[Hammarlund] Hammarlund power

[Roy Morgan]

At 11:11 PM 2/6/2007, Mike Taylor wrote:
>Thanks for the replies. I must not be asking the question correctly. I 
>understand that if I use a three conductor power cord, and connect the 
>green wire to receiver chassis, then the receiver cabinet is connected to 
>the earth.


Not exactly.  The green wire in the line cord and the safety ground wire 
from your three wire outlet go to the ground in your electric panel. That 
is connected, most likely, to your cold water pipe, and possibly to a 
ground rod outsied your house, and to the ground out at the utility pole in 
the street (or the ground mounted transformer box if that is what is used 
in your neighborhood.)  All this is for electrical safety.  A short circuit 
from the line ("hot") wire to the frame of grounded electrical equipment 
will go to ground and hopefully not through the arm of your three year old 
kid to ground.

>  Is there something different in using a two wire power cord, and 
> connecting the "G" terminal on the antenna input strip to a good earth 
> ground (copper rod driven into the ground or metal water pipe connection)?

For RADIO SIGNALS, there may well be a difference.  Often the electrical 
system safety ground does not provide a good ground for radio signals. It 
may, but it may not.


Unfortunately a copper rod driven into the ground or metal water pipe 
connection also may not provide a good radio frequency ground. There are a 
number of reasons, among them are:

1) the wire you run from the radio to the ground may be inductive or 
capacitve at the frequency of interest simply because of its length.  (Note 
a quarter wavelength of wire acts as an open circuit.)

2) The wire may be inductive because it's thin. A one inch wide copper 
strap is less inductive than the same length of thin wire.

3) The rod in the ground may be very poor at conducting any currents. This 
depends on the soil type, any "stuff" in it like fertilzer, and the 
dampness it has.  Salt water, or a wet salt marsh is a nearly perfect 
conductor.  Normal soil is about medium.  Dry desert sand is a nearly 
perfect insulator.

I strongly recommend that you try things out.  First, put a three wire 
power cord on your radio and use a properly grounded outlet.  That is for 
safety, to keep your wife from becoming a widow.

Then, make whatever connections to "ground" you find practical: water pipe, 
grounding rod or copper pipe driven into the earth, Grandap's '46 Chevvy 
just outside your shack window which has sunk 6 inches into the dirt*, 
whatever.  Then run your radio and hook up the ground and unhook it. Notice 
if your reception improves or not.  Then tell us about what you found, please.

* I suggest the old car not completely in jest. On my train ride into work 
each day, I see a junk yard with some 40 old trucks, cars, busses, and farm 
machines, all in a state of nearly complete disintegration, and all sunk 
into the dirt at least a few inches. A moderate amount of wire and some 
sheet metal screws could bond the lot into one fine ground plane.

Roy

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing
13033 Downey Mill Road, Lovettsville, VA 20180
Phone 540-822-5911   Cell 301-928-7794
Work: Voice: 301-975-3254,  Fax: 301-975-6097
roy.morgan at nist.gov --