"Nate Bargmann" wrote in message
news
On Sun, 23 Sep 2007 12:59:49 -0500, Richard Fry wrote:

"Rick wrote

... What say you all?

Read "Ground Systems as a Factor in Antenna Efficiency" by Brown, Lewis
& Epstein of RCA Labs, published in the June, 1937 issue of The
Proceedings of the I.R.E.

It proves otherwise.

Honest question, does it matter whether the objective is a strong ground
wave as in AM broadcast or skywave as in amateur operation?

I am installing a Hustler 4BTV this fall and have put down (so far) 16
radials that range from about 18 to 35 feet in length due to my servere
space restrictions. I may add 16 more later this fall as an experiment.

73, de Nate

It would be interesting to follow the change in VSWR as you add individual
radials. Some years ago, there was a discussion of adding radials until the
VSWR stopped increasing. This was based on an expected feedpoint resistance
of 36 ohms, and an assumption that the ground losses were 15 ohms or less.
So at the worst case, the VSWR was near 1:1. The best case, with a ground
loss approaching 0 ohms, would have a VSWR of 50/36= 1.39:1.

I want to attribute the original discussion to W2DU, but I stop short of
that, in case I don't remember correctly.

On Wed, 26 Sep 2007 16:56:27 GMT, "Wayne"
wrote:

It would be interesting to follow the change in VSWR as you add individual
radials. Some years ago, there was a discussion of adding radials until the
VSWR stopped increasing. This was based on an expected feedpoint resistance
of 36 ohms, and an assumption that the ground losses were 15 ohms or less.
So at the worst case, the VSWR was near 1:1. The best case, with a ground
loss approaching 0 ohms, would have a VSWR of 50/36= 1.39:1.

Hi Wayne,

This strategy may also have you stop adding radials too early when
your antenna presented 36 Ohms looking into a ground loss of 33 Ohms
(same SWR of 1.39).

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
The best case, with a ground loss approaching 0 ohms, would
have a VSWR of 50/36= 1.39:1.
___________

A set of 120 buried radials each at least 1/4-wave long (free space value)
will produce an r-f ground resistance of around 2 ohms, maybe less in soil
with very good conductivity.

But in any case the impedance existing between the base of a series-fed
vertical monopole and the common point of the buried radials will depend on
the electrical height of the monopole which includes the ratio of its height
to its width, as well as the r-f resistance in the ground system itself.

Broadcast stations will install the tower and radials, measure the Z from
the tower base to the radials, and transform whatever that value is to 50
+j0 ohms using a network at the base of the tower.

Fewer radials will mean that the ground loss will increase, and system
radiation efficiency will decrease (even if the VSWR is 1:1)

RF

"Richard Clark" wrote in message
...
On Wed, 26 Sep 2007 16:56:27 GMT, "Wayne"
wrote:

It would be interesting to follow the change in VSWR as you add individual
radials. Some years ago, there was a discussion of adding radials until
the
VSWR stopped increasing. This was based on an expected feedpoint
resistance
of 36 ohms, and an assumption that the ground losses were 15 ohms or less.
So at the worst case, the VSWR was near 1:1. The best case, with a ground
loss approaching 0 ohms, would have a VSWR of 50/36= 1.39:1.

Hi Wayne,

This strategy may also have you stop adding radials too early when
your antenna presented 36 Ohms looking into a ground loss of 33 Ohms
(same SWR of 1.39).

73's
Richard Clark, KB7QHC

Right. I guess the better way to state it is to stop adding radials when
the r component stops dropping. I've always wanted to try that experiment,
but real estate considerations have prevented it.

On Sep 26, 9:56 am, "Wayne" wrote:
"Nate Bargmann" wrote in message

news
On Sun, 23 Sep 2007 12:59:49 -0500, Richard Fry wrote:

"Rick wrote

... What say you all?

Read "Ground Systems as a Factor in Antenna Efficiency" by Brown, Lewis
& Epstein of RCA Labs, published in the June, 1937 issue of The
Proceedings of the I.R.E.

It proves otherwise.

Honest question, does it matter whether the objective is a strong ground
wave as in AM broadcast or skywave as in amateur operation?

I am installing a Hustler 4BTV this fall and have put down (so far) 16
radials that range from about 18 to 35 feet in length due to my servere
space restrictions. I may add 16 more later this fall as an experiment.

73, de Nate

It would be interesting to follow the change in VSWR as you add individual
radials. Some years ago, there was a discussion of adding radials until the
VSWR stopped increasing. This was based on an expected feedpoint resistance
of 36 ohms, and an assumption that the ground losses were 15 ohms or less.
So at the worst case, the VSWR was near 1:1. The best case, with a ground
loss approaching 0 ohms, would have a VSWR of 50/36= 1.39:1.

I want to attribute the original discussion to W2DU, but I stop short of
that, in case I don't remember correctly.

I think it would be a lot MORE interesting to follow the change in
_impedance_ as you add wires. I can see a lot that can go wrong with
"adding radials till the SWR stops increasing." I don't think that
the case of 33 ohms ground resistance is one to seriously consider*,
but if you're operating over really poor ground and/or your "quarter
wave" antenna isn't really a quarter electrical wave, you may see
significant reactive component that you'll never resolve with an SWR
meter. You'll likely get very confused by it instead.

*What's the "ground resistance" with as few as two radials, even if
there's no earth ground nearby? What if there are no radials but the
ground is really awful? Some "what-ifs" with EZNEC or the like can
give you an appreciation for what happens...

Cheers,
Tom