https://www.youtube.com/watch?
I didn't have the money to get the aluminium sheet at $105.00AUD each (at Masters) and I needed two so I came up with the next best thing, a roll of Hardaz Vermin Wire Mesh 6.5X6.5mm, 15cmx10M roll for about $20.00AUD. It wasn't wide enough so I modified it by soldering two lengths together and it almost came out at the correct size, so close it didn't matter to me anyway. Now to make a CONE is a bit tricky and it took me a few goes with big sheets of paper first but it worked okay in the end, mind you it isn't pretty but it tests perfectly electrically and works very well.
The top and bottom formers are 10mm MDF and the three supports are good quality dowel, I also cut out some curved MDF to hold the wire in the centre and as circular as possible, you can just see one of them to the right of the centre dowel on the bottom former. All the dimensions are in the video for the wire and you will need to design your own support frame. As I said it isn't perfect, even a bit wonky but it works very well. The RTL.SDR comes with a Small antenna and simply didn't work at all in my location so I made up a 2M coaxial co liner dipole with three elements and it works fantastically on the amateur band but not much good above and below that. The bi-conical was picking up hundreds of automotive RF remote door lock transmitters on my first try, amazing to listen to, yes I'm nuts I know, also I was listening to aircraft coming and going from Sydney airport and I live in Bathurst, on a big hill and I look towards Sydney from my yard and I couldn't do that on the original antenna or the coaxial antenna so if you want to build a cheap antenna that works amazingly this is the one for you. By the way get it up as high as possible and it will blow you away I'm sure, it did me.
PS. I forgot to mention that I got the RTL.SDR so I could receive and play with the Cubesat, Amsat and othersat's out there so I will be building a yargi or two to get good signals for them and most of the sensors have arrived for the Arduino home based sat so more on that later as well.
How did you make the calculations for angle, length, gap, etc? I've been combing the internet for a calculator or formula, but haven't found one. I only found one for discone.
ReplyDeleteHi Alex, Sorry it took so long to get back to you I have been studying for my Standard Amateur Licence and lost track of the days, the dimensions are given in the video that I got the idea from but you will need to do some maths for the cone and I got that from wikihow, because you know that the diameter of the cone is 28cm and that the cone height is also 28cm you can work out the shape to cut out to make the cone, it took me a few goes to get it right and I did a test run with thin cardboard to make sure that the cone shape would work. Try www.cleavebooks.co.uk/scol/calcone.htm which is Cleave Books Cone Calculator web page, that made it really easy for me. The space between the two cones is about 10 to 20mm, it's not that critical but don't make it to wide. Hope that helps because it is a fantastic receive antenna, I have even transmitted on it but I don't recommend it, SWR is way off.
ReplyDeleteThank you Terrence, for your reply. One thing I find puzzling is what dimension determines the bandwidth. What would the gap between cones represent in terms of performance and what is the function of the angle of the cone. Your's look 45 degrees from center line right angle to the hypotenuse. To summarize:
ReplyDelete1. What determines bandwidth?
2. What performance characteristic would the cone-tip to cone-tip gap affect?
4. What performance characteristic is affected by the cone angle?
3. Confirm you total cone angle of your antenna is 90 degrees (45 degrees from center line).
I appreciate your assistance. Calculators for discone antennas are widely available but it seems there is resource hole for bicones (biconicals).
I'm going to attempt it with copper or tin plated sheet metal unless I can find a pretty perforated sheet like the one in the video.
Cheers.
Alex
Actually, from the picture it is about 60 degrees, no?
ReplyDeleteThe biconical antenna has a broad bandwith because it is an example of a travelling wave structure, basic statement I know but if you google it you will get a large number of theory sites that can tell you a lot more, my understanding of it is very basic, sorry.
ReplyDeleteAntenna theory is a subject I am still studying and I use information from the WIA in Australia or the ARRL in America or I just google the subject and sort through the information as needed. The cone angle does come out at about 60 degrees but if you draw your circle with a diameter of 28cm (radious of 14cm) and cut the section out using the 161 degrees angle so you get a cut out like a piece of pie and join the ends together you will get the exact demsions needed for the cone, try it on a sheet of thin cardboard first and you will see what it should look like, it's the smaller piece of the pie that becomes the cone as I'm sure you know. The copper sheet or tin sheet would work perfectly as did my vermin wire and my cones were less than perfect I can tell you but the antenna works perfectly, it will surprise you I know because it did me.
Cheers, Terry. VK2FDGN.