Some Initial Thoughts About the Ground System Shootout
Good morning.
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| Succotash Salt Marsh at Dawn *** |
The A/B testing of the ground rods vs. radial field has produced interesting results; namely, most stateside stations report no difference between the two. Taken on its own, this would appear to corroborate more than refute the contention that, in a salt marsh at least, four (4) ground rods work as well as 25 ground radials. I do not think this is true for the following reasons.
Firstly, when we had the reference vertical up, it was at parity with, or slightly outperformed, the marsh vertical with four ground rods stateside. When we added ground radials to the marsh vertical, we then saw an increase in stateside performance over the reference vertical, and 1 to 3 S-units better performance on longpath/grayline contacts. We would therefore assume that quickly alternating between the marsh vertical's two ground systems would merely reproduce what we saw when each ground system was the only one being used with the vertical. vertical. But this is not the case. What's up with that?
We think that it means that ground currents collected by the ground radial system are coupled to the ground rods via the salty marsh mud. In other words, when we laid-down the ground radials within the near field of the marsh vertical, we altered the ground rods' environment. We increased the density of return currents in the salty marsh mud around the base of the vertical in which the gorund rods were sunk. Thus, the ground rods behaved differently; they were able to transfer more ground current to the vertical than when they were the only ground system installed underneath the vertical.
Secondly, and perhaps more empirically, when the marsh vertical had only the four ground rods as its ground system, it exhibited a 50 Ohm impedance at resonance, as seen below.
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7.0 to 7.3 MHz Experimental Vertical Sweep
Only 4 ground rods underneath the vertical.
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This is no longer the case after we laid-down the 25 ground radials.
It is more likely that 25 ground radials altered the experience of the 4 ground rods than it is that the 4 ground rods affected the experience of the 25 ground radials. One system appeared to enhance the ability of the other system to pass ground current to the aerial. This idea appears corroborated by the significant reduction of the vertical's resonant feedpoint impedance after the radials were deployed. Another possibility is an error in my instrumentation; namely, capacitive coupling between the radials and ground rods via the relays I used. Either way, a better experiment would be AB between the marsh vertical with ground radials ajnd a marsh vertical with ground rods installed at a different location in the marsh. Naturally, should we measure the feedpoint impedance of either vertical, we would make sure both vertical were disconnected from their feedlines before making any such measurement. Thank you to all hams providing their signal reports and comments during our on-air "shoot-out" between the two ground systems.
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7.0 to 7.3 MHz Experimental Vertical Sweep
4 ground rods & 25 radials underneath the vertcal.
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Heading out to the marsh to reorient the feedline perpendicular to the line formed between the two verticals, and to straighten out the ground raidals by anchoring them in the mud with these bamboo skewers procured at Walmart for $0.89/dozen!
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Eco-friendly Ground Radial Stakes
$0.89 per dozen.
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