Data from Dave Bowker
Extracted from antennaware mailing list archives ( at http://lists.contesting.com/pipermail/antennaware/1998-October/000120.html as of 1 May 2006).
Note that the post of 30 Sep 1998 referred to isn't available. It doesn't show up in the archives for antennaware, and the two email addresses for K1FX (at arrl.org and arrl.net) both bounce. The figures below summarize the measurements side by side. Bowker gives all 16 measurements, even though, by reciprocity and symmetry, only 10 needed. This is useful, because it allows one to estimate some of the measurement uncertainties, which, with a casual inspection looks like about 2 ohms or around 5%.
Since my original posting of 30 Sep 1998 (which will be referred to as “Phased Vertical Array Experiment, Part I” in future postings), I have had an opportunity to continue some experiments and gather additional data, particularly in response to emails I received from LB (W4RNL) and Eric (N7CL). Please understand that this array was designed electrically and mechanically to facilitate experimentation and data collection on 4-element square arrays (either cardioid or the more common 4-square) and I welcome any and all suggestions for additional data points and experiments. It is very easy to reconfigure any mechanical/electrical aspect of the array (except for element spacing) for such purposes, as you will see in the entry below ragarding decoupling and isolation of elements and in Part I where I reconfigured it for gathering data at 4.6 MHz. Such reconfigurations usually take less than 1/2-hour to accomplish. I have had a break in the weather (and bird hunting) to continue gathering data. Two new points of interest and associated data follow. First, to follow up on my intentions to retake all the data with a saturated ground and grass overgrown the radial system, I will summarize both the previous data (from Part I) and current data in the table below. I’ve included both self-impedances and coupled impedance's in this note. Also, I failed to mention in the original posting that my radials consist of PVC insulated 24 gauge copper wire (essentially insulated from contact with the sod/earth and that the ‘cross-bus’ through the geometric center of the array is #16 bare copper wire, NOT insulated from the sod/earth). The radials which connect to the ‘cross-bus’ at the inner areas of the array are essentially in contact with sod/earth at the ends of the radial by connection to the bare copper bus. ARRAY CONFIGURATION (numbers indicate element and position) [this will be important to some data and discussion to follow]. 4 2 3 1 INITIAL CONDITIONS & DATA 24 August 1998 4 - 1/4-wave elements @ 7.010 MHz 120 radials under each element (see posting for configuration) Very dry soil conditions. Z1,1 = 45 + j4.64 Z2,2 = 43 + j5.0 Z1,2 = 52 + j24.3 Z2,1 = 46 + j24.3 Z1,3 = 54 + j23.6 Z2,3 = 52.5 + j 7.1 Z1,4 = 59 + j7.1 Z2,4 = 46.6 +j22.1 Z3,3 = 45 + j6.1 Z4,4 = 43 + j3.3 Z3,1 = 50.5 +j 24.3 Z4,1 = 52.5 + j5.3 Z3,2 = 54 + j8.1 Z4,2 = 48.2 +j20.0 Z3,4 = 48 +j24.3 Z4,3 = 46 +j20.7 NEW CONDITIONS AND DATA 02 October 1998 4 - 1/4-wave elements @ 7.010 MHz 120 radials under each element (see Part I for configuration) Very moist earth, approx. 10 hours after heavy rains Z1,1 = 48 + j6 Z2,2 = 45.8 + j8.3 Z1,2 = 52 + j23.3 Z2,1 = 51.0 + j26.3 Z1,3 = 53.1 + j25.0 Z2,3 = 58.5 + j10.7 Z1,4 = 62 + j6.7 Z2,4 = 46.6 +j22.1 Z3,3 = 45 + j9.1 Z4,4 = 45 + j8.3 Z3,1 = 53.5 +j 27.4 Z4,1 = 58 + j8.9 Z3,2 = 59 + j9.6 Z4,2 = 50.5 +j24.3 Z3,4 = 51.5 +j26.7 Z4,3 = 50.1 +j24.7 Second, an additional experiment was carried out this date (02 October 1998), in response to Eric’s email, to investigate how well the “traditional” method of decoupling by open-circuiting 1/4-wave elements achieves TRUE decoupling in a 1/4-wave spaced array. This experiment consisted of selectively and physically removing an element or elements from the array and determining the self-impedance of a single element and the influence of adding elements back into the array and measuring the self-impedance of a single element and comparing the results to the self-impedance of that element when measured in the “traditional” manner. In the diagrams and data below, the numerals 1,2,3,4 indicate the physical presence of a specific element in the array configuration and an “X” indicates that that element has been physically removed from the array for measurement purposes. All data were taken at and are relative to element 3 of the array. The measured impedance's are indicated below the physical description in each case. For comparison, these data should be compared to the self-impedance Z3,3 (45.0 + j9.1) measured on 02 October 1998 (immediately above). This experiment will be repeated next spring in the 1/8-wave spaced elements when the 80M capability is added. X X 3 X ----------------------- Z3,3 = 48 + j9.1 4 2 X 2 3 X 3 X ------------------------- ------------------------ Z3,3 = 46.5 + j9.1 Z3,3 = 47.6 +j9.1 4 X 4 X 3 X 3 1 ----------------------- ------------------------- Z3,3 = 47 + j9.1 Z3,3 = 45.5 + j9.1 INITIAL CONCLUSION Decoupling/isolation of 1/4-wave elements in a 1/4-wave spaced square array by means of open-circuiting the respective element is effective. Although a minimal amount of coupling between open-circuited elements and the element under test appears to be in effect, it is probably insignificant insofar as calculation of mutual impedance's, phasing network component values, and array performance is concerned. The apparent disparity between the commonly accepted self-impedance of a 1/4-wave vertical element over 120 radials of 1/2-wavelength (Brown, Lewis, Epstein) and this experiment remains to be resolved. An additional experiment will be designed, implemented, and data taken to determine the effects of INSULATED wire used in the radial system versus BARE COPPER wire to determine whether or not coupling to the sod/earth constants is a contributing factor in the somewhat higher than expected self-impedances observed. 73, Dave, K1FK Fort Kent, ME