Topband: Beverage grounds

[Tom Rauch]

Hi Larry,

This has been discussed in past threads on measuring ground 
resistance, but unfortunately the low-frequency AC or dc resistance 
has no fixed relationship to RF resistance at various frequencies.

This is why the light bulb ground conductivity tests described by 
W2FMI are useless.    

Such tests are useless because skin depth as well as losses 
change with frequency. The actual resistance or conductivity can 
be better, worse, or the same as we might measure at other 
frequencies.

We always have to measure at or near the operating frequency.     
 
> Across the 270 ohm termination resistor, there is 0.2 VDC with about
> 0.05 VAC modulating it. With the termination removed, I measured 65
> ohms for one polarity and 130 ohms for the opposite. The average would
> be about 100 ohms and this number includes the combined resistance of
> two grounds, the transformer, and at least 20 ohms for the galvanized
> 18 gauge wire. Looks like about 40 to 45 ohms for each ground 

That's true at the measurement frequency, where skin depth is all 
the way to JT1CO's QTH!



Unfortunately measurements at low frequencies or dc have almost 
nothing to do with RF characteristics. .


73, Tom W8JI
W8JI@contesting.com