MT magazine UHF Satcom antenna project
- Thread starter prcguy
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It would be common for US military is SE Asia to communicate back to the US via the UHF satellite over the Pacific and the 172E orbital slot would leave you with an antenna pointing angle under 10 degrees above the horizon. Not an ideal situation.
If you actually had a top secret clearance you would know your not supposed to disclose it to anyone who does not have the need to know.
BTW, I have the clearance just above a double double dog, your momma don't even know, tippie toe top secret.......
prcguy
If you actually had a top secret clearance you would know your not supposed to disclose it to anyone who does not have the need to know.
BTW, I have the clearance just above a double double dog, your momma don't even know, tippie toe top secret.......
prcguy
Hey Prcguy.
Thanks for uploading the instructions.. I printed them out and am slowly gathering the required stuff. The 3 way F T piece was the hardest to find. I also invested (!) in some moistureproof milspec F connectors too... Luckily I have some RG-6 here.
Right, my question is... Do I really need the 48x48" reflector?
Can I get away with having something more akin to the professionally made UHF-satcom antennas?
I'm struggling for space and was going to go for the skeleton look.
Thanks for uploading the instructions.. I printed them out and am slowly gathering the required stuff. The 3 way F T piece was the hardest to find. I also invested (!) in some moistureproof milspec F connectors too... Luckily I have some RG-6 here.
Right, my question is... Do I really need the 48x48" reflector?
Can I get away with having something more akin to the professionally made UHF-satcom antennas?
I'm struggling for space and was going to go for the skeleton look.
CalebATC
Member
Yes, you have to have the ground plane.
The antenna is kinda "backwards" with it's lobes, they are reflector for making the lobes back towards the horizon.
The professional UHF satcom antenna this is based of does have a reflector; the wire mesh on the stand, or the car metal on the car mount version.
Best thing I did was put the antenna on the metal roof and put some screws in. Not only does it look better, but it has no change in performance.
Out of curiosity, what are milspec F connectors? I'd like to see a picture of those. Kinda like a oxymoron
The antenna is kinda "backwards" with it's lobes, they are reflector for making the lobes back towards the horizon.
The professional UHF satcom antenna this is based of does have a reflector; the wire mesh on the stand, or the car metal on the car mount version.
Best thing I did was put the antenna on the metal roof and put some screws in. Not only does it look better, but it has no change in performance.
Out of curiosity, what are milspec F connectors? I'd like to see a picture of those. Kinda like a oxymoron
Out of curiosity, what are milspec F connectors? I'd like to see a picture of those. Kinda like a oxymoron
Yeah, I know the feeling... that's why I mentioned them!
CRIMP 'F' Connector (MIL) Moistureproof
I had plenty of F's in stock, but nothing for RG-6.
I know the antenna needs the ground plane, I just thought I could 'get away' with something aside from the massive 48x48 sheet of screen.
CalebATC
Member
Doesn't look too moisture proof for me I'd prefer a N connector!
If your able, try to do the roof mount. That worked pretty good for me.
And that's if it is a metal roof!
I'd prefer a N connector! If your able, try to do the roof mount. That worked pretty good for me.
And that's if it is a metal roof!
Sure I have a metal roof on the car, but the house has concrete roofing tiles on there
I will wait for Prcguy to come back with some definitive information on the ground plane - where I intend to mount the antenna doesn't realllllly have enough room for a 48x48 sheet of screen Hence my question.
I will wait for Prcguy to come back with some definitive information on the ground plane - where I intend to mount the antenna doesn't realllllly have enough room for a 48x48 sheet of screen
Hence my question.
I would need to analyze my antenna files again to see how small you could go on the ground plane before degradation would be noticeable. Might be awhile before I can get to that.
The tactical satcom antennas with mini umbrella reflectors you see on TV or in magazines hooked to a manpack transceiver are a more of a conventional cross Yagi type and a reflector around 1/2 wavelength across (about 20-24") is appropriate.
The X-wing sits higher above the ground plane and is intended to look more sideways and we put a larger ground plane under it to give the best performance.
