1 Antennas of Field Day Main High Frequency Antennas from the 2009 LARC FARL Field Day Ford Amateur Radio League David Treharne, N8HKU January, 2010
2 The Antennas The G5RV wire dipole: 80m 10m The Carolina Windom: 80m 10m The Cushcraft R7 Vertical: 40m 10m Not Covered: Inverted L: did not make many contacts, it was not working as it should. Satellite antenna
3 Site Layout
4 G5RV Antenna Wire Dipole antenna, 51 ft per side, 102 ft long, ft matching section made of ladder line. Line isolator or balun at the bottom to isolate the coax from the matching section Developed by Louis Varney, G5RV, as a multiband antenna that could fit in the yard of an English residence. Resonant on 20m, needs a tuner for all other bands. Most effective on 80, 40, 20, 15, and 10. Bad on 30m and 17m.
5 Physical dimensions Can be installed as a flat top, a Vee, and the two legs at an angle from 120 degrees to 180 degrees.
6 How it Works The matching section makes the antenna load look better on 80m, even though it it short. The matching section makes the antenna match close on 40m The matching section makes the antenna load look like 50 ohms resistive on 20m.
7 Higher frequencies Multiple wavelengths on 15m, resistive at the bottom. Multiple wavelengths on 10m, resistive and reactive at the bottom.
8 Radiation Angles As expected, the radiation pattern changes with frequency and with height. All of these graphs are with the antenna about 34 ft from the ground. The center of our Field Day set up was about 35 ft high, with one end about 50ft, and the other end less than 30 ft. When is a dipole NOT a dipole? Answer: When it is less than ½ wavelength long.
9 80m G5RV Radiation Elevation: Best radiation is straight up: A cloud warmer that is good for local contacts. Horizon The antenna radiates off the almost as good as broadside. The antenna wire is parallel with the 0 deg line. Antenna
10 20m G5RV Best takeoff angle is 24 degrees, better for long distance. At 24 degrees take off angle, nulls at 22 degrees, and best at 52 degrees from antenna face, 7.7 dbi better than an isotropic radiator. (A perfect dipole is 2.1dBi better) Antenna 22 degrees
11 15m G5RV Good long distance take off. The antenna gets a lot of sharp nulls due to the multiple wavelengths, particularly across the face. Best performance is at 30 degrees from the face, 9.8dBi better than an isotropic radiator.
12 Windom Wire Dipole 133ft long for 80-10m Not fed in the center, but fed approximately 1/3 from one end. The original windom was a single wire, with a good ground system serving as the other side. With a balun transformer at the 1/3 point, the antenna became a dipole. The antenna is harmonically resonant, making it good for the harmonic amateur bands, not good at other frequencies.
13 Windom Antenna (Buckmaster) This antenna is good at 75/80m, 40m, 20m, and 10m, also 6m. It is pretty good at 17m and 12m, but not good at 30m nor at 15m. A classic windom is not recommended to be operated on 15m, even with an antenna tuner. The ferrite balun at the 1/3 point will overheat and damage the antenna.
14 Carolina Windom A variation on the Windom antenna, developed 25 years ago or so to help make a Windom work better on 75m over a North Carolina to Virginia communication path. Makes use of ladder line like a G5RV does. Inserts a matching network of ladder line down from the transformer at the 1/3 point of the antenna. Inserts a balun or isolator at the bottom of the ladder line to coax.
15 RadioWorks Carolina Windom Antenna is longer than a G5RV Similar gain to a G5RV at higher frequencies: Better at 80 and 40 due to increased length? High power transformer and isolator allows an antenna tuner to match it on non resonant frequencies such as 30m and 15m. Vertical radiator probably works similar to G5RV as a wavelenght matching network.
16 Carolina Windom Radiation Pattern Article from RadioWorks indicates that the vertical portion of the antenna does indeed radiate and make the antenna perform at multiple vertical angles. If true, then it will have less gain at the lower angles for longer distances, and it will also pick up more noise. It will be able to handle intermediate distances better than a dipole. There have been some articles comparing the noise of this antenna versus a dipole, and found it 1 s unit noisier.
