[TowerTalk] RF Ground is a Myth

[Patrick Greenlee]

I duct taped a 5/8 wave 2M mag mount to a strut on a Cessna 172 and 
worked a guy mobile in his car nearly 200 miles away on National simplex 
146.52 and always wondered how that worked without a ground wire.  Maybe 
it was something to do with the "unrequited mag flux" due to the strut 
being a non magnetic alloy.  Any comments on the inverted 45 degree 
polarization?  Maybe I should have checked the baggage compartment for a 
Ufer ground!

Patrick  NJ5G  ;)  ;)


On 1/19/2015 7:51 PM, Roger (K8RI) on TT wrote:
> 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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