If you have a means to measure signal strength you could make one with the specified size reflector then try with something smaller butt not less than 24". If you live in a region where you can pickup more than one orbital slot it would be good to try the smaller reflector on both slots to make sure the pattern doesn't drop off at some needed low angle, etc.
prcguy
The tactical satcom antennas with mini umbrella reflectors you see on TV or in magazines hooked to a manpack transceiver are a more of a conventional cross Yagi type and a reflector around 1/2 wavelength across (about 20-24") is appropriate.
The X-wing sits higher above the ground plane and is intended to look more sideways and we put a larger ground plane under it to give the best performance.
If you have a means to measure signal strength you could make one with the specified size reflector then try with something smaller butt not less than 24". If you live in a region where you can pickup more than one orbital slot it would be good to try the smaller reflector on both slots to make sure the pattern doesn't drop off at some needed low angle, etc.
prcguy
Sure I have a metal roof on the car, but the house has concrete roofing tiles on there
I will wait for Prcguy to come back with some definitive information on the ground plane - where I intend to mount the antenna doesn't realllllly have enough room for a 48x48 sheet of screen
Alright, thanks I will give it a try. I am 53N 002W or so (about middle of the UK) and I hear the midatlantic birds fine as well as the ones over Africa (SICRAL etc.).
I have a very basic 3 ele Yagi that I made up, and when I say basic its basic in the extreme. But it works and has some directivity, but I'd like something that I can hear the FLTSATCOM birds on as well as the 'african' ones.
SICRAL / SKYNET carry some of the more interesting traffic from time to time, and no pirates (Yet, knock on wood).
I'll probably be using 1/8th inch aluminium (sic) for my x-wing because its available, but I see in the notes it can be used.
I'll get enough chicken wire to make a 48x48 reflector and enough to make a half sized one too and test them out - if you can get the computer to re-analyse the files that would be great, but don't put yourself out on my account I just want to improve on my antenna system - its a disease I have - I am never happy and always think I can squeeze an extra s-point or 3.
I use a PCR-1000 + talkPCR which uses the 'calibrated' dBm signal meter, which i use to compare sats/antennas, and its fairly good iirc.
Thanks in advance, and for doing the original designing. I'm in awe of antenna designers... mine is mostly guesswork
I have a very basic 3 ele Yagi that I made up, and when I say basic its basic in the extreme. But it works and has some directivity, but I'd like something that I can hear the FLTSATCOM birds on as well as the 'african' ones.
SICRAL / SKYNET carry some of the more interesting traffic from time to time, and no pirates (Yet, knock on wood).
I'll probably be using 1/8th inch aluminium (sic) for my x-wing because its available, but I see in the notes it can be used.
I'll get enough chicken wire to make a 48x48 reflector and enough to make a half sized one too and test them out - if you can get the computer to re-analyse the files that would be great, but don't put yourself out on my account
I just want to improve on my antenna system - its a disease I have - I am never happy and always think I can squeeze an extra s-point or 3.I use a PCR-1000 + talkPCR which uses the 'calibrated' dBm signal meter, which i use to compare sats/antennas, and its fairly good iirc.
Thanks in advance, and for doing the original designing. I'm in awe of antenna designers... mine is mostly guesswork
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SO, update. I built the thing, to spec, as far as I could.
The tee-piece adapter hasn't arrived and I got impatient. So I soldered the braid together of the phasing harness and then the centre conductors. I then soldered a random length of RG-58 to the result of this. Which is basically what the T adapter does, I assume...?
Couple of questions for prcguy: WIll things improve when I actually fit the tee-piece to this thing? Also, should the groundplane be insulated from the 'earthy' side of the antenna? At the moment my GP is an old PC case with a hole drilled to fit an SO-239 socket through it, which is clamped to the PVC pipe with a PL-259 plug. (thus holding the ground plane onto the bottom of my PVC pipe, but also grounding the GP to the earthy side of the coax).
Hope all that makes sense.
The tee-piece adapter hasn't arrived and I got impatient. So I soldered the braid together of the phasing harness and then the centre conductors. I then soldered a random length of RG-58 to the result of this. Which is basically what the T adapter does, I assume...?
