MT magazine UHF Satcom antenna project

[prcguy]

The junction of the four elements will get closer together, which is probably not a big deal and you will have to move the element hole pattern in 1mm from the edge of the elements to match the pattern on the pipe cap.

I would be more concerned with the resonant frequency of the dipoles being too low due to the wider and thicker elements. If you have access to an antenna analyzer you could build everything to spec then trim the element lengths to resonate around 257MHz.
prcguy

Hi, I am going to attempt to build this antenna. The main satcom sat here in Australia is the optus c1 which is a 45 degree look angle which should be great with this antenna.
I found some flat alum at work but its 40mm wide, which is just 2mm over one and a half inch. Would this screw everything up?? I could sand it down i suppose. Its also 1/8th an inch thick which should be all-right.

Cannot get the Tee adapter from anywhere here might have to get it from us.

 

[strandbiker1]

Mike:

I obtained temporary use of an AEA 140-525 antenna analyzer. I used it already to take care of the return loss/ VSWr on a double rhombic antenna I made which works great. I got the VSWR down to 1.07. Tomorrow, I will check the X wing to see how it works. Question, the AEA is only a 50 ohm instrument. I know we used your analyzer up to 261 MHz. This AEA can do auto produce VSWR graphs. Should I keep the 75 ohm RHCP cable attached when measuring the VSWR, as the connecting cable is obviously 50 ohm? This instrument makes things a lot easier to deal with.


Thanks,


Skip

 

[prcguy]

My X-wing is intended to feed 50ohm coax so check the complete antenna over the ground screen as it would feed your radio. If your antenna resonates too low in frequency due to fatter or wider material, trim all four elements keeping them the same length.

The phasing harness dimensions were tweaked with 75ohm loads at the antenna ends to simulate dipoles 1/2 wavelength above ground and a 50ohm Vector Network Analyzer at the common output of the T adapter.
prcguy

Mike:

I obtained temporary use of an AEA 140-525 antenna analyzer. I used it already to take care of the return loss/ VSWr on a double rhombic antenna I made which works great. I got the VSWR down to 1.07. Tomorrow, I will check the X wing to see how it works. Question, the AEA is only a 50 ohm instrument. I know we used your analyzer up to 261 MHz. This AEA can do auto produce VSWR graphs. Should I keep the 75 ohm RHCP cable attached when measuring the VSWR, as the connecting cable is obviously 50 ohm? This instrument makes things a lot easier to deal with.


Thanks,


Skip

 

[prcguy]

I'm overstocked on military satcom antennas and decided to sell one of my Trivec-Avant AV2040 portable fold out antennas featured in the MT magazine article.

The price on these has skyrocketed in the last few years and they usually fetch $400 and up and I'll offer to RR members first for $250. PM me for more info.
prcguy

 

[Rick_bh]

Hi,

you make this antenna to sell?

Thanks

Rick

 

[prcguy]

No, but I'll help you make one.
prcguy

Hi,

you make this antenna to sell?

Thanks

Rick

 

[danibin]

uhf satcom

what is the current status of UHF SATCOM?

 

[K5MPH]

It would be great to see some photos of all these antennas that were home made......

 

[kb1qzh]

I need to get off my rear
I just have to wire mine and cut to the correct height.
It's mounted to a 3 magnet mag mount
I just have the harness and element wiring

 

[krokus]

Here ya go.
prcguy

I just d/l'd the files, and it seems part 1 might have lost some pages. Anyone concur?

Sent via Tapatalk

 

[prcguy]

Its all there, a pdf can't loose any pages.
prcguy

I just d/l'd the files, and it seems part 1 might have lost some pages. Anyone concur?

Sent via Tapatalk

 

[krokus]

Its all there, a pdf can't loose any pages.
prcguy

I thought the disconnected text was odd, but figured some pages got munched in a file corruption. It looks like, during my quick check of the text, I missed how the text was laid out, and thought something was missing. (I didn't see the text of the article stopped before the materials list.)

Sent via Tapatalk

 

[alpha_bravo]

x-wing build

Love this antenna setup and plan on making one next week! I wanted to adjust it with folding elements, and add reflector elements that can be folded in as well. What is the best way to figure out the spacing of reflector elements? If i add those would it completely mess up the performance?

 

[prcguy]

You could make the main elements folding and it already has a reflector, do you mean add director elements in front of the existing elements?

