good morning Elec

In the photo above (antenna on hood), does/could the hood itself increase the efficiency of the antenna?

Depending on what it's made of, the hood should act as a bit of a reflector.

I believe that it is fiberglass.

TR

The effect of the earth ground, vehicles, building roofs, etc.. do not seem to have any effect on the performance of the antenna. You could even hold it in your hand. The bottom loop is the ground plane, so it doesn't matter where you place the anenna as long as it can see the sky and is pointed in the general direction of the satellite.

I wish my homebrews worked as well.

Simple, tuff and efficient… So who holds the patent? :D :munchin

Patent Pending
 

I got the basic idea from the AARL Antenna Handbook. I made numerous antennae that didn't work before I made one that does. Open source. See the instructions in the SF Only section.

Gents,

My favorite antenna guru had this to say about the dual loop antenna posted in this thread.

We might have an opportunity to play with this in the coming months, thanks for bringing it to our attention. It's an interesting structure.

Begin forwarded message:

We have two loops separated by 7 inches or so and fed 180 degrees out of phase.

Whatever the impedance of the loops at the operating freq. (240-320 MHz), the coaxial cable "sees" 1/2 that. Thus if the input impedance to each loop is 100 ohms, the coax connector will see 50 ohm load.

The spacing of the loops is 7 inches or so, and the wavelength is (lets say 280 MHz -- mid-band) approx 42 inches. Thus the spacing is 7/42 wavelengths = 0.17 wavelengths. This is too small to form a "beam" antenna. But; note that the loops have horizontal polarization along the horizon (if held with the plane of the loop horizontal) (it behaves as a magnetic dipole oriented vertically). The loops also have a polarization null directly overhead. And, since they are fed 180 deg. out of phase, they have a null at the horizon. The final pattern is a broad lobe at 30 to 60 degrees or so from vertical and nulls overhead and at the horizon. The polarization is "horizontal" from the point of view of a satellite near 45 degrees from user overhead.

So, we have a donut pattern.

Caution, there is also a downward mirror image pattern. Its reflection from the ground is messy.

Knowing the pattern can we estimate the gain? Not off the top of my head. I will go out on a limb and guess the gain is near 4 dBi minus losses due to the impedance mismatch.
-End of quote.

We built an antenna like the one in the pictures and will run it through testing in the test chamber in the next couple of months.

I will post the test results when they are completed. Not to discount any of the claims here, but claiming a gain above 10db for this antenna is ridiculous and irresponsible. Especially in this forum.

This in no way implies that RF engineers and their antenna modeling software programs are always right. According to most of them my 113 foot long piece of wire laying on the ground should never work, but it does.

I will post the formal results when they are completed.

I agree that the DB rating is a bit overated somewhat. Like mentioned by 69 harley, it's pretty much two full loops (one up-link, the other down link)...well not a quad, because that would be four elements, but two full wave loops somewhat in-phase (I believe). I "assume" the DB readings were taken off the display off the PSC-5, they are not the actual DB readings of the radiation off the antenna (you'd have to put that in an anochoic chamber, or input into some high speed program). I have talked to folks and they say it does work very well in that particular environment (CENTCOM). I would like some of the PACOM/SOUTHCOM commo guys try it out. It may have different characteristics in those areas due to the inherent ground characteristics. You can figure that out just by the AO's they are in.

We will start showing/building this antenna in the 18E course, just another thing to put in their "tool box" we t show them now to build an expedient three element yagi, (for VHF/UHF) amongst a couple of others, but that takes some pieces of wood or whatever for stability and spacing. This one kinda holds its own per se.

Anyway, I wish the 18E's would dive into the ARRL antenna handbook, no telling what may show up as a great expedient antenna, or whatever else they can come up with.

cheers.

Send me the info and I will put it to the test...

regards,
smitty

We have this antenna scheduled to go into the test chamber next week. I think the 44 db gain claim is way off and is borderline silly to claim in this forum.

