PARC now have a new site for you to find out everything you ever wanted to know about amateur radio in Paisley – but were afraid to ask.  Click the link below to visit ( and then bookmark ) our new site.  Hope you enjoy it :-).

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Magnetic loop antennas by GM0FFB & GM4FLX

The Thin Skinned Magnetic Loop

As part of a larger experiment two members of the Paisley Amateur Radio Club, Stephen GM0FFB and Alan GM4FLX have been exploring and building a new form of magnetic loop.

Steve & Alan

Steve & Alan

Stephen is a World class CW specialist able to compete at 60wpm and has built many scores of magnetic loops using copper tube. Alan is an inventor and trouble shooter who had never built a copper tube loop to be a radio aerial but had done a lot of copper tube work in all sizes up to 1.5 inch diameter and has the necessary bending tools and springs

Because the thinking in October 2012 was that they would need two loops each and that the maximum power used would be 3 Watts, they decided to look at the loop itself as a QRP project. Three years earlier Alan had formed solar tunnel support frames by heat bending PVC tubing and many years earlier had used copper foil when wiring a doll’s house for his granddaughter. Thinking about how the electrons flow at the skin of the tube led the two men to set about layering copper foil left over from the doll’s house onto curved PVC tube. This proved easy to do and they bought supplies of 20 millimetres wide copper foil normally for slug control at about £1 a metre plus P&P.

Stephen by using eBay, bought four 90 centimetres Hula-hoops and these have been formed into magnetic loops for 20, 30 and 2 x 40 metre frequency bands by sticking copper foil onto them as one would gold leaf.

The options were :

To wind the ¼”foil like an inductance all the way round the loop and vary the pitch.

To wind 20 mms wide tape in the same way.

To lay the 20mms tape parallel to the circumference outside and inside and the fill the edge gaps with the ¼” tape.

To use Faraday loops, Gamma matches and Delta matches

And to wind coils of one or more turns of single or multi-strand wire inside or outside the plastic tube in any desired way.

Since October 2012 All of these process have been tried out by Stephen on air and all of them have proved worthy of future exploration and development. All but the one described here, take the work out of the safe description of a magnetic loop as understood by most amateurs.

The team has chosen to describe this simple basic apparatus in this article because it incorporates only one major new feature, that of replacing the thick walled copper tube by 2.5 thousandths of an inch thickness of copper foil laid onto a hollow plastic ring. The size and shape of any antenna formed in this way is limited only by the method used to form the basic shape. This could be by purchasing ready made plastic hoops, by forming hoops out of plastic tube or by making hoops by GRP methods around formers such as bicycle tyres, car tyres or tractor tyres, all of which Alan has done at various times or for example entirely within a computer with a 3D printer and or by electro-plating.

At the present time the team is content to say this antenna has been made on a table with the minimum workshop back up of a workmate and hand tools. Tin/lead solder and an ordinary soldering iron have been used throughout. There are no soldered joints between the two ends. There are five connection points. These are: two coax connections, one to the loop and one to the Gamma match, one from the gamma match to the loop and one each from the capacitor to each end of the loop.

The concept is offered for use as an inexpensive an experimental tool that, provided you can source one good quality transmitting capacitor, the loop can be made for less than ten pounds and that, once you get the idea you can change this into a wide variety of other loop antennas, not necessarily to be called magnetic loops but of a generally circular shape. The team remind you that we are in the business of communication and if you take the accepted magnetic loop into a fresh range of successes then that is progress.

Because you are no longer limited to stock diameters of copper tube you can use any cross section you can handle or make. Hula-hoops come in a wide variety of sections and diameter. We suggest to you look at those of 30 mms cross section and 1.25 metres in diameter because that is where we are likely to go next. The loop shown can, by choice of capacitors be made to resonate at 40, 30, and 20 metres with ease. Having access to an MFJ 269 Antenna Analyser saves time but is not essential.

To get the copper tape onto the loop having bought more than enough to go round the perimeter of your chosen tube as many times as is necessary one whole piece at a time. You then must decide where your top point will be and mark the start for the tape about one centimetre away.

