What a diference a mag loop can make!

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joe36
Posts: 36
Joined: Wed Jul 20, 2016 11:09 pm
Location: Cass co. in. 46994

What a diference a mag loop can make!

Post by joe36 » Sun Sep 04, 2016 4:21 am

I am sure that this is nothing new to a lot of you but I was truly impressed.
I am an old ham, 30+ years. I have built many antennas over the years and have a 20 meter dipole a 40 meter dipole, a 2meter/440 collinear and a discone up at this time so I have something to compare to. They are all home brew fed with RG6 at varying heights.
In the past the dipoles did the best on HF and the discone was nice in that it is has a very wide frequency range.
The dipoles and collinear were subject to overdriving the dongles. Even with attenuation they had a lot of intermodulation. Mostly from strong SW stations. The discone did not have as much problems with intermodulation but it was due to less gain and a lot of week signals that were just lost in the noise floor.
Enough with the antennas on hand and on with why I am posting this.
I have been advised to try a magnetic loop. I have talked to a few hams that used them but never tried one. Honestly I did not expect much. I was and still am planning on doing an every few years periodic
maintenance. Just a cleanup and coax replacement. I have a lot of RG6 quad shield on hand with almost nothing $ in it. This brought me to the thought that it won’t help with the intermodulation and overdrive situation.
I watched this short video. https://www.youtube.com/watch?v=J2QBQ45C0b0 the antenna in the video is very easy to build and as you can see. It does not have to be precision made and tuned to the desired band as the tuning is accomplished by the capacitor. I particularly liked this video. Not for the attention to build quality but because of lack of build precision. It is straight to the point and shows the process of building this type of antenna.
Being a bit skeptical as to if I would find the loop any better than any of the others antennas. I put very little effort in the construction. Mine is an approximately 4 foot in diameter loop of ¼ inch copper tubing with an approximately an 8 inch loop vinyl taped just under the bigger loop. Also made of the same tubing.
I chose the tubing because it is what I had on hand. I am sure a wire would have worked. It would be difficult to screw it up as long as you are even close.
The capacitor is an air variable that was in the junk bin. It is a bit bigger than the small receiving caps that I think are from around 20 Pf to 350 Pf. This one might go 500 Pf +/-. I literally through this together in around an hour just to try one out. No precision anything wires tied to a board.
You can find air variable capacitors for around $10 on line.
It was amazing in how well it worked. The tunable range if from 1.87 MHZ. to 16.2 MHZ.
I am using a Ham it up converter with the antenna on the desk in front of the computer
I can tell the exact range! This was the part that was so amazing to me. I am running SDR sharp. You can see where the antenna is tuned by a pronounced and very distinct rise in signal strength on the display.
By having a considerable gain compared to the signals outside the tuning range and only over the tuned frequency range. While attenuating signals outside this very narrow range. It totally stopped the problems with overdrive causing intermodulation problems. Signals that in the past would have been impossible. Are now strong and easily tuned. Did I say I was truly impressed?
I should have made a note of the width of the antenna tuning and the difference in Db of out of band and in band signals. It is past my bed time and the grand daughter is using the computer I use for the dongle so I will have to experiment and post more detailed results later.
I now plan on cleaning up the loop build and playing with smaller loops to cover a bit higher frequencies. This has to be one of the easiest antennas I have ever built.
I am going to call it a night and will update this post soon.
Joe KA9UCN

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