starman wrote in message ...
Mark Keith wrote:

It's the improved decoupling of the feedline
from the antenna that reduces the noise level. "noise ingress" Not
the grounding itself, although the grounding helps in the decoupling
of the line.

I think we're talking semantics here, but how else could you decouple
the feedline of an inverted-L antenna other than using an effective
(short) earth ground connection?

As one mentioned, radials. Or you could use a choke,beads, etc. Lets
say you had a 1/4 wave ground plane that was elevated with a set of
radials. The radials will decouple the feedline pretty well. There is
no need to ground the radials, or the supporting mast, except as a
lightning concern. A choke will decouple the line fairly well. Noise
ingress has nothing to do with being grounded or not. It's an issue of
decoupling the feedline from the antenna. Using a ground connection
under an "L" will decouple it fairly well, but it's just one method
that can be used, and the "ground" is not a required element. It's not
just semantics, because an "rf ground" is not a requirement of good
decoupling. But saying that, I usually do ground the low end of inv
L's. MK

Mark Keith wrote:

starman wrote in message ...
Mark Keith wrote:

It's the improved decoupling of the feedline
from the antenna that reduces the noise level. "noise ingress" Not
the grounding itself, although the grounding helps in the decoupling
of the line.

I think we're talking semantics here, but how else could you decouple
the feedline of an inverted-L antenna other than using an effective
(short) earth ground connection?

As one mentioned, radials. Or you could use a choke,beads, etc. Lets
say you had a 1/4 wave ground plane that was elevated with a set of
radials. The radials will decouple the feedline pretty well. There is
no need to ground the radials, or the supporting mast, except as a
lightning concern. A choke will decouple the line fairly well. Noise
ingress has nothing to do with being grounded or not. It's an issue of
decoupling the feedline from the antenna. Using a ground connection
under an "L" will decouple it fairly well, but it's just one method
that can be used, and the "ground" is not a required element. It's not
just semantics, because an "rf ground" is not a requirement of good
decoupling. But saying that, I usually do ground the low end of inv
L's. MK

I agree that the feedline of an elevated ground plane can be effectively
decoupled using radials but it's not clear to me how you would use
radials with the typical inverted-L. Where would you locate the radials
in that case?


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STARMAN,

At the Base Feed Point of the Inverted "L" Antenna two Radials
opposite each other set at 90 Degrees to the Horizontal Arm as
viewed from the Top. The Radials should be as long as the
Vertical Leg of the Inverted "L" Antenna.

* Inverted "L' Antenna Reading List
http://groups.yahoo.com/group/SWL-AM...na/message/374

* Inverted "L" Antenna for Transmitting by Dr. Ace
http://groups.yahoo.com/group/SWL-AM...na/message/309
Typically: Quarter (1/4) Wave Length Long and 1/8th WL High

* Inverted "L" Antenna as an 'available space' SWL Antenna
http://groups.yahoo.com/group/SWL-AM...nna/message/54
Typically: For a SWL Receive ONLY Antenna of any Random Length
With the Horizontal Arm 'twice' (2X) as long as the Vertical Leg.


iane ~ RHF
..
..
= = = starman
= = = wrote in message ...

Mark Keith wrote:

starman wrote in message ...
Mark Keith wrote:

It's the improved decoupling of the feedline
from the antenna that reduces the noise level. "noise ingress" Not
the grounding itself, although the grounding helps in the decoupling
of the line.

I think we're talking semantics here, but how else could you decouple
the feedline of an inverted-L antenna other than using an effective
(short) earth ground connection?

As one mentioned, radials. Or you could use a choke,beads, etc. Lets
say you had a 1/4 wave ground plane that was elevated with a set of
radials. The radials will decouple the feedline pretty well. There is
no need to ground the radials, or the supporting mast, except as a
lightning concern. A choke will decouple the line fairly well. Noise
ingress has nothing to do with being grounded or not. It's an issue of
decoupling the feedline from the antenna. Using a ground connection
under an "L" will decouple it fairly well, but it's just one method
that can be used, and the "ground" is not a required element. It's not
just semantics, because an "rf ground" is not a requirement of good
decoupling. But saying that, I usually do ground the low end of inv
L's. MK

I agree that the feedline of an elevated ground plane can be effectively
decoupled using radials but it's not clear to me how you would use
radials with the typical inverted-L. Where would you locate the radials
in that case?

starman wrote in message ...


