DIY Inmarsat Antenna

[ab5r]

I am interesting in constructing an antenna for reception of Inmarsat at 54 degrees W 3-F4. I have a couple of questions please:

1) Which is preferred, a patch or helical? Or is this a matter of choice (Ford or Chevy).

2) Would the helix be RHCP or LHCP?

Any help/direction to sites or articles would be appreciated. I am completely ignorant with this endeavor.

Regards,
Jerry

 

[RFI-EMI-GUY]

I built my Inmarsat antenna using a L band helical design and wound the copper tubing helix around a PVC pipe to which I epoxied the turns. I used a pie pan for the reflector. I beleive I used RH polarization. Now this antenna will only hear the ship side, if you want the shore side you need an antenna cut to C band as well.

 

[RFI-EMI-GUY]

Actually I got that backward, you will hear shore side on L band.

 

[ab5r]

Thank you. You actually hear audio or read decoded data? "My" satellite would be at 54 degrees West and all I can see is data from that bird. Like I say, I know nothing about Inmarsat.
Jerry

 

[K5MPH]

Here is an web site that may help you out UHF-Satcom.com - L-band reception and i do think that the antenna needs to LHCP

 

[RFI-EMI-GUY]

Thank you. You actually hear audio or read decoded data? "My" satellite would be at 54 degrees West and all I can see is data from that bird. Like I say, I know nothing about Inmarsat.
Jerry

It has been a long while since I tuned Inmarsat. It was still very much analog when I did so. I have some very interesting recordings. NASA night still be using some analog equipment on certain transponders for their down range tracking stations.

 

[ab5r]

Errrrr? I don't think NASA uses INMARSAT. The above URL suggested by KB5ZCS lists the transponder freqs. and data there.

 

[RFI-EMI-GUY]

Errrrr? I don't think NASA uses INMARSAT. The above URL suggested by KB5ZCS lists the transponder freqs. and data there.

They were listed on some actual loggings during the shuttle missions, dedicated INMARSAT transponders (analog) for NASA range support. Perhaps now abandoned. Use of INMARSAT "Circuits" is alluded to in this document:

https://www.nasa.gov/centers/kennedy/pdf/167472main_TALsites-06.pdf

"Communications at Zaragoza include three INMARSAT satellite circuits and Spanish commercial telephone lines.
Internet capability is available through a local Internet service provider"

 

[ab5r]

You are probably right. Things change. In fact, I am not sure which bird I want to look at. Most things that I found on the internet indicated that from me (North Central Texas) Inmarsat 3-F4 at 54 degrees West was what I needed, BUT the N2YO site listed the bird for "the Americas" as 98 degrees West. Maybe 54 has changed to 98 now. See, I told you I knew nothing. (Grin)

 

[RFI-EMI-GUY]

You are probably right. Things change. In fact, I am not sure which bird I want to look at. Most things that I found on the internet indicated that from me (North Central Texas) Inmarsat 3-F4 at 54 degrees West was what I needed, BUT the N2YO site listed the bird for "the Americas" as 98 degrees West. Maybe 54 has changed to 98 now. See, I told you I knew nothing. (Grin)

Also the satellites are almost all digital now with respect to voice. So pretty much need to be experimenting with SDR and text decoding.

https://www.youtube.com/watch?v=30IHW5I-sKQ

But knowing how slowly NASA makes changes, it would not surprise me if they lease a transponder for analog order wire. You might want to scan for seldom occupied transponders and investigate them over time.

 

[bowtie-man]

I came across this website for measurements for the helix antenna. Just put in your desired frequency and hit calculate and it will show measurements in mm. https://jcoppens.com/ant/helix/calc.en.php

 

[Your_account]

around a PVC pipe

but wich diameter?
Does it need some reflector? And hot to get everything together?

 

[ab5r]

Your_Account: The URL UHF-Satcom.com - L-band reception shows a helical with 58 mm diameter which would be about 2.28 inches. That might be close with thick walled 2" PVC. I saw one photo of a helical with holes drilled in the PVC and plastic cable ties securing the helix. I don't remember if the helix was copper tubing or wire. Sorry

Bow-tie man: Thanks for the video: long but informative

 

[Your_account]

there are nothing sold like this size. So what should i do?

 

[RFI-EMI-GUY]

I used 2 3/8" OD thick wall for mine and it works fine. I used copper tubing 12.5 turns and epoxied it directly to the PVC. I used PVC couplers to fashion two rings to glue on either side of a 9 1/2" Dia pie pan reflector with corresponding hole drilled through it.

By the way, the helical on this page is a short one and left hand polarized to splash a dish as the antenna feed.

If I were to do it again, I might opt for about 16T as the gain was just adequate for the analog transponders.

 

[ab5r]

EXCELLENT info. Do you perhaps have a photo?

 

[RFI-EMI-GUY]

EXCELLENT info. Do you perhaps have a photo?

The black antenna is cut for Inmarsat RHC polarization, the smaller white antenna is cut for AMSAT AO40 uplink 2.4 GHz as a feed for a larger dish, and is LHC polarized as feed, the dish turns it back to RHC at the reflector.

Sorry for the fuzzy pix, they had to be compressed to upload.

 

[ab5r]

Excellent job. I actually bought and installed a tower and UHF & VHF antennas for AMSAT and AO-40 THEN IT CRASHED. Bummer

 

[Your_account]

Since when the Operate on the 2,4 Band?
The lower is for Wifi and the Upper for Radio Amateur.

 

[RFI-EMI-GUY]

Since when the Operate on the 2,4 Band?
The lower is for Wifi and the Upper for Radio Amateur.

Not for WiFi, AO-40 mode LS