"Residential" Off-Centre-Fed Dipole
The quintessential issue with having a QTH antenna is space. Most residential lots tend to be restrictive about what kind of antenna a person can install. So you want the most bang for your buck, so to speak. Or perhaps better said, the most bands for your buck. Enter the Off-Centre-Fed Dipole for residential use. There are other configurations of this that can go all the way up to 80m if you have the space to do it. But this one gives you 40m-10m.
This post was inspired by the following video by Ted Edwards, W3TB. It is an excellent video for highlighting the advantages of an OCFD. In the video, he makes mention of an article that was published in the November 2018 edition of CQ Magazine. I wrote to Ted and he was kind enough to pass it along to me. Click here for the PDF version of that article.
The OCFD antenna needs a 4:1 balun/transformer to knock the ~200ohm impedance down for the rig. This needs to be a Current balun and not a voltage balun. The 4:1 transformers that are produced by LDG are all voltage baluns and should be avoided for this application. You can easily make your own 4:1 transformer by creating two identical 1:1 chokes and connecting them together. The iron ferrite core choice should be either a type 31 or type 43. The following image shows enamel wire wrapped on the 2643251002 type 43 core.
What makes this a "residential" antenna is the shorter overall length. And, it differs a bit from other OCFDs in that it isn't exactly the typical 1/3 2/3 split. This antenna uses 27' and 41' measurements. The article and video goes into full detail about the design considerations as well as the SWR readings - all of which are manageable with an onboard or external tuner. This convenience with low trade offs, as well as gain and the directional nature of this antenna make it an awesome choice for a home setup or for portable use.
In my build, I housed the transformer assembly in a waterproof exterior electrical box. Attaching 200 ohms worth of resistors across the antenna connections showed really good SWR readings under 2:1 on 40m, 20m and 15m. It was slightly over 2:1 on 10m. None of these would be a problem for a rig's internal tuner to clean up.
I ran a WSPR test on this antenna on 30m and this map was the result. As you can gather, the antenna has awesome coverage of North America, Western Europe, and South America! The added perk is you can aim this antenna wherever you want to work more as Ted does for contesting. If you're looking for a slick antenna for your QTH or portable, look no further than the Off-Centre-Fed Dipole!
Thanks for checking out this build!
VE5REV 73!