Projects‎ > ‎

The Lightweight Loop

                                                                                                                 Subscribe to my Radio Blog



Hey all
After building my first magnetic loop the other day I thought I'd have a bit more of a serious attempt at making a portable version.
30/07/13
My first thoughts..

"This time I'm going lightweight, something anyone could use without having to have a membership to Golds Gym.  I want it to be hand portable but still durable enough to take a knock just in case it falls from a stand or I drop it, maybe collapsible for travel.  I want it to be waterproof and most of all fool proof.

This magnetic loop has to cover 20 meters up 10 meters perhaps 6 meters as a bonus.  Its going to be a challenge to make it strong but yet still very light."

Well this is as far as I have got.
Behold I present the "Mansol loop"

The sum of its parts

There is a spare T piece in the picture I purchased for a slightly different design idea.
The 20mm white pipe, the white T pieces, the box and the box adapters are all 20mm conduit fittings.
The Copper pipe is 13mm, so hows it going to work Mark?
Well that's where the rubber grommets come into play.

I cut a very small piece out of each of the grommets so they fit really snug in the 20mm fittings


I pushed the grommets down inside to the lip in the fittings and the box using a marker pen (sharpie).



I fitted another grommet on outside and I intend on filling the gap with silicone sealant to make everything 100% water tight.

The inserted rubber grommets fit really snug
Sometimes a video makes it easier to explain.

The first update video


It took a bit of lube to slide the fittings to plastic covered 13mm copper pipe but once they slid into place they really grip and are not movable even without the silicone sealant.

The tuning capacitor will be at the top in the waterproof box, the shaft from the cap will run down the inside of the pipe to a adjustment dial in the lower cross piece.  The center cross piece has two functions, one is to hold the cross braces in place, the second is I intend to put a transparent cover so you can see the tuning shaft and read the dial attached for quick rough tune indicator as pictured here in my naff diagram.  I'm probably going to make the indicator dial from an old champagne cork!
The excess conduit pipe could be used as the handle as pictured but It might need a bamboo cane inside to add to rigidity.


*UPDATE 31/07/2013*

Hey all
I'm still waiting on the capacitor arriving before I finish everything, after everything is done and its all 100% working I will take it all apart and measure everything for future reference. 

Every 20mm pipe to plastic joint will be glued, the two white T pieces will be filled with silicone sealant to hold the copper pipe in place if the loop gets dropped also between the pairs of O-rings will also be sealed.

I've decided instead of using the excess 20mm pipe as the handle directly into the bottom of the lower four-way box its going to be clipped directly onto the back using these follow parts.

I glued them together first with gorilla glue


I then put a plastic bolt though with a metal nut to make sure they don't split and also the bolts close up the gap in the clips stopping the loop slipping.

I used one of the same black clips with adhesive cable tie carrier stuck on for the inner loop clamp.


The inner loop in made from 480mm of Westflex W103 the same as the ugly loop with the inner and outer conductors soldered together




I'm torn between an SO-239 and a length of RG-58 as the output..
I'll make this decision after the Capacitor tuning rod is fitted

I'm still waiting on the glue going off on the inner loop clamp so its not shown in the above picture.
The black lid that you can see on the box will need to come off and have a slot cut for the thumb control tuning dial but for now I fitted so I don't loose the screws!

I first drilled the holes for the inner loop in the box starting off with a 2mm then up to 8mm, I then finished the holes with my trusty dremmel to ensure a super snug fit on the PVC outer of the Westflex W103

Second update





*01/08/2013 UPDATE*

Hey all

Still waiting on the capacitor but maybe I'm thinking now that is a good thing, it gives me more time to think about options in the design a bit more thoroughly, perhaps add some nice touches and make it more ergonomic.  I've steered away from adding anything cosmetic and nonfunctional to the loop on purpose or it might just get too daft!

Today I looked at the loop and spotted something I didn't like..
Its the back of the box that the capacitor is going to be, its got holes in the back to screw it to a wall.
Well as I'm not going to be screwing this box to the wall I don't need the fixing points and wondered how I could tidy this bit up/make more useful.

Then it came to me.. Why not cut it out and replace it with a clear piece of plastic so you can see all the workings and the capacitor moving.  I thought to myself its all right trying to explain the concept of the loop to people and to point out the various parts of this loop but what good is pointing to a gray box and saying "there is a air spaced variable capacitor inside there" when most new/recently licensed hams/random people might not know what a a air spaced variable capacitor looks like or what it does!


