HOMEMADE ANTENNA TUNER PORTABLE

The components were all found on the surplus market and even though it looks very old it's really only a few years old. Below are some more photos of my T-network. I've always used PI-networks but component values can become unwieldy at the lower frequencies for such a network. It is a simple T-network and I have found that it can match any unbalanced antenna system I've ever put on it. There is nothing special about the antenna tuner described on this page. If you are not in a hurry all of the necessary components can be found used for very reasonable prices. I realize that good antenna tuner components can be quite expensive when purchased new if you are even lucky enough to find a supplier. They are so very simple to make that I find it hard to justify purchasing a store bought unit.

Commercial antenna tuners are very expensive and often of questionable quality. Whenever I would go to a sidewalk sale or hamfest I would pick up any components that might someday come in handy to make an antenna tuner. Even then, it is unlikely that the radio would be damaged - modern radios have protection circuits to prevent the final amplifier from overheating.For years I've thrown together simple antenna tuners to get me on the air when needed. You would want to take more care with a higher power mobile radio installed in the car, such as checking with an antenna analyzer. The stock “rubber ducky” antennas they come with are often far from 50 Ω even in perfect conditions. This is necessary, because they are designed to be used hand-held in a wide variety of positions, and all the objects around them will affect the antenna impedance. HTs are designed to survive being used with a wide range of antenna impedances. The antenna is probably just fine as provided, as long as it's installed per the instructions. (For example, my VHF antenna came with a slightly long wire element, to be cut down to length after testing.)īut you will almost certainly not need to do that. But for VHF/UHF, it works quite well to design one antenna that is a reasonable compromise across the entirety of those two bands.įor a new mobile installation, the best option is to obtain the use of an antenna analyzer, which can tell you not only what the SWR is across the bands, but also where the antenna's resonant peaks are - allowing adjustment if the antenna provides any room for adjustment. Both of these are activities are common on the HF bands (including up to 50 MHz, which is where HF and VHF techniques and antenna designs start to cross over).

HOMEMADE ANTENNA TUNER PORTABLE

This is because antenna tuners are needed when you want to use one antenna across different bands and wide bands, or to use an improvised antenna whose exact length and coupling to the environment are unpredictable (for portable operation). That's quite good for a mobile antenna.Īs a general rule, antenna tuners - adjustable impedance-matching networks - are not used for VHF/UHF antenna systems. While this antenna's length is close to 1/2 wave, it also has a loading coil in the middle, which means its electrical behavior is not equal to that of a 1/2 wave wire.Ĭomet's page says this antenna should have a SWR of 1.5:1 or less across its bands. 1/2 wave end-fed antennas require specialized matching networks. This is either not a true 1/2 wave antenna (I see it has a loading coil in the middle) or the description is made of lies. Usually the trouble is if you're using an antenna not designed for that band. It probably won't be exactly 50 ohms across both bands, but that's fine as long as the difference (as measured in SWR) is not too high.

An antenna of this kind should be designed to have a 50 ohm impedance (when properly installed on top of a ground plane such as a car roof).

Homemade antenna tuner