Carrying on from my previous JAERO/L-BAND blog post linked below
It should be noted that both of the antennas detailed below I intend to use with the excellent LNA Amplifier /Saw Filter Combination, The “Saw Bird io” by Nooelec which is bespoke designed for the intended frequency range (around 1545-1550mhz).
For supplier details, refer to the link above.
It should be mentioned that during this difficult time effecting all of us around the world, Nooelec are giving away 10 NESDR bundles worth over $100USD each to front line medical workers (Heros)…What a kind gesture ..Well Done Nooelec !
Making the 1550mhz Centre freq Helix for L-Band areo
I decided to construct a LHCP helix antenna for L-Band to use with a satellite dish.
I searched around the internet for sizes and solutions, one design which seemed popular and builders were pleased with the performance was this one provided by this website link below .
A 200mm circular ground plane with a 4 / 4.5 turn 58mm diameter helix element with 49mm spacing between turns. The first quarter turn runs close to the reflector to facilitate impedance matching.
Im not great with a jigsaw to cut a neat circular plate so for ease of construction I decided to use a 200mm x 200mm square reflector which was supplied guillotine cut by the suppler.
My Plan looked something like this,The light grey section indicating the location of a supporting structure for the element.
Now to the helix support, I searched around lots and I explored many ways of supporting the helix.
Eventually I stumbled upon a user who had made a 3d printed support tube and end cap along with a 40mm standard size dish clamp.
He had used standard PLA standard plastic 3d printing filament.
I contacted a UK based 3d print enthusiast from ebay who has the correct equipment and sent him the files/request, he suggested that it would be better to use outdoor /temperature stable filament which I believe is called PET-G. Details of the supplier are at the foot of this section.
I made some changes to the end cap thickness as the flange on original one was as thin as a wafer when it arrived and it soon started to unwind itself after a few ons and offs.
Here is the original end cap, an excellent fit onto the tube but you can see the flange issue and the filament unwinding as I tried it on and off a few times, the modified re-designed one with a 2mm thick flange that features in this article can be seen on the floor.
Also I asked the supplier to make a new design clamp for “sky mini dish” (a 44cm eliptical design of dish,very popular indeed in Europe for B-Sky B reception from the Astra group of satellites @ 28.2 east) this has a different size lnb holder of 37mm diameter.
My order was placed and here are the results for the clamps, a choice of options to suit your dish requirements.
The other 3D parts supplied by ebay supplier Graham were excellent quality and vary good value. Considering the tube support alone takes a good few hours to make on the 3d printer, £11 for the tube and the cap was inexpensive. The clamps were £2.25/£2.50 respectively. Details at the end of this section.
Here a 40mm version is shown, the slot for the reflector plate for up to 2mm thick plate (but much cheaper 1.2mm or 1.5mm thick plate will be fine, I used 1.5mm thick) and there is a 3mm hole which runs through from one side to the other so that you can insert a bolt to secure the reflector plate firmly. The plate fixing hole is located at the same co-ordinates (12mm from bottom of plate) for both 37mm and 40mm versions so if you have both size dishes you could leave the clamps in place in the LNB holder of your dish and swap antennas between the two systems by unscrewing and replacing one reflector securing bolt and not disturbing things too much. Nice idea !
One neat thing about the clamps is that you can fit them facing dish or in reverse facing away from the dish no changes to the hole in the reflector, this will give some flexibility/fine tuning to achieve the optimum distance between the antenna and dish.
Heres the other side
For the element, I used some 2.5mm diameter copper capillary tube which is used by refrigeration engineers. This is much stiffer than solid copper wire as there must be materials other than copper in its construction and this was chosen because it retains required shape and does not tend to sag.
I obatined a 1.5mm thick 200mm x 200mm square aluminium plate from an ebay supplier, marked the centre.
Then I drilled some 4mm diameter holes at locations shown. You can use 3mm diameter if you so wish.
Note the 4mm diameter hole at the edge of the plate 12mm up from the bottom edge and dead centre at 100mm from the plate corner. This is the hole for the clamp securing bolt.
Fix the helix tube base and look at the area marked, you will need to drill a hole here for your chosen connector BNC or SMA but leave enough room from the cap outermost rim edge so that the helix support can be mounted later.
A washer can help with marking the centre of the hole, a 10mm hole is required for BNC and as you can see when the hole is cut we have enough room to work the tube on and off without intererence.
After the 10mm hole is cut the plate looks something like this.