This antenna is different than a conventional UHF satcom antenna in that most are a type of Yagi or log periodic with maximum gain in the direction of the boom and you point it at the satellite of interest. This X wing is designed to sit on the ground and have a null in the direction of the boom pointing straight up and it has an omni directional Right Hand Circular Polarity main lobe that covers from about 20deg off the horizon to about 60deg. This is where you will find most of the UHF satellites from anywhere in the Continental US or similar Latitude above or below the equator.

Adding directors would not be beneficial and I recommend the 48" square reflector but something smaller like 24" across may work just fine. I would have to dig up the old EZNEC files and run the program again to find out, which is unlikely.

The antenna was laid out to be easily duplicated (in my opinion) and its best left as is and built exactly as shown to ensure it works the same as the two prototypes made for the article.
prcguy

Love this antenna setup and plan on making one next week! I wanted to adjust it with folding elements, and add reflector elements that can be folded in as well. What is the best way to figure out the spacing of reflector elements? If i add those would it completely mess up the performance?

 

[alpha_bravo]

Yeah I agree on keeping it within exact specs and plan on it for the 1st build. Regarding the reflector elements, I was more referring to something like this in the attached photo. For my humvee's I was thinking of putting this setup on a small tripod, so I could bring it around with me camping, etc.

Although this antenna sits flat above the ground reflector, I was just curious if putting a reflector setup like the photo would decrease performance. Clearly my humvee's would be a great reflector on the truck roof, It would be nice to have a 2nd antenna in a compact fold-able unit that works as good.

On the 48" x 48" ground screen... what happens if it was only 24" x 24", does it cut the performance in half or more for this particular setup?

 

[alpha_bravo]

Scratch the question about the 48" screen size, since you answered that.

 

[prcguy]

The antenna you show is a pair of half wave dipoles over a ground plane that's a little bigger than 1/2 wavelength across at the lowest operating frequency and the signal is sent or received in line with the boom. The MT X-wing sends or receives upward and sideways, so without more analysis my opinion is the ground plane should be larger than what's needed for your type of antenna.

The MT X-wing is not something you would normally put on a tilting tripod since it doesn't really need to tilt unless your trying to receive something down near the horizon. The antenna you show needs to be pointed in the general direction of the satellite, although it has a very broad pattern over 45deg wide.

Here is a thread of someone comparing the X wing on the ground with and without a ground screen showing the large reflective ground plane is at least better than the dirt under it: http://forums.radioreference.com/sa...-ground-plane-make-x-wing-heres-how-much.html

There are two ways to see if you can get away with a smaller ground plane, one is to model the antenna with different size ground planes and the other is to build one and measure performance with different size ground planes. How about building one and doing some tests to see how small the ground plane can get before performance goes down?

Since the roof of a HUMVEE is steel you would love the look of my commercial Trivec-Avant mag mount X-wing sitting on the roof as you drive down the highway. Here is a pic of one on my wifees car: http://forums.radioreference.com/sa...orum/217635-mobile-milcom-milsat-antenna.html

The problem with these antennas is the pattern is about 45deg straight up and in many locations there is no UHF satellite straight above you.
prcguy

Yeah I agree on keeping it within exact specs and plan on it for the 1st build. Regarding the reflector elements, I was more referring to something like this in the attached photo. For my humvee's I was thinking of putting this setup on a small tripod, so I could bring it around with me camping, etc.

Although this antenna sits flat above the ground reflector, I was just curious if putting a reflector setup like the photo would decrease performance. Clearly my humvee's would be a great reflector on the truck roof, It would be nice to have a 2nd antenna in a compact fold-able unit that works as good.

On the 48" x 48" ground screen... what happens if it was only 24" x 24", does it cut the performance in half or more for this particular setup?

 

[alpha_bravo]

"The MT X-wing is not something you would normally put on a tilting tripod since it doesn't really need to tilt unless your trying to receive something down near the horizon."

Correct, I wasn't planning on tilting it. Love the Trivec on your wife's car, lol. I bet you get a few odd looks having that on there. Making some tests sounds like fun to me, and I found a thread that was posted discussing the signal differences with a 48x48 vs 48x36 ground plane. That with your thread were helpful in visualizing it.

The first one I make will have the magnetic mount to stick on the humvee, like on your car. Can't wait to get it done, and will experiment the screen size as well.

 

[reconrider8]

Does anyone care to build one of these for me? I would pay for everything as parts and shipping and would throw a nice part to you also lol. I just don't think I can build one of these with my skills