Hello and welcome back to my blog. In this posting we will continue talking about antennas, or omnidirectional antennas to be exact. Omnidirectional antennas are probably the most common types of antennas that you will use in your ham radio experience. These antennas range from the antenna that you use in your car, to a vertical antenna that you have on your home station.
First off, lets talk about mobile antennas. Mobile antennas are the ones that you use on your vehicle or even the “rubber ducky” antenna that is on your handheld radio. The rubber ducky on your handheld is normally not worth much when it comes to helping your transmission range as they are basically dummy loads, at least the ones that come with the radio normally are. You can buy after market antennas that have a little bit of gain to them and that can help increase your radiated power output. In my opinion though, its not really worth the extra money to buy one unless you break the one that came with the radio. The gain on most of them is marginal and normally when you are talking on a hand held you are doing so in close proximity with another ham or within range of a repeater.
Antennas that you put on your car and hook to a mobile radio are another story. For one thing, you have to have one otherwise you wont be able to talk very far and you will more than likely hurt your mobile radio if you key up on it and don’t have an antenna hooked up. These antennas come in a variety of mounting options, lengths, gains, etc.
One of the most common types of mobile antennas is the mag-mount version. This type of mount uses a magnet in the base to attach to your roof or truck and is normally strong enough to hold the antenna on at highway speeds. The pros to a mag-mount is that you can easily move it if need be or take it down if you go into a parking garage and you are in a higher clearance vehicle. You also get a nice ground plane from the surface that the antenna is placed. The drawbacks to them are that the metal surface under the magnet can rust after a while and if you hit a low branch or something that is hanging low, it can knock it off and scare the crap out of you when you driving.
Another type of mounting option that you have is a lip mount. This type of mount will mount to the lip of a truck or hood. This option gives you a lower clearance height and is more of a permanent mount. A variant of a lip mount is a rack mount like you would put on a luggage rack on top of your suv. The pros of this type of mount are that it more of a permanent mounting, so it wont blow off at higher speeds or get knocked off by a low hanging object and with the exception of a rack mount it is normally lower on your vehicle so you are less likely to hit it on something anyway. The cons to it is that because it is mounted on the side of your vehicle you don’t get as good of a ground plane like you do with a mag-mount that you can put in the middle of your roof/trunk. If it is mounted on the top of your vehicle like on a rack or even a door frame, when you go into a parking garage your cant take it down as easily. However there are options for just this type of situation. You can get a foldable mount that will fold back either manually or you can spend the big bucks and get one that is motorized where you press a button and it will fold back or up vertical.
The third options you have is a permanent mount. This type of mount you have to drill a hold in your vehicle to do and if you mount it on the roof you have to take down your headliner. You can of course mount it on your truck or on a headache rack on a truck. This type of mount is good because the only way the antenna is ever come off is if you want it to, or if it breaks. You wont have the issues of rusting like you do with a mag mount. The con to it is you have to drill a whole in your vehicle. If you are like me, you just don’t want to do that. The first picture below is a standard lip mount that you have to move manually, the second is the motorized mount. Both are made by Diamond Antennas.
With mobile antennas, it is very hard to build them yourself and is not really worth even trying to build one on your own. The homebrew type antennas are more for your home station, which we will go into now.
House Stations Antennas
Home station antennas can be both homebrew or commercially made. A lot of people like to build their own home station antennas both for the hobby of it and for the ease of building. My first home station antenna was a ¼ wave ground plan. It was very easy to build. All you need is a SO-239 connector and 5 short pieces of shift wire. We used 1/8” copper welding rods. All you have to do is solder one piece that is 19.25 inches tall vertical from the center pin and solder 4 from each corner at a 45 degree down angle that is 20.25 inches long. Then just mount it to a pole, hook up a coax and after checking the SWRs your ready to go. Below is a picture of how it should look like assembled.
Another popular type of home station VHF antenna is a J-pole. The J-pole is an antenna that is built out of some type of conductive tubing, usually copper or aluminum that is shaped like a J. Below is a picture of a 2m J pole antenna that you can easily build. There are ways to make a J-Pole antenna a dual band by modifying it slightly. Arrow antennas sell a dual band antenna that is a very good antenna and is what I currently use at my home station(Even though I don’t have a radio at my home anymore because I sacrificed my office for another kids bedroom). Click Here to buy it through Amazon.com or you can buy it direct from Arrow Antennas
Let’s move on to some HF antennas. Just like with VHF/UHF antennas vertical antennas are a common type of antenna use. You can get both single band and multiband vertical antennas for HF.
Another common type of hf antenna is a long wire or inverted V antenna. This type of antenna is just like it sounds like, it is a long wire with a coax connector in the middle. The main draw-back to this type of antenna is you have to have an antenna tuner to use it otherwise you could hurt your radio. So what does an antenna tuner really do? Well it doesn’t change the length of your antenna or adjust the SWRs of the antenna. What it actually does is transform the impedance at the feed line input to a value that your transceiver can handle, typically 50 Ohms. Once your radio sees the 50 Ohms impedance it can put out the maximum RF output.
The last type of antenna that is used is directional antennas, but we will be talking about that in our next post, so please check back later for information about that. I would like to thank you for coming and checking out my blog. If you like what you have please share my blog with your friends and please like my facebook page. The link to it is in the top right of my page, just click on the Facebook icon or just goto http://www.facebook.com/everythinghamradio.
73 de Curtis, K5CLM