Lay the loop flat on a table. Put the reel of tape on its edge and adjust the height of the loop so that the touching face is in the middle of the tape and plan to only unreal about three inches at a time pressing the centre of the tape onto the loop about two inches away from the reel. Do not rush. Allow about fifteen minutes to get right round. Press the tape down as you go inch by inch. You will get little creases. Just accept them and keep going keeping the tape parallel to the tube all the way round. Cut the protection tape off frequently and push it aside so that it does not interfere with what you are doing. Don’t be afraid to stop and relax.

When you get round to your starting point cut your finishing end to leave a 2 centimetre gap. This will be widened later. Using the handle of a knife or something similar and aiming to start on the centre line pick up the loop very carefully and go all round it rubbing the foil to make it lay smoothly and as evenly as possible right round the ring. You will not produce a perfect job. Do the best you can in short steps. When you have been all the way round and the tape is reasonably well placed then go round again using more speed and more pressure and you should be able to squash most of the creases out. The end result will still not be perfect. Now repeat the process on the inside edge of the tube and you will end up with a gap on both sides of about 5 mms plus or minus 2 mms. With luck some quarter inch tape used on both sides will fill the gap or lay down on top of the edges of the other two strips. How many strips you will need will depend on which tube you purchased.

The beginning and the ends will be close together and if you have not broken the tape you will have no soldered joints in your loop. The worries about soldered joints will not arise. We decided on a gap of 40 millimetres between the two ends. If you have better knowledge then by all means use it.

Where ever you decide to end your copper tube cut it neatly and then wrap at least one layer of tape round the plastic tube over the top of your layers about a couple of millimetres back from the edges of the layers so that you can solder both together to form a joint all the way round all of the edges. Then solder the other side of that ring of tape. The leads from your capacitor will be soldered to these two rings.

We have mounted our variable capacitors 30 millimetres below the gap as you can see in the pictures and 30 millimetres above we have placed a choco-block connector for adding other capacitors. We tried two kinds of ceramic HV capacitors and found they got very hot indicating that we were converting radio energy into heat which was not the idea. Our final capacitors are one fixed one of five lengths of high quality coax with solid insulation and single wire cores surrounded by a closely woven copper screen. Each 300 millimetre length gave us 32 picofarads of capacity. Across this capacitor we have a high quality High Voltage transmitting capacitor with a range of 19 to 150 pfs. We used knitting needles sharply bent at right angles to keep our hands away from the capacitor and to get the necessary leverage to turn the blades. We finished off the arrangement with a knob, a school protractor and a handbag mirror to see where the vanes were for recording purposes. In our case roughly one Pico farad per degree. But it is the numbers relating to the frequency that count. EG 104 degrees = 7.028 MHz. But only on this set up. Yours will definitely be different by at least one degree and all the variations in cut lengths of coax. Don’t worry about it.

There are lots of ways of making gamma matches. We used the inner wire of some good quality coax and its insulating cover to get a good stiff self-supporting link. But, and this is very important, we found that by moving it relative to the main tube we caused a change in the SWR and by winding one turn of it round the edge of the loop as shown we got the SWR lower than in any other place so we kept the arrangement and commend it to you as being both useful and stable.

The positioning of the gamma match was found by trial and error starting with a lead long enough to reach from the coax socket to about 2 O’clock. We found our best position was within a little of four o’clock by patiently watching the SWR meter and keying down for a dash. To determine the length of the gamma match we made it half Pi D where D was the straight line distance from the start of the gamma match to the loop. Then once we had some idea we folded the tin base of a cocoa tin into a narrow Vee and trimmed it with the kitchen scissors to follow the shape of the loop and soldered it on both sides to give the powerful clip a good anchor point that would not tear. We later added a piece of 16g unvarnished wire along the folded edge to improve the grip of our bulldog clip.

When you are satisfied with it, you may decide to wrap your thin copper skin with PVC tape. Our loops are for use indoors and all the work we have done with them has been from indoors either downstairs on the backs of doors or hanging from the dining room ceiling or upstairs in a different house alongside the chimney stack. To get the loop through the trap door, squeeze the sides carefully and pass the loop through the diagonal of the opening.

Obviously these loops require setting by hand and eye to one frequency at a time and are very basic but infinitely adjustable. For other work we have successfully built up gear motor capacitor drives and remote controls and used rotators and we or you might fit any of these tools to your loops. However our aim this time has been to produce a basic working tool for single frequency operation in a bigger project and we saw no point in waiting any longer before telling you.

