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My home-made ferrite antennas

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dfroula:
Here are some photos of my home-made ferrite antennas.

I found a source for some 7.5mm x 50mm ferrite rods with an initial permeability of 2000u - ideal material for a ferrite antenna, but too short to be of practical use. However, the price was very cheap! I ordered 32 of them to experiment with. I decided to try to make some 7.5mm x 250mm cores by gluing 5 of the smaller rods end-to-end. Gluing ferrite in this manner is an accepted practice and has a very small effect on the inductance of the final antenna.

Richo suggested that close-winding a single layer of AWG26 enameled wire on a 10mm x 200mm core, leaving 5mm unwound at the ends, would produce a ferrite antenna with outstanding performance. I figured that a 7.5mm x 250mm rod would be equivalent.

Here is a photo of the 50mm rods and the "Super-thick" commercial grade cyanoacrylate glue I used to assemble the longer rods. The salt shaker is not a part of the procedure!


One drop in the center of the rod is enough.


I used a piece of aluminum channel clamped into a table vice and lined with waxed paper to align the rods as they were glued together. The waxed paper prevents sticking to the aluminum. 30 seconds of pressure was applied to allow the glue time to set.


The third rod ready to be glued...


The final 250mm assembly of 5 rods. I allowed 30 minutes before removing the assembly from the channel. I allowed another 2.5 hours for the glue to fully cure before winding the cores.


This photo shows the first finished antenna. The cores were wound with 26AWG enamled copper wire. I used electrical tape to secure the ends and sections of the coil as I wound to prevent unraveling and to keep the windings tight. When I reached the far end, I loosely wound the free end back to the other end. This is the end of the coil that will be connected to ground, following the example of the commercial antenna provider.


A close-up of the finished first antenna and extra cores...


The second antenna completed and the two additional cores for a second antenna pair.


A close-up of the two completed antennas.


I slipped the antennas into foil-covered and grounded 3/4" PVC conduit sections with a longitudinal gap in the foil to prevent shorting the magnetic field. These things have incredible gain! I am still testing, but they appear to be giving my high-gain flat-panel loop some serious competition!

miraculon:
Thanks for sharing the info. It doesn't look all that difficult to put together.

Where did you get the ferrites?

At this point, the start of winding is obvious, but did you identify it for phasing after is is in the PVC conduit? Did you shrink-wrap them like the ferrites that came from Germany?

When you get them running on your detector, it would be great to know how they compare with the flat panel.

Greg H.

dfroula:
Up and running now! http://projectmf.homelinux.com:8081 to see them in action (use Chrome to avoid scrambled display). Check the stats on lightningmaps.org, station 681.

They look to perform as well or better than my 52-turn flat panels, based on the last 60 minutes of detections.

I have not shrink-wrapped them yet. I may just use electrical tape.

I made a nice housing similar to yours, Greg, with the conduit "L" box and 3/4 inch PVC conduit, covered in aluminum foil with the slit.

Don

dfroula:
I bought the ferrites here. Be sure to order the 2000u, 7.5mm x 50mm rods.

http://www.surplussales.com/Inductors/FerRods/FerRods.html

.75/ea for the 32 I bought! Dirt cheap. 2000u material is next to impossible to find.

I had them 3 days after ordering.

Don

DanS:
Do you know the number of turns you ended up with?  I've been doing similar things here, playing with various tank circuits and ferrite antennas to get different gain results. TIA

Dan

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