Multiband Vertical Loop Antenna 10, 14, 21, 28 MHz

1 Multiband Vertical Loop Antenna 10, 14, 21, 28 MHz Jacques Audet VE2 AZX. Sept. 2016. Web: ve2azx 1. DX Wire Antennas Comparisons Antenna Plus Minus Vertical Delta Loop - Low height and low radiation angle - Essentially a mono-band Antenna - Portable and compact - Depends on ground quality - No radials - Very large on 80m and 160m - Lower Noise Dipole - No radials - Needs Height for DX. Monopole - Low height and low radiation angle - Many radials required - Good on low bands - Depends more on ground quality - Higher Noise ve2azx 2. Vertical Loop Antenna Polarization - The wave emitted by the Vertical loop may be polarized Vertical or horizontal depending on the feedpoint location - Vertical polarization is preferred when the Antenna is low - Select the feed-point for low radiation angle for best DX results ve2azx 3.

2 One wavelength Delta loops 1005 Feed point for low angle radiation Length (ft.) = Vertical Polarization f MHz Impedance: ~ 100 . Support * Support Support Feed Feed * Preferably not conductive ve2azx 4. One wavelength Square or Rectangular loops Feed points for low angle radiation What shape ? Vertical Polarization x x 2x Square Rectangular Rectangular x Loop x Loop x Loop ~ 130 ~ 90 ~ 50 . CVA ou "Closed Vertical Array". CVA sur le site de cet amateur: /2. Folded /2 Dipole ~ 288 . Parallel line ~ 3 (ladder line losses). NOT an Antenna ! ve2azx 5. One wavelength Rectangular loop for 21 MHz Tower 1005 Loop is fed on the Vertical side, giving Vertical polarisation.

3 Length (ft.) = Only the the Vertical sides radiate. f MHz Equivalent to two /2 Vertical dipoles, END COUPLED. Support Support ft. Dip le 2 Dip le 1. 1 on 15 m ( ft.). Length adjusted for resonance at MHz Approx 90 . 10 ft. 10 ft. At resonnance #12 AWG. Wanted: Multiband ! ft. 12 ft. above earth (approx. ). EARTH. ve2azx 6. Measured Loop Impedance using VNA & 1:1 voltage balun This contour corresponds to Z = ~ 0 + jX. (OSL calib. done on balanced side) So it's impossible to dissipate power since resistance = 0. Power is never dissipated in X. Start 5 MHz 0 Hz Inductive +X.

4 9 MHz 0 . 10 20 50 100 200 500 14 MHz Capacitive -X. 29 MHz Stop 40 MHz ve2azx 7. Using a Tuner at the loop feedpoint Option # 1. 1:1 balanced 50 coax Tuner Current Balun OR. Option # 2. 4:1 xfrm 50 coax Current Balun Tuner balanced ve2azx 8. Warning ! The tuner has its matching Limits Tuner Limit 5:1 SWR. 8:1 SWR. Tuner losses increase 6 Circle as you get closer to the limits. 2:1 SWR. Tuner Limit 32:1 SWR. 1600 . 6 . 50 . MFJ 929 Tuner ve2azx 9. Measured Loop Impedance using 1:1 Balun Option # 1. Impedances outside the tuner range ve2azx 10. - Still have impedances outside tuner range Measured Loop Impedance + 4:1 balun / xfrm added Option # 2 - Connecting the Tuner + Balun at feedpoint NOT convenient - Losses in 4:1 balun Impedances outside the tuner range Marginal ve2azx 11.

5 Measured Loop SWR curves with / without 4:1 balun / xfrm added Options # 1 & 2. Measured SWR. 50 . No transformer Option #1. Calculated SWR. Using 4:1 transformer: Option #2. But may be lossy at high SWR. Easy matching region ve2azx 12. Option # 3. Impedance Transformations with a 400 balanced line 400 ladder line ft. Wireman # 551. Loop Antenna Pre-Tuner 50 / 75 MFJ. 1 on 15 m ( ft.) With BALUN. #12 AWG NO xfrm coax Tuner The ladder line acts as an impedance transformer: ~ at 10 MHz (Hi Z changes to Low ZO). ~ at 14 MHz (Reactance present). ~ at 21 MHz (Little change in Z).

