Antenna Gain

 I just wanted to say a little bit about antenna gain. I know that you have seen advertisements describing an antenna that has a lot of gain and it sounds really impressive. They just make you want to lay down the money and wait for the delivery truck to come in and you will be working the freaking world!  

    There is a tricky thing about antenna gain. I have read that it really doesn't exist and I have also read that it can't be trusted and at the same time it is the greatest measurement to use when picking an antenna. 

    So let's get down to the nuts and bolts of the matter. In the actual world, an antenna can't have any gain at all. An antenna is a passive device and regardless of what you do, an antenna can't ever transmit more power than what it is given. So if you decide to go QRO and dump 10 watts into an antenna, then you can never get more than 10 watts out of it. If you add an amplifier to the mix, you are still only adding more power to the antenna, but you will not get any more power than what you put in. In fact due to feedline losses and losses through connectors, and some losses with the antenna itself you will always get less power from an antenna than what you put into it. 

    A perfect antenna is what we call an isotropic antenna. This is an antenna that radiates equally in every direction. Unfortunately, an isotropic antenna is only theoretical and does not exist. As mentioned earlier an antenna can't give you more power than what you put into it, even an isotropic antenna. To get what we call gain we have to remove antenna performance from one direction in order to add it to another direction. So let's use a yagi antenna as an example. To get a yagi antenna to perform in the way that we wish it to, we remove as much performance and sensitivity in three directs (rear, and both sides) and direct the performance that we just removed and add it to the front of the antenna. So in essence you focus all of the antenna's performance in one direction. So not the front of the yagi becomes a really good antenna but it loses performance in three directions. This is why yagi antennas are on rotators. For example let's say that I have a yagi at my QTH here in Oklahoma City. I'm working on my QRP WAS and I need Rhode Island. So I have my big and mighty antenna pointed to the northeast towards RI. Then someone in Nepal is needing Oklahoma for their QRP WAS. Nepal would look good in my logbook. However, because my yagi has sensitivity removed from three sides, I may not hear Nepal calling CQ OK. But anyone in RI will hear me pretty good and I can hear them pretty well because I have all of the performance of my antenna crammed into one direction. So next time that you see an antenna that is advertised as having 14 db of gain, just remember that the 14 db of gain comes at a cost of 14db of gain in other directions. Also having gain on an antenna is a very good thing. It focuses all of your transmitted power into a narrower beam and that gives your signal a bit more punch which will only improve the performance of your station. You just need to make sure that all of that gin is going in the direction that you desire. 

    I appreciate you visiting my blog. If you have any questions or comments please leave them in the comment section below this post. You can also reach me at my email which is Aaron@k5atg.com. Until next time my friend, be safe, and may your DX be aplenty.