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

So now it’s V-Lad vs Big Green Stick (FA 1090)…
Equivalent cables, radios, connectors, dump1090 settings, etc. Optimal gain was 44db for both antennas.

V-Lad:
image

Big Green Stick:
image

It’s V-Lad FTW!

DISCLAIMER: Once again, these results shouldn’t imply that there’s anything wrong with the FA 1090 antenna. It does imply that @abcd567 is very good. :slight_smile:

2 Likes

Wow! The V-Lad blows the FA antenna away for your location. Not even close judging by the above. Thanks for running that comparison. Goes to show how location changes everything.

The FA antenna seems to be susceptible to some forms of interference.
Curious if a filter would reduce the difference.

The radios already have a 1090 filter built in (after the amp but I can’t confirm) but I tried adding a RadarBox 1090 filter to the FA antenna but the results only got worse, even when I bumped the gain up by a few db to compensate for the insertion loss.

Hmm, i’d say either the filter is crap or there is something else wrong with your FA antenna.
I wouldn’t expect that much of a performance difference even to the DPD antenna, but really we don’t have good test data.

Might also be that you just got a bad apple, that would suck.

 

Here is scan result for Radarbox24’s 1090 MHz filter

I can sweep the standalone filters later this afternoon but also remember, I’m in a very high out-of-band RF signal environment with FM and TV transmitters nearby.

Oops, just saw @abcd567’s post. I want to sweep the filters down in the 88-248MHz range.

The coiled antenna in this simulation is similar (but not same) as Flightaware antenna. However the off-frequency behaviour should be similar.

1 Like

CLICK ON IMAGE TO SEE LARGER SIZE

https://www.nasa.gov/sites/default/files/thumbnails/image/january_2016_spectrum_wall_chart.jpg

That chart is on my wall. :slight_smile: The TV transmitters near me are all VHF-HI in that 174-216 block.

1 Like

Is this a random ebay antenna design or are the dimensions from a specific, single frequency 1090 MHz antenna?

An antenna of this design is often a half wave over quarter wave design or sometimes a 5/8 over 1/4 wave.

What design and frequency is this antenna?

This antenna is tuned for 438MHz and works well but is completely useless at 146MHz.

1 Like

No, it is NOT an ebay antenna. It is a single frequency (1090 MHz) antenna designed by me. Plese see design frequency marked in the simulation output below. The dimensions are in the in red rectangle on left of this screenshot:

Click on the image to see larger size
Click again to see full size

Thanks for that.

In terms of wavelengths, what is the design length of the Lower Vertical and Upper Vertical wires?

S.

Please see the screenshot in my post above (on image, single click twice to see full size).

On the screenshot, the dimensions in mm are given as below:
image

Calculating in terms of wavelength:
Lower wire = 36 mm = 36/275 Wavelength = 0.13 Wavelength
Upper Wire = 196 mm = 196/275 Wavelengt = 0.71 Wavelength

ummm … why?
How did you come up with those dimensions?
Is there any mathematical theory that lead you to believe the 0.13λ is a useful antenna?

Why not?
These dimensions gave me a SWR < 1.5 and Gain = 4.17. Please see simulation results in the screenshot posted two posts above.

No theory, only by trial and error.
Ran simulation sweep function to plot swr vs length and gain vs length to arrive at these dimensions.

Obviously if it doesn’t perform, it’s not interesting.
I’ve done enough computer simulations (CFD, FEI +) to know you need to validate your simulations.

If you build it and it works - then I’ll be impressed.

See @gtj0 posts and results above. His build of this model performed admirably for his location to say the least. His test methodology was sound - side by side tests. I usually take simulations with a grain of salt myself, but the real-world results shown above are tough to argue with. It doesn’t matter if someone uses a hubcap on a stick so long as it works…

I never presented the “Whip with Coil & Decoupling Sleeve” simulation and sweep results as a design intended to be built.

This simulation model was prepared exclusively to perform a very wide frequency sweep through computer simulation to see how such designs respond to various frequencies, as the title of that thread said, and that is the basic point you have missed:

Off Designed-Frequency Behavior of 2 Types of Antennas

Frequency Sweep (From 100 MHz to 2500 MHz) of Wire Collinear Antenna and 1/4 Wavelength Ground Plane Antenna.

Hi, what length of bottom V-Stub segment supposed to be if I want to connect it directly to coax and not Mag Mount? 62mm (as in post #4 diagram) or 62+20 (if counting base of Mag Mount)? Does it matter if it made from steel or copper wire?