Looking for Inmarsat antenna and preamp homebrew

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F1TJJ

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Apr 21, 2007
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Hi guys,

I've an AOR5000 and I want to set an Inmarsat A reception station.
I've designed the helical feed for dish from Paul J Marsh but can't find again the website..
Moreover I have no time to install the the 5.5" dish so I'd like to experience an easy homebrew. Maybe an helical antenna ?

I know that traffic on Inmarsat A is given to disappear in a near futur, but right now I'm sure we can still receive some stuffs...

Any recommendation on the topic highly appreciated.
Thanks
Stephane, F1TJJ
 

F1TJJ

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thanks for the information rbm

I had already seen this website. In fact, part of the old Paul J Marsh website has been moved there, but some pages have disappeared.. And unfortunately, the ones I need !

thanks again
Best
Stephane
 

jlh

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f1tjj, have you searched this forum for inmarsat posts? been a lot of threads about it in the past year. and you might get lucky, mr marsh has been known to browse this forum.
 

F1TJJ

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Thanks for your answer Paul,

If I remember well on the page you were describing the helical feed with non joined turns, there was also a description for an helical antenna. This is what I'd like to find again.

As said, I've built the feed you described but I have no really time to mount my dish so I was wondering if a simple helical would help me starting monitoring some sats...

Thanks
Stephane
 

Cobra_Commander

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xz said:
Stephane, let me know what pages you needed from the old 'pjm' website and I'll move them to the uhf-satcom.com.

All, we're usually online via IRC details at http://www.uhf-satcom.com/irc/ so stop by if you want to catch up or ask questions - there are generally a few guys around that are monitoring stuff.

cheers,

Paul
www.uhf-satcom.com
Hey paul i have a question for you do you have a teams peak server where i can go and hear live satcom feeds?
 

w8jjr

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I think I know what your talking about. Is it the one with the cooper tubing. I most likely have that one archived on dvd. If this is the one I'll take a good long look and with luck most likely find it.

Yes, still some good listening. I am using my 5000 in ssb mode working quite well.
Most users are those that cant upgrade due to cost... ect.
Those users and the best to listen too. ;)
 
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F1TJJ

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I would be interrested if you can find it...
Once QRV with L-band, I'm pretty sure I will discover some other sats to listen too with my AR5000
Thanks
Stephane
 

w8jjr

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w8jjr said:
I think I know what your talking about. Is it the one with the cooper tubing. I most likely have that one archived on dvd. If this is the one I'll take a good long look and with luck most likely find it.

Yes, still some good listening. I am using my 5000 in ssb mode working quite well.
Most users are those that cant upgrade due to cost... ect.
Those users and the best to listen too. ;)


Sorry, cant find that sucker. Went through 50 cd's, got another 50 to go. I'll keep looking. In the mean time it was in monitoring times a few years back in someone has back issues.
 

mancow

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I have an MTI fold out 4 foot dish from an old A band sat phone and a few preams. It worked great but I put it a away for a few months due to being busy with other things. When I drug it back out the other day the channels were silent. I only spent one evening trying to listen again but I'm thinking that they may have finally shut the A band analog stuff down.

When I first got into it about a year ago there were maybe 3 or 4 channels that were active. Only a very few carried voice traffic. Most sounded to be dialup digital or fax.

But, if you want to give it a try you can do so for a-lot less money than I invested. I built a helical using dimensions from Marsh's site as well as others. I would say it was about 50 to 60% as good as the dish. With a good preamp it was definitely enough to pull in the signals. I have a Down East Microwave preamp but I found the minikits 1500 Mhz kit preamp to work the best and it was only $30 or so.

I made my antenna from dowel rods and a slinky. The first was made from L bracket aluminum and some plexi standoffs but the metal center seemed to degrade the performance. I got a 3/4" dowel and drilled holes through it every inch. I inserted 3/8" (I think) dowels along it alternating back and forth every other side. I took a dremel and made angled notches in the ends. I then suspended the Slinky by placing each turn in one of the dowel grooves as I went along. The metal reflector was a 7" stainless steel range top burner cover from wal-mart for a few dollars. I drilled a hold in it and put a BNC bulk head connector then soldered that to the Slinky at the bottom. It's lightweight, strong, and seems to work fairly well.


I tried to find the closeup pics but I guess I deleted them.

This one shows the helical on the left in the background and the one on the right is the MTI dish I got from a member of the board here.

IMAG0001.jpg
 
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Location
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Mancow, that MTI dish is a real thing of beauty. I'd leave that set up in my radio room just to admire. Heck, I'd leave it set up in my living room but I'm weird like that.

Technical junk is the most wonderful junk in the world.
I've had more conversations go something like:

"Why on earth do want a <insert odd technical junk here> ?"

"Because! It's a <insert odd technical junk here>!"

They just don't get it.
 

k9rzz

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Milwaukee, WI
Well, I never thought I would do it, but I heard Inmarsat today!

I was goofing around with my 7 ft C band dish on the 255mhz satellite band when it struck me how I could make a 1.5ghz feed so easy, that I had to try it. I just stripped an inch and a half of RG6 back to make a 3 inch dipole and taped it right in front of the regular C band feed.

Initially I tried it through 100 ft of RG6 but I couldn't hear anything. So I chopped it down to about 12 feet, with the radio sitting on the truck of my car, using a cheap Walmart audio recorder to tape what I heard. (I have 15 second .wav files of what I heard, but Winzip isn't letting me zip them, and this forum doesn't accept .wav files ... so your loss ! )

1518593708_3fe9cdc01d.jpg


Initially I was on Inmarsat 2 at 98 west, but I'm shooting through some oak limbs that absolutely kill C band sat sigs (and that's why I don't use it much ... I need to move the dish soon).

