On Mon, Dec 26, 2016 at 3:45 PM, Edward Mccann via TowerTalk
<towertalk@contesting.com> wrote:
> As far as the "Measurement they are, and Measurements they is, and we're
> stuck with them," I would also be interested in the measurements, and look
> forward to learning more about this.
Really not much to learn. UV and likely outdoor wetness turned THHN
into a MEASURED linear resistor at RF.
What IS complicated is how so many clearly have some kind of stake in
it NOT being true.
Measurements and test method posted several times in prior posts. It's
not a secret.
Radial effective series resistance test, with UV deteriorated
insulation, showed 81 ohms resistance per 1/8 w radial at 1.83 MHz.
Old radials replaced with bright new bare wire in less than an hour,
**only thing different is the wire**. Bright shiny bare copper
measurement is down to 18 ohms per radial. With 4 radials, effective
series resistance of four radial system would be OLD: 20.25 ohms and
NEW: 4.5 ohms. This level of loss would be like inserting a 15 ohm
resistor between the coax center conductor and the vertical wire.
The test is done by initially separating all the individual radial
wires from each other and the common point. The radials measured need
to be identical length. They need to be very close to or at 90 or 180
degree orientation from each other.
With compass orientations for illustration of concept and angles
between measured wires only...
The N radial is connected to the S radial at the center. The E radial
is connected to the W radial at the center.
The SO239 center conductor is connected to the N-S junction and SO239
shell to E-W connection. Measure. This is two radial pairs. Each pair
is two radials in parallel. The two radial pairs are then in series.
Divided by two and then multiplied by two, the result is the average
effective series resistance of a single radial.
Of which hopefully only a tiny percentage is R loss in the wire.
For equally long and spaced radials, the effective series resistance
of the radial system is then the test result divided by the number of
radials.
Use an instrument that can reliably measure the R value separate from
the X value. Best done with more modern graphing instruments, where
the design takes R and X seriously. This test cannot be done with an
SWR meter.
Measured on several instruments, all readings very close, including an
old MFJ 259x. The AEA VIA analyzer was recently repaired, calibrated
and certified by their lab. This instrument is reliably within a
percent of the AIM 4170.
Readings on the identical radials for the other phased vertical were
within 5% of the first radial set, both the deteriorated measurement
and with new bare copper. The second set, of course, is over a
different patch of back yard.
Surface, per se, of old copper wire appeared a quite dull bronze
color, not greenish, with small etch lines, similar to the gripping
surface of basketballs and footballs, with the little mounds and
valleys, except much smaller mounds.
73, Guy K2AV
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|