-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
RF grounding and antenna concepts:

Before opening this can of worms I want to explain the steps that lead
to this thinking.
The following is the result of a casual comment by William Fieldstone.
I don't remember
the exact question as it was in the middle of a frustrating antenna
testing session. But
several hours later I was thinking about his basic question and
realized that in spite of
being a SWL for over 40 years, a ham for over 25 years and an EE, I
had never really
bothered to think about the random wire antenna that many SWLs use.

Perhaps because I started in radio way before I had any understanding
and just had
never bothered to reconcile the way I treated random antennas and what
I knew to be
the physics of how antennas operate. Either I can call it an epiphany
or, as the new
agers would say, a "paradigm shift". Or more likely I had simply been
guilty of sloppy
or muddled thinking.

As I developed the thoughts that follow, I had many conversations with
fellow hams,
SWLs and some professional engineers that specialize in RF. Some of
the conversations
got very heated. I was spouting what was viewed as heresy. But after
the dust settled
everyone agreed with my conclusions. That doesn't mean I am correct,
maybe my
friends just gave in to my insane ravings to shut me up.

I even went back to my college text books and reviewed the section of
EM wave theory
and antenna function.

Before we discuss grounds we need a quick review of how antennas
really work. Most
of think that 'good RF ground' is a requirement. But stop and think a
moment. A TV
UHF antenna is a dipole. While we ground such antennas for safety
reasons, a ground
doesn't effect reception. Hams that operate in the HF, or SW, bands
often use dipoles,
beams, or loops. None of which need a ground to operate. It is true
the ground near the
antenna has a pronounced effect on many characteristics such as angle
of radiation
and to some degree the actual impedance and bandwidth. But a dipole
would work
just fine in free space.

With the exception of 'Long Wire Antennas', Beverage and other
surface or traveling
wave antennas, all other forms of antennas are either loops or some
form of dipoles.
Loops and dipoles simply do not need a ground.

Back in 1984 I was interested in low power, QRP, Ham HF operations. I
used a simple
home brew HF transmitter, direct conversion receiver and a dipole. I
operated for several
weekends from a friend's cabin in the Daniel Boone National Forrest
and I used a dipole
suspended between two convenient trees. I operated off my motorcycle
battery and nothing
was grounded. The battery was sitting on a wooden front porch picnic
table. I worked 17
countries and 38 states in 3 weekends.

While doing some R&D for a commercial WWV receiver installation I
experimented with a
dipole and a Panasonic RF2300. I was on the metal roof of a
manufacturing plant, and I was
not connected to ground in any way. And I had very good reception
across the HF band with
a dipole cut for 10.0MHz

Will's question made me realize that with the exception of loops, all
of the antennas I normally
use are a dipole. In the case of the ever popular random wire antenna,
the wire was clearly one
element and the earth was the non obvious other half of the dipole.

Take a look at any taxi, cop car, fire truck or even a car or truck
with a CB. The vertical whip is
part of the dipole and the car/truck body is the other part of the
dipole. We call such antennas
ground planes.

A very effective 2M ham antenna can be made with a 19" vertical rod
and a 40" diameter metal
plate, or picnic table top. A 10 or 11 meter antenna can be created
with a ~100" vertical whip
and a ~200" metal roof. Both antennas do not need the 'ground plane'
connected to the earth.

Many hams use vertical antennas and all commercial MW stations in the
US use vertical
antennas. The FCC requires MW stations to use about 122 radials that
form an effective
ground plane. A few MW stations use an elevated set of radials that
don't need to be
grounded for proper operation. For lightning protection a ground is
needed, but not for
operation.

Hams, and SWLs, that use verticals need to have enough radials to
reduce the losses
caused by poor soil conductivity. A 1/4 wavelength vertical element
and an 8' NEC ground
rod will be a very poor antenna.

The all too common random wire antenna that is using the soil, a poor
conductor unless
you live in a salt marsh, is a very inefficient antenna. In extremely
RF quiet locations such
a setup works very well. My friend with the cabin deep in the Daniel
Boone National Forrest
lets my wife and me spend a week there every fall. There is no
electricity, telephone, or cable
TV service within a mile or so. In that location, a single random wire
antenna, with no feed
line, and using the well casing as a ground works VERY well.

