[IRCA] grounds, radials and efficiency

[Charles A Taylor <MWDXer@xxxxxxx>]

At 01:55 AM 6/23/2007 -0700, you wrote:
>Gary,
>
>Very interesting about your reception of KOHI. They are on top of the
>frequency here 60 miles away only off the Eastern beverage. On any other
>antennas, if I get them they are under KVRI or KOPT. Even in St. Helens
>the other day, they were quite weak and distorted for a local station.
>They never have been "gangbusters" with 1 KW, but they still were local
>in the area. But their signal seems to vary from day to day too.
>
>73,
>
>Patrick
>
>Patrick Martin

Patrick,

 From experience, a groundwave signal that varies from day to day
indicates an inadequate ground system. Rain increases the conduct-
ivity of the soil around the ground point (which effectively may
only be a ground rod) and hence the efficiency of the radiating
system.

This from my pirate days.

The last pirate station I was involved in before I went into the
Navy was WQRK-1540/1560 (operated on 1540 day, then went to 1560
night.

I had access to a calibrated RCA WX2C field intensity meter,
and ran field intensity measurements at a mile on at least four
points on WQRK.

We put up an 18-foot vertical with some 100 feet of top loading
(three wires fastened to two power poles and the house, and which
met at a point and which was the shape of a "Y," from which the
18-foot vertical descended to the small antenna tuning unit
(fabricated in a wooden box) and a ground rod.

My transmitter was calibrated and I set it to 10 watts (+/- 10%).

First run, I used just the ground rod and we put about 0.75 A
R-F into the antenna.

Field intensity at one mile was about 550 microvolts per meter.

After laying 16 radials (#20 tinned copper) of about 75 feet
each:

Antenna current was 2.6 A, and field intensity at one mile was
2.67 millivolts per meter!

That's equivalent to an increase of transmitter power of 23.6
times (!!).

Even with that enhanced antenna/counterpoise system, my
best guess is that for 10 W we were getting 85 milliwatts of
effective power.


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   Charles A Taylor, WD4INP
  Greenville, North Carolina 


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