1 “BUILDING QUICK TAPE ANTENNAS” Dr. Al Torres KP4AQI FEBRUARY 2015

2 Briefing Outline Introduction The Fundamentals Impact of Dielectrics Impact of Tape Thickness Skin Effect (no soldering!) The Free Computer Program Items that you will need (hardware wise) The Simple Dipole The Simple Monopole Fabrication Demonstration Antenna Testing

3 Introduction Why build tape antennas? Can be done very quickly, requires minimum number of materials, and can be used for emergency situations or while traveling (hotels large bay windows) Easy to fabricate with common materials Choice of monopoles (0 dBi gain) or dipoles (2.14 dBi gain) Simple feed lines No soldering (the Wow factor) No tuning! Even better! No massive calculations needed (use the AT Free Computer program and presto all the numbers are there!) ALMOST HAM PROOF!

4 The Fundamentals Easy formulas for building monopoles and dipoles Good performance for VHF and UHF antennas Can be placed “covertly” in most places (apartments, hotels, etc.) Easy to find materials (MFJ, Lumber yard, etc.) Can be build quickly (about 5-10 minutes); Ken, 2 hrs. Excellent antenna matching to 50 ohms Much better performance than “rubber ducks” Great for emergency situations Free computational program provided to make it Ken Proof (KP)

5 Impact of Dielectrics WHERE you mount the antenna makes a difference to antenna resonance The dielectric lowers the resonant frequency of an antenna as compared to free space (air) Typical relative dielectric values for the following materials,  R – Glass: 4.0 to 7.0; window glass, 6.5 – Plastics: 3.0 to 4.0 – Wood: 1.4 to 2.9 (Dry wood, 2.1) (Lumber yard wood ~ 2.6) – Plywood: 2.5 – Drywall: 2.4 – PVC: 3.19 – Concrete: 4.5 – Styrofoam: 1.11 Resonant Frequency = Free Space Frequency/  FF –  FF = (1 +  R )/2

6 Impact of Tape Thickness The ratio of length to width makes a difference on the resonance frequency of the antenna As the antenna conductor gets WIDER the LENGTH for the same frequency gets SHORTER. As the ratio of length to width gets smaller, the bandwidth of the antenna gets larger. Broadband Antennas are basically “electrically” FAT (some are also physically FAT). FAT in antennas is beautiful (one of the few places!)… Gordita For a 2 meter antenna, at 146 MHz is inches and a 2 inch Aluminum tape, has a L/W ratio of 39 Length reduction is approximately 5.5 to 6% Since the antenna is now Broadband, exact dimensions are no longer that CRITICAL

7 Ratio of Free Space Wavelength to Conductor Diameter

8 Skin Effect (No Soldering) RF energy travels on the “surface” of a conductor. Very little energy is in the inside of the conductor We call this phenomena the Skin Effect or the Skin Depth Skin Effect equation is as follows: – Skin Depth =  (  /  f  ) (meters) f = frequency in hertz  = permeability, air is 4  x H/m  = resistivity of material, copper 1.69 x  m Next slide shows some examples for the different “Ham” frequencies So RF connections can be made with conductive adhesive copper tape without any significant loss

9 Skin Effect (Continued) Resistivity values for some common materials: – Silver: 1.63 x  m – Copper: 1.65 x  m – Aluminum: 2.65 x  m In Copper, depth of penetration, as a function of frequency: – 50 MHz: mils – 146 MHz: mils – 220 MHz: mils – 450 MHz: mils

10 Free Computer Program (Calculates all of the Parameters)

11 Items That You Will Need (Hardware Wise) Aluminum Tape, 2 inch wide (Lowes or Home-depot) Copper Tape, 0.5” or 1” wide; conductive adhesive Pair of Scissors (K-mart) Electrical Black Tape (Lowes) Coaxial Balun (MFJ-700A) for RG-58 or toroid Some RG-58 with a BNC Connector at one end (fits my handheld); pig tail on the other end (Walmart) A plastic squeegee (Lowes)

12 The Simple Dipole Most Hams like Dipoles Better gain than monopoles (2.14 dBi theoretical) Easy to fabricate using a simple formula: Length (ft) = 492/ f (MHz) Spacing between elements at VHF not critical (0.25” to 0.75”) Needs a 1:1 Balun (coax type) Does not need ground plane Balun 0.50”

13 The Simple Monopole Most Hams can built Monopoles Typical gain of 0 dBi (theoretical) Easy to fabricate using a simple formula: Length (ft) = 234/ f (MHz) Matching is close to 50 ohms, end fed Does not need a Balun (coax type) Does need ground plane or radials (quarter wavelength) Radials /4

14 Fabrication Demonstration Glass Dipole (Windows) Wood (1 x 4) Dipole (Attic Trusses) Other Materials: – Sewer Vent Pipe – Vinyl Siding – Dry Wall – Plastic Anything

15 Antenna Verification Using MFJ Antenna Analyzer (MFJ-269) Measures Complex Impedance of the Antenna (R  jX) Measures VSWR (should be less than 2:1) We can Declare “VICTORY”!

16 More Information Copy of this briefing which includes the free Excel program can be obtained by sending request to: Al Torres, KP4AQI