Topband: DOG

[K4SAV]

K2AV said:
"DOG conductor in contact with ground moisture near the ends could 
completely skewer results. That's an electrical 1/4 wave between center 
and either end of the DOG. Inadvertently grounding an end will be 
transformed around the surge impedance of the wire to a quite higher 
impedance at center. An inadvertent partial grounding near the ends 
along with variation in ground surface moisture would explain erratic 
observations of high R and no resonance."


Thanks for the suggestions Guy.  I understand your suggestions and agree 
that it is possible.  None of my measurements were done immediately 
after a rain but no doubt that ground moisture content would have 
changed between measurements.

Maybe I should have listed a wider impedance range for total impedance 
(not just R).  Looking back at my data I see that I did have some 
measurements where the total impedance was near 200 ohms. Those were all 
at the frequency where the reactance went to zero (not the case for 
measurements where the wire showed no resonance). Some data showed an 
almost perfect match for 200 ohms (SWR < 1.1) at resonance while other 
measurements at different times showed an SWR of 20 to 1 or greater 
anywhere near the same frequency.  An impedance of 500 ohms was a better 
match over a much wider frequency range for all the measurements.

All the measurements left me scratching my head because they didn't make 
much sense.  Variations were too great to make any good conclusions.  I 
still have that dipole so I just now inspected it. It is good quality 
#16 TFFN with no bare spots.  Chew marks on wires on the ground are very 
common at my location but this dipole had none.

Maybe I will repeat these measurements but I can't do it during the 
summer.  Grass would bury the wire within a week at the rate it is 
growing now.  A single measurement would probably be misleading.  I may 
also repeat the measurements of current along a BOG wire too since that 
data was totally unexpected.  Currents along the wire dissipated much 
quicker with length than predicted.  I find it frustrating that I can't 
simulate any reasonably believable performance of a BOG.  Measurements 
have to agree reasonably with simulations and I have yet to make that 
happen.

Jerry, K4SAV