Alan GM4FLX is well known to members of RAIBC as the narrator of Radcom for the Reading Rattle from 1976 until about 2001 and thanks RAIBC for the variable capacitors used in the project.



Photo 1. A view of the Copper foil Magnetic loop.

Photo 2 The tuning capacitor end of the loop.

Photo 3 The Tuning Capacitor lever arm and read-off scale and its sighting mirror

Photo 4 The feeder connection point and gamma match flying lead showing how it is wrapped around the main loop to bring the SWR down

Photo 5 The Gamma Match tuning arrangement that provides a gripping surface for the clip.

Photo 6. Lengths of high quality coax cable formed into a high Voltage Fixed capacitor to bring the working range of the variable capacitor into the desired frequency range.

( I have copied this from a document sent to me, but as I have no knowledge of magnetic loops etc, I only hope I have managed to put the pictures in the correct order.  Also, many thanks to the boys for sharing this info with us all, a lot of time and effort went into the article and even more so the antenna. Good work lads.  2m0iob )

Mag loop

Mag loop







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New Club “Yahoo Group” site

The Club is trailing a new Yahoo group site where we can meet up and see what’s going on. Here’s a link to it 🙂

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Visit to GB3PA on 8 Aug 2013

Something that had been talked about a few times but never quite materialised was a Club outing to visit the GB3PA repeater station which is our local offering from the CSFMG or Central Scotland FM Group.  A posting on the Club Forum by Alex GM7OAW at the end of June got the ball rolling, with interested parties adding their names to the posting on the Forum site.   Eventually a date was set, and on the evening of Thursday 8 August we trooped up to the arranged meeting point approximately between Port Glasgow and Langbank.

Silhouetted against the North sky.

Silhouetted against the North sky.

On my arrival, accompanied by Bobby GAX,   Alex OAW, and Ian SUS were in attendance together with Brian the Hells Angel HMZ.  Across the airwaves came a call from Stuart PAZ asking for directions to our location – “Second star to the right and straight on ’til morning” would have been my J.M.Barrie inspired reply, but as I wasn’t in control of a microphone, OAW gave him the correct reply and soon he was joining us and parked his car off the side of the single track road.  Stuart was accompanied by his daughter Julie who will soon sit her foundation exam, and Jim NAE.    With us assembled, we headed down the track to pass by a lonely cottage which had at least one very vocal dog inside.  Passing across a field and through a second gate, we encountered a heard of inquisitive bull calves.   After that it was a quick uphill section and

Solar panels and control box.

Solar panels and control box.

we found ourselves at the repeater site.

Alex removed the heavy steel protective covers from the repeater to show us the Storno, batteries and other associated electronics that go together to make up a repeater.  PA as it is known, had until recently, a wind driven generator attached to it to keep the batteries topped up.  No such thing as a mains supply out here!   With the wind generator removed, it is up to the four solar panels to keep the batteries in a healthy state – a job that they appear to accomplish without issue.

What's in the box?

What’s in the box?

The assembled group listened with interest as Alex gave us a wee talk on the history of PA, what it was like in the past and where the CSFMG gathers the parts to build these very handy pieces of infrastructure which as radio amateurs will all agree, can be an invaluable aid to long distance communications.  The WX stayed kind to us and we all enjoyed the scenery too, and looking longingly at the nearby Vodaphone and Water Board comms masts, I’m pretty sure we all wished we could have a shack somewhere like this with a big tower along side it.  We can but dream.

Many thanks go to Alex for a very enjoyable evening, I’m glad I could make it along to see the repeater “in the flesh”, and I’m pretty sure everyone else that was there on the night would wish me to thank Alex through these pages.

Cavity filters

Cavity filters

Storno and batteries

Storno and batteries

Antenna systems belonging to Voda and water board.

Antenna systems belonging to Voda and water board.

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New Club Forum

Dear reader, the club now has a Forum where all sorts of general chit chat goes on.  To become a member of this forum you must be a registered user which is quickly and easily achieved by submitting a few details.  There is a link on the right hand side of the page under the heading Club Forum.  Just click on this and you will be taken to a new page where all you need to do is input a few simple details – all very easy.

