Before I get started on today's blog about what I am going to talk about, I am going to throw one picture out there so that my followers who are not as technically savvy or not as keen on understanding, or who do not understand are warned...
That is all... I promise to all of my non-technical followers, I will post a special blog up for you all later this week.
Now we go on to today's topic: one which all amateur radio operators should be aware of: the use of antennas and how DB, or decibels work.
Think back to the days when you studied and took the technician examination for your first license... You learned about antennas, and touched ground on the basic concepts of how they work. Today, I will be talking about these in a mobile sense, or in car operation.
As many of you are aware, most mobile antennas mounted on cars are omnidirectional. There are some cases, however, where unidirectional antennas can be used on a vehicle, which are predomintly for VHF and higher, like this one below are predominantly found on rover station for VHF and UHF contesting.
(5 Element yagi pair used for direction finding)
Now that I talked a little about antennas, I want to now talk about the factor that drives antenna, or gain. Gain is measured in the unit decibel, which is very similar to sound. It is a logarithmic measurement of the intensity given to a specific reference point, and in the case of amateur radio there are two of them. dBi, or decibels to an isotropic radiator, or theoretical antenna that radiates the same intensity in all directions, or dBd, or decibels to a half wavelength dipole. dBd is approximetely 3.1 dBi. Most antennas that are used in VHF mobile operation range from about 2-4 dBi, and 3-7 for UHF. Common ways to mount such antennas is via a magnetic base, which was commonplace for a while, and lastly NMO mounted, or those who do not want to use a magnet to stick their antennas on their cars and mount them somewhere, usually on the trunk or off to the side of the car. I am going to answer right away how you can improve your overall gain on your VHF mobile antenna setup. First of all, if your car can support it, always try to purchase a 5/8 or 3/4 wavelength antenna, since they will provide more gain then the usual ones out there in comparison. Second, try to mount the antenna at the highest point on the vehicle if possible, being careful to take in account low clearance areas that will not hit your antenna. My rule of thumb is to keep it below 7', since most drive-thru clearances are about that height.
That is all I have to say for now, until then this is N2ASD signing you clear.
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