Radome for DIY L-Band Antenna Kit

I have started making a fiberglass polyester resin Radome for my L-Band Antenna Kit.

Fiberglass apparently has good attenuation for L-Band signal but I do not know exactly how good it is.

I have rounded all corners so that I hopefully will eliminate distorting the signal.

The offsets for the time being are at the front and hold off the front face of the L-Band antenna. This means a small part of the offset is also blocking the signal.

I have allowed 2cm above the antenna front face so as to avoid / lower the interference Syed was talking about from having the Lantern plastic to close to the antenna.

I will not paint the Radome for a few weeks to get a feel for the attenuation with plain fiberglass. I plan to paint it white.

The electronics will sit on a fiberglass plate under the antenna. I thought about lining the plate with foil to stop the E4000 and the LNA interfering with the antenna but as the LNA and E4000 are in metal boxes I am happy to try it without foil.

One problem is the e4000 and the LNA come with direct connection so there is not a lot of room to fit it in. I will order a 90 degree SMA elbow but for the time being I will use a small sma pigtail to help fit it in.

I do not want to put any force or bending on the thin coax.

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How did you fabricate that.

The rest of the team really needs to see this: @zoltan @branko @andrean @Abhishek @rachel

We made a male mold and just put polyester resin and 200 gram/sq meter cloth. I wanted it thin.

I currently have it under two waterproof plastic tarps (which are blocking the satellite) and I have it lying flat and I get a SNR of 5.

So I am very happy.

Radome Part 2

L-Band DIY in action. 5 db SNR under tarpaulin.

Prototype one next to prototype two.

Sea of cables untill I get a 90 degree SMA Elbow. But it works.

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Adding team to this one. @rachel @branko @andrean @Abhishek

Really nice job! :slight_smile:
Thanks for sharing this!

Fiberglass apparently has good attenuation for L-Band signal but I do not know exactly how good it is.

Is there a list of good materials for a cover for this antenna? What about the materials that Shapeways offers–acrylate, PLA, elasto plastic? http://www.shapeways.com/materials?li=footer

It would be nice to have the option to order an outernet-specific radome for the DIY kit.

Not yet, We’re still working on the finishing the various pieces of software, to we may need to rely on the community to develop a list. It might be time to create a new category just for antennas.

I put my “oar in the water” early on this issue, but the plastic kitchen storage container I’m using just to cover the Lantern to keep it dry is made of 2mm thick polypropylene ( 5 PP) - - not 2mm thick Acrylonitrile butadiene styrene (ABS) as the Lantern is made (I pretty sure that’s what Syed told me in another post)


I have no signal degradation even when I put a 5PP cover right on top of the antenna. To refresh here’s my setup: Ken

We are going to be switching to polycarbonate pretty soon.

We had clear skies forecast overnight, so I left my receiver outside for a bit of weather testing. It was -6°C this morning.

SNR was between 5.5 and 6.5 with all of that frost. Without the frost, the peaks are maybe 1 dB better. We have snow forecast later this week, so I’m going to upgrade to a Universal Radome (plastic bucket).

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The ABS NEMA enclosure I’ve used, Bud Industries NBF-32210 is about $15, outdoor rated and a perfect fit for the antenna and equipment. I’ve posted pictures of it on the forum. It works fine indoors and outdoors, open or closed.

The problem it has, as with any sealed moisture proof enclosure, is cooling, if all of the components are to be housed within a closed box. In a marine environment, more so than any other, protection from moisture and salt is of paramount importance for electronics. In some other environments, the moisture may not be an issue.

I operated a ADS-B system with all the gear, including the POE converter, RPi, LNA and RTL dongle in a slightly different Bud enclosure, but with a 2.5" splash proof vent, for several months through all sorts of inclement weather, electrical storms, hailstorms, wind, rain, direct sunlight and 98 degree days, you name it, and it was perfectly fine. Seems the gear ran just hot enough to evaporate any condensation that might have tried to appear inside, but not enough to fry… However, this is South Texas and fairly mild weather, so more Northern, wetter, colder areas, or more humid, hot areas may be a different story for this type of setup.

All of that said, I’ve done a lot of experimenting, design, construction and implementation of RF and computer gear in outdoor enclosures (by trade).

The main problem is the sensitivity of the receiver and CHIP to high temperatures.

My observation on this particular application of the patch antenna, LNA, dongle and CHIP, is that the “best” way to build this system for 24/7/365 operation in an outdoor environment is to separate the antenna/LNA combination from the RTL/CHIP combination.

For temporary or sporadic portable operation, having it all in one box is fine as long as air can circulate.

In a commercial full-time application, I would house it all in one enclosure with solid state cooling. That is quite expensive, but reliable.

