Inmarsat monitoring

[GadsdenP25]

Here is a good link I have found they talk about modifing a GPS amp for Inmarsat reception. http://www.geocities.com/ResearchTri.../inmarsat.html

Craig

[mancow]

Scott... and the rest

Do you think I could get away with a couple feet of the white ultraflex rg-58 if I used a foot or so from the feed too the preamp and then maybe max 4 feet more to the radio from there?

I have some Andrew ultraflex hardline but I hate to waste a nice 50' run with ends just for a few feet and I don't have TNC's for it and that's what the preamp uses. I do have TNC crimps for 58.

[jlh]

mancow, i used about 15 or 20 ft of RG-6 with mine, worked fine. also used a couple of LSD amps from radio shack, in place of the modified preamp. the antenna i built was based on paul marsh's design, similar to the one in craig's link.

paul stopped by here one day recently, he is a genius when it comes to this stuff, maybe he'll drop back in.

PS i also sent you a pm with a link to a pic of the one i built

[mancow]

Here are my projects so far. The helix seems to work but I think I need a better preamp. I still don't know if the metal center is doing it harm either.

The dish is under attack by the gremlin there every time I try to work on it. The wife got roped into sewing the reflective fabric. It's some cheezy Wal-Mart mylar woven stuff. I don't know if she will be able to make it smooth enough to work but she's giving it a try. She has two petals sewn so far and has cussed it every step of the way.

I put the yard stick in there for reference and showed a side shot to see if the experts here could tell me if it's accurate enough to keep pursuing the project or not.

It folds up neatly. I think I will get a good tripod for it and do my best to make it a true fold up and stow away system if it works.

[jlh]

mancow, you built all that? impressive. i'm going to look again for that helix, you would have a field day with it. i'll pm you if i ever find it.

[K0ATC]

The dish is looking good. That helix is identical to what i built, but I used a .5/.5 center rather then the L segment you are using. Did you make a matching network at the base prior to attaching it to the feed? That could be your problem with the reception. Great craftsmanship!!! Did you use a slinky? I used coiled copper wire, but i like your idea much better, maybe i'll build one with a slinky for 2.4 gig.

[mancow]

Yea, it's a slinky. They are something like 2.7 inches wide or so and hold their shape perfectly. It's alot cheaper than copper wire too.

I found that the slkinky Jr. is the perfect size for 2.4 Ghz. You might give that a try. I picked one up for 89 cents and I'm going to try making one for that range to pull in wireless cams.

I picked up a 950-2040 satellite TV preamp at RadioShack today. Maybe that will help a little. If not, I'm going to grab the old satellite TV offset dish from my parent's garage and give that a try.

[jlh]

mancow, i used the ratshack preamps on mine, they work fine

[mancow]

Something's up then. They had some RCA D903 13-18 dB 950-2050 Mhz amps on clearance for #$5 so I picked up two. They run on 14-18 vdc at 25-40 mA.

I also got one of the more expensive cylinder type with the wall wart and power injector block.


Nothing works. I hear that data stream again on 1534.775 and a couple of dead carriers but I don't know if the carriers are local interference. That's it. There is nothing else there. When I do get a carrier and that data stream it's always from that same spot but nothing else seems to be there. I have heard some stuff that sounds like PCS 1900 type mhz stuff up around 1560 but it's burried in the noise.

I guess it's the antenna.....?
I wouldn't mind trying another type but I wish I knew whether or not there's even anything still there worth messing with. I got an email recently from someone that said the A service is going away in 2007. Is it even used anymore?

[mancow]

Originally Posted by scott4957

The dish is looking good. That helix is identical to what i built, but I used a .5/.5 center rather then the L segment you are using. Did you make a matching network at the base prior to attaching it to the feed? That could be your problem with the reception. Great craftsmanship!!! Did you use a slinky? I used coiled copper wire, but i like your idea much better, maybe i'll build one with a slinky for 2.4 gig.

Thanks for the compliments.

What type of center did you use? Do you mean it was a square box tube?

[mancow]

I think I'm possibly stupid.


Look at the antenna winding. Am I correct that it's wound for Left Hand Polarization?

If so that would probably explain alot.


I just noticed this.

[jlh]

mancow, your polarization is opposite to mine, but mine was made to point at a dish, while yours is deigned to point directly at the bird, so maybe that explains the difference

[jlh]

you folks with new inmarsat setups may want to listen this morning for shuttle launch control talking to the emergency landing sites

[burts]

does the core of a helix need to be metal or could it be plastic,if so could it be plastic tube of the correct dia to just wind the copper wire around and fix ?


thanks from burt

[fez_uk]

Would I be able to pick these satalites up here in the UK?

Also do you need to move the antenna to follow the sat?

[xz]

Originally Posted by fez_uk

Would I be able to pick these satalites up here in the UK?

Also do you need to move the antenna to follow the sat?

Ello,

You can see a few Inmarsat birds from the UK. AORE at 54W, AORW at 15E, IOR at 64E and IOR-W at 25E. All have L and C band downlinks.

You dont need a tracking antenna, a 60-90cm dish, simple helical feed and low noise LNA is all that is required. A UK radio mag, 'monitoring-monthly' has LNA kits that are pretty cheap http://tinyurl.com/4kl3lb is the link to them.

The NASA TAL site links are no longer analogue, but there is stuff like Inmarsat-C which can be decoded.

regards,

pjm.

[ernest1]

How can i monitor Inmarsat B,C,M,mimi-M services in RF frequency by spectrum analyzer??
Is anyone?