17 SWR Carolina Windom SWR 4 Carolina Windom Carolina Windom courtesy of Dan Parks. WT8F Jan, Frequency (khz) Not as good of SWR as a Windom, but tunable via an antenna tuner.
18 80M; G5RV and Carolina Windom Note on the comparison: The G5RV worked SSB, the Carolina Windom worked CW. Direct comparisons are difficult given the 2.3kHz bandwidth of SSB versus 60 Hz for CW. The Windom got a wider initial range and a double skip to CA, the G5RV only a single skip. Both antennas made contacts broadside and off the ends, like the radiation pattern indicated it would.
19 40M; G5RV and Carolina Windom The Windom got good moderate distance range to Indiana and Ohio, and better to the Southwest. The G5RV did better to the Northwest part of the US
20 20M; G5RV and Carolina Windom Here, the G5RV also had better performance to the Northwest US and western Canadian provinces. The G5RV also had slightly better near in coverage and east coast coverage. Both antennas still got signals off the ends of the antenna.
21 15M; G5RV and Carolina Windom Both antennas now have predominantly low angles of radiation, and pretty well defined skip zones. The G5RV contacts are all within a single skip zone, the Carolina Windom has two skip zones defined. The Windom still worked some off the end of the antenna, but better off of the side.
22 10M; G5RV and Carolina Windom No contacts made by the G5RV, and a single skip distance by the Windom, off angle to the direction of the antenna, consistent with a multiple wavelength dipole antenna.
23 Cushcraft R7 Vertical Trap vertical antenna for 40m, 30m, 20m, 17m, 15m, 12m and 10m 22.5 ft tall (6.9m), 100 in wide from counterpoise end to end Acts like a dipole antenna, so no ground radials are required. Antenna is vertically polarized. Uses capacitive hats for resonance loading along with the traps Uses a matching network for the coax to the antenna.
24 Cushcraft R7 Vertical Vertically polarized antennas generally transmit a low angle of radiation toward the horizon. (locating this antenna 50ft + above ground may have added some high angle (short skip) lobes. The wire antennas were horizontally polarized, making this antenna coexist well with the other two antennas This antenna is electrically extremely short, therefore has a poor radiation resistance. The resistance of the L and C in the matching network and traps consumes a lot of the power. Because this antenna does not need a system of ground radials, it can be mounted significantly above ground, which we took advantage of by locating the antenna at the top of the antenna tower.
25 Cushcraft R7 Vertical Antenna is tuned from the highest frequency (10m) down to the lowest frequency by adjusting the various distances between traps. Note that one must choose the part of the 40m band to cover. This was not done before assembling this antenna for the 2009 Field Day, resulting in a low frequency resonance that could not be modified even with an antenna tuner. All other bands functioned in the SSB area without the need of an antenna tuner.
26 Cushcraft R7 Vertical 40 meter tuning section A Trap: A L-C tuned circuit that looks high impedance at its resonant point, and inductive at lower frequencies. A Trap cuts off the antenna beyond its resonant frequency, and adds electrical length to the antenna at lower frequencies. Capacitive hat 30 meter trap 20 meter trap 17 meter trap 15meter trap Capacitive hat 10 meter radiating section Counterpoise (eliminates ground radials) Matching section (mostly inductance)
27 20M; R7 and G5RV Comparing the R7 and G5RV since both operated SSB Good east-west coverage on the R7, as well as some north and south. R7 picked up some Southwestern states missed by the G5RV, and was the only Alaska contact!
28 15M; R7 and Carolina Windom Used the Carolina Windom here because it had more contacts. The R7 vertical did work Idaho and Western Washington that were missed by the Windom. Good single and double skip coverage, and some short skip (Wisconsin and Ohio) that was not made by the wire antennas.
29 10M; R7 and Carolina Windom R7 made a few contacts here. The entire band was not open much due to the sunspot cycle.
30 Conclusions Both the G5RV and Carolina Windom antennas worked very well on multiple bands, and showed omnidirectional capability at the lower frequencies, indicating our positioning of them 90 degrees from one another did not cause any disadvantages. Both antennas had good performance at the higher frequencies, but both had blind zones. The R7 vertical did very well for its size, and was advantaged by placing it high, perhaps improving both long range and short skip or ground plane performance.
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