Chameleon P-Loop 2.0 & A Real Shark Attack- K6UDA Radio Episode 46

I'm pretty sure a lack of "inclination" is the only obstacle to building a loop that is better than one of these coax-cable STLs. The physical ability and skill level needed to build a nice STL from the basic components isn't really any higher than it takes to assemble one of these $500 commercial "kits."

As you say, people can spend their money as they wish... it's a little aggravating, though, that so many opinions of what an STL can or can't do are based upon these tiny coax-cable designs. I'm glad that not all verticals are judged by 4' screwdriver antennas with #24 loading coils... and I'm glad not all dipoles are judged by Buddipole. There is such a thing as a high-performance STL, but it's not as well-known as other antenna designs because so many of the commercial offerings are cheap (yet expensive) coaxial cable designs, or they are just too small for the bands for which they are advertised.

I saw a post just the other day from a ham who bought one of these coax-cable designs, and ran it in his living room, and decided that the performance just sucked, and as a result, he concluded that all STL designs suck, and he wants to try to find some kind of wire antenna now to squeezed into some random space in his apartment or rent-house. It's a shame that the idea of building a real, performant STL didn't even occur to him because the poor STL design he bought (for a lot of money) was such a poor performer on the band that he wanted to run. People who sell loops like that are slowly destroying their own target market, IMHO, and that's very unfortunate for everyone.

STLs are one of the last antenna designs where home-brew can still crush nearly all commercial products, sometimes by an order of magnitude or more. I can call HRO or DXE and get a high-performance antenna design for just about any other type of antenna. But the STL is still home-brew-central for anybody who wants a good, performant product. I think that's very cool from a ham hobbyist perspective, but it's unfortunate for people who are new to the hobby and don't realize it because of the poor commercial products being floated.

 

Well, not so sure about this. I performed tests about a year ago using two identical loop antennas, one with 95% braid RG-213 and the other using 1/2 diameter solid copper tubing.

Here are the methods and results:

Both antennas used identical all metal air-variable capacitors.
Both antennas 33" in diameter.
Both antennas mounted on tripods and located 48" above floor level.
Before each test, both antennas were precisely tuned to the test frequency using a signal generator and spectrum analyzer.

Test #1: A field strength meter was placed at a distance of 18" from both antennas, with each antenna pointed directly at the meter - i.e. meter within the antenna main radiation lobe.
Power was fed to each antenna in turn at the 1-watt level at 7.100mhz and again at 14.100mhz and results read from the field strength meter. No detectable differences were seen between the two antennas.

Test #2: Each of the above antennas was connected in turn to an Instek GSP-810 spectrum analyzer, with the analyzer set to center at 7.100mhz and -40dbm reference level. Across the room (18-20 ft. away) was an HP model 8656B signal generator connected to a 24" steel whip vertical antenna mounted on a small tripod.

Power from the signal generator was varied and fed to its antenna. The resulting signals were observed on the spectrum analyzer for differences in receive strength between the two loop antennas (1dbm level accuracy) and none of significance were noted. Test was repeated at 14.100mhz with same results.

Test #3: Real world test - Coax & copper tubing antennas alternately connected to an SDRPlay RSP1 SDR receiver using HDSDR software for display. Both antennas were tried on various bands & frequencies while generally tuning around and no detectable receive performance difference between the two antennas was noted.

Test #4: WSPR. An FT-817nd at 5-watts of tx power was connected to the coax loop on 40m and results obtained over a 4hr period. Same test was performed the following day at the same time of the day with the copper loop. Results were not significantly different between the two days with the same stations reporting signals.
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So, based on these tests I have concluded that GOOD QUALITY coaxial cable is not inferior to solid copper (and most likely aluminum also but I didn't test that) for use in these applications.

 

I'm really sorry to hear about the fellow with the bad experience and you are right. But not all commercial designs are bad and not all are out to make lots of money. My own company makes and quietly markets such an antenna which costs about 1/3 that of most others and is primarily aimed at the trail hiker/backpack camper. Good quality and many have had good results with them.

It really all depends on so many variables such as a person's needs & expectations, band conditions at time of use, surrounding objects, antenna placement, etc.etc that really no antenna - STL or otherwise, commercial or homebrew, will suit every situation.

 

I'm trying to figure out why companies are selling commercial 33" STLs that are advertised for use on 40m at all? Sure, you can resonate a sub-3' loop on 40m -- you can resonate such a loop on 160m if the tuning cap is big enough (in all of pF, kV, and A ratings). But it's really too small for 40m work, because the electrons just can't move far enough to generate a good signal, no matter what super-metal is used to construct the loop. You could make it really thick and coat it with polished silver, but the much simpler fix is to just make it a little bigger. Making it QRO just requires using a better cap.

Yet people are selling very expensive antennas that only do QRP on 40m into a loop not much bigger than an extra-large pizza pan, and they are doing so in the middle of a sunspot minimum. I just can't accept that as honest advertising, or even honest engineering for that matter.

Thanks for sharing your test results. I think "good quality" is the key to your A/B comparison.

 

I'm assuming that is your company from your prior post?

I'm curious what you are trying to patent in that design? Something in the cap enclosure? Since you are seeking a patent, it will be public knowledge anyway. A loop of wire and a tuning capacitor has a long history of prior art, so I'm trying to figure out what performance-based characteristic you could be trying to patent as a new idea in a coax-cable loop.

 

That is the little company . We truly love it when somebody wants one of these antennas and it certainly helps us to pay bills and give back to the economy but not trying too hard to market it right now because these are quite labor intense and our main focus is in non ham radio areas.

I am aware that our patent system is flawed and that it really offers little to no real-world protection even if a patent is granted. The design and theory of this antenna have always been freely available in PDF form to anybody who wishes to see it and I do encourage those who wish to homebrew their own from our design. If you or anybody else would like a copy of the schematic & full design details then feel free to contact us via the contact form on the Caras Mfg. website and request a copy and I will send you the PDF via email. The patent was for the antenna system as a whole due to the band switching and loop conductor use allowing lower frequency use with reasonable efficiency without the need to switch in additional capacitance but this patent will likely not be pursued any further due to the fact that anybody who really wants to compete with it can walk right around the patent by making a few small changes anyway .

 

Done. I look forward to reading about what you are doing.

Okay, I think I may know what you have done in your design, then. I would like to model that idea, but I don't think a NEC engine can be configured to represent that particular structure. :-/ It shouldn't be difficult to mock one up, however.

 

Sorry, my mistake, should have been circumference NOT diameter. A twenty two foot diameter primary loop would be formidable!

 

Interesting but as I'm sure you know, real world results and simulations are often vastly different. According to many online loop calculators & simulators, many of these small STL antennas shouldn't work at all and yet they often work very well.

Anyway, have fun - I really didn't want to turn comments about Bob's video into an antenna discussion . Take care.

 

Bob, you have made my day!

 

The Sharks were epic.

 

Thanks for the explanation.

 

I agree on the DX part, good going and look forward to hearing you on the air some time. We need more people standing up for what is right,
Thanks for the DXpedition
N7HSI Skip Pickens

 

nice video..73