Now mount the BNC and centre cap, secure cap with nylon locking nut, fit the plate clamp and secure with a bolt.
Round the back the BNC needs a backing washer to stop the ferrule at the front from sticking out too much at the front.
Now offer up the tube to the cap and try things out to see how it all looks.
The connector should line up with the flat part of the helix, if not turn the tube until it sits right the first quarter turn of the element runs parallel to the plate for impedance matching.
Starting at the top, wind the element on to the support grooves, when you reach the bottom slide on some heatshrink tube (about 50-70mm length, 6mm bore) then make a joint to BNC by using some thinner copper wire. Lightly Tin solder the capilliary tube first, then wind on a few turns of thinner wire which will fit into the BNC ferrule then solder up the capilliary end leaving a few inches of thinner wire to work with at the BNC.
Finally Solder up at the BNC ferrule end and slide over the heat shrink and apply heat to it to make a good seal, (it is quite difficult to shrink down when the tube is out of shape) this part of the element runs close to the reflector so I thought it best to provide some weather protection to prevent short circuits.
Apply some epoxy dabs to points along the grooves to keep the element secure and pop some adhesive into the end of the heat shrink tube.
I knew those coffee stirring sticks from McD would come in useful one day !
The final product
Around the back
Forgive the test conditions, which is a total mess and using a very old rusty decommissioned 44cm “sky mini dish”. Very Very Roughly pointed at 25 east (Alphasat/Inmarsat-4A F4).
The output of the very rough setup, promising…
Helix Antenna Supplier list :
3D Printed items supplier and options.
Send message to seller and Graham will create a special listing for you for the parts you need. Graham isnt a radio geek but he provides a great print service (he usually prints parts for gaming geeks hence the ebay name), excellent packaging and quick dispatch. Dont forget to specify LHCP or RHCP if ordering the support tube component.
Printing at 0.2mm 10% gyroid infill in PETG black costs are :
Feeder_40mm clamp_Mount £2.50
Feeder_40mm_Mount variant y at 37mm £2.25
Feeder_Support Tube LHCP or RHCP (specify your requiremements) £10
Feeder_Support_Bottom cap £1.00
P+P will be £3.50 royal mail second class up to 2KG
Considering that the tube support alone takes a good few hours to make on the printer,I think the prices are very reasonable.
I should add at this point I have no affiliation with Graham, he was an ebay 3D printing service supplier I found that had excellent feedback when searching around vendors listings. He had industrial grade large printer equipment, 3D design software and given the application he suggested the change in filament material for rigidity which I appreciated. Messages were responded to very rapidly.
Aluminium Plate 200mm square 1.5mm thick £3.00
Chassis BNC Connector (Tyco/TE Connectivity)
Copper Capillary tubing 1.5mm ,2.0mm,2.5mm or 3mm OD will be ok.
Alternatively 3/32 inch OD should be fine (2.38mm in new money)…steam model hobbyist suppliers sell this.
You could use copper wire for the element,
Prepare : Cut 75cms of 2.5mm solid pvc covered wire fix one end solid to bench or vice , grab the other end in pliers and pull straight and tight, then twist the pliers, keep going and you must keep the wire pulled tight as possible as you make turns on the pliers, this will provide rigidity to the copper, then make the element.
Sundries: heat shrink tube, m4 x 25 bolts, nylock nut
DIY L-Band Patch Antenna Construction LHCP.
I had tried building a patch antenna before using the instructions from a video by Adam 9A4QV from Croatia (incidentally producer of the LNA4ALL family of amplifiers)
I again followed this tried and tested design but for LHCP (for using with a dish) but I had a further idea, why not use the dish clamp again…
If I could include this in the design, I would be able to swap out helix or patch by leaving the clamp in the LNB arm just loosening one bolt, extract it, unplud BNC and swap out antennas in 30 seconds….sounds great..
Here we go,
I thought about making this from copper clad PCB/FR-4 material but the copper sheet is very thin so I decided to use 0.7mm thick copper/1.5mm thick aluminium sheets for better performance.
I purchased a 200mm 1.5mm thick aluminium plate, the ebay seller provided 2 cuts for free so I requested they cut the plate to 170mm square.
Next I marked the centre and scored 4 very small lines/marks along the diagonals 35mm from the centre point.
Mark out the 35mm spaced element supports, the 25mm point for antenna connector and the 12mm/85mm dish lnb clamp hole as shown
Drill out qty 5 , 4mm diameter holes, 4 for the 35mm spaced supports and 1 for the clamp
Drill out a 10mm diameter hole for BNC
Next some 100mm x 100mm 0.7mm copper sheet again from an ebay seller in the uk and again a message request to supplier for 98mm x 98mm cut was granted.
