FlightAware Discussions

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

This design (V-stub) is my thought. It may have existed, but I have never seen it anywhere.

 

Simply because when the wire is cut and bend, it is the measurement from the threaded screw which is required & used.

If someone wants to simulate the design, then he has to add to 58mm, the length from screw to the point of separation of coax. This lenght is inside base and is about 15~20 mm depending on individual make of the mag mount whip.

Just to complete the records, I have now measured the lengths in my mag-mount base and marked these on the diagram below.

The dimensions may vary few mm in mag-mounts from different manufacturers/suppliers.

 

mag-mount base

Yep - understand.

Is the 30mm gap a random length or have you played with the dimension to optermise it?

I started with 10mm, increased in steps of 5mm up to 30 mm (did not try other sizes of gap).

Conclusion: Bigger the gap, better the performance.

Another comparison between FA antenna & mag-mount with V-Stub

The two antennas are now in the same window at a distance of about 25cm with each other.

FA = FA 26" antenna + 60 cm RG 316 pigtail + FA light blue filter + FA ProStick Plus - Gain=48

V-Stub = Mag-mount base with V-Stub wire collinear + 3 meters RG174 coax + Radarbox24 FlightStick Green - Gain=49.6

FA

V-Stub

FA

V-Stub

FA

V-Stub

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Tweaked dimensions using simulation software followed by physical trimming. Got improved performance over original design of first post.

Compared V-Stub whip with 52mm optimized whip. Conducted test by swapping the two whips. No changes in any other Hardware/Software. Results below:

27-06-2020_62mm_Lower_Wire_aircraft-8h-R

27-06-2020_62mm_Lower_Wire_message_rate-8h-R

27-06-2020_62mm_Lower_Wire_range-8h-R

 

CLICK ON IMAGE TO SEE LARGER SIZE

 

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.

 

mag-mount base-b

MEASUREMENTS

SIMULATION RESULTS

V-Stub-62mm-lower-Radiation-Pattern

 

Simulation Results

 

4 Likes

Nice and neat built!

To tune the antenna to best receptiom/SWR, instead of cutting the wire, use a sliding piece of wire attached at top wire with a sleeve or tape. Once sweet point is found, solder the two wires in position.

V-Stub-curtko-3

 

CLICK ON IMAGE BELOW TO SEE LARGER SIZE

 

CLICK ON IMAGE BELOW TO SEE LARGER SIZE

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@abcd567 You said in the other thread…


…so I did.

I had to make a modification to the radials though. With 4 horizontal, I couldn’t get a good impedance match so I wound up using the 4-double arrangement and bending the radials UP almost like a co-linear. With that though…
image

I just started testing it next to my mutant spider so I’ll see how it does over the next day or so. So far it doesn’t look like it needs to be double filtered to reject all the RF crap around me. I’ll also test what effect rotating the “V” has on message rates and gain. It does have a slight effect on impedance as you might expect.

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It looks like a dead spider at the hand of Vlad The Impaler.

2 Likes

Available in kit form

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You guys are too funny!

Here’s a two hour comparison with my mutant spider.
Same RadarBox 1090 SDRs, no additional filter, same coax, etc.
Same dump1090-fa settings… gain 44.

The Mutant Spider:

The V-Lad (previously V-Stub):

They’re very close in terms of performance.

@abcd567 suggested I try with the radials back at horizontal which I just did just after I captured the above graphs. I’ll post the results in about an hour and a half.

2 Likes

Too bad there is no attributable gain between 44.5 and 48 since it appears your setup could use a touch more. Interesting results, keep them coming.

With the radials flat…

The Mutant Spider:

V-Lad:

I’d say they were identical (give or take a bit)

Looks slightly better with the radials the way you had them judging by the averages. That’s my interpretation anyhow. Can try one more side by side using your original radial position and 48 gain on the Mutant? (May be too much gain, but I’m curious…) - keep the watermark the same.

EDIT/ADD: If you have Virtual Radar Server setup, you can drag data from both setups at the same time and compare messages to go along with your graphs. It can help tell a good story. I love side-by-sides :+1:t2:

Oh, let me clarify. I didn’t touch the spider; I only flattened the V-Lad. I wanted to keep the spider stable as a reference.

Current Mutant Spider:
image

Current V-Lad:

The V-Lad improved with the radials flat vs the radials bent upward. I’ll run the VNA on it after lunch.

Ohh, OK, either way, the first Mutant Spider (very top graph) test appears to be showing the best result the way I see it - but it could have been the V-Lad adjustment flattening the curve since they were much more comparable on the bottom test - so flat radials on the V-Lad helped me thinks. I initially read it that you were adjusting the Mutant - so your watermarks are on the top graphs. I’m in the game now. LOL

Perfect time to toss a little more gain on one of them since they are so close to see how it changes things.

V-Lad appears to be showing ~1-2db more on your signal than the (Mutant) spider as well

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.

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%

 

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