[TenTec] When Is Ground Really Ground?

[Bob & Linda McGraw K4TAX]

In response to several inquiries, here's my thoughts on ground.

There's 3 basic types of radio system grounds.  

(a) DC ground:
Best described as a conductor running from the radio to a driven ground
rod.  It is better than nothing in most cases but can be quite
troublesome due to the length and inductance contained therein. 
Sometimes one is better off with out this system.  In many cases the 3rd
pin on the AC wiring serves this purpose better and thus provides a
safety ground.  

(b) Lightening protection ground:
Very heavy conductors (I use 1/2" soft copper water pipe) running from
the base of the tower to several (4 or more) driven grounds (1/2" dia
copper clad, 8 ft long), preferrably in a 8 ft or greater radius from
the base of the tower.  Also, the house AC mains ground must be
connected to this system via a #6AWG or larger wire.  Failure to do this
will most surely produce a ground system potential difference,
especially during a nearby lightening strike, leaving the radio
connected in between the two grounds.  Due to a difference in ground
potential, most likely damage will occure to the radio.

(c) RF ground:
A very short, heavy, low inductance conductor running from the radio to
the lightening protection ground. A 2" wide to 6" wide copper strap is a
good example here.  Keep in mind that the length of a conductor, and its
inductance, becomes some part of a wavelenth.  At certain lengths and at
certain frequencies thus approaching 1/4 or 3/4 wavelength, this
combination will put a radio at the maximum voltage point above ground. 
Not a good thing.  Remember that long grounds electrically will
radiate.....into house wiring, TVs, VCRs telephones and a host of other
things......namely the neighbors stuff.

And finally......add more grounds.....not necessarly better.  Ideally
each piece of radio equipment should be connected to a central ground
point.  One station PSU is a good starting point.  That ground point is
then connected as in (c) above.  This is referred to as a "star" ground
system.  Multiple ground paths will produce "ground loops" i.e. current
flowing in the ground system.  These are especially troublesome where RF
is involved.  Ground loops are oftem times the cause of audio humm and
buzz in many applications.  Different ground potential between the
computer and the radio will cause humm or buzz problems in modes like
PSK-31.

I've found that crimp type connectors are very convenient.  However,
I've found better results when they are of proper size for the wire and
are crimped with a proper crimping tool........and then soldered. 
Should one not use a proper crimping tool.......I then call 'em "mash
on" connectors, most likely to fall off when least expected.

If you have specific questions or concerns.......ask.

73
Bob K4TAX


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