My first project for the radio section of my website, and a nice easy one at that! This is a loaded dipole for the 40m/7MHz band, this design was chosen mainly due to the fact I don’t have enough room to hang a full size dipole. I created the design using a great calculator I found here. There are many great calculators on that website (I also used the air-core inductor calculator for this antenna), well worth bookmarking!!.
I punched in a maximum length of 7m into the calculator and started fiddling with the values until I got something useful. 7 meters happens to be the longest length on the roof where I can easily hang a dipole (relatively) straight. Saved me having to put up a tower/supports, and also meant it was very discrete and out of the way.
The antenna is very basic in its construction, made from .75mm enamled wire I pulled out of an old transformer. Loading coils are formed on 1″ ID PVC pipe, and the center insulator holding the BNC connector and balun is a piece of plastic packaging I found in the bin in the garage. This is one very low cost antenna as pretty much all materials were recycled, even the bolts in the loading coils which recycled from the transformer I pulled apart. The only thing I purchased was the BNC connector.
Total time spent building and hanging it was probably around the 2 hour mark. While I was finishing the balun, I had the antenna strung up about half a meter off the ground. Thought I’d do some quick testing with my VR-500 receiver (not very good on HF…), and managed to listen in to a very clear SSB transmission from Tasmania (VK7), which is around 400km’s from where I live in Victoria! Since hanging it up on the roof I’ve been able to listen in on several SSB transmissions, and plenty of CW too. Just need to learn morse code…