However at my home, such a setup is an absolute failure.

The biggest problem with the all too common random wire antenna is the
lack of isolation and
the inherent high impedance and the extreme difficulty of achieving
sufficient isolation from the
noise within the home.

So now we come to the main question:
"What is a good RF ground?"

It depends.....

A better first question might "why do I need a good RF ground?"

Remember that the earth is almost always an extremely poor conductor.
Imagine trying to put up
an antenna on a soil less rocky mountain top. Kind of hard to get any
sort of ground. I have seen
such a location that took a direct lightning strike. Given that
lightning has traveled through several
thousand feet of the world's best insulator, air, even the poor
conductivity of rock looks like a very
good ground. The surface of the rock was covered by what physicists
call a dendrite pattern. Looked
kind of like frost on a window.

So why do we insist on trying to use such a poor conductor as part of
our antenna system?

Habit?

Since SWLs typically listen from 100KHz to 30MHz, I am including LW
and MW here, and since
hams most often operate on a few narrow bands of frequencies the
antenna we use are very often
very dissimilar. A ham can get by with a couple of dipoles or even a
single dipole with "traps" to
add additional bands. SWLs can't do that. For a dipole the only ground
that is needed is a safety
ground. In a proper dipole there will be no ground currents.

So if one is going to use a random wire antenna, we need to understand
it is a poor compromise
but it will work. By adding a 8' NEC ground rod at the feed line end,
and by adding as many radials
that are as long as feasible, we can boast both the performance of
such an antenna, but more
importantly we can achieve much higher attenuation of the noise from
the home. Let's face it; on
lower HF the background noise is high enough so that greater
efficiency isn't that helpful. The
improved unobvious leg of the dipole, the "ground", would have much
better conductivity. But more
important the conductivity for efficiency is the improved conductivity
converts the pseudo dipole
formed by the random wire antenna, into a more effective dipole. And
this will allow a better match
to the feed line. Better match equals increased isolation can lower
the noise from within your home
by at least 1 S-unit and many times by 3 or more S-Units. This is
manna from heaven.

If we decide to go with an active monopole antenna then the ground
needs are very similar. Again
a 8' NEC ground rod and as many radials as practical will create a
"good RF ground. Of course
we could forget the grounding rod and just go with a set of elevated
radials, or in my case a metal
roof and have very good reception.

An active dipole doesn't need a ground for operation, although for
safety and precipitation static an
earth ground is very important.

I am not a fan of loops, but if one decides a loop is the way to go,
the RF ground really doesn't
matter. The feed line does need to be bonded to the NEC required
safety ground for lightning
protection.

In any case, the antenna ground ALWAYS needs to be bonded to the NEC
safety ground.
If you want to isolate the antenna ground then you need to use a
broadband 1:1 RF transformer
to achieve electrical isolation between the antenna/ground system and
the house NEC ground.
In a lightning strike that 1:1 will short and your antenna/ground will
become some what connected
to the NEC ground.

In my experience, any time connecting the antenna ground to the NEC
ground increases noise
level, there are other issues in either the homes grounding system or
power distribution system
that needs careful attention.

In closing, I believe that since the beginning of radio the concept of
'ground' has been misunderstood.
In the past the deficiencies of a random wire antenna connected to
whatever convenient piece of metal
that happened to be connected to the ground. In the 1930's concerns
about antenna efficiency didn't
exist. And even today "efficiency" in it's self is not an issue.


In the 30' my father's family had a battery powered MW receiver from
Sears. They were deep in the
eastern KY hills, with no AC in the county. No telephone. In other
words a damn near perfect radio
environment. Dad told me stories of the distant stations he received
on the 3 stage TRF radio. No
local noise, fairly high natural back ground noise, meant the
deficiencies meaningless. The same
antenna in the same location in the mid 1960's showed the deficiencies
imposed serious limitations.
My father couldn't understand why my better receiver performed much
worse then the older simpler
receiver he had used.

