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MT magazine UHF Satcom antenna project

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Alliance01TX

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#6
SATCOM Antenna (MT Article)

Howdy

It was indeed a great article in the MT magazine and someone can perhaps post the Bill of Materials (BOM) for you as well...much less expensive than buying a Mil-Spec X-Wing Antenna and suspect the performance is close to the commercial units.

The antenna (if built to spec) would be Omni and RHCP (Right Hand Circular Polarity) if you are generally wanting to pick UHF Mil-SAT Comm's in the ~ 255. MHz range.

I would also hope the MT author can tackle a like project for an "Egg Beater" antenna for the 137. MHz Weather Sat too, as his explanations / approach are very straight forward and simple, versus some other designs (drawings) we have seen...

Let us know how the build goes.....

Thx

Bill
 

mancow

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#7
Would someone be gracious enough to send me a scan of it? I would go buy it but I don't see where you can purchase back copies from them.
 
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#8
Steve,
Did you use the same dimensions in the MT article for your driven elements or calculate new ones? The reason I'm asking is the MT article dipole elements sit about 1/2 wavelength above the reflector and have no directors. The element dimensions and phasing harness are a compromise to get everything to play nice.

The impedance in that case is about 75 ohms compared to the typical spacing in a Trivec-Avant or D&M satcom antenna where the driven element sits about 1/4 wavelength from the reflector and director and the impedance is closer to 50 ohms and probably lower. The element dimensions and phasing harness for a Trivec or D&M style antenna will be much different from the MT article.
prcguy



Both articles helped immeasurably in building my own SATCOM antenna. Great articles!
 

mancow

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#9
I just finished the MT article's design this evening and it kicks ass!

It is actually out performing my Dorne and Margolin DMC-120 (non extended element model)

It's just sitting on 4' x 4' of window screen on the floor right now. I will probably staple the screen to a light frame or maybe directly to the attic floor.




 
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#14
Thanks prcguy, just got it built. Havent tested it yet though, although I did snag some sat communications with the AT-197 discone today while I was at school, come to find out it was on AM instead of FM... gotta go fix that, so I didn't hear anything really.
 
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#16
Will do. I haven't built the reflector. But, while I was testing it on the 2 ARTCC's I get near my house, I was getting about the same as my AT-197, and at times, a little better when pointed towards the right direction. So should I not do the reflector?
 
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#17
It must have the reflector to give the proper upward lobe for sat reception. The polarity will also be wrong, UHF milsats are Right Hand Circular Polarity downlink and the antenna design is Left Hand Circular Polarity without the reflector. Circular polarity reverses with the signal bounce off the reflector.

The antenna is not really designed for terrestrial reception but it will resonate in the 240-270MHz range and mostly horizontal polarity off the sides without the reflector.
prcguy

Will do. I haven't built the reflector. But, while I was testing it on the 2 ARTCC's I get near my house, I was getting about the same as my AT-197, and at times, a little better when pointed towards the right direction. So should I not do the reflector?
 
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#18
Ok, I figured it had to do with the circular pattern. I will build it later today, and then get it up.

Thanks, and I will post some pics when I get home from school later today.
 
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#19
Going to wait until tomorrow to get the screen up. Gotta go get the staple gun from my grandmas. I will get the final picture up next to the fireplace away from all the other antennas on the roof some time later in the week.

I could not find the connectors that had the skinny end like Manacow, but these worked almost just as well. Had to use the good lead solder to get it to solder to the screw, instead of using another connector. My dad trimmed the wire before we figured out we should of stuck another one on the screw like the other two. Anyway, it still works, just as well I guess.

I had to do the same thing Manacow did with the cap, I just used PVC.. I dont know why they wanted to use ABS. I also am gonna cammo it with spraypaint when I get it up.

And does the pipe have to be 18" since the top connector is about 2" longer than what it should be? Also, I have to get one more bottom cap to get it on the roof. I swear the roof is going to collapse one day with all the antennas I have on it :) Also, I used 1/8" instead of 1/16" wide, still works just as good as the AT-197 when pointed perfectly, and the AT-197 gets some gain off the preamp, not much though, and that was on ARTCC's.
 

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#20
You should duplicate the elements, element spacing, connector placement and wires to the elements, coax phasing harness length and height above the screen exactally as the instructions.

ABS pipe was my first choice since it was on hand but the PVC looks like a good alternative, I always welcome upgrades, mods and suggestions.
prcguy
 
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