I agree that the feedline of an elevated ground plane can be effectively
decoupled using radials but it's not clear to me how you would use
radials with the typical inverted-L. Where would you locate the radials
in that case?




On the ground. And in that case, I almost always do ground the radials
to earth at the feedpoint. Radials on the ground are detuned, and are
not required to be cut to any certain length. So they are not really
resonant at any given freq like elevated radials, or if they are, it's
likely not where you would expect. They normally need to be resonant
to decouple the feedline, so it's best to also ground them if they are
on the ground and detuned. If you had an elevated GP with 1/4 wave
radials for a certain freq, they will not work at say twice that freq.
"1/2 waves" They would show a high impedance, and the radial system
would not function properly, and the decoupling would be poor. But 3/4
wave radials can work ok, as they show a low Z. The best ground
planes, verticals , etc use twin decoupling sections. IE: a 1/4 wave
ground plane with a set of 1/4 wave radials, would have a second set
of 1/4 wave radials, 1/4 wave below the main set. Or if a sleeve
vertical, two sets of cones, tubes, etc. You can also use chokes,
ferrite beads as extra decoupling with any coax system. I'm not
against grounding in some cases. I just wanted to clarify that it's
really the improved decoupling, rather than the addition of ground per
say, that reduces the noise ingress. Grounding is just one method used
to improve decoupling of the line in some cases. Usually with radials
on the ground, or when using no radials at all. If the antenna is
already balanced and properly decoupled, adding an "rf ground" will
not do a thing as far as noise ingress. Might even make things worse
being ground is usually a noise source. MK

Mark Keith wrote:

starman wrote in message ...


I agree that the feedline of an elevated ground plane can be effectively
decoupled using radials but it's not clear to me how you would use
radials with the typical inverted-L. Where would you locate the radials
in that case?



On the ground. And in that case, I almost always do ground the radials
to earth at the feedpoint. Radials on the ground are detuned, and are
not required to be cut to any certain length. So they are not really
resonant at any given freq like elevated radials, or if they are, it's
likely not where you would expect. They normally need to be resonant
to decouple the feedline, so it's best to also ground them if they are
on the ground and detuned. If you had an elevated GP with 1/4 wave
radials for a certain freq, they will not work at say twice that freq.
"1/2 waves" They would show a high impedance, and the radial system
would not function properly, and the decoupling would be poor. But 3/4
wave radials can work ok, as they show a low Z. The best ground
planes, verticals , etc use twin decoupling sections. IE: a 1/4 wave
ground plane with a set of 1/4 wave radials, would have a second set
of 1/4 wave radials, 1/4 wave below the main set. Or if a sleeve
vertical, two sets of cones, tubes, etc. You can also use chokes,
ferrite beads as extra decoupling with any coax system. I'm not
against grounding in some cases. I just wanted to clarify that it's
really the improved decoupling, rather than the addition of ground per
say, that reduces the noise ingress. Grounding is just one method used
to improve decoupling of the line in some cases. Usually with radials
on the ground, or when using no radials at all. If the antenna is
already balanced and properly decoupled, adding an "rf ground" will
not do a thing as far as noise ingress. Might even make things worse
being ground is usually a noise source. MK

Why would someone build such a radial system for an inverted-L when the
'Doty-L' achieves the same or better results with a simple earth ground?


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From a pure efficiency standpoint, a simple ground rod is pretty poor. In a
receiving application, you are not likely to notice but try transmitting
with an inverted L. The ground system is much more important and the radial
system is far superior.

"starman" wrote in message
...
Why would someone build such a radial system for an inverted-L when the
'Doty-L' achieves the same or better results with a simple earth ground?


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