RadCom Basics May 2022, Edition 28

RadCom Basics 23 VHF antenna choices for the home a primer by James Stevens, M0JCQ Introduction When thinking about VHF anten- nas for the home QTH you have a few choices to make. This arti- cle will cover the main options you have and the relative merits of each. Each antenna will have certain applications over others and really, it’s about choosing what works best for you and your QTH. Gain and Directionality Before we dive in, we first need to understand the relationship be- tween gain and directionality. To get gain we need to understand that this can only be in a certain direction(s), to the sacrifice of others. A Yagi will provide signifi - cant gain over a dipole, but only in a certain direction. Reviewing the radiation plot of a Yagi will show that it’s particularly good in front of the antenna, but much worse at the sides and off the back. Sadly, you cannot have an omni-direc- tional antenna and a lot of gain, physics doesn’t work like that.You can think of it as if the antenna is directing all the RF fed to it into a narrow beam pointing in a certain direction, the more gain (and ele- ments) you have, the narrower and stronger the beam becomes, until it’s almost akin to a laser beam. On any band this can be both an advantage and disadvantage. If you are using aYagi and pointing towards a station, then they will hear you really well (and vice-versa).Anyone however to the side or back of your Yagi may hear you, but you’ll be sig- nificantly weaker. During contests I find you can work local stations off the back of theYagi, but off the sides is very difficult. dBi vs dBd Now we have to mention a little about some acronyms; dBi and dBd. It pays to understand these