A 5 element coco made from coax (soldered) with a shorted stub.
I picked the solder method because after building a few coco's aerials and comparing the results. With a coco made by pushing the elements together they are very unstable and vary massively on the network analyser by many dB's with the slightest movement unlike the soldered ones which remain fairly constant.
Sorry there is just a little bit of maths to know
to get the wavelength of 1090MHz you need to use the following formula
λ=C / f Where C is the speed of light and f is the frequency.
this works out to be 299792458 / 1090000000 which equals 0.275m or 275mm (i worked to more decimal places than displayed here)
however because we are using coax cable, we have to account for the velocity factor of the cable.
For the cable i am using.
cable.jpg
If you look up the data sheet (website wouldn't let me link the PDF) it has a velocity factor of 85% so taking our length of 275mm and multiplying it by 0.85 we end up with a wavelength of 233mm now for the coco we will be working with half and quarter (for end piece) so they are wavelengths of 117mm and 58mm.
I would recommend buying a pre-made BNC to BNC coax cable I will explain at the end of the trio of posts. However i will start with how I make each element.
Taking a piece of coax remove about 15mm of the PVC outer, I personally you a scalpel nice and sharp so you dont have to use any pressure. Taking your knife roll the knife around the outer of the cable remember you dont have to press hard because when you bend the cable it will tear the outer.
roll.jpg
tear.jpg
Remove the outer PVC and twist the braid together off to one side.
braid.jpg
tin and trim the braid and centre core making sure that the braid is trimmed to the length of white centre of the cable. I aim to have 5mm of dielectric showing and then a further 5mm of the centre copper showing.
prepped.jpg
I picked the solder method because after building a few coco's aerials and comparing the results. With a coco made by pushing the elements together they are very unstable and vary massively on the network analyser by many dB's with the slightest movement unlike the soldered ones which remain fairly constant.
Sorry there is just a little bit of maths to know
to get the wavelength of 1090MHz you need to use the following formula
λ=C / f Where C is the speed of light and f is the frequency.
this works out to be 299792458 / 1090000000 which equals 0.275m or 275mm (i worked to more decimal places than displayed here)
however because we are using coax cable, we have to account for the velocity factor of the cable.
For the cable i am using.
cable.jpg
If you look up the data sheet (website wouldn't let me link the PDF) it has a velocity factor of 85% so taking our length of 275mm and multiplying it by 0.85 we end up with a wavelength of 233mm now for the coco we will be working with half and quarter (for end piece) so they are wavelengths of 117mm and 58mm.
I would recommend buying a pre-made BNC to BNC coax cable I will explain at the end of the trio of posts. However i will start with how I make each element.
Taking a piece of coax remove about 15mm of the PVC outer, I personally you a scalpel nice and sharp so you dont have to use any pressure. Taking your knife roll the knife around the outer of the cable remember you dont have to press hard because when you bend the cable it will tear the outer.
roll.jpg
tear.jpg
Remove the outer PVC and twist the braid together off to one side.
braid.jpg
tin and trim the braid and centre core making sure that the braid is trimmed to the length of white centre of the cable. I aim to have 5mm of dielectric showing and then a further 5mm of the centre copper showing.
prepped.jpg
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