Sequoia Aircraft Corporation F.8L Falco, Construction Manual

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F.8L Falco Construction Manual 14–1 Revision 4, March 1, 2002
Chapter 14
Antenna Installation
The internal antenna system described in this chapter provides for the installation of antennas for
dual VHF COM, dual VHF NAV (VOR-LOC-GS), DME, ADF, transponder, and marker beacon
within the wooden structure of the Falco. This system was designed by Radio Systems
Technology, which once offered kits for the Falco. RST stopped selling airplane-specific kits, so
the complete kits are now available from Sequoia Aircraft, however RST still offers components.
Builders who wish to order the antennas separately from RST may use the “materials required” list
for each antenna, but we would strongly advise that all antennas be installed even though no
immediate use of the antennas is planned, as it will be quite a problem to install them after the
aircraft is complete. Radio Systems Technology is
not available to custom engineer any
modification of this system.
No. 1 Communications Antenna Installation
See Drawings No. 160 and 161. The primary VHF communications antenna consists of a ferrite-
foil antenna located in the vertical fin. The foil antenna elements are sticky-back and may be
temporarily attached to any clean, dry wooden surface. It is absolutely mandatory to cover the
elements with varnish, epoxy or some other nonconductive coating to ensure that the elements
are firmly and permanently attached to the airframe.
The antenna radiators consist of two pieces of copper tape arranged as a vertical dipole along the
leading edge of the vertical fin. Each “ear” of the dipole element is 20.3” long, with a 5-10mm
center gap. It is important that the antenna be placed as far forward on the vertical fin as is
reasonably possible to get the antenna away from the metal hinges. There are several methods of
installing the antenna. The antenna may be installed on the inside of one of the side skins
between the skin and the ribs, or the antenna may be installed on the outside of the skin, with a
small hole drilled in the skin for the lead to the coaxial cable and balun. The balun is the name
for the assembly of ferrite toroids. Three toroids are all that are required. Sometimes four are
used, but it doesn’t make any difference. The toroids should be as near to the end of the cable
within reason, but there is no critical distance—anything within about an inch is fine. The
coaxial cable and ferrite balun assembly should be fastened firmly against the skin so that they will
not vibrate loose during service. Epoxy resin with a small strip of fiberglass cloth should do the
job nicely. In particular, the solder joints at the coaxial cable-to-elements must be coated with
epoxy and fiberglass cloth so that years of airframe vibration will not break the joints. There is no
critical length of coaxial cable or matching network required for this antenna.
Keep the coaxial cable and any other metal fittings as far away as possible from the antenna tips.
(Metal near the center of the antenna—that is, near the coaxial cable attach points—has little
effect on the proper operation, but the tips are rather sensitive.) The coaxial cable should run aft
at right angles to the antenna elements and then down the main fin beam, along the upper right
side longeron to frame No. 7, then to the center console area, then forward to frame No. 3 and up
to the radio. The coaxial cable will require one UG88 (male) and one UG89 (female) BNC cable
connector at frame No. 8. Do not run the coaxial cable along the bottom of the fuselage as it will
interfere with the marker beacon antenna.
Because the length of the antenna is important for good reception, it is preferable that the
antenna elements be laid straight on (or under) the skin, and if the elements are run “up and
over” the rib cap strips, the reception of the system will suffer.