Topband: BOG data

[K4SAV]

I meant to sent this post to the group but somehow only sent it to 
K2AV.  So second try.

The system has messed up my data formatting to the point where it is not 
readable.  The data has been reformatted below.  Maybe this will be better.

A little more info on the tests.  The source was a small rig operated 
from a battery.  The feedline length was about 3 feet. There was also a 
transformer included to match the rig output to the impedance of the 
BOG.  SWR was less than 1.3 to 1.  I know the BOG is too long but the 
object of the test is the comparison between measured data and what 
EZNEC predicts.  If there is no model where EZNEC can predict currents 
that are close, then any patterns generated will be wrong.  It also 
becomes painfully obvious that published BOG patterns by others are wrong.

There are no buried wires anywhere near the wires in these tests.

When monkeying with EZNEC parameters to get anything that might be give 
results close to what I measured, I tried all possible ground 
parameters, including those that were absurd and could not possible 
exist.  None produced close results.  I tried all heights, regardless of 
actual height.  None were close.   I tried some wilder stuff too.  I 
even tried my own ground using distributed resistors, capacitors, and 
inductors over a MININEC ground.  I tried to SPICE it but that was 
doomed due to not modeling the mutual inductance between segments. I 
planned on transferring those parameters to EZNEC but that SPICE 
simulation was wrong. In summary, nothing came close to the right answer.

I have not tried the plane wave analysis, but I will.  Thanks for the 
suggestion.

EZNEC models of the BOG included radials for terminations, two at each 
end, at right angles to the BOG.  Radial length was adjusted such that 
they were resonant exactly on the frequency being plotted.  Their length 
varied between bands and varied for different heights.  Incidentally, 
non-resonant radials of the right length can improve the front to back, 
according to the simulations.  This is where the idea of a resistive 
plus reactive termination came from. Simulation shows that for a long 
BOG the front to back can be improved significantly, but I suspect that 
is just wishful thinking since the simulations are in error.

The dipole-on-the-ground to determine the velocity factor was 118.25 ft 
long, insulated #16 PVC jacket 0.019 inches thick, and resonated at 2.25 
MHz.  Just by varying the ground parameters in EZNEC I was unable to 
predict this.  By setting the wire height to 0.2 inches and average 
ground EZNEC came close.  When using that height for the BOG, results 
were not close.  I also did a test for 80 meters. Duplicating that 
result required placing the wire height to 0.25 inches.  Wire actual 
height was 1.5 to 2 inches.

Jerry, K4SAV


DATA:

Current measurements on a 364 ft BOG. Height above ground estimated to 
be 1.5 to 2 inches, lying on the top of short grass mowed just before 
the test, dry high ground, red Alabama clay.

Load data taken at the end of the BOG:

Freq MHz ___ Source ma __ Load ma ___ EZNEC  predicts ma
1.84 ________120__________25_________99
3.52 ________150  _________5 _________67
7.01 ________150  ________<1  ________ 22
10.11 _______130  ________<1 _________9.9


Measured at the 212.25 ft (58.3%) point from the source:

Freq MHz ___ Source ma  __58.3%, ma __ EZNEC predicts ma
1.84__________120 ________70__________102
3.52 _________150 ________73 __________71
7.01 _________150 ________35 __________44
10.11________ 130 ________15 __________2.7

I also measured the velocity factor of a wire in the same place where 
the BOG was.  On 2.25 MHz it was 0.67.  At a second place the 
measurement was close to the same.