Couple of questions for prcguy: WIll things improve when I actually fit the tee-piece to this thing? Also, should the groundplane be insulated from the 'earthy' side of the antenna? At the moment my GP is an old PC case with a hole drilled to fit an SO-239 socket through it, which is clamped to the PVC pipe with a PL-259 plug. (thus holding the ground plane onto the bottom of my PVC pipe, but also grounding the GP to the earthy side of the coax).
Hope all that makes sense.
Soldering the coax together accomplishes the same task as the T adapter but in this case the length of the RG-6 lines were tweaked for a perfect 90deg phase shift between dipoles including the internal length of the T adapter. The harness sweet spot would be shifted up a little in frequency and you'll eat up some of the fudge factor budget that allows a few minor mistakes before the antenna becomes nothing more than a sock drier or bird perch.
Its also difficult to solder most RG-6 due to the sparse braid and you want to keep the exposed center conductors very short, like about 3mm or less.
The ground screen does not have to be connected electrically to the antenna and I'm looking at a medium large computer case which is about 14 X 16" and I think too small to be an effective ground plane for this antenna.
The completed antenna is Right Hand Circular Polarity but the dipoles and phasing harness create a Left Hand Circular Pol antenna (in free space) without the ground screen because circular polarity reverses with a reflection. If the ground screen is too small the antenna may not become RHCP, the pattern may shift to something that points the wrong direction and satellite reception will really suffer.
Sit the antenna dipoles and mast on a car hood or something large and metallic to verify its put together correctly and picks up stuff then substitute your smaller ground plane and see what you get.
prcguy
Its also difficult to solder most RG-6 due to the sparse braid and you want to keep the exposed center conductors very short, like about 3mm or less.
The ground screen does not have to be connected electrically to the antenna and I'm looking at a medium large computer case which is about 14 X 16" and I think too small to be an effective ground plane for this antenna.
The completed antenna is Right Hand Circular Polarity but the dipoles and phasing harness create a Left Hand Circular Pol antenna (in free space) without the ground screen because circular polarity reverses with a reflection. If the ground screen is too small the antenna may not become RHCP, the pattern may shift to something that points the wrong direction and satellite reception will really suffer.
Sit the antenna dipoles and mast on a car hood or something large and metallic to verify its put together correctly and picks up stuff then substitute your smaller ground plane and see what you get.
prcguy
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Thanks. I think I verified this myself earlier. Held it above the car's roof and signals were pretty strong, but without it / just the PC case very weak and almost not worth it.
I will wait until I have the Tee-piece and something to make a bigger reflector - I tried with some chickenwire I had here but again it did nothing for the signals. It's not helping that the F connectors I _DO_ have aren't the right size for this RG-6 *roll eyes*.
This supplier I bought from needs to hurry up!
Wish the UK had RadioShack
I will wait until I have the Tee-piece and something to make a bigger reflector - I tried with some chickenwire I had here but again it did nothing for the signals. It's not helping that the F connectors I _DO_ have aren't the right size for this RG-6 *roll eyes*.
This supplier I bought from needs to hurry up!
Wish the UK had RadioShack
Finally got the required parts as specified by the PDF.
The dipole elements are exactly 19.9inches above the bottom end cap (ie: 20 inches above the groundplane).
When rested on the car roof, signals are pretty weak... if I hold it up about an inch or two the signal improves by 1 bar... if I tilt it the signal improves too. Not sure if rotating it has any effect yet because my fly lead is so short.
I'm at 53 degrees north, which maybe puts the AOR satellites just below 20 degrees...?
All the elements are within 1 mm of 10 inches (!). The phasing harness is exactly 13.5 inches and its all connected as per the PDF.
How will I know if I've got the wrong polarisation...? Will the signals be completely gone or just very faint. I'm assuming if I have it the wrong way round, the signals will be BETTER without the ground plane.
The dipole elements are exactly 19.9inches above the bottom end cap (ie: 20 inches above the groundplane).
When rested on the car roof, signals are pretty weak... if I hold it up about an inch or two the signal improves by 1 bar... if I tilt it the signal improves too. Not sure if rotating it has any effect yet because my fly lead is so short.
I'm at 53 degrees north, which maybe puts the AOR satellites just below 20 degrees...?
All the elements are within 1 mm of 10 inches (!). The phasing harness is exactly 13.5 inches and its all connected as per the PDF.
