Images and Notes from Other Loop Builders, Inventors, and Enthusiasts
N3KNZ Takes it Far Beyond the Next Level with
Several Very Nice Loop Designs
Inspired by his first magnetic loop featured on this site, John takes loop building by the horns, and comes up with some excellent designs
This is John's Second Article
Loops by John Gbur, N3KNZ
|John's Magnetic Loop Version 2.0
This loop is basically the loop off of Brian's page with a few minor
modifications. I used copper straps at the top to hook on the
I came up with the design based on seeing other peoples designs for loop stands. I wanted something very sturdy which is good as the loop and my capacitor housing ended up to be pretty hefty. The feet of the stand are 2x6. The mast is 2x4. The spreaders on the mast are pine [Editor: wood does not make an ideal support system for magnetic loops as it is a water retaining material. Some loop experts consider it a very poor material and think it degrades loop performance. John later changed his mounting scheme. If you do use wood, make sure it is painted with non-metallic paint or lacquer.] The triangle at the base is plywood on both sides with a 2x4 in the middle. Screws are used at all junctions. I would give dimensions, but since your loop may very in size I will leave the size up to the builder.
To mount the loop to the stand I used metal U-Bolts. I have seen this recommended in some articles. I tried it and it works for me.
The capacitor base was made of 1/4 inch Lexan. I used a 3x12 piece in for this project, but this will vary depending on what type of capacitor and reducers are used. I was also able to use aluminum angle bracket cut to length for this stand. I fastened it to the Lexan with a small bolt and nut. I have also used small wood blocks successfully. I used an acrylic rod to get the length I needed. I plan to motorize the tuning in the future, but this model has a manual system. The capacitor I used in this version was a 25-500 uf Henry Radio transmitting capacitor.
Due to the odd size of the capacitor, I found most tupperware too small or too large. I plan to use Lexan boxes or tupperware in the future, but for this project I opted to use PVC pipe. I didn't come up with this idea myself, I saw this on some of the other loop project pages. The capacitor housing is made of 4" schedule 40 pvc. An end cap is used on the bottom. At the top a screw plug and female adapter are used to allow access to the capacitor. The lexan plate for the capacitor base is mounted in the tube with a screw and bolt in the center of each end. I countersunk the holes and used epoxy instead of plumbers cement to allow more time to tap the ends in place. Two holes drilled near the end of the tube allow exit points for the capacitor straps made out of RG8X braid and eyelet that were crimped and soldered.
The brackets I used were fairly expensive. They fasten in the center with a large bolt through the 2x4. They work great, but the 4" metal straps sold at most hardware stores are cheaper. I was going to use a lexan plate, but found it was too thin and would have had to been shimmed. I had these brackets as a backup plan so I use them instead (instead of cutting a plywood square and using the metal straps). To use the metal straps, a piece of plywood would be cut to size and mounted to the 2x4. Then the PVC capacitor housing would be mounted to the plywood with two metal straps. Optionally large plastic tie wraps could be used, but I felt the metal would be sturdier.
I plan to build a small version of the stand that is easier to transport. But the design here is very sturdy for stay at home use. I also put a piece of 2x4 on the back. This allows it to rest level when transporting or optionally operate in horizontal instead of vertical fashion.
There are alot of great loop articles and plans out there. Once
you build your first one and get it working don't stop there.
Improving on your first loop is when it really gets fun!
This picture is of a quick and dirty stand I used for field day. Basically it is a 1 by 4 piece of wood attached to a base plate. I mounted the 1 by 4 to the base plate with two L brackets cut from a length of an Aluminum L. I may shorten it or try composite, but it works pretty nice as is for now. When my octagon loop is complete I will probably epoxy the loop onto the stand to keep it from moving around. Though I don't think it would move a lot anyway. Also I plan to use different capacitors than either used. Either the Henry Radio or B&W probably. Or possibly a vacuum variable in the future. For now it will probably be caseless although I may build a lexan box. I will start with just the lexan plates. The loop is not soldered yet still have to finalize how I want to do it. I will have to solder it while it is on the pvc support or I won't be able to get it in. That should be fun but doable. The base and support come apart into two pieces for transport.
Here is my octagon loop based on an article I found on the Elecraft
site. It was fun trying to get stuff straight on the PVC support.
I only had one heat problem. When I went to solder the straps where
the capacitor connectors are located. By the way, the white stuff at the
connectors is marine epoxy. I epoxied the loop to the supports so it won't
move around. The black stuff on the SO239 and the capacitor straps
is liquid tape. I may solder the straps on eventually but for now am using
nuts to hold them on. I needed to add a PVC union at the top because I
accidentally made my support a little too short. I will have to shim
my capacitor plate out but for now just tightened it in place. I am going
to replace the wood blocks with aluminum L brackets but wanted to test
the antenna first. It is working well so far. I worked Argentina on 5 watts
PSK31 today and got good reports during up and down band conditions.
This one is a lot more portable than the others. When I get my vacuum variable's
ready, I will probably try one on this loop.
John Gbur, N3KNZ
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