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70cms – 9el yagi‏ by Stephen GM0FFB

Once again the Xmas/new year season is upon us and with it, traditionally, come excellent conditions on the vhf/uhf/shf bands. I usually miss out on any lift that appears on 70cms and, although I enjoy any vhf lifts that may appear, 70cms lifts always elude me. Not this year I thought and I promptly set about designing a yagi for 70cms.
I wanted something that could be dismantled if necessary, high gain and not too big. I eventually settled upon a 9 element, 1.16mtrs long yagi, offering 13.8dbi gain and a healthy front to back ratio of 24.93db, with an input impedance of 24 Ohms.

To make the antenna I required:

Boom – 2mtrs of 25mm rigid white cable conduit (B&Q)
Elements – 4mm aluminium round rod (B&Q)
Element holders – 30amp connecting block internals (B&Q)
One small piece of circuit board
A length of 50 Ohm coax to make the impedance doubler and feed-line.
A glue gun.

Once all the items had been purchased then the build could begin:

First task was to strip the 30amp connecting block internals by undoing all the screws and tapping out the brass liners. Two liners will be required per antenna element. Put a piece of rod or bbq skewer through two liners and secure using some of the removed screws. The liners need to be inline and touching each other. Solder them together, once the solder is set release them and setup the next two. For a 9 element yagi you will require 2 for the reflector, 2 for the driven element, and 2 for each of the directors (7), a total of 18. Divide this by 2 and that’s the amount of blocks required (B&Q sell them in strips of 10). Remember to leave 2 unsoldered, these will make up the driven element.

Next we have to mark the boom with a straight line running from one end to the other, this can be done easily by holding the boom up alongside a straight edge (like a door frame) and drawing the line. Once the boom is lined start from one end and mark up all the element places.

Next I cut a small piece of circuit board just narrower than the tube and about 1” in length. I grind the copper off the board down the centre so that I have 2 long narrow copper pads on the same board. I then build up solder on these pads. Put the two single connectors onto a rod/skewer about 3-4mm apart (as wide as the gap between the two solder pads) and screw them down. Whilst holding the rod down onto the circuit board, solder the liners onto the solder pads.

We then have to make up the impedance doubler and we need to transform the design impedance of 24 Ohm to 50 Ohm or thereabouts. Two times 24 = 48 and we require 52, forty eight is close enough.
We will require 2 x quarter wave lengths of coax for the coaxial transformer and the calculation to work out the length is as follows:


So, 300 divided by 433 MHz = 0.69284
0.69284 * 0.66(velocity factor of 50 Ohm coax) = 0.457
0.457 / 4 (1/4 wavelength) = 114mm

Cut two pieces of coaxial cable, outer cover to outer cover = 112mm (slightly less than required to take account of the connection length). Put the two coaxial lengths parallel to each other and solder the centre conductors to each other at both ends and the shields together at both ends. Solder the centre conductor at one end of the balun to one side of the circuit board solder pad and the shield of the balun at the same end to the other solder pad on the circuit board. At the opposite end of the balun solder the centre conductor to the centre conductor of the feed-line coax and the shield to the shield, that is the balun complete.

For the next stage I use a hot knife, I cut out slots at each of the element places about the depth of the soldered liners. With the exception of the driven element, which requires a one inch lid cutting out with the top edge aligning with the element line, (this allows room for the circuit board to sit in the tube). Push sticks into each soldered liner and secure with the screws, place each soldered liner into its slot and glue into place, using the sticks to keep each of the elements aligned.

Finally push the plug end of the feed-line coax through the driven element slot and towards the back of the antenna and out into the big wide world. Pull the coax through until the circuit board sits firmly into its slot – glue into place, replace the lid and seal with glue.

Cut each element with a pair of pliers, measure, measure and re-measure before the cut. The driven element needs to be cut into two equal halves and seated into the two holders.

Solder a PL259 or N type plug onto the feed-line. Tune to resonance by trimming 1-2mm from each of the two elements a time and observing the SWR on a VSWR meter.

