Faraday Coupling Loop

Here we will discuss only topics related to the Portable and foldable Magnetic Loop antenna
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George
Posts: 16
Joined: Sun Oct 07, 2012 3:44 pm

Faraday Coupling Loop

Post by George » Tue Oct 30, 2012 9:22 pm

A few questions on your coupling loop. I have built a few mag loops and researched most of what information I could find on them. Most of all that I have read uses a Faraday loop for coupling and it is mounted at the bottom, both of which were done for the maximum performance of the loop. I noticed that both you and Alex do not use a Faraday loop (just straight coax) and have the whole loop antenna inverted from the original designs which have the capacitor at the top and the coupling loop at the bottom. I understand the mechanical reasons for this inverted design, but is there a trade-off in performance?

Speaking of which, I think I saw in your video a vertical antenna in the background. Have you done a A/B test between it and your loop?

I built a loop (same diameter as yours) using 19mm (3/4 inch) copper tubing and had it outside up at about 6 meters for two years. During that time I also had a 15m dipole, a 90 foot Broad Band Folded Dipole, and a 44 foot doublet fed with 28 feet of 300 ohm twin lead to a Elecraft T1 remote tuner (not all up at the same time) at roughly the same height. Not too many times in the 2 years of A/B testing did I find the loop to be better than or equal to the other antennas on 20m - 10m. I should also say that before I started building the mag loops I did have a MFJ-1789 (Magnetic Loop) which I found performed pretty much the same as the ones I later built.

I also have a portable loop using 9913 coax and a Faraday coupling loop. While this loop does out perform small antennas such as my Miracle Whip, PAC-12, and HamSticks, this year for Field Day I also used a home made EFHW (End Fed Half Wave) with coupler on 20 meters and it noticeably out performed the loop. That being said, for a 1 meter tall antenna that only needs to be maybe 2 meters off the ground I would say that it's the best in that size and pretty hard to beat so maybe that is what makes it so popular.

So I guess my two questions would be: Have you compared the Faraday loop vs just a loop made from RG-58 (or heard any Pro/Con about the two), and have you compared your loop antenna A/B wise to any other antennas?

I loved your trees in your video by the way :)

73's

de George
WD0AKZ

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yo3ggx
Site Admin
Posts: 650
Joined: Wed Aug 15, 2012 8:30 pm

Re: Faraday Coupling Loop

Post by yo3ggx » Tue Oct 30, 2012 10:33 pm

Hi George,

I've tried several types of coupling loops, including Faraday with variants and I've seen no difference between them.
Considering the simplicity, at the end I decided to stay with a simple loop which can be made from plain copper or coax.
I am not aware of any downfall of mounting the coupling loop on top.

I don't have any HF vertical antenna in that location, but comparing the ML with my 80-40-30-17-15-12-10m Carolina Windom antenna mounted on top of a 8 floors concrete building(normally connected to my WebSDR server farm), the S/N ratio is in the favor of the ML. On the other side the received signal level is lower by 1-2 S on the ML.

The MFJ ML does not offer a higher performance than a cheap home build ML. You pay mainly for the automation part.

Regarding the trees, I will update the movie next springtime :-)

Thank you for your feedback and best regards,
73 Dan YO3GGX

George
Posts: 16
Joined: Sun Oct 07, 2012 3:44 pm

Re: Faraday Coupling Loop

Post by George » Thu Nov 01, 2012 2:26 pm

Thanks for your reply Dan..

"I don't have any HF vertical antenna in that location, but comparing the ML with my 80-40-30-17-15-12-10m Carolina Windom antenna mounted on top of a 8 floors concrete building(normally connected to my WebSDR server farm), the S/N ratio is in the favor of the ML. On the other side the received signal level is lower by 1-2 S on the ML."

Yup, I was also seeing much better S/N but 1-2 S-Unit lower on the ML's. I have chatted to a number of folks that built/use ML's but very few of them ever have the ability to do a A/B comparison to anything else. I was thinking that maybe my loops were for some reason sub standard.

But as I said in my previous post, for it's size I don't think there is any other antenna out there that will beat the Magnetic Loop.

I'll be watching for trees next spring.

73's

de George
WD0AKZ

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