His mom was a packrat, I am doomed I have the packrat gene from both
sides, and still had the
receiver. So over the winter of 1967 I rebuilt the receiver. On my
home antenna it was clear that
my super-het Zenith beat the pants of the Sears TRF. The next summer
with a new antenna ran
from the same supports my Zenith still beat the Sears hands down. Dad
just couldn't understand
why the reception was so much worse. Of course the entire county was
then wired with AC,
telephones and everyone had a TV. And most of the TV's had several
hundred feet of twin lead
running up the hill sides to antennas mounted up high enough to "see"
the distant TV stations.
Dad, and I, just didn't understand how much local RF noise had been
added.

Had I been more knowledgeable I could have realized way back then the
importance of proper
antenna design and the role antennas can play in fighting RFI.
Recently I had a chance to visit
Dad's old home, a first cousin still lives there. We took on of our
R2000's, and several antennas.
The 100' random wire with ground that consisted of the homes NEC
grounding system, lighting
grounding system and a deep 4" steel well head, that we bonded before
my tests, was still a very
poor performer. One of Dallas Lankford's active dipoles was best and
his 15' relay tuned vertical
was a close second. When I added 8 15' radials staked out on the
ground the 15' antenna had a
slight edge on the active dipole. My cousin has several PCs, several
TVs, a DBS and cable TV.
Hardly the pristine RF dreamland my dad experienced 70 years ago.

So back to the question "What makes a "Good RF Ground?" The sad answer
is it depends. For
well designed antennas other then random wire, a "Good RF Ground" is
simple a safety ground.
Assuming the home has a NEC compliant ground system, this will work
quiet nicely.

If one is insistent on using a ~100' random wire, then something like
a whole house ground ring
works very well. Rather silly. I know I have one. There are several
very weak TIS (low power traffic
information stations) that were inaudible with my ~75' random wire
antenna. Several summers ago
a friend's brother gave me enough 3/8 copper tubing to surround our
home, His brother my friend
is a commercial electrician and had a Ditch Witch rented for a job
that got canceled. Since the
client had already paid for the rental, my friend brought it down. He
dug an 18~24" trench around
our home. We laid the tubing in, and another friend welded the
sections into one giant circle. We
drove 8' NEC ground rods at the corners
and bonded it to the service ground with 4AWG.

A neighbor works for a quarry and he brought a dump truck load of
ground clay and sand mix down
and we back filled the trench with about a foot of the mixture. I laid
a soaker hose and we dumped
another 6" of the mixture then topped it off the original soil.
Another neighbor needed the left over
soil to fill in a large depression in his back yard. Think sink hole.
I was amazed to receive a 10W
TIS from Winchester Ky and another one from Richmond, both about 30
miles away. I visited the
Winchester TIS and it is a very poor installation. A 10' whip mounted
to a roof top AC air handler.
Last summer I received a new TIS like signal on 1640. It is a
continuous rebroadcast of the Jackson
KY NWS audio stream. Most likely the Irvine KY NOAA WX signal. NOAA
doesn't know who is
running this, the Richmond DES doesn't know and the Blue Grass Army
Depot won't admit that
they know anything. Several RDF trips suggest that it is a line
source, leaky coax, inside of the
Depot near the south west end.

This signal is just detectable on a 70' random wire antenna using my
"super" ground. It is much
stronger, S2, on the Lankford 15' antenna, and better yet with a
Lankford 15' antenna with a set
of 16' elevated radials. But it is even better with a Lankford Active
Dipole and best with the latest
Lankford design, an improved derivative of the PA0RDT mounted on the
ridge of our metal roof.
The roof is grounded, but I suspect the ground is not an issue.

A "good rf ground" is only needed with the wrong antenna. If I had a
chance to not install my
super ground I would clearly avoid the exercise. While it did offer
significant improvements in
my reception, there are simply better antennas that avoid the need for
such extreme efforts.

I know I have created a paradox. Simple random wire antennas in very
quiet RF locations, with
marginal grounds will offer outstanding performance. However in most
real world locations, the
local noise will be coupled to a random wire antenna unless extreme
steps are taken. There are
simply better antenna choices that avoid the need for "Good RF
Grounds"

If the ground, soil, or earth, is such a good conductor, why is the
power distributed via metallic
conductors and the only use for grounds is for lightning protection
and, for the end user, to clear
fault conditions. Energy is simple not carried through the ground
because the losses would be
extremely high.

Flame shields up.