We built one of these, and were able to close the loop on a good SC 25K bird. We did some preliminary testing using a PSC-5D and a 117F in manpack mode, with and external 25 watt amplifier (RAMP-25) and an external 100 watt amplifier (TSE-AM-SAT-100). In all three modes we did side by side testing with the experimental antenna, an AV-2055 without extenders and an AV-2011.

The 117F and PSC-5D were able to max all loopback tests with the 2011, regardless of amplifiers used or not used. With the 2055, loopback test were consistently in the 80 percent range. The experimental antenna averaged 65 percent.

The 20011 has 15 db of gain, the 2055 without extenders is 5 db, we guess the experimental to be around 4 db of gain.

This antenna works, but nowhere near the 44 db claimed.

Like I said, next week it will go into the RF test chamber, the results will be posted here.

Like Glebo said before they are taking reading of of their radios. They do not have access to the equipment you must have and you have to give them credit for trying to reduce the load and make a item that will work in their environment. Please do not stifle their creativeness with High Tech Lab critiques. I work with a lot of Electronics Engineers that are smarter than all of us. They can build a lot of stuff in a Lab but it does not make the grade out side. We all know that the db readings are not right but this antenna does work. I have built 2 (soldered/Connecters) and have used them in SA in the last week. Not as good as the factory ones but it is not intended to totally replace them. You can put it in your pouch and get up and running, if your factory one breaks/blown up/etc you now know how to make a field expedient one.

I applaud Electron for thinking outside the box and it looks like 18E's are and have been using them with success. Looking forward to the bench test next week. Never hurts to have an extra antenna. Remenber 1 is none, 2 is 1.

I concur with what SF_BHT had to say. My hats off to electron for figuring this thing out and getting it out to the 18E and commo community. As far as 69 Harley wanting to test the antenna, that is a good idea so we really know what its capabilities and characteristics are. I don't think (and I am speaking for myself) we are trying to denegrate that antenna. Just trying to get the correct facts out, after all we are supposed to be the "experts".

I think its another great tool for the E toolbox, anything to help out the Joe's is great.

Anyway, my .02 worth.

keep the shiny side up!

Anyone able to shoot me the specs so we can give it a try out our way? Be nice to have for the air insertions we are doing on a regular basis right now, for use with the 148 to report up the chain. Using the 2055 right now, but if it can save some setup time and make moving around on the ground with it available for use, that would be great. We've been pulling out the 2055 when we hit the ground and just walking around with it setup, but when you're on the ground 2 hours being tethered to that thing can get to be kind of an annoyance. Thanks guys.

There are two non-Trivec antennas that I have used and really like.

One is made by RF Concepts and marketed exclusively by TSE Inc, has a quick draw holster, a solid 6db of gain and is very light. My wife can un-stow it, make comms and holster it in under 30 seconds. My wife has never been in the military, I just use her to test stuff.

Attachment 9943


The other antenna is made by Syntonics, very light weight and incredibly rugged, not impossible to break, but much more durable than anything made by Trivec. This antenna includes a true reflector and provides 5 or 8db of gain, depending on if the gain extender is used.

Attachment 9944

Unlike anything made by Trivec, both of these antennas are available from TSE in less than 30 days.

Gain
 

The gain reading of 40+ was taken from the display from the PSC-5D with the antenna on the roof of an RG-31 while deployed with the satellite at a high angle at mid-afternoon and the gain reading of 34 was taken from the PSC-5D front panel with the antenna resting on the ground (again deployed, late afternoon with a high-angle satellite).

I look forward to test results from "the chamber" to get some actual scientific data and true gain readings. I am not claiming this to be the greatest thing since the pyramids, but it is useful as a field-expedient antenna if your X-wing or AV-2040 is out of commission.

I fully support and recommend putting this through the gambit of tests. One word to the personnel testing the antenna, try connecting a trimmer capacitor (6-70 pF) and connect it between the (+) and the (-). This may help with tuning.