I know the inside edge isn't perfect, its the prototype.. I did it as well as I could with a Dremel tool.  You can also see the transparent center cover in the shot, this is transparent so its going to possible to read the numbers from the rotating drum inside giving you a quick indication which band is which direction.

The center cover will have a kind of gauge of some description perhaps engraved into it, I've not finished thinking through all the possibility's yet but I imagine vertical lines that will correspond with the some more vertical lines on the rotating drum inside.  This drum was initially going to made from a champagne cork but I think an empty cotton reel would fit better as well as being easier to write on.

Update 3



I've come up with an idea for the front of the capacitor housing, I knew I had to do something with the box cover, it has to have a use, it cannot just be a boring lid,  thoughts of cutting the cover and adding more of the same Go-Pro packaging plastic as another window into the workings was one idea but then...
   I was brainstorming lots of ideas for how to showcase the amount of voltage that is on the capacitor while transmitting/tuning and how this voltage peaked on the sweet spot.  As I posted earlier I'm trying to stay away from adding things to this loop that are not relevant and being strict with not allowing it to either get too silly or far to serious.

 LED's that light up on peak tuning was one idea but I'm not sure if it would not look cheap and gimmicky but then I remembered an old moving coil meter I had rescued from an old jump starter pack.  I intend to use this meter to make a RF field strength meter mounted above the capacitor in the lid of the box and try and calibrate it as such it will peak when tuned "for maximum smoke"



*UPDATE 02/08/2013*

Hey all great news the capacitor has arrived!


The black plastic screw heads you can see in the corners act like little feet, I didn't like the idea of putting the loop down and scratching or marking the perspex window, they are numberplate screws that I had knocking around in my parts rack.

 As you can see other than then circumference this loop didn't really follow a design as such, the tuning indicator window, the clear window in the capacitor housing were not items in the original mental image, it just had to follow some rules.
  1. This loop had to be lightweight, the ugly loop was huge!
  2. No gimmicks or irreverent items glued to it.
  3. It has to be hand portable.
  4. It has to be durable and capable of taking a knock.
  5. It has to be waterproof.
  6. Most importantly it has to be fool proof.
Some more eureka moments have occurred with the tuning mechanism with the way the shaft is going to run down the pipe.  The tuning shaft material is going to be  threaded plastic 5mm rod, M5 as it fitted through the center of the bearings which are to be fitted in the pipe.  The bearings are going to be manufactured from plastic if I available to try and keep the weight down (see rule 1).

 The bearings ensure the shaft stays central in the pipe so the threaded rod cannot bend in the middle or rattle on the inside of the pipe.  There are probably cheaper options but with the fit so perfect with the pipes themselves hold the bearings in place I had to do it, I suppose even a Polo mint would have worked as a bush!


Here you can see a metal bearing being tested for size.


As per usual a video to help understand.. maybe

Update 4 on the loop - M0VST



Since shooting the video the capacitor is fitted and I'm moving on to the task of joining the outer loop to the capacitor gangs neatly inside the box. Its worked out in such a way that the pipe can basically be soldered straight onto the rear gang and I'll add a switch somewhere so I have the function of shorting the second gang.  All the work to the copper pipe has to be done outside the enclosure as there is barely enough room for a soldering iron.

*UPDATE 04/08/2013*

I nearly have all the parts now, a very successful day at Kings Lynn radio rally swerves the design again.  I found lots of reduction drives and lots of variable air spaced capacitors...

A few of the capacitors....

Still waiting on the tuning drive rod, might end up choosing a different material.

*UPDATE 05/08/2013*

Hey all
I buckled down and have 95% finished the loop, I ended up installing a completely different capacitor in the end, the Alps cap I bought new on ebay was nice an all but I would have been worried about about flash overs with the very small air gap.

The install of the much larger single gang capacitor from a FT101 made it slightly more difficult and I had to install each part exactly in the right order to be able to fit it all together.
The side T pieces are hot glue gunned up to the grommets, the cap housing is also sealed with hot glue which trickled into the space around the copper pipe and made for a tidy job.