The measurements for the antenna are as follows:
Length of element,   Space from driven element
Ref: 339mm 153mm
Drv: 327mm
D1 315mm 106mm
Space from previous element
D2 300mm 115mm
D3 299mm 134mm
D4 298mm 135mm
D5 298mm 157mm
D6 294mm 162mm
D7 279mm 196mm

Initial tests indicate that the antenna is very good, so I will be taking it out in the car with me for further testing.
Maybe I’ll see you on air, 73’s
Stephen GM0FFB

Many thanks to Steve for taking the time to write this article and sending in some pictures to accompany it.  So there you are, there’s no excuse now for not being heard on 70 cms now, and with 9 elements there should be plenty of people to hear you!

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20m/40m Antenna mod by Roddy 2m0iob

 This is not a club project, but I thought I’d include this here as some members may be interested in having a cheap antenna system for two of the popular HF bands.  This antenna is very cheap and easy to make up, and I hope this post will give some the impetus to have a go themselves.

 Not having had the time or weather to go too far recently, I decided to have a wee go at modifying a 20m wire dipole. What I was after was an antenna to do both 20 and 40m.  The idea is simple, a linked dipole is basically a dipole cut for the lowest frequency you want to use, but with connectors on it so you can unplug some of the length and have a tuned dipole for a higher frequency.  These can have 4 or 5 connectors on them depending on how many bands you want to use, but for this antenna all I wanted was 20m and 40m.

I had in the past read up about these antennas and the connector of choice seemed to be the Anderson Powerpole.  I duly ordered a quantity of said items and left them lying around for the best part of a year.  I always meant to get round to it, but as you know, it’s always easier said than done.    It was now time to put my plan into action. 

The day was Remembrance Sunday, and after attending at the local cenotaph for the Service of Remembrance with one of the dogs, we headed up Tower hill to let him stretch his legs after sitting so well during the service.  On the way I spoke to Iain WJZ with my trusty vx7 who was on Beinn Bhuidhe doing a SOTA activation.  Once up on Tower hill itself I spoke to Graeme GIL who was also out with his dog, can’t remember the hill, but it is just above the Whangie.  The WX was glorious, so I thought it was time to set about the linked dipole job.

  A ten minute walk and I was home.  I then set off out in the car to the hill just behind Greenock.  Here, there would be plenty of space to set up the dipole and the remote location ensured minimal QRM from power lines and transformers etc.  I normally use a ‘drive-on’ antenna support which holds the fibreglass fishing pole solidly whether it has a wire attached, or 2m beam for chasing distant stations.  

The dipole I was going to modify was homebrew.  Very simply made, it only consists of a suitable length of co-ax, 1.5mm csa wire ( from the electrical factor ) for the elements and a plastic cable or ‘stuffing’ gland.  The co-ax is stripped back to reveal the inner and outer cores, two lengths of the 1.5mm wire are then soldered to the suitably tinned and prepared wires of the co-ax, and then the cable gland is slid over the co-ax up to the point that the newly made connections are inside the gland.  while ensuring that the cores remain separated from each other, fill the cable gland with Araldite or similar two pack glue.  Once set, this makes a very good, waterproof and robust dipole centre.  Other ‘containers’ may be pressed into service, a 35mm film canister perhaps or whatever you can think on to make the connections in.  I chose the stuffing gland as I had it lying around. 

Remembering that the dipole is half wave, then for 20m operation, the total length should be about 10m, so each element is roughly 5m long.  This is a good starting point and you can tune the antenna for exact SWR from there.  I also wound 6 turns of co-ax at the centre of the dipole to provide a balun.  This works very well and I have had no problems when using this antenna.  To attach the centre to the top of the fishing pole, I have attached a piece of bent aluminium bar that was lying handy at the time.  I could have looked for something prettier, but this works.  On the ends of the 20m dipole I have fitted Anderson powerpole connections ( suitable ‘how-to’ videos can be found on YouTube ) and a plastic insulator which the 40m extensions connect to.  Again, powerpole connectors are fitted to the 40m extensions so they can be plugged into the 20m section.  Once I had trimmed the antenna so that I had a great SWR on 40m, I fitted keyring split-rings to the ends of the wires so I could easily attach some guy wires to pull the elements into tension.  For this, I use the orange line found on an old hand-held fishing set  –  not the kind of line you would get on a rod/reel.  I either use handy rocks to tie the ends off to, or a couple of tent pegs. 

So, that is basically that.  A simple way to have 20 and 40 metre operation on a cheap antenna.  You also have the satisfaction of ‘getting out there’ with something you have made yourself.

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