Original Posted By: owner-pietenpol-list-server(at)matronics.com
You want the antenna as far from the ignition as possible so I would not putit on the cowling. Likewise, vibration and prop blast would tear it off inno time. finally, if you use a dipole antenna, you won't need a groundplane.Here is how my dad, the US Mechant Marine radio operator in the big onedouble you double you eye eye taught me years ago to make a quality, simpledipole that has but one connection at, aprly named, the connector (hencereally reliable on an iced over ship in the North Atlantic in 1944):Take a piece of 50 ohm coax with the multistranded core, braided shield, anda nonfoam (uses a nylon like material instead) insulator between the coreand the shielding. I use RG-58A/U available at Aircraft Spruce and otherplaces.From one end of your coax, carefully cut off the black rubber/plastic thatcovers the shielding. Do this for about 30 inches or so (might be 20" ifyou use a 1/8 wavelength - see below) from one end of your coax. Bunch upthe braided sheilding so that it can slide up the nylon core insulation.Now, slide the shielding up and over itself so that the sheilding now issliding up the wire the other way. In other words, double the shieldingback up upon itself with the remaining black rubber/plastic that covers theshielding separating the shielding from itself. Pull it up as far as it cango. If you have a piece of heatshrink tubing, begin sliding it up and overthe nylon with the core inside until it is up and over the braiding that hasturned up and over itself. The length of each pole of the dipole should be1/4 wavelength or about 21" or so for the middle of the 118-136 Mhz bandthat we use so trim the nylon end to 21" and the upturned braid to 21". Ifyou want, you can make it 1/8 of a wavelength or 10-1/2" for each pole, thatis ok with a miniscule degradation of performance. It will fit in a pietbetter that way. Trim the shielding to the 21 or 10-1/2 inch length andalso trim the insulated core end of the wire to the same length. Finishsliding the heatshrink up and over the upturned braid and heat it til itshrinks. I use a paint stripping gun. The antenna portion is thus either42" long or 21" long depending upon whether youa re doing the 1/4 or 1/8wavelength antenna.Attach a BNC connector to the other end of the wire. Make sure that thereis no shorting between the sheilding and the core at the BNC connector or itwill ruin your radio.There you have it. A dipole antenna tuned to the frequency band we use.Locate this as vertical as you can with some ribstich cord in the fuselage.I would make the 1/8 wavelength and attach it to the fuselage side diagonalthat starts just aft of the bellcrank bearing after running the wire alongthe top longeron. From where the doubled over shelding begins to the otherend of the wire at the end of the nylon covered core, this should be asstraight run as possible as this is your antenna. What the rest of the coaxdoes, does not matter as long as you obey the radius of bend rule below.Also the total length of the rest of the coax does not matter but try not tohave any extra. Also, do not pull the ribstich cord too tight as the coaxproperties get really screwed up if you crush in the wall of the coreinsulation. That is why we don't use foam insulation in airplane coax.Also keep the radius of bend of the coax to a big number like 6". (Tiewrapswill usually crumble in a few years so that is why I would use ribstichthread or something of equal longevity.)Materials needed is maybe 12 feet of coax and the BNC connector and two feetof 1/2" heatshrink.You can mess with this off the airplane and see that it works well. I willtry to get some pictures together.Chris bobka-----Original Message-----
RE: Pietenpol-List: Q&A on internal antenna for wood or compositeaircraft
RE: Pietenpol-List: Q&A on internal antenna for wood or composite
Original Posted By: Kip & Beth Gardner