Going the separated route, the patch antenna/LNA combo can live very nicely in a modified WiFi patch antenna outdoor case. I have one to play with. Just need to get another Outernet patch antenna in to test.(hint). The RTL/CHIP can live in a ventilated small project case.

Maximum coax length using LMR-240 should be about 25-50 ft. I’ll do some testing by putting that much coax in between the LNA and RTL and get back with the results.

There are other permutations, of course…

One could simply have the RTL/CHIP outside but in a shaded area with ventilated case, and a short coax lead to the antenna/LNA facing skyward.

For seriously dry to slightly wet areas, a simple integrated sunshade over the ventilated equipment enclosure would suffice. This consists of a cover about 1" off the main equipment case, held in place with 1" standoffs to keep the sun off and the air circulating around the box. The sunshade could actually be the antenna/LNA enclosure. Get the idea?

I like the fiberglass radome idea for the marine application, but still there is the problem of heat and accessibility.

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I am seriously going through this COAX EXTENSION issue now. I am debating weather to use a 50 ohm Coax and have the RTL and CHIP inside. As opposed to a 15 foot USB cable and the RTLSDR , Filter and antenna outside.

I think the cooling heating issue is a big issue.

One of the issues in my mind is should a loose connection happen and the coax is carrying the dc power to the filter from the RTL dongle , will I be more susceptible to electronic damage.

But in one perspective this gear is getting so cheap that if the heat shortens the life of the Outernet RTL Dongle then it might be cheaper to replace it each time, than to go to the trouble of extra cables etc.

Putting more devices outside makes more connections that are susceptible to loosening and corrosion, etc. That said, you won’t run much risk of damaging things if a power connection is loose. You just won’t see any signal.

My suggestion should you go down the “separates” road, which, in the marine use case, I highly recommend, would be to take the excellent mounting method you already have for the patch antenna, and the fiberglass plate behind it, and attach the LNA to the fiberglass plate using some nylon standoffs so that it’s nice and secure.

Now for the fancy engineering stuff :slight_smile:

Then, find a “cover” for the LNA. Maybe a small plastic box or something the size of a matchbox that you can put over it as a “hood”, with a groove on each end for the coax to come through, then plan to seal it to the plate with RTV. That will protect the LNA from moisture intrusion. It doesn’t generate any appreciable heat so it’s OK to be encapsulated.

Depending on how you envision the final product being mounted, you could use a SMA Male to Female bulkhead jumper from the output side of the LNA to either:

A. the side of your radome
B. the fiberglass plate.

This will serve as a “strain relief” for the Feedline to LNA interface.

Now, before you mount it and seal it all up, put the connections on, and use a tiny bit of silicone grease on the threads, careful not to spread it all over the connector, and tighten it up snug using a small wrench. Not too tight, just snug. Then, use some “Liquid Electrical Tape” on that connection. That will seal it up and keep the nut from backing off. Same on the other connector.

For your Coax to Bulkhead female connection, do the same trick with the bit of silicone grease and Liquid Electrical Tape (not sure what the equivalent product is called where you are, but it is this: http://a.co/gvFiWGl )

Tonight, I’ll do a comparison reception report between just the regular setup, and then using a 50ft. LMR-240 coax between the LNA and RTL. We’ll see what happens, and I’ll report back.

Ideally, IMO, an outdoor system would have the LNA already encapsulated in some sort of small metal or plastic enclosure, depending on which model of LNA it is. This would make it easier to mount and provide protection. The LNA style with the metal can over the components can be in a plastic enclosure, while the LNA with the exposed components (like the one I got) will probably fare better in a tiny metal enclosure, or a plastic one wrapped with aluminum tape.

Ok, just did a quick test with 25’ of LMR-240. With the system peaking at SNR 3.82 to 4, inserted the LMR-240 and dropped to peaks of SNR 2.86 to 3. Still usable. Mind you, this is with the antenna inside, looking through a window frame, glass, and fiberglass window screen.

Obviously 25 feet is a lot of Coax for 1.6ghz signal but as you say it could be acceptable if the unit was outside and in direct line of sight.

I have considered potting the LNA in epoxy or silicone, but the clearance with the connectors is very very tight.

You could easily make a custom form out of a matchbox or similar. Line it with Saran Wrap or spray with silicone spray, add potting material, cure, enjoy. Put a wrap of tape around the connectors to keep them clean.

I’m considering to put the antenna+LNB in a lunchbox (e.g. SISTEMA Sandwich box), still have to find one.
I think I will put the LNA in a small tinplate box (soldered) and attach it to the rear side of the antenna.

Or everyone’s favorite hacker box, the Altoids tin!
-C

-Officially swiped from Adafruit

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