[HCARC] Grounding Straps For Safety Ground

[Gary and Arlene Johnson]

SOOOO,  If I take my new (to me) super whiz bang 72 foot antenna tower and 
run an inverted L for the low bands (80/160 meters) I probably won't have 
any RF trouble because they are a long wavelength, but if I were to run an 
inverted L for 10 meters (not sure why I would do that - a really small L) I 
might have RF in the shack problems, and the wider I make my ground 
wire/cable/strip the better and to keep it as short as possible.  The 
braided wire strap I was going to get to use is tinned copper braid at 1.5 
inches wide.  I measured and I can probably get the run down to about 5 feet 
if I put the desk in the corner.  This is one time where having a straw bale 
wall that is 20 inches thick is working to my disadvantage.  On an inverted 
L, do I also try to ground the antenna at the tower before I run the 
feedline into the shack and what kind of feedline do I use with an inverted 
L in the first place.

Gary J
N5BAA
HCARC Secretary (2013)


----- Original Message ----- 
From: "Kerry Sandstrom" <kerryk5ks at hughes.net>
To: "Gary and Arlene Johnson" <qltfnish at omniglobal.net>
Sent: Monday, December 03, 2012 7:07 PM
Subject: Re: [HCARC] Grounding Straps For Safety Ground


> Gary,
>
> The basic problem with RF grounds is that any piece of wire has an RF 
> impedance that depends on the length of the wire.  What is a low impedance 
> at the grounded end of the ground wire can become a quite high impedance 
> at the equipment end.  The only sure way to keep the impedance low is to 
> have a ground wire that is a very small portion of a wavelength at the 
> highest frequency you intend to use.
>
> At 60 Hz, the wavelength is incredibly long so impedance is not an issue 
> so your safety ground can be almost any length.  At ten meters, it should 
> be much less than ten feet.  One way to lower the impedance is to make the 
> ground strap very wide, but that isn't really practical either.  To 
> compound the problem, you've got a wire between the ground rod and the 
> ground bar and a length of ground bar and then another wire from the 
> ground bar to the equipment.
>
> If you have an antenna that is "balanced" like a dipole, then you don't 
> need an RF ground, only a safety ground.  A coax fed dipole is still 
> "balanced" in this sense.  A ground plane that has 3 or 4 quarter wave 
> radials has it's own RF ground system and doesn't need a wire to RF 
> ground, it just needs a safety/lightning ground.  A long wire, inverted L, 
> vertical, etc work against a ground and only have one wire.  They always 
> need an RF ground.
>
> A "ground rod" is not and never has been an RF ground.  An RF ground 
> invariably means a network of conductors covering as large an area as 
> possible.  The radials for a ground mounted vertical are an example of an 
> RF ground.  The VLF and LF stations had acres of conductors for their 
> grounds. AM broadcast stations have large radial fields.  For shortwaves, 
> the size doesn't have to be quite as large.  A ground rod is only for 
> safety and lightning.
>
> If you have a problem with RF in your shack, that is an indication that 
> you have a problem with how you are feeding your antenna or how your 
> equipment is interconnected and /or shielded.  I don't believe grounding 
> is the solution.  Sometimes it will work and sometimes it won't.  MFJ used 
> to sell a ground tuner, I'm not sure what they actually called it, but it 
> was similar to an antenna tuner that you put between the equipment and the 
> ground rod in series with the ground wire.  It had to be adjusted for each 
> frequency you operated on and essentially made your ground wire part of 
> the antenna and placed your transmitter part way up the antenna.  You 
> ended up adjusting the tuner so your transmitter weas at a low voltage 
> point on the antenna.  I don't think it was a very good idea unless I was 
> selling ground tuners!
>
> For dipoles, you don't need an RF ground.  For verticals, the RF ground is 
> your radial system at the antenna, you don't need a separate RF ground at 
> the transmitter end.
>
> If you have questions, keep asking, Gary.
>
> Kerry
>
>
>
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