How will I know if I've got the wrong polarisation...? Will the signals be completely gone or just very faint. I'm assuming if I have it the wrong way round, the signals will be BETTER without the ground plane.
There should be a huge difference in signals if the phasing harness is reversed and the bigger the difference the better meaning the phasing harness and element tuning is right on.
Reversing the connectors at the dipoles will reverse the polarization.
The antenna will work better in free space or way above a ground plane if its reversed but not nearly as good as with the ground plane and correct polarization. The dipole distance above the ground plane determines the pattern and whatever the article dimensions are will give an upward lobe that favors around 20 to 6o deg above the horizon.
If you raise the elements slightly above the groundplane (if assembled per spec) it will lower the lobes a little but they already sit close to the lowest angle you are likely to get. Building the antenna per spec and tilting the antenna a little is probably better for your sub 20deg look angle.
prcguy
Reversing the connectors at the dipoles will reverse the polarization.
The antenna will work better in free space or way above a ground plane if its reversed but not nearly as good as with the ground plane and correct polarization. The dipole distance above the ground plane determines the pattern and whatever the article dimensions are will give an upward lobe that favors around 20 to 6o deg above the horizon.
If you raise the elements slightly above the groundplane (if assembled per spec) it will lower the lobes a little but they already sit close to the lowest angle you are likely to get. Building the antenna per spec and tilting the antenna a little is probably better for your sub 20deg look angle.
prcguy
Hello, I want to understand better how the coupling of dipoles on the x-wing, the net I found the "turnstile"which may be similar but the pair of dipoles is made of two coaxial lines in RG58 + 2 other lines in cable TV , basically: (1 / 2 +1 / 4 RG58) + (1 / 4 +1 / 4 TV coax).
Can't add extra elements to this one because it has a null straight up and the pattern is optimized to pick up 360deg omni directional looking at satellites from about 20 to 60deg above the horizon when the antenna is pointing straight up.
If you lowered the elements to about .2 or so wavelength above the reflector you would then have a main lobe straight up and could add extra elements Yagi style for more gain and a smaller reflector around 24" would be appropriate.
However, the element dimensions and phasing harness in the article are tuned specifically for a dipole height closer to about .5 wavelengths above the ground plane and will not work very well at a lower height, you would need to start from scratch for a directional version.
prcguy
If you lowered the elements to about .2 or so wavelength above the reflector you would then have a main lobe straight up and could add extra elements Yagi style for more gain and a smaller reflector around 24" would be appropriate.
However, the element dimensions and phasing harness in the article are tuned specifically for a dipole height closer to about .5 wavelengths above the ground plane and will not work very well at a lower height, you would need to start from scratch for a directional version.
prcguy
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The dipoles in the X-wing are turnstyle type and there are many ways to feed them for proper matching and in this case, creating Right Hand Circular Polarization.
It might be technically more accurate to use critical length 50 ohm phasing lines to delay one dipole 90degrees from the other and then use another set of critical length 75 ohm lines to match the two 50 ohm dipoles to a single 50 ohm feedline.
You can also just use 75 ohm cables for the phasing and matching and one dipole may not be matched perfectly but, but this antenna was designed for a magazine article and people have to be able to reproduce it without having an antenna lab in the garage.
Since the X-wing dipoles sit almost .5 wavelengths above a reflector they are not 50 ohms at resonance and probably closer to the 60-70 ohm range, so the dipole lengths and phasing lines were custom tuned and not quite text book dimensions.
prcguy
It might be technically more accurate to use critical length 50 ohm phasing lines to delay one dipole 90degrees from the other and then use another set of critical length 75 ohm lines to match the two 50 ohm dipoles to a single 50 ohm feedline.
You can also just use 75 ohm cables for the phasing and matching and one dipole may not be matched perfectly but, but this antenna was designed for a magazine article and people have to be able to reproduce it without having an antenna lab in the garage.
Since the X-wing dipoles sit almost .5 wavelengths above a reflector they are not 50 ohms at resonance and probably closer to the 60-70 ohm range, so the dipole lengths and phasing lines were custom tuned and not quite text book dimensions.
prcguy
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