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[KC6RWI]

Just curious, I see the very high price $1800 and just read a glowing review. What makes it good?, It looks like a metal frame with a loop inside I assume. If this antenna was so good why aren't there diy copies. Its not even a round loop, it looks like a jack that you  crank to lift the car and that jack is in its closed position,    Is it a  grand design or marketing?

[W6MK]

It's twice the price of an MFJ loop, but no doubt much better engineered and no doubt stealthier, given that the loop involved is squashed down.

I am sure that an experimenter could DIY a similar loop, but we live in the era of plug-and-play ham radio. Once upon a time hams at least made their own wire antennas. Nowadays even that kind of homebuilt effort seems unusual.

There's nothing magical about any antenna and there is no reason that a squashed loop design which can cover 40M and higher shouldn't be relatively expensive if it is well-built.

[KB8CR]

My SK friend has one that we are selling from his estate.  I used it with him on several occasions. It works very well. The materials used in its construction are not like DIY loops. The capacitor is at the top, and consists of thick aluminum vanes that mesh upon movement of the loop. It also has an auto-tuning controller that tracks the frequency of the VFO in many radios (we used it with an IC-7300) A frequency can also be entered using it's external keypad. It would not be so easy to DIY copy this antenna.
  http://cincysouth.com/w8sai/stealthloop.jpg

Charlie KB8CR

[KC6RWI]

Interesting, is the body made out of metal? if it is, would there be a loop of wires in there? wow, I guess the capacitor on top is motor driven and like you said is in tune with the vfo of the radio.

Thanks for the picture, it looks like a heavy duty build.

[K6JH]

I believe the arms are welded aluminum. One side is fixed, with a welded aluminum feed. The other side tilts, and has a copper (?) strap jumper over the hinge joint. Lots of cross section in the arms for good conductivity. The whole thing is painted or powder coated.

Loops can be any shape. It just depends on the area. A circular loop is usually most efficient as it maximizes the area and minimizes the circumference (and resistance). But if it’s made heavy like this, it can have a lower profile and still be efficient. You can hide this behind patio furniture or a planter or something, to make it harder for the HOA Karens to spot. Or move it around on its dolly wheels. But it isn’t exactly small.

[AK5B]

Interesting, is the body made out of metal? if it is, would there be a loop of wires in there? wow, I guess the capacitor on top is motor driven and like you said is in tune with the vfo of the radio.

Thanks for the picture, it looks like a heavy duty build.

The hinged frame is aluminum and is the actual loop.  With small transmitting loops a large diameter radiator is beneficial because of the skin effect (especially the lower one goes in frequency). The two sets of vanes form an air variable capacitor, and while I'm not 100% sure I believe the Stealth model only handles 150 watts.  The circular TIG-welded Midi and Baby Loops handle around 800 watts by comparison.  Ciro Mazzoni is probably the best available STL among the few commercial offerings out there, and the price is proportional to the build quality and auto-tuning controller included.  I've never used one myself but have done considerable research since I like to DIY my own QRO-capable STLs with vacuum variable capacitors (instead of air variables which are prone to rain and humidity problems) and HVAC pure copper tubing or corrugated copper Heliax.  Search "If you really want to build an optimized STL..." in the QRZ Antenna Forum for my "10 Commandments of STLs" article if interested further.

73,

Jeff, AK5B
The Loopy Guy in South Texas

[KC6RWI]

Now I know alot more about the stealth loop, really interesting that the body, arm size are built into the design, Thanks Jeff, I wonder if you have ever though of a design with a loop 6' or 10' in diameter, or do you loose signal rather than gain.

[N2ZD]

   Although I don't have a stealth loop, I do have the baby and midi loop. They work great, the big chunk of the cost.are two things. The cost to ship these from Italy to the US and DX engineering pricing it high. The quality of the.materials is very good, the Welding could be better. Nevertheless, for a compromise they work far better than you'll ever know.

    The stealth benefits from the optional plate that goes underneath it from what I'm told.

Regards Richy N2ZD

[AK5B]

Now I know alot more about the stealth loop, really interesting that the body, arm size are built into the design, Thanks Jeff, I wonder if you have ever though of a design with a loop 6' or 10' in diameter, or do you loose signal rather than gain.

It's a long story but I built a 40m loop that is 7 feet in diameter and sometime I may get around to building an 80m loop that will be about 13.5' feet in diameter (@40-42' of 1 inch Heliax suspended from one of my trees).  The size is dependent on both the capacitor required and the frequency it's optimized for---read my QRZ article I mentioned earlier---it's a complex situation that requires a bit of planning to get it right.  (Also much easier to post text and photos as well as reply on QRZ (which I much prefer over this antiquated eham format).

73,

Jeff

[W9IQ]

It is helpful to keep in mind that gain is defined as directivity times efficiency. A small loop antenna generally suffers from poor efficiency which translates to poor gain.

The directivity of the small loop antenna is largely fixed and is equal to that of a short dipole antenna. Only when the loop circumference becomes large enough that the current around the loop is no longer essentially uniform will the directivity begin to diverge. Generally, a loop with a circumference that is 1/10 of a wavelength or less is considered a small loop antenna with nearly uniform current.

The poor efficiency of the small loop antenna is largely due to its very low radiation resistance. As the area/diameter/radius of the (circular) loop is increased, its radiation resistance increases as the square of the area. So increasing the area of the loop can dramatically improved the radiation resistance and thus the efficiency and gain of the antenna.

Decreasing losses in the antenna also improves the efficiency of the small loop antenna. Larger, less resistive surface areas and better connections are often the most productive ways of decreasing RF resistive losses.

One might reason that increasing the area of the loop in order to increase radiation resistance will also increase the losses in the loop. This is true. However, the radiation resistance increases as the square of the area while the resistive losses generally increase linearly with the circumference of the loop. So while the losses are increasing, the more rapidly increasing radiation resistance more than makes up for the additional losses so efficiency can be dramatically improved.

- Glenn W9IQ

[KC6RWI]

Thanks, I read that 3 or 4 times, seems you could drive yourself crazy trying to find the correct diameter and surface component to make a loop work in just one band, I say one band as I can see how complex it would be to be able to tune many bands,
I am also going to check the ten comandments of stls.

[AC3Y]

RWI, to get an animated view of how the numbers work, check out the VK3CPU interactive loop calculator:

https://miguelvaca.github.io/vk3cpu/magloop.html

Beyond that, there's the question of the mechanical/electrical considerations to optimize efficiency. Lots of advice to be had on that from AK5B and others.

[KC6RWI]

Thats alot to take in, I will study that in quiet time, but I must say for a builder that quite intimidating.

[W1VT]

Everything I've read suggests that TIG welding is a difficult yet valuable skill in making low loss transmitting antennas out of aluminum.
I have a small 2M loop that was TIG welded.  Most experts say that welding can be used to make low loss electrical connections.

[WA3SKN]

This antenna has all the negatives of a small loop.
It is also built like a tank!  The only real question is "can you afford it?"  It will handle abuse well.

-Mike.