Terry

On Nov 30, 9:14 am, wrote:
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
RF grounding and antenna concepts:

Before opening this can of worms I want to explain the steps that lead
to this thinking.
The following is the result of a casual comment by William Fieldstone.
I don't remember
the exact question as it was in the middle of a frustrating antenna
testing session. But
several hours later I was thinking about his basic question and
realized that in spite of
being a SWL for over 40 years, a ham for over 25 years and an EE, I
had never really
bothered to think about the random wire antenna that many SWLs use.

Perhaps because I started in radio way before I had any understanding
and just had
never bothered to reconcile the way I treated random antennas and what
I knew to be
the physics of how antennas operate. Either I can call it an epiphany
or, as the new
agers would say, a "paradigm shift". Or more likely I had simply been
guilty of sloppy
or muddled thinking.

As I developed the thoughts that follow, I had many conversations with
fellow hams,
SWLs and some professional engineers that specialize in RF. Some of
the conversations
got very heated. I was spouting what was viewed as heresy. But after
the dust settled
everyone agreed with my conclusions. That doesn't mean I am correct,
maybe my
friends just gave in to my insane ravings to shut me up.

I even went back to my college text books and reviewed the section of
EM wave theory
and antenna function.

Before we discuss grounds we need a quick review of how antennas
really work. Most
of think that 'good RF ground' is a requirement. But stop and think a
moment. A TV
UHF antenna is a dipole. While we ground such antennas for safety
reasons, a ground
doesn't effect reception. Hams that operate in the HF, or SW, bands
often use dipoles,
beams, or loops. None of which need a ground to operate. It is true
the ground near the
antenna has a pronounced effect on many characteristics such as angle
of radiation
and to some degree the actual impedance and bandwidth. But a dipole
would work
just fine in free space.

With the exception of 'Long Wire Antennas', Beverage and other
surface or traveling
wave antennas, all other forms of antennas are either loops or some
form of dipoles.
Loops and dipoles simply do not need a ground.

Back in 1984 I was interested in low power, QRP, Ham HF operations. I
used a simple
home brew HF transmitter, direct conversion receiver and a dipole. I
operated for several
weekends from a friend's cabin in the Daniel Boone National Forrest
and I used a dipole
suspended between two convenient trees. I operated off my motorcycle
battery and nothing
was grounded. The battery was sitting on a wooden front porch picnic
table. I worked 17
countries and 38 states in 3 weekends.

While doing some R&D for a commercial WWV receiver installation I
experimented with a
dipole and a Panasonic RF2300. I was on the metal roof of a
manufacturing plant, and I was
not connected to ground in any way. And I had very good reception
across the HF band with
a dipole cut for 10.0MHz

Will's question made me realize that with the exception of loops, all
of the antennas I normally
use are a dipole. In the case of the ever popular random wire antenna,
the wire was clearly one
element and the earth was the non obvious other half of the dipole.

Take a look at any taxi, cop car, fire truck or even a car or truck
with a CB. The vertical whip is
part of the dipole and the car/truck body is the other part of the
dipole. We call such antennas
ground planes.

A very effective 2M ham antenna can be made with a 19" vertical rod
and a 40" diameter metal
plate, or picnic table top. A 10 or 11 meter antenna can be created
with a ~100" vertical whip
and a ~200" metal roof. Both antennas do not need the 'ground plane'
connected to the earth.

Many hams use vertical antennas and all commercial MW stations in the
US use vertical
antennas. The FCC requires MW stations to use about 122 radials that
form an effective
ground plane. A few MW stations use an elevated set of radials that
don't need to be
grounded for proper operation. For lightning protection a ground is
needed, but not for
operation.

Hams, and SWLs, that use verticals need to have enough radials to
reduce the losses
caused by poor soil conductivity. A 1/4 wavelength vertical element
and an 8' NEC ground
rod will be a very poor antenna.

The all too common random wire antenna that is using the soil, a poor
conductor unless
you live in a salt marsh, is a very inefficient antenna. In extremely
RF quiet locations such
a setup works very well. My friend with the cabin deep in the Daniel
Boone National Forrest
lets my wife and me spend a week there every fall. There is no
electricity, telephone, or cable
TV service within a mile or so. In that location, a single random wire
antenna, with no feed
line, and using the well casing as a ground works VERY well.