6 ~ at 29 MHz (Hi Z changes to Low ZO). Examples 400 ohm line Zo: or . 4000 40 Odd multiples of /4. 10xZo Zo 10. 400 ohm line Zo: or 1 . 90 90 Even multiples of /2. etc etc ve2azx 13. Loop and pre-matching circuit Uses a ladder line as impedance transformer Loop pre-matching circuit Opened on 20m Shorted on 30m, 15m and 10m RG-8X. 400 ladder line ft. C Coax Balun Wireman # 551 To Antenna tuner Loop Antenna 1 on 15 m ( ft.) via approx 51 ft. RG-8. #12 AWG C Length not critical. The length of the ladder line is approx. /2 at 21 MHz. Obtained from simulations. The 90 loop impedance is transformed to about the same value on 21 MHz.

7 On 29 MHz, the ladder line transforms the loop high impedance to a value around 30 . On 14 MHz, the impedance seen at the pre-matching circuit is 60 + j 750 . This reactance is cancelled by the series capacitors: C. ve2azx 14. ve2azx 15. View of the Loop Pre-Matching Circuit Coaxial Capacitor Relay RG-58. Balun ve2azx 16. VIEW OF BALUN. 4 Turns RG-8X on two oval ferrite cores #43 type Fair-Rite # 2643167851. (#43 mix). ve2azx 17. BALUN. Measurements ve2azx 18. 30m, 15m and 10 m coverage Loop SWR curves with ft Ladder Line + 51 ft RG-8. We have low SWR on 3 bands We have three SWR dips SWR reduction with at 10, 21, 29 MHz RG-8 comes from high coax losses At the end of the Ladder Line Ladder Line + 51 ft.

8 RG-8 Ladder Line + 51 ft. RG-8. 30m 20m 15m 10m ve2azx 19. MEASUREMENTS vs SIMULATIONS. Show good agreement SWR curves ve2azx 20. MEASUREMENTS vs SIMULATIONS. (At the shack end of the RG-8 feeder). -Uses series capacitor - Loop resonance has moved up in frequency as measured in dry conditions. It is affected by humidity (rain). which decreases the center frequency by about 200 KHz. 20m No adjustment done here Shows resonance on 15m and 10m In ALL casesO. An Antenna tuner is used to bring 15m 10m the residual SWR close to 1:1. 21. Computing the Losses How much power is lost in the transmission lines ?

9 Loop Coax Balun Coax to shack To: Antenna tuner Ladder Line Approx. 51 ft. Coaxial RG-8, RG-8X, RG-58. Capacitors ve2azx 22. Feeder Losses Compared RG-8 Cable Loss Measured (zig-zag) and Modelled (pink) RG-8 Foam (orange) RG-11 Foam (black) Ladder Line (blue). 0. 400 line RG-11 Foam dB Loss RG-8 Foam My RG-8. -1. 0 5 10 15 20 25 30 35 40. MHz Ref.: ve2azx 23. Calculating the Total Losses Loop RG-8 or RG-11. Balun Coax Feeder to shack Ladder Line To: Antenna tuner Approx. 51 ft. ve2azx 24. My Loop Antenna ve2azx 25. The Balun / Pre-Tuner ve2azx 26. Radiation Patterns Bottom wire 12 ft.

10 Above ground 10 MHz Loop Loop Top view Side view 14 MHz Radiation Patterns Bottom wire 12 ft. above ground 21 MHz 29 MHz Radiation Patterns @ 21 MHz Changing the height 21 MHz Bottom wire @ 12 ft. 21 MHz Bottom wire @ 17 ft. Radiation Patterns @ 21 MHz Vertical pol. vs Horizontal pol. 21 MHz Bottom wire @ 12 ft. Vertical Polarization Horizontal Polarization (Bottom fed). Radiation Patterns Vertical Loop vs Dipole at Top Wire Height (22 ft.). MHz Dipole - The Loop rejects high angle signals Loop - Rejection is best at 14 MHz MHz Dipole Loop Operating the loop at 18 and 25 MHz by changing the length of the ladder line RG-8X.