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

FlightAware ADS-B Flight Tracking
23

That could just be time related. I have 2 instances of dump1090-fa running so you can compare V-Lad vs Mutant Spider at the same instant in time, you can’t really compare to earlier samples. The traffic here varies a lot depending on the time.

The bottom line is that Mutant Spider had the edge when V-Lad’s radials were turned upward to make the VNA results better but when flat, V-Lad is statistically the same as Mutant Spider. It re-enforces a point both @abcd567 and I made in the other thread… You can make it look perfect on the VNA but that doesn’t mean it’ll be any good in real life.

Oh, I’ll flatten Mutant Spider after lunch for the hell of it.

24

Thanks a lot @gtj0 for performing tests and posting results here.

I am a bit surprised that your Mutant Spider and V-Lad (with horizontal radials) performed nearly equal. I expected V-Lad should perform slightly better, if not much better.

I have used FA 26" antenna as benchmark, and did not compare V-Stub with Standard Spider. My results were as follows (figures are not precise, only indicative):

FA 26" Antenna = 100%
V-Stub with 4 horizontal legs = 80%
Magnetic base stock antenna with whip cut to 52 mm = 50%

 

1 Like
25

Well, other than bending the radials, I’ve done no tuning since I had it on the VNA and I haven’t touched the gain at all. Let me tune it a bit while it’s connected to the SDR and see what happens.

26

You mean by sliding the tuner piece of top wire up/down?

gtj0-V-Stub
gtj0-V-Stub353×645 50.5 KB

27

And rotating the V notch and tweaking the radials a bit.
I can also add the pre-filter and play with the gain.

EDIT: and back to single radials.

28

VNA is just not a good tool for this kind of reception. Basically an LC group would be perfect on plot but very bad a a real antenna.

The signals from airplanes can come from any angles, so the shape of the lobes are more important.

29

 

True.

These 3 things combined decide performance of antenna

  1. Gain
  2. SWR
  3. Radiation Pattern (shape of the lobes)

High gain (3 dB or more), and low SWR (1.5 or less) are necessary for a good antenna.

As regards the shape of the lobes (Radiation Pattern), for being able to receive far away planes (which the antenna sees at horizon) the ideal shape of Radiation Pattern is lazy-eight ∞ which has maximum gain in horizontal direction.

1 Like
30

So, I’ve been tuning various things and I can’t get it any better than yesterday. Remember though, my environment is far from optimal. This just may be the best it can get sitting on my back deck. Unfortunately, I can test a bit more today but that’ll be it for a few days. We’re going to have a rather abrupt weather change on Tuesday and I’ve got lots of stuff to do before then…

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In the mean time… @abcd567 do you have the latest simulation far-field vertical-plane plot for V-Lad (sorry about the rename :slight_smile: )? I see the one above in this thread but I the dimensions aren’t the same as the version I’m testing. I’d like to compare it to Mutant Spider’s…

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If you want to share an .ez or .maa file, that’d be cool as well.

31

Snow??? Gosh I am so glad I moved in South-Eastern VA!
I can just start working on my cars in a relaxed fashion now that is cooling down some here!

32

What are the dimensions you are using? If you give me all dimensions, I can make a simulation model using these and run the simulation.

  1. Length & number of Radials (mine is 69mm x 4)
  2. Angle of Radials above / below horizontal (mine is 0 degrees i.e. horizontal)
  3. Lower wire (mine is 82 mm)
  4. Wire length in each of the two sections of V (mine is 69 mm)
  5. Mouth of V (mine is 45 mm)
  6. Upper wire (mine is 147 mm)
33

I took the dimensions from the other thread…

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The difference seems to be the upper element. You quoted 168 in the other thread but 147 here. In fact, when I tuned it on the VNA, it turned out to be about 150mm :slight_smile: The only other thing is that the radials extend about 53mm from the mounting flange so the tips are 69mm from the center conductor.

You don’t have to create a model if you don’t already have one. I can do it easily enough.

34

I used to live in Northern VA/DC. The winters there were much worse than here in Colorado. Cold and damp. The winters here are actually much milder and dryer.

1 Like
35

NoVA traffic is beating all of those. I had job offers up there, I just could not care to spend my life in that traffic. Not that here in Hampton Roads is much better, but…
Enjoy the fresh snow :slight_smile:

36

The upper wire 168 mm was a mistake in writeup on the drawing.
Good that you caught it. I will correct the drawing. It actually tuned at 148 mm.

Copy-paste following in Notepad, save, then change file extension from .txt to .maa. Double click the .mma file to open it in sofware MMANA-GAL.

To Download:
Basic version MMANA-GAL (free, ~ 2,62 MB, current version 3.0.0.30).