However at my home, such a setup is an absolute failure.

The biggest problem with the all too common random wire antenna is the
lack of isolation and
the inherent high impedance and the extreme difficulty of achieving
sufficient isolation from the
noise within the home.

So now we come to the main question:
"What is a good RF ground?"

It depends.....

A better first question might "why do I need a good RF ground?"

Remember that the earth is almost always an extremely poor conductor.
Imagine trying to put up
an antenna on a soil less rocky mountain top. Kind of hard to get any
sort of ground. I have seen
such a location that took a direct lightning strike. Given that
lightning has traveled through several
thousand feet of the world's best insulator, air, even the poor
conductivity of rock looks like a very
good ground. The surface of the rock was covered by what physicists
call a dendrite pattern. Looked
kind of like frost on a window.

So why do we insist on trying to use such a poor conductor as part of
our antenna system?

Habit?

Since SWLs typically listen from 100KHz to 30MHz, I am including LW
and MW here, and since
hams most often operate on a few narrow bands of frequencies the
antenna we use are very often
very dissimilar. A ham can get by with a couple of dipoles or even a
single dipole with "traps" to
add additional bands. SWLs can't do that. For a dipole the only ground
that is needed is a safety
ground. In a proper dipole there will be no ground currents.

So if one is going to use a random wire antenna, we need to understand
it is a poor compromise
but it will work. By adding a 8' NEC ground rod at the feed line end,
and by adding as many radials
that are as long as feasible, we can boast both the performance of
such an antenna, but more
importantly we can achieve much higher attenuation of the noise from
the home. Let's face it; on
lower HF the background noise is high enough so that greater
efficiency isn't that helpful. The
improved unobvious leg of the dipole, the "ground", would have much
better conductivity. But more
important the conductivity for efficiency is the improved conductivity
converts the pseudo dipole
formed by the random wire antenna, into a more effective dipole. And
this will allow a better match
to the feed line. Better match equals increased isolation can lower
the noise from within your home
by at least 1 S-unit and many times by 3 or more S-Units. This is
manna from heaven.

If we decide to go with an active monopole antenna then the ground
needs are very similar. Again
a 8' NEC ground rod and as many radials as practical will create a
"good RF ground. Of course
we could forget the grounding rod and just go with a set of elevated
radials, or in my case a metal
roof and have very good reception.

An active dipole doesn't need a ground for operation, although for
safety and precipitation static an
earth ground is very important.

I am not a fan of loops, but if one decides a loop is the way to go,
the RF ground really doesn't
matter. The feed line does need to be bonded to the NEC required
safety ground for lightning
protection.

In any case, the antenna ground ALWAYS needs to be bonded to the NEC
safety ground.
If you want to isolate the antenna ground then you need to use a
broadband 1:1 RF transformer
to achieve electrical isolation between the antenna/ground system and
the house NEC ground.
In a lightning strike that 1:1 will short and your antenna/ground will
become some what connected
to the NEC ground.

In my experience, any time connecting the antenna ground to the NEC
ground increases noise
level, there are other issues in either the homes grounding system or
power distribution system
that needs careful attention.

In closing, I believe that since the beginning of radio the concept of
'ground' has been misunderstood.
In the past the deficiencies of a random wire antenna connected to
whatever convenient piece of metal
that happened to be connected to the ground. In the 1930's concerns
about antenna efficiency didn't
exist. And even today "efficiency" in it's self is not an issue.

In the 30' my father's family had a battery powered MW receiver from
Sears. They were deep in the
eastern KY hills, with no AC in the county. No telephone. In other
words a damn near perfect radio
environment. Dad told me stories of the distant stations he received
on the 3 stage TRF radio. No
local noise, fairly high natural back ground noise, meant the
deficiencies meaningless. The same
antenna in the same location in the mid 1960's showed the deficiencies
imposed serious limitations.
My father couldn't understand why my better receiver performed much
worse then the older simpler
receiver he had used.