Measure 21mm from corners and cut 2 opposite corners off leaving this strange shape, drill the holes as indicated.
I purchased 300pcs box of m3 black nylon spacers nuts and set screws, I stripped off the protective backing from the reflector.
Now working with the reflector again insert some M3 x 7mm spacers and nuts (The box of 300 nylon parts only had 8mm spacers so I sanded off 1mm with 60/240 grit paper on a flat surface until the spacer was 7mm long..it took 30 seconds for each one )
Now the reflector looks like this
Now I offered up the reflector to the copper element using some bolts to assist the line up and check the holes, especially the BNC to see if all was centre and square.
Now is the time to ream out the holes slighlty is you need to. As you can see I am making 2 antennas here.
Now fix up the elements together using the nylon set screws.
Although I am making two LHCP antennas, I have laid out as a demo both polarisation options. Using a dish you need LHCP , using no dish and pointing the patch straight into the sky you need RHCP
Next take the BNC connector and file down the tube ferrule to about 4-5mm long at first and then offer it up to the reflector, continue with the file until you achieve a point where the bnc ferrule is lower than the 7mm nylon stand offs…6mm is ideal.
Put on the BNC remembering to install a large washer at the back, now take a look at the BNC tube in relation to standoffs, the BNC tube should be fractionally lower, like this. Why not 7mm ? This will become clearer at the next stage..
Take some stiff copper wire, (stripped out earth wire from 1.5mm twin and earth cable is good) just the right size for the tube.
Ideally Apply solder paste into tube, tin the ends of the wire and insert, make a solid joint with the iron.
Then run some solder further up the wire a little, not too much. Cut the end about 15-20mm from the base plate.
Tighten up the bnc nut snug against the plate and serrated washer, (Heres where you get issues with cheap BNCs because the threads strip out when a bit of torque is applied) use a bnc adaptor to get a better grip at the back and two sets of pliers, holding the rear with the adaptor still in the pliers ..nip the nut up good at the front.
Apply some rosin/thread lock adhesive or nail varnish to the threads of the connector..In the photo above I used rosin with a dab of heat from the iron.
Next up..Take the copper element and offer it up to the reflector with the wire sticking out..
With a bit of luck.. This should be the result. Put in the 4 nylon M3 metric machine screws.
If it doesnt fit first time, try loosening the nylon stand off pegs a little, the holes were drilled in the copper at 3.5mm which is deliberately a little over size than M3 so there so a little bit of room for fine adjustments/alignment.
Nearly all done, Cut the wire at a point where it is just barely showing sticking out of the front of the copper plate.. apply a tiny dab of solder paste to the cut end and solder up as neat as you can. Now the wire is touching the plate ,you will need quite a bit of heat from the iron as the copper plate disperses a lot of it out of your target area. You have to be brave enough to apply the heat without melting the dielectric material of the connector below..Fine tuning is required with the heat. Do not mess up here as if you melt the dielectric the ferrule will be loose and rattle around. The whole job can be trash and you will have to strip down and get out a fresh BNC and start all over again.
Fit the clamp and thats it, job done.
I think its really good to be able to switch antennas within a minute on the same dish, or use the antenna on another dish..easy to swap around with those neat plate /LNB clamps.
Experimenting further, I found small but significant signal /signal quality improvements were made by shorting the reflector and patch element in the exact centre with an M3 machine screw and nut. This was part of the original design by Adam (9A4QV) in his youtube video shown earlier in this article. This feature is there to prevent static build up in the air gap between the patch element and reflector which could damage components in the receiving chain.
Here is a short video of the results with a rusty old decommissioned Sky Minidish roughly pointed at 25 east, the dish support is 2 pieces of timber driven in to the ground.
Patch Antenna Supplier list.
Aluminium plate 200mm x 200mm 1.5mm thick, around £3.00 :Ebay https://www.ebay.co.uk/str/aluminiumdroitwich
(Free cut to 170×170)
Copper sheet 0.7mm thick 100 x 100 £3.95 for 2 sheets (custom cut free of charge to 98mm x 98mm with ebay message to seller)
300pcs nylon spacers/screws/nuts
BNC, I only use TE Connectivity/Tyco..the last thing you need is cheaping out here and screwing up a BNC nut on to a connector thread as soft as chesse.
Another previous article on Jaero L-Band Experiments