(1) Spider-45deg-slanting-radials.maa

Standard Spider 45 deg Slanting Radials
*
1090.0
***Wires***
9
0.0,	0.0,	0.0,	0.0488,	0.0,	-0.0488,	8.000e-04,	-1
0.0,	0.0,	0.0,	0.0345,	0.0345,	-0.0488,	5.000e-04,	-1
0.0,	0.0,	0.0,	0.0,	0.0488,	-0.0488,	5.000e-04,	-1
0.0,	0.0,	0.0,	-0.0345,	0.0345,	-0.0488,	5.000e-04,	-1
0.0,	0.0,	0.0,	-0.0488,	0.0,	-0.0488,	5.000e-04,	-1
0.0,	0.0,	0.0,	-0.0345,	-0.0345,	-0.0488,	5.000e-04,	-1
0.0,	0.0,	0.0,	0.0,	-0.0488,	-0.0488,	5.000e-04,	-1
0.0,	0.0,	0.0,	0.0345,	-0.0345,	-0.0488,	5.000e-04,	-1
0.0,	0.0,	0.0,	0.0,	0.0,	0.069,	5.000e-04,	-1
***Source***
1,	0
w9b,	0.0,	1.0
***Load***
0,	0
***Segmentation***
800,	80,	2.0,	2
***G/H/M/R/AzEl/X***
0,	20.0,	0,	50.0,	120,	60,	0.0

 

(2) Spider-horizontal-radials.maa

Spider-horizontal-radials.maa
*
1090.0
***Wires***
9
0.0,	0.0,	0.0,	0.069,	0.0,	0.0,	8.000e-04,	-1
0.0,	0.0,	0.0,	0.0488,	0.0488,	0.0,	5.000e-04,	-1
0.0,	0.0,	0.0,	0.0,	0.069,	0.0,	5.000e-04,	-1
0.0,	0.0,	0.0,	-0.0488,	0.0488,	0.0,	5.000e-04,	-1
0.0,	0.0,	0.0,	-0.069,	0.0,	0.0,	5.000e-04,	-1
0.0,	0.0,	0.0,	-0.0488,	-0.0488,	0.0,	5.000e-04,	-1
0.0,	0.0,	0.0,	0.0,	-0.069,	0.0,	5.000e-04,	-1
0.0,	0.0,	0.0,	0.0488,	-0.0488,	0.0,	5.000e-04,	-1
0.0,	0.0,	0.0,	0.0,	0.0,	0.069,	5.000e-04,	-1
***Source***
1,	0
w9b,	0.0,	1.0
***Load***
0,	0
***Segmentation***
800,	80,	2.0,	2
***G/H/M/R/AzEl/X***
0,	20.0,	0,	50.0,	120,	60,	0.0

 

(3) V-Stub.maa

V-Stub
*
1090.0
***Wires***
8
0.0,	0.0,	0.0,	0.069,	0.0,	0.0,	8.000e-04,	-1
0.0,	0.0,	0.0,	0.0,	0.069,	0.0,	5.000e-04,	-1
0.0,	0.0,	0.0,	-0.069,	0.0,	0.0,	5.000e-04,	-1
0.0,	0.0,	0.0,	0.0,	-0.069,	0.0,	5.000e-04,	-1
0.0,	0.0,	0.0,	0.0,	0.0,	0.082,	5.000e-04,	-1
0.0,	0.0,	0.082,	0.06527,	0.0,	0.1045,	5.000e-04,	-1
0.06524,	0.0,	0.1045,	0.0,	0.0,	0.127,	5.000e-04,	-1
0.0,	0.0,	0.127,	0.0,	0.0,	0.274,	5.000e-04,	-1
***Source***
1,	0
w5b,	0.0,	1.0
***Load***
0,	0
***Segmentation***
800,	80,	2.0,	2
***G/H/M/R/AzEl/X***
0,	20.0,	0,	50.0,	120,	60,	0.0
37

The Standard 1/4 WLSpider with 45 deg slanting down radials should have SWR < 1.5, but MMANA-GAL results show SWR = 2.4

Obviously the simulation results by MMANA-GAL are wrong. Dont know why. Checked my simulation models (which I posted above), but could not find any bug.

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image
image771×554 18.4 KB

 

V-Stub results seem better, but as Spider results are wrong, it makes V-Stub’s results also doubtful

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image
image771×555 16.8 KB

38

Not gonna worry about the spiders but one thing I noticed with the v-stub is that there’s some gain in the horizontal field which takes some away from the vertical field. Did you expect that?

red=vertical blue=horizontal

image
image1480×751 39.3 KB

39

A 3D picture gives a better visualization.
The colored 3D radiation pattern below is what is ideal for ADS-B : Maximum gain in horizontal direction (where the distant planes are seen by antenna), reducing gain as the angle of view of plane increases (plane cones nearer)

image

 

The Spider’s radiation curve is more sphere like, while V-Stub is a squashed sphere, a better one, with more gain in horizontal direction (plane far away) and less gain in vertical direction (plane overhead)

Spider

image

 

V-Stub

image

2 Likes
40

Yep. Change the selection to just the H field for all 3 and see what you get. It should be minimal for the spider but check the V.

EDIT: I meant check the H field for the V-Stub.

41

Yes, V-Stub has an upper lobe, but when elevation exceeds 75 degree (i.e. plane very close), the gain starts to drop sharply, just like spider, the donut shape.

42

Yeah I get that and I just realized I had a typo in my previous message. What I meant to point out is that for the V-Stub, some of it’s gain is in the H field and therefore wasted since we’[re only interested in vertical polarization.