His mom was a packrat, I am doomed I have the packrat gene from both
sides, and still had the
receiver. So over the winter of 1967 I rebuilt the receiver. On my
home antenna it was clear that
my super-het Zenith beat the pants of the Sears TRF. The next summer
with a new antenna ran
from the same supports my Zenith still beat the Sears hands down. Dad
just couldn't understand
why the reception was so much worse. Of course the entire county was
then wired with AC,
telephones and everyone had a TV. And most of the TV's had several
hundred feet of twin lead
running up the hill sides to antennas mounted up high enough to "see"
the distant TV stations.
Dad, and I, just didn't understand how much local RF noise had been
added.

Had I been more knowledgeable I could have realized way back then the
importance of proper
antenna design and the role antennas can play in fighting RFI.
Recently I had a chance to visit
Dad's old home, a first cousin still lives there. We took on of our
R2000's, and several antennas.
The 100' random wire with ground that consisted of the homes NEC
grounding system, lighting
grounding system and a deep 4" steel well head, that we bonded before
my tests, was still a very
poor performer. One of Dallas Lankford's active dipoles was best and
his 15' relay tuned vertical
was a close second. When I added 8 15' radials staked out on the
ground the 15' antenna had a
slight edge on the active dipole. My cousin has several PCs, several
TVs, a DBS and cable TV.
Hardly the pristine RF dreamland my dad experienced 70 years ago.

So back to the question "What makes a "Good RF Ground?" The sad answer
is it depends. For
well designed antennas other then random wire, a "Good RF Ground" is
simple a safety ground.
Assuming the home has a NEC compliant ground system, this will work
quiet nicely.

If one is insistent on using a ~100' random wire, then something like
a whole house ground ring
works very well. Rather silly. I know I have one. There are several
very weak TIS (low power traffic
information stations) that were inaudible with my ~75' random wire
antenna. Several summers ago
a friend's brother gave me enough 3/8 copper tubing to surround our
home, His brother my friend
is a commercial electrician and had a Ditch Witch rented for a job
that got canceled. Since the
client had already paid for the rental, my friend brought it down. He
dug an 18~24" trench around
our home. We laid the tubing in, and another friend welded the
sections into one giant circle. We
drove 8' NEC ground rods at the corners
and bonded it to the service ground with 4AWG.

A neighbor works for a quarry and he brought a dump truck load of
ground clay and sand mix down
and we back filled the trench with about a foot of the mixture. I laid
a soaker hose and we dumped
another 6" of the mixture then topped it off the original soil.
Another neighbor needed the left over
soil to fill in a large depression in his back yard. Think sink hole.
I was amazed to receive a 10W
TIS from Winchester Ky and another one from Richmond, both about 30
miles away. I visited the
Winchester TIS and it is a very poor installation. A 10' whip mounted
to a roof top AC air handler.
Last summer I received a new TIS like signal on 1640. It is a
continuous rebroadcast of the Jackson
KY NWS audio stream. Most likely the Irvine KY NOAA WX signal. NOAA
doesn't know who is
running this, the Richmond DES doesn't know and the Blue Grass Army
Depot won't admit that
they know anything. Several RDF trips suggest that it is a line
source, leaky coax, inside of the
Depot near the south west end.

This signal is just detectable on a 70' random wire antenna using my
"super" ground. It is much
stronger, S2, on the Lankford 15' antenna, and better yet with a
Lankford 15' antenna with a set
of 16' elevated radials. But it is even better with a Lankford Active
Dipole and best with the latest
Lankford design, an improved derivative of the PA0RDT mounted on the
ridge of our metal roof.
The roof is grounded, but I suspect the ground is not an issue.

A "good rf ground" is only needed with the wrong antenna. If I had a
chance to not install my
super ground I would clearly avoid the exercise. While it did offer
significant improvements in
my reception, there are simply better antennas that avoid the need for
such extreme efforts.

I know I have created a paradox. Simple random wire antennas in very
quiet RF locations, with
marginal grounds will offer outstanding performance. However in most
real world locations, the
local noise will be coupled to a random wire antenna unless extreme
steps are taken. There are
simply better antenna choices that avoid the need for "Good RF
Grounds"

If the ground, soil, or earth, is such a good conductor, why is the
power distributed via metallic
conductors and the only use for grounds is for lightning protection
and, for the end user, to clear
fault conditions. Energy is simple not carried through the ground
because the losses would be
extremely high.

Flame shields up.

Terry

I use a dual band j-pole antenna on 2 meters and 70 cm. It works very
well above ground.