The tuning dial ended up being located on the very bottom as I ran out of space to have one on the lid of the enclosure, this intern made me change the idea of the feeder leaving from the bottom exit.
The quick tuning indicator dial in the center worked out fine, if not a little small but it 100% does the job and lands the cap very close to the desired frequency tuning.

I've yet to finish the field strength meter mounted on the lid but I will shortly.  I'm very pleased with how the build went with only a few snags, all of which were overcome.

The 817 battery lasted long enough to hear some great signals on the bands, it works!

Pictures and video update to follow.


*UPDATE 06/08/2013*
I went for it, late last night, the final push in what felt like forever...
Changing the cap at such a late time in the build was a bit daft but I'm glad I did, holding on to get all these caps to see if I could find a better one delayed the whole project.
The tuning rod now had to be in two pieces with the joining sleve to the capacitor being inside the top tube, this in itself made the entire build more complicated as each item/screw, grommet had to go on in exactly the right order.
The screw heads had to be removed before it would even enter the top tube, the screws were 4mm to long.
The length of each part of the tuning rod was critical, I chose the measure it and measure again before going anywhere near it with a saw as now it would be impossible to replace the top section!

I had to take it out a cut another 1mm off twice, one mistake would be game over.

You can see the reduction drive in the bottom of the enclosure.

The reduction drive, the ceramic joiner and the capacitor for this project came from a  FT101 carcass.

 I managed to pick up a few the other day a local rally, they were sitting there all day with no takers! unbelievable.. Its not as if the stall holder was asking the earth for them, perhaps the ease of all the modern shack in a box transceivers no one can see all the interesting bits and bobs useful for building things.  I got to the rally really late as well, it was hard to park, I couldn't believe it when I saw them.
Each 101 contains at least four reduction drives, three of which are planetary reduction drives and the last being gearbox type. Each 101 also contains a couple of trimmers and at least 2 air spaced capacitors I used the larger one from the PA stage in this project.

Testing testing 123 - M0VST







It didn't end up covering 10 meters as planned but weirdly covered 40 meters?!?
Here's the band coverage

Whats it cover?




Here is another video I forgot to post here, its not much but it is the first contact on the loop.
The conditions were terrible with a full on geo magnetic storm happening while I'm building and testing the antenna, unknown to me!

Remember the 5 watts from the 817 doesn't end up with much emitted with only a 3% efficient antenna, but he heard me, I'm sure with even normal flat conditions it would be fine.

Contact !




*UPDATE 10/08/2013*
I've tried several approaches to the band indicator so far, all of them worked but I wasn't happy with any of them.  I've left this part for now while I await fresh ideas to finish it.

I've moved on to another side project, its really so I can finish the Ugly loop antenna that I started before this project.  I've built a controller for the 0.6rpm motor that is going to tune the ugly loop, its probably going to be used to tune this lightweight loop if I can make an quick fit adapter


As you can see its all built into a small waterproof project box.  It includes duel speed control for the tuning, either 0.6rpm if your close or 1.2rpm if your some way off, its all self contained and has its own power source inside which is topped up via the solar panel on the top.  Initial tests have been very positive with remote tuning of the capacitor made very very simple and easy to land on a SWR of 1.01. The cap moves so slowly is made it a real pleasure to use.


I'm very happy with the results and when I get chance I'll shoot a video to update you all.

*UPDATE 15/08/2013*

The remote tuning box gizmo worked out fine and performs as expected.  The 0.6RPM motor compliments the 6:1 reduction drive perfectly with just a flick of a switch to fine tune.
Its real use will be with the "ugly loop" as it was not the easiest to tune.
Here it is in use.

It works!


The main thought was to able to remotely tune the loop if I had placed it in the loft or outside on the roof but now I could see it useful on SOTA activations were adverse weather conditions might drive the op into a tent for shelter, without this device or some other remote control it means getting cold when QSYing!

Maybe it could be of some use to the HAM that doesn't have a garden, perhaps just a window box or even in a retirement home etc, the Ham that is less mobile perhaps?  It was good fun to make in any case.

20 meters ticked off


Another hour in the sun saw a quick contact on 20 meters with the lightweight loop, not massively strong signal but still very happy with the 5/5 report received with the 5 watts from the 817.
In this video you can partly see one of the tuning indicator attempts, I marked each band on the edge of the ceramic insulator with different colored felt tip pens, crude but it works, this was attempt 3 to complete the indicator.






To be continued.



Comments