How much difference does the ground plane make on an X-Wing. Here's how much

[rbm]

I've used my X-Wing antenna for a few years and it performs quite well considering the cost.

But, I don't leave it set up constantly.
Whenever I want to use it, I drag out the ground plane and place the antenna in the center of it. On the ground.

The other day (while I was dragging it out yet again) I was wondering how much difference a smaller ground plane would make. Or even better, NO ground plane at all.

So, I captured a screenshot with and without the ground plane.
Some things to keep in mind.
My X-Wing sits right on the ground, or very close to it.
I have an LNA-580 low noise preamp mounted inside the PVC base of the antenna.
If you aren't using a preamp, you'll need to crank up the RF gain in SDRSharp by around 15 dB to come close to the same signal levels.
I used SDRSharp to capture the images just a few minutes apart.
Nothing at all was changed except for the ground plane.

So, if you ever thought about building an X-Wing but were put off by the big ground plane, you may want to rethink that.

Rich

X-Wing WITH the ground plane:



X-Wing with NO ground plane.

 

[rbm]

With and without the ground plane.

With:



Without:

 

[prcguy]

I honestly never tried the antenna on the ground with no screen during development but placing it on the "dirt" ground should provide some reasonable reflection back to the elements and produce the desired pattern. The prototypes used an aluminum patio table about 48" dia for the ground plane.

The published design has the elements about 1/2 wavelength above the screen and if you elevate the antenna slowly off the ground or screen the pattern should change from upward lobes with a null overhead, to one main lobe at 3/4 wavelength up, then back to a null overhead at 1 wavelength high, etc. Problem is the feedpoint impedance and element length and phasing harness are all optimized for the specific 1/2 wavelength height above a screen.
prcguy

I've used my X-Wing antenna for a few years and it performs quite well considering the cost.
H
But, I don't leave it set up constantly.
Whenever I want to use it, I drag out the ground plane and place the antenna in the center of it. On the ground.

The other day (while I was dragging it out yet again) I was wondering how much difference a smaller ground plane would make. Or even better, NO ground plane at all.

So, I captured a screenshot with and without the ground plane.
Some things to keep in mind.
My X-Wing sits right on the ground, or very close to it.
I have an LNA-580 low noise preamp mounted inside the PVC base of the antenna.
If you aren't using a preamp, you'll need to crank up the RF gain in SDRSharp by around 15 dB to come close to the same signal levels.
I used SDRSharp to capture the images just a few minutes apart.
Nothing at all was changed except for the ground plane.

So, if you ever thought about building an X-Wing but were put off by the big ground plane, you may want to rethink that.

Rich

X-Wing WITH the ground plane:



X-Wing with NO ground plane.

 

[rbm]

I honestly never tried the antenna on the ground with no screen during development but placing it on the "dirt" ground should provide some reasonable reflection back to the elements and produce the desired pattern. The prototypes used an aluminum patio table about 48" dia for the ground plane.

The published design has the elements about 1/2 wavelength above the screen and if you elevate the antenna slowly off the ground or screen the pattern should change from upward lobes with a null overhead, to one main lobe at 3/4 wavelength up, then back to a null overhead at 1 wavelength high, etc. Problem is the feedpoint impedance and element length and phasing harness are all optimized for the specific 1/2 wavelength height above a screen.
prcguy

prcguy
I've been impressed not only with the X-Wing performance, but also the low cost and ease of construction.

Rich

 

[ab5r]

X-Wing Antenna Elements

Interesting facts about with or without a ground plane.

I'm wondering why the 1 1/2" width of the elements? It seems to be the standard with both professional and homemade X-wing. But, wished someone would explain why the flat vs, a wire of proper length?????


Regards,
Jerry

 

[prcguy]

The X-wing project element widths were chosen for several reasons. Its similar to the dimensions of commercially made satcom antennas, its wide enough for reasonable band width and 1.5" wide aluminum is available at Home Depot, Lowes, etc. The latter is most important for a successful and repeatable project.

The UHF satcom receive band is about 245 to 270MHz, or 25MHz wide. A thin wire would not have the bandwidth to provide a good match across the entire band and that would affect the ideal 45deg phase shift of the phasing harness, so something wider or fatter is needed. 3/4" copper pipe would have been good but it would complicate the construction, unless you got some 5 sided PVC pipe unions, which will make a spiffy antenna but their not available in every neighborhood. You can design a great antenna but if people can't get the exact components to make it and substitute parts, then you have lost the repeatability.

The MT X-wing project like many progressed in several steps. The inception, which came about when I acquired a commercial/military mag mount X-wing from Trivec-Avant and noticed it's upward pattern was not that great for my location, being straight up and about 90deg wide leaving out satellites closer to the horizon. Being in the satellite industry I knew the general look angles for most satellites from the Continental US is about 20 to 60deg off the horizon and not straight up and there had to be a better design.

With some help from my good friend and brilliant antenna mentor Bart WB6HQK (now SK) we found the ideal height above a ground plane for the main lobe to favor the 20 to 60deg elevation with the antenna sitting flat and stationary. Basically it will pick up most any useable UHF satellite in the US without having to point it. The MT X-wing has a null straight overhead and that's a problem if you live in Hawaii or Brazil but fine for the US and much of Europe, Australia and other locations with similar latitude above/below the equator.

Then came the prototyping and measurements to determine the best element lengths, impedance (which was a problem) and the phasing harness. I logged many hours on a vector network analyzer with the phasing harness design finding the best compromise for a 45deg phase shift between dipoles while feeding a not so ideal match using common Home Depot grade RG-6 coax.

Then I had to make a couple more antennas to make sure the design was repeatable, which it was. The end result was a home made antenna that doesn't need pointing that works better than a $7,000+ Trivec-Avant X-wing. Any more questions?
prcguy

Interesting facts about with or without a ground plane.

I'm wondering why the 1 1/2" width of the elements? It seems to be the standard with both professional and homemade X-wing. But, wished someone would explain why the flat vs, a wire of proper length?????


Regards,
Jerry

 

[ab5r]

Excellent Excellent reply. Thank You. I was curious about laying flat too, but you answered that question.

Regards,
Jerry

 

[prcguy]

I think the antenna will work the same if the elements were turned 90deg, but that would take the element mounting in a completely different direction. I suppose the "boom" could have been made from some 1" X 1" hardwood with the elements screwed to the sides of one end leaving them turned 90deg from the current design.

My head is starting to hurt just thinking of any changes to the design but feel free to experiment. I think Monitoring Times magazine got their monies worth on that article considering the hours spent in research, testing and all the supplies that were purchased.
prcguy

BTW, I was just up the road from ab5r in Richardson for the last 2 weeks. Boy it gets hot and humid there!

Excellent Excellent reply. Thank You. I was curious about laying flat too, but you answered that question.

Regards,
Jerry

 

[prcguy]

I just noticed there is now a UHF satcom antenna offered in the RR classified section!
prcguy

 

[ab5r]

I take you and Rich words as LAW, believe me! Humid? Come back in July.
73,
Jerry