Cough cough... may I interject?

I am in an urban location and I am in no position to put up a dipole for
my SWL needs. The best options as I see them in order of preference are
(1) a broadband loop such as a Wellbrook ALA1530+ (2) an Inverted-L (3) a
random wire. I have about 5m up and 5m horizontal to play with, so for
most HF listening I'm probably going to have a high impedance for the
wires and a low one for the loop.

From what I've been reading, the random wire in an urban environment is
probably the worst of my options, since it will be e-field dominated and
pick up all manner of horrific local/near-field noise.

That leaves the next option, the inverted-L. The consensus is to use a 9:1
or 3:1 un-un at the base point with a common ground with a coax feeder
running back to the shack. I don't see how this would work without at
least an attempt at grounding the base of the antenna. Or should I ground
the high-impedance winding connected to the L wire and then float the
coax that runs back to the RX?

The loop is obviously by far the most elegant design, since as you say,
it obviates the need for any rf grounding. However, the Wellbrook designs,
however wonderful their IMD and nulling are, are a bit pricey for someone
who's just bought an SDR-IQ and is thinking about buying a Perseus next
month.

The inverted-L will cost me about nothing. However, can I emulate a
Wellbrook loop with a good Norton amp (either single-ended or push-pull)
and my own 1-2m diameter hoop of copper tube (I have loads of 1/2" lying
around here)? If I do this, what should I aim for as a middle-of-the-road
source impedance from the loop so a can wind the right kind of toriod? (I
want to listen from the bottom of the MW band to 10m).

Any practical experiences with inverted-L's or untuned loops would be most
welcome - since my SDR-IQ will be arriving on Monday and I do need to "get
some wire in the air"!

Cheers

Alex

Many thanks for that - I will look at these sources before deciding on a
permanent installation.

Cheers

Alex

On Nov 30, 11:22 pm, Alex wrote:
Many thanks for that - I will look at these sources before deciding on a
permanent installation.

Cheers

Alex

Try the simpler antenna in the "Reducing noise" file first.

While the specified FET is clearly the best, if you are lucky enough
to be far enough
from local MW stations, a MPF102 or 2N3819 will work. They are both
far from
optimal but may be easier to find locally.

Terry

In article
,
wrote:

Steve wrote:
On Nov 30, 9:14 am, wrote:
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
RF grounding and antenna concepts:

I use a dual band j-pole antenna on 2 meters and 70 cm. It works
very well above ground.

My whole point with the post that with the correct antenna, we avoid
trying to use the poor conductivity of the earth as a major part of
the antenna. And J-poles are great antennas.

I have a ~850MHz trunking antenna that mounts on a standard MNO
connector. We streteched it slightly and the VSWR on 146 is 1.1:1 and
mid band 70cM is 1.3:1. More then enough for local mobile comms.

Trying to document any type of situation is as endless as the
possibilities they represent. That's why you are far better off citing
general principles for antennas or grounding or EMI/RFI for that matter.

Quite frankly I'm not willing to go through very log posts that address
many issues. Better to pick one issue at a time so the resulting threads
make sense.

--
Telamon
Ventura, California

In article
,
wrote:

On Nov 30, 11:22 pm, Alex wrote:
Many thanks for that - I will look at these sources before deciding on a
permanent installation.

Cheers

Alex

Try the simpler antenna in the "Reducing noise" file first.

While the specified FET is clearly the best, if you are lucky enough
to be far enough from local MW stations, a MPF102 or 2N3819 will
work. They are both far from optimal but may be easier to find
locally.

There are objective ways of looking at information to see whether it
makes sense.

There are principles of operation of antennas that can work for or
against common mode noise, which is generally object of a low noise
antenna. As far as far field noise is concerned about the only way to
improve that aspect would be to limit the BW of the antenna. Generally
as a side effect of balanced antennas, or complete antennas, or what is
known as Hertzian antennas are that they are resonant and have by their
nature a narrow BW.

If you add amplification to an antenna design then another dimension is
added to the design. Here generally you would want a high degree of
common mode rejection and of course the amplifier would have to generate
very little noise by itself. Here you might decide to limit the BW of
the amplifier.

--
Telamon
Ventura, California