1518593712_e78efe2cc6.jpg


So I swung around to Inmarsat 4 at 53 west and that was a little better. Sigs are still noisy , but without a pre-amp, I was very happy to hear them at all.

Here you can see my view over some bushes and the feed I used. I could just reach it and move it around for the best signal which turned out not to be centered after all.

1518593726_075be17785.jpg


I finally gave up when a lawn service across the street fired up their leaf blowers and I couldn't hear the radio anymore.

Knowing that the analog stuff is going away permanently, it would be nice to find some
decoding software that doesn't cost an arm and a leg.

smile.gif
 

mancow

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Was it analog FM voice traffic? ! ?

If so, I might drag my setup out again. Maybe I should mount the helical outside and give it another try.


Interesting...


BTW, build a small left hand three turn helical (reversed due to dish reflection). I bet your signal will multiply when using that huge dish. It's really simple. Heck you could use some old copper wire or even a bit of slinky like I did, just shorter for the dish feed.


Your tree problem is exactly like mine. My only option seems to be the corner of the house or on the house itself.
 

k9rzz

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That's a good idea. I'll try some wire to give me the circular polarization I need. With the dish low enough to the horzon that I can reach the feed, it would be simple to experiment with it.

Hmmmmm.

No analog heard today. If I do I will report it!

I finally got AOL to accept my files. As you can hear, it wasn't very loud, but I found it encouraging that at least I could hear it without a pre-amp.

http://hometown.aol.com/J999w/INMARSAT1.wav
http://hometown.aol.com/J999w/INMARSAT2.wav

I'll keep playing around with it.
 

oZscan

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Jul 11, 2007
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more pics.
 

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k9rzz

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Dec 12, 2005
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Milwaukee, WI
Nice craftsmanship! (wait until you see what I built)

I got out just after daylight and messed around a little, I was able to tweak the dish a little so now the best sig is 1 inch in front of the C band feed instead of 6 inches to the left. I also put some F connectors on my RG6 so I could play with different feeds.

This is the simple feed (a piece of RG58 stripped):

1523930855_e0811045c4.jpg


This is a Left hand circular polarized (LHCP) feed I slapped together on a piece of aluminum from a junked VCR (I got a big box of aluminum plates and pieces for just this reason):

1523930895_33c6c70117.jpg


It was longer, but as I manipulated the dimensions to tweak the response, I also trimmed it down:

1523930905_9d0b35fafc.jpg


The simple feed was just slightly better than the best I could get out of my LHCP. Equally as good or equally as bad?

I can hear just about every channel on Inmarsat 4 (53w) which is all data of one form or another. I did swing the antenna down to the horizon and to my surprise, I can actually hear Inmarsat 3 at 15w ! It is weaker though (no surprise).

1523930963_60802a87cd.jpg


You can see that I'm right on my horizon to hear this one (I'm in Milwaukee, WI), you folks on the east coast or Europe can hit it easy I'm sure. Yes the dish is mounted on an old tree trunk and you can see my radio sitting on a chair with the headphones on top. Right at 7am the city shows up and starts working on the street. They made so much noise I had to get the headphones out to hear anything. ARRRRRGH!!!

So thats all the time I have to work on it this week. I'll watch eBay for a suitable pre-amp and see what that does for me.

73!
 

k9rzz

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Dec 12, 2005
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Milwaukee, WI
I just got in from the big dish and I tried my new preamp on Inmarsat (see other threads for which preamp I'm referring to). Bupkis. Granted, it's rated to 970mhz and I'm trying to push it to 1540mhz, so it should not be a surprise that what I can hear without the preamp disappears when I put it in line.
 

ON2BJ

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Jul 19, 2011
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Nice craftsmanship! (wait until you see what I built)

I got out just after daylight and messed around a little, I was able to tweak the dish a little so now the best sig is 1 inch in front of the C band feed instead of 6 inches to the left. I also put some F connectors on my RG6 so I could play with different feeds.

This is the simple feed (a piece of RG58 stripped):

1523930855_e0811045c4.jpg


This is a Left hand circular polarized (LHCP) feed I slapped together on a piece of aluminum from a junked VCR (I got a big box of aluminum plates and pieces for just this reason):

1523930895_33c6c70117.jpg


It was longer, but as I manipulated the dimensions to tweak the response, I also trimmed it down:

1523930905_9d0b35fafc.jpg


The simple feed was just slightly better than the best I could get out of my LHCP. Equally as good or equally as bad?

I can hear just about every channel on Inmarsat 4 (53w) which is all data of one form or another. I did swing the antenna down to the horizon and to my surprise, I can actually hear Inmarsat 3 at 15w ! It is weaker though (no surprise).

1523930963_60802a87cd.jpg


You can see that I'm right on my horizon to hear this one (I'm in Milwaukee, WI), you folks on the east coast or Europe can hit it easy I'm sure. Yes the dish is mounted on an old tree trunk and you can see my radio sitting on a chair with the headphones on top. Right at 7am the city shows up and starts working on the street. They made so much noise I had to get the headphones out to hear anything. ARRRRRGH!!!

So thats all the time I have to work on it this week. I'll watch eBay for a suitable pre-amp and see what that does for me.

73!
..........................................................................

Hello,

it very carefully I observe your Inmarsat antenna!
I intend to build one but I do not have all the pictures on this forum!

How many turns has this antenna?

For my part, I bought a preamp that covers 900 to 2500 MHz in Minikits!

I will try all I built the antenna

I'll keep you informed!

top 73

ON2BJ
 
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