GMRS J-Pole Antenna

2/27/2005 marc 57 comments

A j-pole antenna for GMRS/FRS frequencies (462.550MHz – 467.725MHz)

This article will outline how to build a j-pole antenna for the GMRS/FRS radios. These radios are the type you can buy at sporting goods stores such as REI, Cabelas, etc. There are several radio manufacturers who make GMRS/FRS radios with removable antennas. This antenna can increase the range of these radios by miles!

NOTE: 1) You can only use this antenna with GMRS or GMRS/FRS combo radios which are built with removable antenna (you cannot use this antenna on or modify an FRS-only radio or as I understand it, GMRS/FRS radios which do not have a removable antenna). 2) You need an FCC license to use GMRS radios in the US (read the packaging on the radios you get for more info). Know your local laws to make sure it’s legal to use this antenna before building it!

WARNING: Torches, soldering irons and solder (especially, silver solder) are very HOT. Be very careful while building this antenna! Always wear safety goggles and other appropriate safety equipment.

What does an external antenna do for you?

Why would you want to build an external antenna in the first place? What advantages does it have over the stock, built-in stubby antenna on the radio? There are a lot of reasons. The stub antenna which comes standard on hand-held radios is a minimum compromise between size and power, typically weighted towards a smaller size rather than towards power. In fact, you might say the small antennas are sub-optimal when it comes to capability.

With a small handheld GMRS/FRS radio like those made by various manufactureres such as Motorola, Midland, Cobra, etc., you will be lucky if you get the reported range and more likely you will get half or a quarter of that in real-world use. The radios I have used in this article are the Midland G-28. Now out out production, you should still be able to find them on E-Bay or some on-line retailers. It’s a great radio and it has a removable antenna which in my opinion is a necessary feature for all GMRS/FRS radios that I purchase. There are other manufacturers which make radios with removable antenna. Look around for them – they’re worth every cent extra you might have to pay for this feature.

So, what kind of performance increase can you expect with one of these antennas? Everyone’s experience is different. You can’t say “this antenna will give you n miles greater range”. That would be similar to saying “How far does that flashlight beam project?” – well, it depends on the particulates in the air, the obstacles in the beam’s path, the rocks and trees in the way, etc, etc. An antenna’s range is affected by various factors. All you can really do is say how much a given antenna will increase effective power output of a source (really, focus in a certain direction). The j-pole antenna gives approximately 2.5 dBi gain over a unity-gain antenna which is slightly better than a vertical dipole and much better than the built-in stub antenna. For more information on j-pole design see the references at the end of the article.

For me, the real-world experience has been great. With one of these antennas on both mine and my father’s car, we were able to communicate over approximately 18 miles of semi-mountainous terrain. The distance was between Heber, UT and Marion, UT which is near the base of the Uinta mountains. I was also able to pick up (but did not try to communicate) a conversation at Kimball Junction, UT near Park City, UT from about 40 miles away in Springville, UT. Everyone’s experience will be different. The conditions for the 40 mile distance were optimal with cloud cover which provided a ceiling for the radio signals to reflect. YMMV.

The next page describes J-Pole design.