What I recently learned about Antennas
I call this "my weird wire dipole antenna with self selecting frequency that some people would maybe call a Fan dipole but I don't have a balun (in form of an inverted V)" What a catchy name that is... I hate buying things, and it's a field that is supposed to be experimented with.
There is a lot of science about and around antennas. Like ... a lot. Reading up on it I quickly felt overwhelmed so I decided to just "go for it". What annoys me a lot these days when you try to find information about things people build themselves - much of the time they seem to have endless supplies and some totally overkill workshop to do things in. As much as I would like that; I don't have that, and likely most people don't - this may result in frustration and then people just buying ... an Antenna. But where is the fun in that?
So... there I was. Wire; as high in the air as you can and you're good to go, right? Well. Yes. But no. But also yes.
I wanted to build my own antenna - on a budget. A low budged that is - with items I could easily get my hands on without the need for a workshop. And believe it or not ... in many (?) scenarios it's not very easy to get your hands on even the simpler things. Like ferrite cores. Building my own basic radio is very doable but I do like to have a radio with modern capabilities and a cool Waterfall display.
Starting with this antenna, at first I felt I was going nowhere. the VSWR got worse and worse whatever I tried, it was deaf as a Dummyload and even the cheap pullout steel antenna of my HackRF was better.
After some frustration and a few "days off", I started over and build a completely new antenna. Still keeping this on a very small budget I bought:
- Cheap coax cablePost title
- 2x 15m of steel cable
- 80m cheap random "12V wire"
- 100m string
- 10 wireclamps with a "U" at the end
- A bit of "Flower-Wire" - essentially just very cheap wire
- A handfull of screws
- A handfull of "hook screws" (They look like a questionmark)
What else is used:
- A plastic box, in my case I used an old plastic box wood-screws come in.
- A piece of leftover wood-plank
- An old "load strap" (also called tie down straps, a rope wouPost titleld do. I used this to wrap the contraption around my chimney; drilling 2 Holes would also work just fine, but I dont have a drill with a "hammer" option.)
RESULTS
- STEEL CABLE: 7mhz, dry conditions, SWR 1:1,5 across the band.
- WIRE: 14mhz (5.023m), dry conditions, SWR 1:1 up to 1:1,5
- 80m SWR ca 1:1.3
- over all bands a great reception with my hackRF.
I found plenty of antenna calculators online, but this one I found to be the best. https://www.omnicalculator.com/physics/dipole
The rebuild started with me trying to make this "universal" and easy to extend, modify etc. So I started to build the base, which allows me to attach the wires to it as easy as possible.
I strung the wires from my chimney across my house to the trees.
- for 14m I used the steel cable, with each leg of 991 cm lenght.
- for 7m I added 1056 cm of my wire
- for 80m I added 2x 399 cm of wire.
I foled some back in later on essentially shortening it about 14 cm.
I'm very fortunate that my garden allows for all these bands to have full length legs without having to do any bends... Z shapes or anthing.
Using the string I threw on the trees I was able to pull the wires up very easily. And its pretty much invisible too!
All anntena cables are directly connected to the coax shield and core respectively. I wound a "coil" halfway down the antenna cable around a piece of left over plastic tube. I have not used any baluns. I can only run 10W max, so I'm not really worried about RF coming back.
And after my first frustration - this time ...no fuss ... I barely had to adjust anything. I got pretty good SWR 14Mhz, 7Mhz and 3,5Mhz which are the bands I'm most interested in for now out of the box like this. It happens to work also just fine on 433Mhz and 144Mhz. I'm not a huge fan of UHF, but it works kind a. I guess with quite some loss?
I'm honestly not sure as why it seems to be workign well - I believe the coax I bought of amazon accidentally acts as a BALUN. Possibly the coax also acts a 3.leg - with my current tools Im not sure if/how I can confirm or check that (yet) of if that is good or bad ... Luckily where I live there is very little to almost no noise floor, so that's not really a concern. The most important thing you can learn (if anything) from all this ... don't get "scared" or discuraged. Just try. I'm usually not very good learning stuff from books so I tend to try and error and then figure out things somehow. With a budget of around 30-40 euros I was able to build a multiband antenna that works surprisingly well and I a learned a ton doing it. And it was fun too!