At the KCRA, November 16th meeting we will build quarter wave ground plane antennas.  You will measure, cut, assemble, and take home an antenna in one of the following bands that you choose, 2-meter (144 Mhz), 1.25 meter (220 Mhz), or 70cm  (440 Mhz).  Using some simple math and a few inexpensive tools and parts, you should have yourself an antenna ready to operate and take home after the Tuesday KCRA meeting.  A quarter wave ground plane antenna can be used as a base antenna, back up portable antenna, emergency antenna or when lightning is flashing a good inside antenna to keep you safely on the air.

     Why a ground plane antenna?   Well first it is quite simple to put together and requires minimal skills, tools and inexpensive products.  It is a very versatile and fun to play with antenna allowing for some experimenting.  With the drooping quarter wave ground radials at a 45-degree angle exhibits a nominal 50 Ohms impedance, the antenna most closely matches a 50 Ohms coax cable, and will not require a matching network.  These 45-degree drooping radials simulate an artificial ground and lead to a 50 Ohms impedance.  It functions in the same way a magnetic mount on the car, using the roof as a ground.

     The quarter wave antenna is vertically polarized and for FM voice work it is perfect for repeater usage or local simplex.  The physical size of the antenna also allows itself to be easily moved, set up where needed or installed permanently or taken apart and packed in a travel bag.   The antennas we will make will be good weather antennas not be exposed to rain but with some pvc tubes or shrink wrap and silicone they can be made waterproof for outdoor inclement weather.  Also, since we will use SO-239 chassis mount it will be quite easy to connect your mobile/base radio using a coax with a PL259 and operate at higher wattage than a HT. ­*(NOTE THE ARTIFICIAL GROUND DOES NOT REPLACE A COMPLETE ELECTRICAL GROUND FOR YOUR STATION ).

     The formula below and ground plane antennas can be used on the 50 Mhz as well as all the HF frequencies.  The allotted time at this meeting will prevent constructing HF antennas, but in the future, if the members wish a 10, 15 17 or 20 meter antenna could be built.  The quarter wave antenna can be used for dx and the polarity will not be an issue.  It can be made portable or set up permanent.  A portable version would use #10 pvc water pipe at the top section support and metal conduit to get a longer mast and get the antenna up height in the air on its own mast and easily held with a tripod, fence post, bench, guy wires, tied to a tree, or any idea that works.

     A quarter wave ground plane antenna has three equal length radials and looks like an upside down Y.  The length of each radial is dependent on the frequency or band you wish to operate on.  So choose your frequency in the middle of frequency ranger or perhaps use the KCRA repeater frequency input as the center frequency.  The center frequency you choose will have the lowest impedance and most closely match the 50 Ohms and as you vary from this frequency so will the impedance and SWR.  To calculate the lengths of all three radials us the following formula:  Length in feet equals 234 divided by the frequency in Mhz. *(note due to velocity factor a 5% change is used from the standard formula for calculating length).  For the KCRA repeater input frequency we get the following length.  234 divided by 146.430 and give a length of 1.598 feet or 19.176 inches. 

      This is the length we will use to construct or project.  If you wish to use the 220 Mhz or 440 Mhz band the calculation is the same.   Looking forward to seeing you at the meeting and helping you put together a antenna!