekend.

[Scroggie]

I did make the one with 53mm long, 5mm dia, 16 turn coil, and did measure SWR. Please see this post:

https://forum.flightradar24.com/foru...150#post184150

However I did NOT make the one with your coil. You made it, and based on your measurements, I did computer simulation and posted results of simulation




This is Flightaware antenna with pvc pipe removed.

image_10493.jpg

That is interesting - the top looks very similar to what we've been discussing but with a 4 or 5 turn coil. Could I please ask you to run your computer simulation using your measurements 60,53,137 mm but with 1.5 mm copper wire coil (1.54 mm with insulation) of 6.9 mm diameter (Wire centre to wire centre), 8.44 mm overall. It should be much worse than what you achieved but I'm curious as to how different it is to the 10 turn close wound.

Scroggie

[abcd567]

Are you just using software to give those results or constructing the antenna and making measurements with a generator?

I did make the one with 53mm long, 5mm dia, 16 turn coil, and did measure SWR. Please see this post:

https://forum.flightradar24.com/foru...150#post184150

However I did NOT make the one with your coil. You made it, and based on your measurements, I did computer simulation and posted results of simulation

It would be interesting to see what's inside the commercial Flightaware antenna - must be something like this.

This is Flightaware antenna with pvc pipe removed.

image_10493.jpg

[Scroggie]

That's very interesting. I'm not seeing that 1dBi less gain with just a coil change perhaps because I see your calculation is using a 50 ohm feed impedance and I'm feeding the dongle with exactly half a wavelength of 75 Ohm coax (it's all I had to hand)
I'll make one with your dimensions and compare them again. Are you just using software to give those results or constructing the antenna and making measurements with a generator? I don't want to take up your time unnecessarily but would be interested to know what the best coil dimensions would be using the thicker wire. I have no way of producing the detailed analysis that you do unfortunately.
It would be interesting to see what's inside the commercial Flightaware antenna - must be something like this.
Anyway thanks again for all your efforts, I'm sure it's appreciated by all on here.

Scroggie

[abcd567]

Scroggie:

Simulation shows that with your coil i.e. 10 turns, length of coil 16.3 mm, 5.1 mm inner dia, wire dia 1.54mm (mean dia 6.64mm ), the lower wire of 50mm length gives best SWR.

Monopole with Coil 2 - Sweep Lower vs SWR.png


Monopole with Coil 2 - Sweep Lower vs Gain.png


Monopole Collinear With Coil - 50mm lower- Radials 45 degree down.png

[abcd567]

Scroggie:

You are basing your designs on coil inductance only. Please also consider these effects of the coil:

(1) The coil not only acts as inductance, but it also intercepts radio waves like the vertical straight wires do, and hence in additon, it acts as antenna wire also, and its height also counts.

(2) The coil height determines the vertical sepertion between upper and lower straight wires, and this separation also affects antenna parameters & performance.

It is a complicated situation. Simulation software take these two factors into consideration. When making actual antenna, trial and error can give you best results.

[Scroggie]

Coil Calculator.jpg This was the software calculation I used to calculate the required inductance from your measurements. There are online calculators as well and they don't agree with each other!! But this method did produce a working antenna. I think I might try adding another coil + another top 137 mm (I suspect that 130 mm is probably what is needed at the top because of "End effect" but haven't tried that yet - you found that I see above) I'm finding the ground plane radials difficult to construct tidily
I'll watch this space and see how you get on - I'm self-isolating at the moment so have a lot of spare time!!

Scroggie

[abcd567]

The wire diameter is actually 1.54 mm (1.5 mm + insulation) so if I had been able to wind it perfectly it would be 15.4 mm long but it was done rather crudely and actually it measures 16.3 mm. The plan was to make the inductance the same as yours which the software I used suggested was 0.212 microHenries. Even if that software wasn't accurate I figured that any error was the same for both calculations and it looks like it must have been more or less correct.

Scroggie

Thanks for providing the details of coil. Next weekend I will try to make one like yours and see.

The mean dia of coil = inner dia of coil (which is the dia of drill bit on which the coil is wound) + dia of wire. It is mean dia of wire which is used in calculations & simulations.

In your case the mean dia of coil is 5.1 mm + 1.54 mm = 6.64 mm.