On 1/19/2015 1:59 PM, Jim Brown wrote:
Those aircraft were only running 10W or less, AM VHF rigs. Most of them
still do.
Hard to imagine, state of the art aircraft still using 10W AM radios.
Many of the larger ones now use digital via the transponder. Clearances
"of some" can actually be programmed in automatically, while the "read
back" is a digital AK. Location is automatically returned via links to
the airline as are route changes.
I used to sit on the back end of the center console of the company
planes. (Violation of company policy) and only "strap in" on take offs
and landings, or turbulence. If on company business, we couldn't even
serve as crew.
Even with my own plane, I'd have to take vacation to fly to a meeting
the next day and take vacation to fly backThey were not at all; happy
about that and were trying to think of a way to ban that procedure as I
could claim The meeting gave me a reason to go a day early to get
"something". I really disliked having to take commercial flights in
those "cattle cars", even if I did manage to catch Business, or first class.
I could work the local repeater in Midland MI from that position @ FL
220 over central Ohio without keying up repeaters under, to either side,
or behind us with a 5W HT. Now that would take one whale of a ground
wire <:-))
73
Roger (K8RI)
The real issue is that the concept of "RF Ground" is a myth and the
result of fuzzy thinking. Part of the reason is what Jim has addressed
below. The other reason is simply that a connection to earth does NOT
make TX antennas work better, and is NOT part of a solution to hum,
buzz, or RFI. The earth is NOT a sink into which noise and RF is
dumped. The ONLY reasons for an earth connection are to sink lightning
current and other equipment-related surge currents on the AC line.
My late colleague, Neil Muncy, ex-W3WJE, taught classes on power and
grounding for many years to audio professionals, and I took over those
classes when he no longer had the health to do them. He is also the
guy who alerted the world to "The Pin One Problem" back in 1994. He
gave one of my favorite teaching examples. He would say to a class,
"park yourself at the end of the runway of the nearest major airport
with a good pair of binoculars, and call me collect when you see an
aircraft take off trailing a ground wire."
73, Jim K9YC
On Mon,1/19/2015 9:15 AM, Jim Lux wrote:
Are there different answers depending on why we have the ground
rod? (RF ground, power line ground, or lightning protection)
Yes..
ground rods make terrible RF grounds, in general (where RF is HF and
up): skin effect means that wires and rods have high ac resistance.
(skin depth in copper at 10 MHz is about 0.8 mils/0.02 mm.)
They also have significant series L (1 microhenry/meter for a wire..
so a 30 foot run to the rod is a 10 uH inductor, that's 600 ohms
reactive impedance.
Rods are really for electrical safety ground and/or lightning ground.
And they don't work all that well for that, unless deployed in large
numbers. The advantage of a rod is that it's easy to install by
driving, but as an electrical connection to the earth, it's just not
that wonderful: the surface area is quite small (8 foot rod, 1" in
diameter is only 300 square inches. You could probably do better,
electrically, by burying a 1 foot square plate (288 square inches).
Rods are also used in phone and power line applications.. you drive a
rod at every pole (or wrap the ground wire around the foot of the
pole when planting it). Even if any one rod has crummy
characteristics, there's lots of other rods in the circuit to help
establish the common voltage reference and provide a fault current
return. I've had telco installers drive a new rod next to the
existing rods on the general principle that at least they knew the
new rod was in good condition: faster to just do a new rod than to
test the existing one
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73
Roger (K8RI)
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